# To BMS or not to BMS



## rwaudio (May 22, 2008)

I'm not sure if hours has anything to do with it, otherwise that might well be Jack R. one of the no-bms guys. But he does have a few cars, all BMS free and what he reports as working perfect. Others use a BMS and are working perfect, I'm kind of in the middle, I would love to go BMS free as I think it is the best solution, however it might not be the right solution. I've decided to charge individual cells instead of a series string eliminating the need for a BMS during charging. (I will have monitoring during discharging).

To all others, I hope this is a nice discussion even though there probably isn't an answer to this question. It's your choice to make, and your responsibility to research on your own and make the choice that's right for you.


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## spdas (Nov 28, 2009)

I guess I should first ask "What is the function of a BMS? Does it regulate down a charge for each individual cell attached to it from a series string of cells? Or does it actually boost a charge coming from a series of charging cells? In my mind individual chargers would be the go, but using one for each cell (50) would start to get $ and heavy as it needs to put out to charge a 200ah cell. Maybe get a good 12v charger and group 4 cells?? 

***also what is the best instrument brand name that shows the state of charge of each cell simultaneously? ie can any show 50 cells at the same time?

francis


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## rwaudio (May 22, 2008)

spdas said:


> I guess I should first ask "What is the function of a BMS? Does it regulate down a charge for each individual cell attached to it from a series string of cells? Or does it actually boost a charge coming from a series of charging cells? In my mind individual chargers would be the go, but using one for each cell (50) would start to get $ and heavy as it needs to put out to charge a 200ah cell. Maybe get a good 12v charger and group 4 cells??
> 
> ***also what is the best instrument brand name that shows the state of charge of each cell simultaneously? ie can any show 50 cells at the same time?
> 
> francis


The function and even meaning of a BMS can vary wildly. "Battery Management System" or "Battery Monitoring System" are two entirely different things. Then there is Shunting, or non-shunting, and some that can re-distribute power to reduce wasted power. Some trigger chargers to turn off with a HVC, some trigger controllers to reduce power with a LVC.

The main thing to remember is safety, anything can be dangerous. Nitrous in street racers can explode and destroy cars, garages, houses. The same goes for anything that you attach to you high voltage pack. All wiring must be safe, ideally fused and properly secured. 

I've seen a car burn to the ground from an improperly installed car stereo using a single 12v battery, it can happen to anyone.


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## ElectriCar (Jun 15, 2008)

I'm going free when mine arrives. For one, it will a large chunk to your battery cost and a lot of time to install. The costs can be over $1000 even 2000. 

After watching this and this you'll have a good idea of what you want to do. 

My plans are to not discharge to the edge of the cliff and not charge to the hilltop. Discharge to say 90-95% and charge up to within 5-10% of max. *You will need to educate yourself if you plan to DIY or you may toast $12000 worth of batteries. * 

That guys philosophy is that in order to know how deep to discharge you MUST have an amp-hour counter installed. So if you have a 200Ah cell you can discharge the pack down to within 10Ah or so of being dead. However to do so, you MUST bottom balance the cells in the pack so they are at the same state of charge at bottom. 

Jacks testing shows that using a BMS to "Top Balance" cells to get them charged to the MAX will cause them to likely be out of balance at the bottom (discharge end) thus when you're running the pack low you risk one cell bottoming before the rest and if that happens it's toast!

Yes IF, and that's a big IF, the BMS works correctly it should prevent that from happening. But doing so in the first place is placing a needless burden on the batteries if you want them to last longer. Discharging cells very low shortens their life as does over charging them. However if you stop before getting too low and before getting too high, you'll get longer life anyway.

*Here's a bit of my reasoning for staying away from a BMS. *My career for about two decades was in electronics and circuit board repair. Have you ever known electronics to fail? I have seen MANY. Electronics, no matter how well designed do fail from time to time. Lightning striking a tree NEARBY gives off enough EMI to destroy electronics from a distance, even in your garage. 

Here's a scenario. You're asleep and a storm comes through, strikes a tree nearby and the EMI radiated from it torches a circuit board on one of your cells. If that cell shorts across the battery who knows what it could take out, the BMS controller it's attached to, wiring between the two, could fry the harness starting a fire etc. Who knows what could happen with a failure but there have been many fires documented due to BMS board failures. I don't want anything capable of failing and shorting a battery in my car while I sleep or while I drive!


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## dimitri (May 16, 2008)

ElectriCar said:


> there have been many fires documented due to BMS board failures


Actually there have been *ZERO* fires documented due to BMS failure. Lets not propagate baseless stories here. In every reported fire there were a dozen of things that could have gone wrong not even counting the BMS.

I am biased and I am not promoting my BMS or any others, but let's stick to facts and leave the fiction where it belongs, in TV shows and books.

Yes, electronics fail, but so do all other things. Based on your logic you should live in a cave and never step outside since you can be killed by lightning. I'm sure many people who are hit by lightning every year regret leaving the house that particular day, but it doesn't turn them or most others into hermits.

My point is there are 2 sides to every story. Even if I wasn't selling MiniBMS but just made one set for my own use, I would not regret it. Even though you have a solid theory of how not to damage your pack you have not had any practice yet. I have been using mine every day for 2 years. let's compare our notes after you get 2 years from your BMSless pack. Including how much time you spend caring for your pack and how much your time is worth to you.

I'd be the first one to tell you that its certainly possible to go without BMS if several other conditions are met. However, just because all these conditions are met by one person's project, it does not give him the right to yell all over the world that everyone else SHOULD BE FINE because he has shown that HE IS FINE. Almost every EV conversion has some unique combination of parts and you can't judge one from looking at another.

I wish that every one who supports BMS'less approach had guts to come back and tell the story when something goes against their theory, few people do that. The judgement is still out which way works better.


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## frodus (Apr 12, 2008)

Wait, Didn't Jack Rickard ruin an entire pack of thundersky because there was nothing to stop the charger from overcharging? Had he had a cell-level HVC installed (one form of BMS) he'd have saved the pack. Not something you hear much about on the forums.... Very interesting. Not someone I'll be taking advice from.

IMHO, you ABSOLUTELY need monitoring on a cell level. You need something to look for overvoltage while charging (not on the pack level, on the cell level). If it senses a high cell, it turns off the charger. Then you need to look for overdischarge (LVC) and throw an alarm and reduce the throttle somehow. 

In regards to cell balancing, I don't care if people want to top balance, bottom balance, coulomb count, individually charge. There's no RIGHT way. They all work. My point is, and I think most agree, you should monitor the cells individually. Even if you're using a cheap Cell-Log 8 with the alarms optoisolated and linked together or have a fully fledged BMS balancing/monitoring system.


So what am I using? Elithion. Why? Because I could afford it at the time and because I worked at EVComponents providing support for that system. Now I work for Davide as a consultant and own his BMS book, which is a great read. Not only does Elithion balance, it monitors temperature, voltage and SOC and gives me a TON of useful information back from my pack, which I intend to publish reguardless of results. I want the data and thats why I bought it. It'l be logged via Canbus through bluetooth on an Android device.


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## GerhardRP (Nov 17, 2009)

dimitri said:


> Actually there have been *ZERO* fires documented due to BMS failure. Lets not propagate baseless stories here. In every reported fire there were a dozen of things that could have gone wrong not even counting the BMS.


Do the statistics exist? Of all the fires reported, how many had BMS systems and how many did not? I know stastics lie, but if there are no BMS absent fires, lets think.
Gerhard


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## Bellistner (Dec 12, 2010)

If I'm going to throw $5000 - $10,000 at pack. I'm going to spend a little more to protect it. I just haven't decided which BMS to use.


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## frodus (Apr 12, 2008)

Bellistner said:


> If I'm going to throw $5000 - $10,000 at pack. I'm going to spend a little more to protect it.


I second that. Sounds risky without something that'l protect the pack from being overcharged or overdischarged. Until I see more empirical data on this, I'm just going to use what I've bought and log.


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## dimitri (May 16, 2008)

GerhardRP said:


> Do the statistics exist? Of all the fires reported, how many had BMS systems and how many did not? I know stastics lie, but if there are no BMS absent fires, lets think.
> Gerhard


This just makes no sense to me. From relatively small number of EV conversions on the road, and even smaller percentage of those using Lithium packs where BMS is typically used, it will be hard to get meaningful stats based on the fact that car had BMS or not vs. same car burning down or not. Especially that Lithium packs are relatively new, making the count even more difficult. I can't see any logical connection here.

If 1000 cars had Lithium packs, of which 900 had BMS and 100 did not and there were 5 fires reported, all of which had BMS in them. Does that say anything about BMS causing it or simply that vast majority had it to begin with, hence larger chance of fire in a car with BMS than without one.

90%/10% was a very generous split too just to make the point. I think in real life its more like 98%/2% of BMS vs. no BMS conversions.


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## ElectriCar (Jun 15, 2008)

Dimitri I haven't studied and read exhaustively the details of purported BMS fires but I've read others writings about them and it coincides with my experience and knowledge of electronics, enough so that I'm convinced that BMS is not needed and is IMO a liability. Unlike you, I have no dog in this fight. I'm only answering the OP's call *from my perspective*.

I'm glad we agree that electronics do fail. As I said, I've seen lots of failures in 20 years of electronics, some dangerous, some benign. That said my charger could fail and torch the pack left to it's own devices but that is easily rectified without a BMS. Actually BMS circuitry could be modified or configured in a circuit to kill the charger at a predetermined voltage. But again, nothing is certain but death and taxes.

My point, as is Jacks to the best of my knowledge is this. One can buy your BMS and install 50 electronic circuit boards assembled of the finest components with the greatest care, spend hours wiring 5 pounds of cabling running through the vehicle to the dash and elsewhere, confident it is the holy grail of battery protection and will prevent battery failure. 

Or one can buy a meter with Ah counting capacity, set the low levels to notify the driver at 20% remaining and again when the tank is empty and I'm about to destroy my pack, even have it shut down the vehicle or take it to limp mode. I'll have the charger set to charge to a voltage less than full which will give me more life according to the OEM. All I need to do is bottom balance and keep from bottoming out a cell. Even that may be unnecessary, not real sure. I can also install redundant protection on the pack to kill the charger should it decide to fail. Simple and inexpensive. 

Should I take your advice and one of your quality boards fail shorted, that cell is dead and come hell or high water you (the driver) nor your BMS is likely going to stop it. No, Lifepo4 isn't going to catch fire from what I've read but don't throw me under the bus because I haven't consulted an expert directly nor have I proven to myself that it can't. Again that's what I've read. And one or two cells is likely less than your BMS system if somehow one of them does go south.

You guys hocking your BMS wares certainly have reason to bash those of us who rationally decide NOT to send you our money and chose another route, a route that is much less potentially harmful and blatantly simple. So go ahead if it makes you feel better brother!


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## dimitri (May 16, 2008)

The only reason I responded to your post is this statement you made, which is as blatant lie as it gets, with very serious consequences to people involved in these issues. 


> there have been many fires documented due to BMS board failures


I know you did not make this up yourself, you just repeat blindly what you hear on EVTV.

I have full respect for your plans to go without BMS and I am not pushing anything to anyone, I just try to stop lies from propagating, which seems a futile effort since everyone likes drama more than facts. Pros and cons of BMS have been discussed to death on this forum, no reason to repeat everything again, so I stay away except when lies are posted as facts.

As for your plan, it sounds great. I only ask one thing, come back 2 years from now and honestly share how real life experience differs from your plans and how much time/money you spent avoiding to use BMS.


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## tomofreno (Mar 3, 2009)

> If 1000 cars had Lithium packs, of which 900 had BMS and 100 did not and there were 5 fires reported, all of which had BMS in them. Does that say anything about BMS causing it or simply that vast majority had it to begin with, hence larger chance of fire in a car with BMS than without one.


 Sure, you can correct for unequal sample sizes. The difficulty would be in getting unbiased data. Many people don't like to admit their mistakes.

Did Jack really destroy an entire pack? I don't recall hearing about that.


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## dimitri (May 16, 2008)

tomofreno said:


> Did Jack really destroy an entire pack? I don't recall hearing about that.


No, he just killed a couple cells, not a huge deal. This "killing whole pack" is another urban legend that just keeps spreading itself. I can't imagine how you can kill the whole pack at once, other than having BMS set it on fire 

You would kill the weakest cell in each incident, replace it, then kill the next weakest cell in the next incident, etc etc, but not the whole pack at once.


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## spdas (Nov 28, 2009)

Aloha, all. Best to keep an open mind on the bms as there is a lot of testimony coming out for pros and cons, so best to take it all in Objectively and decide on the merits. Jack R has a lot of good info and so do the pro guys. I think some sort of balancing will win out, (either top or probably bottom) as I see cells wandering off over time. (at least in AGM). So far I think charging to 90-95% and discharging to no less than 35-40% is in order, so I think it pays to buy bigger ah than absolutely needed and treat them with care. Using a good individual cell monitor and culling out a cell that is out of range is a good idea. For my agm setup I see the suggestion of using this homemade cheap "BMS" is a great idea. http://www.evdl.org/pages/hartregs.html (since I bought my car with AGM from a guy that only series charged and never balanced, and was only getting 5 miles on his pack. I balanced and am up to about 15 miles and hope to get to 20 miles after a little more TLC on the batteries) But lets wait and see.
Francis


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## DavidDymaxion (Dec 1, 2008)

Here's something I would love to see: Run a BMS on half the pack, and go BMS free on the other. May the best half of the pack win!

Also, test for yourself! You can buy Headways for ~$20 each, an RC charger for ~$75, and a load tester with Voltmeter and Ammeter for $50 at Harbor Freight. Get an IR thermometer, a voltmeter, and a timer, and you are ready to rock.

Here's my limited experience: 

Lead acid: On an Optima pack, it would go very quickly out of balance with weak regens. Doing a small number of 500+ Amp regens during a drive keeps the batteries well balanced, within about +-0.02 V.

Lithium: Once bottom balanced, 4 China HiPower 10 Ahr cells stayed well balanced over about 20 severe cycles, without BMS. It appears Jack was right for this small number of cycles.

I pushed them until 2 of them vented. How's this for an idea, discharge one cell and fully charge the other. Then do gentle charge/discharge cycles, and see if they'll grow into balance like Jack claims. I think this would be a good test for if a BMS is needed -- do cells naturally balance? Anyone else out there game to test this idea and see if we get the same results?

I just got some Headways and have more China HiPowers on order, the testing continues. I'll post up details, good or bad, when I'm done.


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## brainzel (Jun 15, 2009)

I don't use a "BMS" in my car.
Why? I haven't found one that monitores my LiFePo-pack the way I want to a price that I could afford and with the safety issues I need.

Do I monitor the whole pack? Yes, that's neccessary I think.
Whole voltage, amphours, amps, but no tiny boards or "spaghetti"-wiring.

After ~40 - 50 charges (Zivan NG3), all cells (SkyEnergy/CALB 121AHA) are still close together in voltage.



> there have been many fires documented due to BMS board failures


I have read about only one car that burned to the ground because the owner overcharged his pack dramaticly.
Every other case of fire I read (six I guess) was a vehicle with a mounted "BMS" on it.
Thats my personal statistic. Fell free to widen it


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## Jozzer (Mar 29, 2009)

When you have thousands of dollars/pounds tied up in your pack, a fire isn't the only problem that can ruin your EV day.
I've run a conversion business for years, and tested a huge quantity of cells and system setups, and I'd like to say that I'd never run a Lipo or LifePo4 (especially LifePo4) pack without a BMS for more than 2 or 3 cycles. You can take that advice or leave it, I have written this only because I am so alarmed that so many would advise a BMS is not nesaccary.
It cost many hundreds worth of cells to come to this conclusion, over a large number of EV's (no fires however). You don't have to replace many battery's to cover the cost of a BMS, not to mention the inconvenience of stripping down a pack to replace cells (not all packs are as easily built as cheap thundersky's!).

Steve

PS, for Gottdi, I've lost 4 banks of cells due to BMS failures (mainly during a prototyping and testing period), this in no way compares to the hundreds of cells I have sitting around that were damaged by NOT being managed, or the several customers who have homebuilt EV's rotting in their garage because they believed they would not need a BMS and lost thousands worth of cells, 3 users did indeed lose the whole pack (or more than 70% therof), 2 by overdicharging and 1 by overcharging.


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## GerhardRP (Nov 17, 2009)

DavidDymaxion said:


> How's this for an idea, discharge one cell and fully charge the other. Then do gentle charge/discharge cycles, and see if they'll grow into balance like Jack claims. I think this would be a good test for if a BMS is needed -- do cells naturally balance? Anyone else out there game to test this idea and see if we get the same results?
> 
> I just got some Headways and have more China HiPowers on order, the testing continues. I'll post up details, good or bad, when I'm done.


I've been thinking about a test almost like the one you propose:
Take three matched batteries. Discharge them all in parallel to 2 volts. Put 10% of the capacity into one, 20% into another and leave the third one at zero. 
Connect in series and then repeatedly charge and discharge at 1C, stopping when one battery reaches 3.8 volts on charge and 2 volts on discharge. See if they drift closer to balance or not. 
At the end of many cycles, remeasure the capacity to find out which is more damaging, running near the bottom or near the top.


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## ElectriCar (Jun 15, 2008)

Not sure anyone said cells can't be damaged so I'm not using a BMS. I said I was planning on going a different route. Only an idiot would stick the batteries in their car and just drive with no monitoring of any type, that or a high roller! I'm neither. 

In addition to my planned monitoring of the entire string, I'm going to initially monitor the entire pack manually for the first few cycles to get initial data about the cells. Once I have that I'll send the charger off for custom programming.

Fortunately I have a background in electronics and am designing something so far I've not found, a device to override the charger should it malfunction. 

*For you BMS proponents, don't be shy, here's your chance to make a sale! Describe what your BMS will do for this scenario and if you handle it without a cell level monitoring system. *If so I'm open to it but I don't think you can do it for anywhere near what it will cost me. 

Say someone is running a pack at 96V using a Zivan NG5 wired on 240V charger for quick charging like I have mine. It is programmed to stop charging at 3.6V/cell or 108V max. This charger is capable of putting out 190V, probably more. 

So Joe Sixpack comes home & rolls into the garage, plugs in and goes inside for the evening, entrusting his home, vehicle and battery pack to his charger and your BMS. When the pack hits the point to go into CV mode, it malfunctions and continues in the CC mode, the voltage continues to climb, applying 200VDC at 25A to the pack. What does your BMS do? Now you're at 6.66V per cell.


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## Jozzer (Mar 29, 2009)

The bare minimum a BMS needs to do is monitor for HVC and LVC as well as temperature and be able to independantly cut off charge and discharge. 
Better still, it could be able to balance and limit charge current to balance current. 

The non BMS folk keep pointing out that all you need to do is count AH into and out of the pack, just how do you manage that (without ever losing count, or forgetting to reset it etc)? This is exactly what happened to one of my customers who now has £8k of dead LifeBatt cells. He used the vehicle daily for 6 months or so with no problems, then one day the Cycle Analyst farted (or he forgot to reset it) and thought he had 20 AH more than he actually had. He found out that when the pack is low, cells drop below voltage and go into reversal within seconds. The real irony here was, that he had an LVC circuit installed, but didn't bother hooking it up to the throttle! (like this one, that costs around £3 per series cell, http://endless-sphere.com/forums/viewtopic.php?f=31&t=21695&start=0)

Another customer assumed charging to an average of 3.55v per cell on a pack would never overcharge. One day whilst using my charging facilities in the yard on his way past, a passerby came in to tell us that the car outside was "popping". 1 bank of cells had reached full charge and the voltage had skyrocketed to 4.4v or so, they then vented and went 0v, causing even more voltage to be available to overcharge the next cell.

Running without a BMS is an experiment in luck and mechanical sympathy. 

I would want to see a LOT of such experiments end well before publicly telling new users to try without a BMS!

I believe Kendrick (see the link above) is planning to produce a version with HVC also, this would offer the basic protection required for Lipo and LifePo4 at absolutely minimul cost and complexity. No excuse not to run with at least these installed!

Steve


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## Jan (Oct 5, 2009)

Jozzer said:


> He found out that when the pack is low, cells drop below voltage and go into reversal within seconds.


Can you explain how this can happen? I asume they were top balanced, and prety much out of range regarding capacity?



> 1 bank of cells had reached full charge and the voltage had skyrocketed to 4.4v or so, they then vented and went 0v, causing even more voltage to be available to overcharge the next cell.


And can you explain this situation too? How was it possible a whole bank went to 4.4 and the charger kept measuring an average below 3.55?


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## Jan (Oct 5, 2009)

And regarding testing cell drift; JR is monitoring its cells of one of his cars. The imbalance so far was caused by some circuitry (not sure what exactly) that was only attached to the first 10 cells orso. The saga continues.


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## Jozzer (Mar 29, 2009)

After 6 months without a balance ANY pack will be out of balance..

As for overcharging, 144v pack of 48 LifePo4 cells. He charged to 170v (3.55 per cell). If 47 of those cells have not peaked yet, they will still be at 3.4v or so, 47 x 3.4v = 159.8. So his charger had a good 10v in hand to give the 48th cell that had peaked before the rest (and this would have happened sooner of course if the cells had been bottom balanced). 
So, this overcharged cell peaks out, goes POP and reads suddenly 0v. When the next cell peaks there is an even higher potential to damage further cells.

A good point of note here, is that in many many charge cycles with a BMS, I don't think I've ever seen all the cells reach the "knee" simultaneously (talking LifePo4 here, LiPo are actually a lot easier to work with in this respect, since they dont run away at the end of charge).

I've not got all day to argue this, it's up to the vehicle operator to decide if he is happy risking his pack (or perhaps his vehicle or even his home and family), I just wanted to make sure that anyone reading this thread has complete information in order to make his/her decision.

Since I already pointed out in the previous thread that minimum protection to make your pack live a long happy life need cost only 1-3% of the price of even a small pack, whats the point in arguing about it?
It's a bit like deciding not to fit a contactor to your EV to save pennies...

Steve


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## Jan (Oct 5, 2009)

Jozzer said:


> So, this overcharged cell peaks out, goes POP and reads suddenly 0v. When the next cell peaks there is an even higher potential to damage further cells.




Ah, ok. You first wrote a whole bank was at 4.4 volts. 
And my other question? Are my assumptions correct?


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## Jozzer (Mar 29, 2009)

By bank, I meant cells in parallel not series.

Other assumptions? you mean your comment that the cells were poorly balanced or top balanced?
As I said above, ANY pack that hasn't been balanced for 6 months should be considered unbalanced. 
In this case, before construction all the cells in the pack had been connected to a 3.65v powersupply and trickled (many in parallel at a time) until less than 100ma was required for them to maintain voltage. 

One point for those who ARE cycling within boundries of 20%-80%, is that it is not possible to verify the SOC of a LifePo4 cell by any other means than charging or discharging it until the voltage knee is reached. You could be just one more charge away from over/undervoltang the weakest cell and not even have an idea. Just how many cycles has anyone managed using this approach without needing to rebalance or service in any way?
The customers mentioned above all had less than 25 cycles on their packs before learning thier lesson, though I can think of one person I know who ran a pack for many years with no BMS. That person however, is one of the best known motor invertors of this generation, and perhaps the most mechanically sympathetic guy I know..

Steve


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## Jan (Oct 5, 2009)

Jozzer said:


> By bank, I meant cells in parallel not series.


Ah, ok. A whole parallel bank was at 4.4 volts, while all others where not near their knee.



> Other assumptions? you mean your comment that the cells were poorly balanced or top balanced?


My other assumption was, that the pack was top balanced and the cells where very different in capacity. Because within seconds the weak cells went in reversal. That's fast. 



> As I said above, ANY pack that hasn't been balanced for 6 months should be considered unbalanced.


That's the question. There's not much data to be sure.


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## frodus (Apr 12, 2008)

This is not directed towards anyone in particular,

In my work with Lifepo4 at 2 different companies, I've heard of more issues of people without BMS than with them (actually have only heard about problems with wiring, or dead boards). I've heard of no fires or issues with the two different that I've sold (Elithion and Manzanita Micro). I've helped well over 50 customers, none of which have had any issue. I have heard of some of the cheap chinese bike BMS having issues, but one was definately user error, the other was undetermined and the customer never contacted us further after digging more. There were no fires, just sparks and magic smoke. I would not qualify those for use in a vehicle larger than a bike, so I can safely say, I've not heard of any fires due to a failed BMS in a car or motorcycle. That is my direct experience, and I've also built over 10 battery packs of varying capacity. 

If you guys want to do things your way, fine, no one is stopping you. But since you're entitled to your opinions, so are we. We're sharing our extensive knowledge about batteries and BMS and the issues that we've seen over the years that we've been involved. I started off as an enthusiast (like jozzer) and then worked as a consultant. I've learned a lot through trial and error, and so have many customers. 

I've come to the following conclusion:
*You absolutely need a cell-level monitoring system.*
(notice I don't mention balancing. Because I think top balancing, bottom balancing, individual charging and self-balancing are all valid ways to keep a pack balanced. I'm not here to argue which is better. I have a couple preferences actually)

With regards to HVC:
Jozzer has pointed out what happens when you don't have HVC, and so have I. Without cell level monitoring, the charger only sees pack voltage. It doesn't know if a cell with different IR went high before the others (which it absolutely will, I've NEVER seen a pack simultaniously reach their knee at the same time, Especially if it was bottom balanced before assembling the pack). So if you're at 170V on the charger, all cells except one are normal, but that one is overvoltaged, it shorts out and fails. Now your voltage drops by 4V or whatever. Well, now your charger sees 166V and maybe goes back into constant current mode, with a higher current. So the next battery that was high gets higher, higher and then overcharged, shorts and the pack now sees 4V less. Rinse and repeat. This can happen very quickly, but without monitoring, you'd never know until its too late, and there's nothing to shut off the charger.

With respect to cell reversal, read this:
http://en.wikipedia.org/wiki/Rechargeable_battery#Reverse_charging

I've seen it happen several times and it completely kills the battery. It's not only for lead acid. It can happen with any type of battery put in a series string.



Now a personal request, since we're all adults.....please don't discount people like myself, Jozzer and Dimitri with loads of experience in this realm. Many people talking about BMS have never put together a pack, although some have put together small packs. We have built many more than that and are sharing our experience.

And as far as Jack Rickard's pack, He may have only ruined a couple cells beyond use, but that is not what I heard from more than one trusted source. If its untrue, appologies. My point was, an HVC and LVC circuit would have completely protected this from happening.


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## rwaudio (May 22, 2008)

just a comment, since I don't know the specifics of all the BMS systems out there, but everyone assumes they are going to fail, yet everyone assumes that their AH meter or "Alternate" protection to a BMS will never fail. Odd?

It's also assumed (or atleast mentioned frequently) that a BMS will fail short circuit and drain a cell, I find that hard to believe since anything close to short circuit on the terminals of a battery will vaporize pretty quick (IE blow like a fuse, not start a fire). However if I was a BMS designer I would do everything I could to have it fail "open" and at the same time trigger some sort of fault HVC/LVC/anything you just need to know it's broken, be blunt ask the manufacturer how/why it can fail, ask if they've tested it, ask what it does when it fails and if they considered that in the design, if they haven't move on.

I think "spagetti" wiring is the worst excuse not to use a BMS that anyone has ever come up with. Use some common sense, wire it properly and safely, secure and protect the wiring. If you aren't capable of that you shouldn't be building an EV in the first place, and that is no fault of a BMS.

On the other hand I hope my system will allow me to go BMS free, or atleast BMS disabled unless I want to bring it online once a month to balance the cells.

Don't tell others what to do, tell others what you did and let them make their own choice. BMS makers seem pushy at making you think you need a BMS but those against BMS are way more forceful with their "opinion" that a BMS is going to burn your car to the ground. *Tell the facts, share your experience and let the user decide, it's their car not yours, it's their choice not yours.*


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## Qer (May 7, 2008)

Not even gonna touch the BMS-discussion with a ten feet pole, that topic is way too infected for me to even bother with and you seem to be quite capable of pissing each other off without my help. 

However:



rwaudio said:


> I think "spagetti" wiring is the worst excuse not to use a BMS that anyone has ever come up with. Use some common sense, wire it properly and safely, secure and protect the wiring. If you aren't capable of that you shouldn't be building an EV in the first place, and that is no fault of a BMS.


I once worked for the Swedish Telephone company. All of the old electro-mechanical telephone stations had racks of hundreds or thousands of relays, all the wires were painstakingly bundled together with some kind of waxed string in perfect, pedantic order! Every single rack had hundreds of single wires running straight as arrows, cut just long enough to reach their terminal and between the racks ran thousands and thousands of wires, all color coded, bundled together and extremely easy to trace despite the sheer number of them.

Spaghetti wiring is nothing but sloppy craftsmanship. Period.


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## frodus (Apr 12, 2008)

gottdi said:


> Like Frodus said, this is not focused on any one person.
> 
> Now you see, this is the issue with this ongoing debate. All the professionals from what I have been reading ONLY state this is what I have heard from.... Holy crap guys. I hear that crap all the time. My brothers cousins sisters brothers, friend said...........WOW, it must be true.


I've heard of more issues DIRECTLY from the customers. Not from this person who told me that, who heard it from someone. I've actually helped these particular people deal with more issues without a BMS than not.


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## Jimdear2 (Oct 12, 2008)

I'm going to run on a bit so be prepared.

I'll throw this out again on the pro / con BMS debate and let you all decide if it is a BMS and if it's worth looking at during planning your system

Right now using off the shelf stuff we (Myself, RWaudio and a few others) are actually building this.

We are going at it with a top balancing, limited voltage charge protocal and LVC or LVW.

What we plan is using, one, reletivly inexpensive, isolated DC to DC converter attached to each battery (large format prismatics) or battery group (small formats other then prismatics) to charge it. 

The DC to DC is set to be able to only charge to a specific set voltage. The DC to DC then *CAN NOT/WILL NOT* over charge the cell. Since many of the DC to DC units can have a trim pot each unit can be adjusted to bring your cells in to perfect top balance.

So for top end charging we set the voltage of the DC to DC to a safe 90% for the cells. Now the DC to DC units I am using (thanks RWaudio) can pass 25 amps at 3.65 volts and will accept any voltage between 35 and 76 volts. They can be turned on and off individually and have over and undervolt and over temp protections and a lot of others I don't understand. 

Chargeing power can be handled by any of a number of inexpensive units with whatever voltages within the range of the DC to DC units because of the DC to DC units built in protection protection.

Then for LVC or LVM we use a simple voltage device like the Cell Log8M to monitor each cell (large format prismatic) or battery group (small formats other then prismatics). The Cell Logs have a warning system that can be set up to monitor each cell and trigger an alarm that could be used as an audible warning or to trigger an event such as power cut back, main contactor disconnect or whatever. 

So for bottom end we set the Cell Logs for some safe limit voltage say 80-90% DOD. What happens here depends on your set up It could shut you down until you fix/charge or with the proper controller back off power each time a cell log hits low voltage. 

This should keep you in the fat/flat area of the charge/discharge curve and do wonders for your pack life.

As long as you plan your pack size for the middle 80-90% of your pack this shold work pretty well. 

Let's face it, when you consider the above it's not unlike filling a gas tank. You should never fill a tank all the way (100%), If you fill the expansion space you're eventually going to get a boom when things heat up. Most people never use their reserve fuel, if the do they'er in trouble eventually.

Remember this is all off the shelf stuff so it's going to be a bit crude. and have some holes in it that require personal monitoring. I'll depend on you smart guys to find a way to put this all on a board, with programming to do everything including washing the dishes.

When you get down to it, I'll have a 50 cell (50, 3 cell buddy packs in my case) protective charging system with high and low cell monitoring and LVC or LVM. 

You will also have very high charge rate, it could be a 48 volt dump pack with a tickle charger at home and you could carry a good variable input voltage 48 volt 20 amp charger or power supply with the car. You don't need fancy/fussy $1500.00 battery chargers. and +$1000.00 BMS. 

Again using off the shelf components, I've got everything so far for $1000.00 +-10%. Want to bet what some smart EE could come up with? 

Sorry, I do run on.

Jim


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## frodus (Apr 12, 2008)

Jim, Thats a great idea.... It's referred to as the power conversion type of BMS I stated above. I used pretty much the same system on my lead pack for my motorcycle several years ago. individual DC-DC converters that charged each battery. The only diff was, I didn't have Cell Logs, I used microcontrollers on each DC-DC that looked at volts and controlled the ON/OFF of the DC-DC so they would use less power in standby. They'd comm to a mother unit that could cut off the contactor if needed. 

Functionally, your cell-log and dc-dc converter system is the same. I actually have 36 Vicor 3.7V DC-DC 20A converters with a 48V input sitting in my garage. I also have a few 48V DC-DC power supplies that can output 800W on 110V and 1500W at 220 and can be hooked together. Only thing missing is an HVC/LVC. The cell-log would work great.

Another thing...... your system balances the pack EVERY charge. Resistive balancers can often take several charges to balance an unbalanced pack. With yours, you never have to worry. Charge: Protected. Discharge: Protected (depending on how you "react" when you hit LVC).


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## EVfun (Mar 14, 2010)

Jimdear2 said:


> What we plan is using, one, reletivly inexpensive, isolated DC to DC converter attached to each battery (large format prismatics) or battery group (small formats other then prismatics) to charge it.
> 
> The DC to DC is set to be able to only charge to a specific set voltage. The DC to DC then *CAN NOT/WILL NOT* over charge the cell. Since many of the DC to DC units can have a trim pot each unit can be adjusted to bring your cells in to perfect top balance.


I want to point out that you need to use *very* reliable cell level DC to DC converters. If you are using units with a 100,000 hour MTBF (mean time between failure) with a 50 cell pack then you can expect to experience a cell not charged issue about once a year. It is important that your system can detect that failure ASAP, hopefully before you are 5 miles from home.


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## Jimdear2 (Oct 12, 2008)

Frodus,

Thanks for the praise, but I can't take all of the credit.

RWaudio is also on this path (a bit ahead of me in fact in actual hardware and research) and I've seen many others I think that are getting there or have been most of the way there (like you).

IMHO the OEM battery makers, at least for the prismatics should be the ones picking up on this. I.E. each battery comes with the charger built in or snapped on and a set of 2 wire connector cables to go between DC to DC units for the charger power loop. They can have voltage sensing to turn them selves off when the battery reaches charge, warning triggers, etc. etc. built in. The DC to DC I've bought cost about $5.00 each in the volumn the battery makers would need I bet that could go waaaaaay down. each board could be given a unique ID so all of the sensing could be a CAN bus loop and a generic CPU could sort out what battery is doing what for diagnostics and servicing as well as LVC or LVM, no matter what the battery count.

Enough preaching,
Jim


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## rwaudio (May 22, 2008)

Jimdear2 said:


> So for top end charging we set the voltage of the DC to DC to a safe 90% for the cells. Now the DC to DC units I am using (thanks RWaudio) can pass 25 amps at 3.65 volts and will accept any voltage between 35 and 76 volts. They can be turned on and off individually and have over and undervolt and over temp protections and a lot of others I don't understand.


No problem Jim, my *personal* opinion is it's the best system for *my* car. I won't push the system on anyone, but I'd be happy to help anyone with similar goals.

I'm designing boards for 15 converter blocks (48v nominal input, 48v nominal battery block), Onboard 20 turn pots for easy output voltage adjustment. It'll have monitoring capability but those parts could be left out if not required/wanted.


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## Jimdear2 (Oct 12, 2008)

EVfun said:


> I want to point out that you need to use *very* reliable cell level DC to DC converters. If you are using units with a 100,000 hour MTBF (mean time between failure) with a 50 cell pack then you can expect to experience a cell not charged issue about once a year. It is important that your system can detect that failure ASAP, hopefully before you are 5 miles from home.


EVfun, 

For our setup, in competition we might see 25 runs a year and lots of persona management. For people with on the road EVs that's what the Cell Log warning systems are for. 

Each Cell Has A High and Low Voltage Monitor. This should catch a bad board pretty quick. The Low Voltage Warning Buzzer would go off and you would need to go to the Cell Logs to find the bad Dc to Dc. 

A professionally designed board with CAN bus would do all of this and I'm sure that some EE or programming wizbang could even figure how to bypass that cell. Im sure this could all be made modular snap togther, plug in and a lot less expensive then what's out there.

Jim


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## Jimdear2 (Oct 12, 2008)

rwaudio said:


> No problem Jim, my *personal* opinion is it's the best system for *my* car. I won't push the system on anyone, but I'd be happy to help anyone with similar goals.
> 
> I'm designing boards for 15 converter blocks (48v nominal input, 48v nominal battery block), Onboard 20 turn pots for easy output voltage adjustment. It'll have monitoring capability but those parts could be left out if not required/wanted.


RWaudio,

Lordy! I hope i'm not coming off as pushing this on everyone. If I am I'm sorry. I guess I am a bit enthuisatic, but that's my nature when I see/think of something I think is wonderful. 

An up front *thanks* again to you. 

I've been thinking about this for months, but not being in any way shape or form "electronic" I couldn't find a decient DC to DC (didn't/don't know how to look). The board you showed me tripped me over the edge and made it all come together for the setup I want for our tractor.

Jim


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## rwaudio (May 22, 2008)

EVfun said:


> I want to point out that you need to use *very* reliable cell level DC to DC converters. If you are using units with a 100,000 hour MTBF (mean time between failure) with a 50 cell pack then you can expect to experience a cell not charged issue about once a year. It is important that your system can detect that failure ASAP, hopefully before you are 5 miles from home.


As per the dc/dc converter data sheet:
*RELIABILITY CHARACTERISTICS*​ 
Calculated MTBF 2.8 10
​​6 Hrs. Telcordia TR-NWT-000332; 80% load,300LFM, 40oC Ta​ 
Calculated MTBF 1.8 10​ 

6 Hrs. MIL-HDBK-217F; 80% load, 300LFM, 40oC Ta
Demonstrated MTBF >25 106 Hrs. Field demonstrated MTBF​ 
Formatting didn't come through 10
6 Hrs. is 10 to the power 6 or multiples or one million hours.​ 
Demonstrated MTBF greater than 25million hours seems pretty good to me. 
The power supplies I am using have a 5 million hour MTBF.​


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## rwaudio (May 22, 2008)

Jimdear2 said:


> RWaudio,
> 
> Lordy! I hope i'm not coming off as pushing this on everyone. If I am I'm sorry. I guess I am a bit enthuisatic, but that's my nature when I see/think of something I think is wonderful.
> 
> ...


I don't believe you’re coming across pushy, I'm just making clear my stance in this very volatile issue. I made the mistake of asking Jack R. what he thought of the idea once, he did have a very polite response though, so I respect him for that. Things did go south after that and I was told I am not allowed to have my own opinion. But initially a very pleasant gentleman. 

_"Bottom line is you're expending some serious engineering effort to do what looks to me like a really quite good implementation of a really bad thing."_


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## frodus (Apr 12, 2008)

Bad how?

Did he elaborate on why charging each battery to its full potential is a bad thing?


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## Overlander23 (Jun 15, 2009)

If you're going completely BMS-less... What happens if a cell/multiple cells go(es) bad? I mean, manufacturer defect-type of thing.


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## Jimdear2 (Oct 12, 2008)

Overlander23 said:


> If you're going completely BMS-less... What happens if a cell/multiple cells go(es) bad? I mean, manufacturer defect-type of thing.


If I understand your question.

First, we are not going completely Battery Monitoring-Less, there are the Cell Logs with their low voltage warnings. 

In a single series system the warning would go off when the battery went below the set voltage and you would most likly come to a complete stop if the battery failed open. If the battery faled shorted you might continue at greatly reduced power, again the warning would go off when the battery went below the set voltage.

Refering to the Cell Log readouts would tell you which battery was failed. you could then jump out (to get you home) or replace the defective.

In a parallel system depending on how you wire your parallel packs you might not immediatly notice if one battery of a buddy set went down, but a look through of the cell log readings would/should show you a pack with an out of sync reading. E.G. If all other cells/cell sets showed 3.65 volts and one shows 3.50 volts you would probably want to look into it.

Even if you were to have a cell in a buddie pack go down open the current should still flow around that battery and what I beleive would happen is that cell group would discharge faster do to the lost capacity and would reach Low Voltage and trip the warning sooner then all others. A quick look at the Cell Logs should tell you quickly what is wrong.

No system is perfect, especially one built up from off the shelf generaic parts, you just do the best you can. 

Jim


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## rwaudio (May 22, 2008)

frodus said:


> Bad how?
> 
> Did he elaborate on why charging each battery to its full potential is a bad thing?


I think Jacks idea of "bad thing" refered to anything connected to the batteries that could be considered BMS related. As well as the fact that I will be top balancing every time I charge and Jack is against top balancing almost as much as he's against BMS systems.

Personally I like the idea of top balancing way better than bottom balancing because my pack will spend 100-200 cycles at the top for every 1 cycle that I may even come close to the bottom.

And from a safety perspective, sure I can damage/destroy cells with overdischarge, but they don't seem explode like an overcharged cell. If something bad is going to happen I would prefer a LiFePO4 paperweight to LiFePO4 shrapnel. So for me it's better to be safe that 100-200 charge cycles instead of being safe that 1 discharge cycle that I push the car too far.


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## EVfun (Mar 14, 2010)

rwaudio said:


> Demonstrated MTBF greater than 25million hours seems pretty good to me.


Sounds like you are using the right stuff to me. I've seen modular charging systems before and most of them where built using cheap consumer chargers. That usually ends badly when chargers start failing in any of several different ways.


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## Jimdear2 (Oct 12, 2008)

EVfun said:


> Sounds like you are using the right stuff to me. I've seen modular charging systems before and most of them where built using cheap consumer chargers. That usually ends badly when chargers start failing in any of several different ways.


EVfun,

I agree, as I found out with my 6 fairly good quality name brand chargers for the 72 volt tractor. All that wire twisted around and here I am tripping, banging and dropping "WATT A MEZZ" but the modular charging is what got me thinking so long ago about the Headway, LiFePo4 system as I've described it. I put it off just because I thought it was too expensive (it is) and I found a good deal on a 72 volt programed charger. But I'm 67 and in poor health. I can't wait around forever so I went ahead and got the big motor, started the HV controller and built the tractor and bit the bullet and bought the batteries. 

Tried to figure the charging monitoring system with my young partner helping but got stuck in research until I stumbled across rwaudio and he put me on the right path.

Once rwaudio pointed me at the right Dc to Dc I was off.

This one won't be perfect because it's built from generic parts, but it's a start. 

I know, I know, TMI,
Jim


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## JRP3 (Mar 7, 2008)

How did I miss this one?  Some thoughts. Early BMS's have certainly killed some cells, Tomofreno had this happen to him, as did some others, so a bad BMS can kill a cell. Obviously running without a BMS can also kill a cell. In his Gem car Jack purposely ran down a top balanced pack and killed some cells to prove a point but I don't think he killed the entire pack for reasons that have already been mentioned. I'm not sure it was necessary but Jack likes drama and can afford it. Running without a BMS doesn't mean hooking up your cells and ignoring them, occasional manual balancing will probably be necessary, depending on how closely matched your pack is. With or without a BMS the best thing you can do for your pack is to get as closely matched cells as possible, people have been getting packs with less than 2% variation lately. The closer they are to begin with the less they are likely to deviate during use. Before I put it up for the winter I had about 8 months and 5k miles on my bottom balanced pack with no BMS. So far no dead cells, even after a limp home event with 1.77 v per cell under load and occasional 5.5C draws. All cells still seem to be in the same relationship to each other at this point, won't know for sure until I do a near 100% DOD again next year. The biggest issue I've had is the Manzanita's habit of allowing voltage to creep up when charging at different currents and from different voltages. If set to charge properly at 240VAC and 20amps it can slightly overcharge at 120VAC and 10 amps so I either have to adjust it or watch it at 120. Most of my charging is at 240VAC so I have it set for that. Of course I undercharge the pack and rarely go below 40% SOC. A more accurate pack level monitor that shuts off the charger through the reg bus as a backup would probably be useful for the Manzanita's. I plan to keep living on the edge without a BMS until I kill or damage a cell, or until I find that $2 per cell wireless BMS I've been dreaming of


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## ElectriCar (Jun 15, 2008)

ElectriCar said:


> *For you BMS proponents, don't be shy, here's your chance to make a sale! Describe what your BMS will do for this scenario and if you handle it without a cell level monitoring system. *If so I'm open to it but I don't think you can do it for anywhere near what it will cost me.
> 
> Say someone is running a pack at 96V using a Zivan NG5 wired on 240V charger for quick charging like I have mine. It is programmed to stop charging at 3.6V/cell or 108V max. This charger is capable of putting out 190V, probably more.
> 
> So Joe Sixpack comes home & rolls into the garage, plugs in and goes inside for the evening, entrusting his home, vehicle and battery pack to his charger and your BMS. When the pack hits the point to go into CV mode, it malfunctions and continues in the CC mode, the voltage continues to climb, applying 200VDC at 25A to the pack. What does your BMS do? Now you're at 6.66V per cell.


As old Sargent Carter used to tell Gomer Pyle...* "I CAN'T HEAR YOUUUUUU!"* So what's the deal? *Can you guys handle this or not?* Well if you can't do it you should certainly find a way to make it happen. *I think if you don't offer it soon you're certainly hosing your customers who've spent thousands on your product to protect their pack only to have the tops blowing off like popcorn.*


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## JRP3 (Mar 7, 2008)

Most of them do have a HVC cutoff which would shut down the charger.


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## frodus (Apr 12, 2008)

ElectriCar said:


> As old Sargent Carter used to tell Gomer Pyle...* "I CAN'T HEAR YOUUUUUU!"* So what's the deal? *Can you guys handle this or not?* Well if you can't do it you should certainly find a way to make it happen. *I think if you don't offer it soon you're certainly hosing your customers who've spent thousands on your product to protect their pack only to have the tops blowing off like popcorn.*


But then people will complain that we're trying to sell a system..... But I'll bite.... since I don't get comission on any BMS or battery sales 

Well, I work for two different BMS companies as a consultant... and both the Manzanita Micro BMS and the Elithion BMS do what you need. Both are a full Monitoring and Balancing system. They will disconnect a contactor/relay whatever... if the voltage goes too high or low. You configure your setpoints for everything. Even temperature if you want.

You don't throttle back the charger, you completely shut it off, either via the disable on the charger, or a solid state AC relay on the input of the charger.

Just program the overvoltage you want and if any cell gets that high, it will disconnect the mains to the charger. Then set LVC and it'l set a warning light if it hits LVC and then disable contactor if it goes really low.


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## dimitri (May 16, 2008)

ElectriCar said:


> *"I CAN'T HEAR YOUUUUUU!"*


Not only you can't hear, you also don't bother reading. Your question has been answered many times. I, for one, am tired of wasting my time repeating same info over and over.

I find it amusing that biggest anti-BMS posters here happen to be clueless of what some common BMS systems actually do and what safety features they have. Why bother reading 10 page user guide or looking at wiring diagram when you can just repeat some dramatic stories you heard on TV and proclaim them as facts.


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## ElectriCar (Jun 15, 2008)

frodus said:


> But then people will complain that we're trying to sell a system..... But I'll bite.... since I don't get comission on any BMS or battery sales
> 
> Well, I work for two different BMS companies as a consultant... and both the Manzanita Micro BMS and the Elithion BMS do what you need. Both are a full Monitoring and Balancing system. They will disconnect a contactor/relay whatever... if the voltage goes too high or low. You configure your setpoints for everything. Even temperature if you want.
> 
> ...


Thanks for biting! Well I will likely have some sort of "monitoring" system, depending on the cost and reputation. I'm really not opposed to "monitoring" per se, just don't want something trying to balance my pack for me. 

I think it's important to know what's going on. I currently have a PakTrakr but it won't do 50 cells so I'm likely to replace it with something else. That system has had so many false alarms I think though due to noise. They don't do a good job of filtering if they do any at all!

In fact until I gain more experience with this battery, I may continue to use it but spread over two cells instead of one. This way I can still get feedback for every two cells. If warranted, I can upgrade to something different. 

So this HVC thing will stop the charger if one cells goes high? That's something to consider. Though I still likely will build a max voltage cutoff device for redundancy.


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## ElectriCar (Jun 15, 2008)

dimitri said:


> Not only you can't hear, you also don't bother reading. Your question has been answered many times. I, for one, am tired of wasting my time repeating same info over and over.
> 
> I find it amusing that biggest anti-BMS posters here happen to be clueless of what some common BMS systems actually do and what safety features they have. Why bother reading 10 page user guide or looking at wiring diagram when you can just repeat some dramatic stories you heard on TV and proclaim them as facts.


Well you started it! Thanks for repeating over and over. Someone new will learn something EACH TIME YOU REPEAT IT! And they may buy a BMS. 

And then there's people who think it's an abomination for someone to ask a question before perusing the entire forum in search for answers. If they don't like it they should ignore it and move on. 

I don't mind answering and helping someone if I have a minute or three. Beats the hell out of expecting someone to read for a couple of hours until they get so sidetracked they forgot what they came for! It doesn't cost anything to be nice.


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## tomofreno (Mar 3, 2009)

> So this HVC thing will stop the charger if one cells goes high?


 You don't have to "read the entire forum" to find out about HVC. There is a search function you know. A good description of how this works can be found at Dimitri's cleanauto website in the minibms manual (see advertisement to rhs of screen). All bms I am aware of have both HVC and LVC, but I am sure there are several I am not aware of. The Elithion site has diagrams on how to hook up to trigger an AC relay to cut power to the charger upon HVC, and on how to shut down the Manzanita chargers using the Regbus input. You could at least read about them before you decide whether you want to use one or not.


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## Overlander23 (Jun 15, 2009)

Jimdear2 said:


> If I understand your question.


I wasn't actually referring to you, specifically. I was directing the question more towards the "absolutely-no-extra-wiring-BMS-regardless-of-what-it-actually-does" crowd.

Even with conservative pack usage (90% full, 30% empty strategy)... what happens when cells fail due to no fault of "drift", overcharging, or over discharging? What happens in the event of simple product (cell) failure?

I myself don't currently use a BMS, but I'm not advocating the use or disuse of one. As with most things in the world, it's rather grey.

There are several BMS types and strategies around. A list of these can be created with pros and cons for each method. At the core, though, we're talking about pack management/monitoring (be it with the help of tools or not) to prevent the user from straying into a battery cell's high or low voltage limits.

In general, the simpler the system, the more reliable the practical implementation. Said in reverse, the more complex and feature-full the BMS is, the more trouble it has the theoretical potential of being. Keep in mind that reliability, in this case, only refers to the engineering solution of the system, not the effectiveness of the system in maintaining pack reliability.

So here we go... from most reliable implementation to least reliable (also keep in mind that in practical use, the range could be tiny, but as with all solutions, crappy implementation of anything is still... well, crappy).

*De-rating* - Much like Toyota does with Prius batteries, the easiest and most effective path to pack reliability and safety is de-rating. Using 50% of the theoretical capability of a pack will result in longer cell life and larger safety margins. Even as (or if) cell capacities change or resistances grow, you've got room to play in the margins. An entire cell, or groups of cells, could die and you probably wouldn't be in danger of getting into trouble with other cells if you're limiting pack usage to something very conservative in the middle of SOC. *Pros:* Easy and reliable to implement. Cheapest method of management, but not necessarily when you take into consideration... *Cons:* Potentially unacceptable use of available resources. From a "value" standpoint it's not cheap since you're carrying around more battery than you need. If a cell dies in the pack, you won't necessarily know, but since you're not using all of the SOC, it may not be an issue as the safety margins become a little smaller. In this case, money buys you a degree of insurance.
*
Symmetrical voltage monitoring* - Much the way monitoring the voltage of an entire pack gives you rudimentary knowledge of what's going on inside the pack, splitting a series pack into symmetrical groups allows you to get a comparative idea of what's happening between groups. If one group starts to read differently than another, something is not quite right at a cell level within the weak group. The more groups the pack is split into/monitored, the more accurate the picture becomes. At the very least you _could_ be alerted to a cell problem with this solution. It may be the only practical way of monitoring cylindrical cells, since many more cells are used. *Pros:* Easy and cheap to implement. Fairly reliable engineering solution due to the limited amount of monitoring hardware and wiring connections. *Cons:* Resolves the cell story a little more, but is still broad. If not used in conjunction with conservative pack use (de-rating strategy), the method does nothing to ensure the usage of appropriate pack limits.

*"Active" HVC and LVC at a pack level -* This is already done, in some systems, without a BMS through voltage-limited charging, or LVC-capable motor controllers. It's a blunt method of pack management/monitoring compared to per-cell monitoring with HVC/LVC capability... but I'm running down a list here. While the methods listed above represent the need for fairly conservative pack usage, the use of active HVC/LVC controls at the pack level just makes this job easier. The method is still rewarded by conservative usage, but allows for the potential of looser limits (ie. smaller margins) *Pros:* Basically protects a pack from hitting high and low voltage limits. Inexpensive to implement. Very reliable engineering. *Cons:* The resolution may not be high enough. Doesn't address what's happening inside the pack. Absolutely does *not* insure that individual cells can't fail... but it gives the user a little more leeway with pack usage since the system actively reacts to conditions rather than relying on the user to notice and intervene.

(_This basic strategy could really be coupled with, or related to, the initial strategy of de-rating._)

*"Active" HVC and LVC at a single cell or group level - *This is monitoring a single cell or a handful of cells that you've identified as the "bolters", those cells that hit HVC or LVC first (the weak cells). Consider this the complement to group monitoring. *Pros:* Inexpensive. Reliability getting more complex, but still relatively simple. The more cells you monitor the more information you get. Starts to deal with individual cell behavior, but... *Cons:* Still not a complete pack picture. More wiring means comparatively more unreliability potential. More complexity. Requires much more setup work due to the need to identify initially weak cells. The more cells you monitor the more expensive it gets.

*Per cell HVC/LVC control* - In this strategy, each cell is monitored and HVC/LVC controls triggered if any individual cell strays outside of set bounds. This method doesn't provide voltage feedback monitoring (short of something like an LED activating on the individual cell circuits when a control is tripped). However, the monitoring may be irrelevant if the HVC/LVC control does its job and steps in to prevent cell damage. You may not know exactly what went down, but the controls intervened. *Pros:* Has the potential to protect the individual cells in a pack. Not as complicated or expensive an implementation as having access to individual cell data. *Cons:* Doesn't provide individual cell data. Implementing an engineering solution on a per cell basis starts to add cost and complexity, the latter increases the potential for unreliability. Cost scales with pack size.

*Monitoring (with or without active HVC/LVC control) at a per cell level* - This penultimate strategy gives the user the most complete picture of the pack. With HVC/LVC in tow, the user has the ability to know exactly what's going on at the cell level, and is protected in case any of those cells' limits are breached. As with all strategies, thoughtful implementation is required. In this case, coupling the strategy with conservative pack use will result in more cell reliability than using the strategy while pushing pack limits. Theoretically it's all the strategy you really need. Practically it's complicated and has more room for engineering failure than the previous methods. *Pros:* Complete picture with active controls for using a cell within its appropriate capabilities. *Cons:* Much more engineering complexity. Much more cost. Potential for unreliable data monitoring due to much more exposure to electrical noise interference is high. If the system makes decisions at a "head" unit rather than at the cell level, the potential for noise interference could corrupt the reliability of the active controls.

*Individual cell monitoring with HVC/LVC controls plus energy management* - The big Kahuna of BMS systems. This system does everything listed above and also attempts to manage energy distribution within/between individual cells. Methods for doing the latter vary, ranging from resistor bleed-off of excess energy, to active charge shuttling where energy is shifted from the cells with more of it to cells with less. *Pros:* In a theoretical world, this strategy allows for full pack monitoring, safety, and maintenance. In addition, it potentially allows for the use of maximum pack capability, extending limits. The most user-friendly from a back-end standpoint if everything is done behind-the-scenes. The most extensive implementation of a BMS. *Cons:* Also the most expensive implementation of a BMS. Has the highest potential of unreliability since not only does the method require a large amount of support hardware, but it also directly attempts to actively manage energy within an individual cell.

That's the way I see it. The list* increases* in terms of *cost, complexity, accuracy/resolution/clarity, feature capability, and implementation complexity*. It *decreases* in terms of *potential reliability*. 

In a theoretical world, the list increases in terms of safety, however, in the real world, reliability concerns may eat into the safety the system is designed for.

The question is, how much do you, the reader, rate the concerns of reliability over the concerns of capability? And for that, I just don't see it as black and white.

For me, the very least would be de-rating along with symmetrical, group-voltage monitoring. That seems to me a practical way of operating while still having an inkling of what's happening within the system. I recognize that it's not necessarily the best value, though.

I also have particular requirements. My pack sits idle for months at a time necessitating a monitoring system that does not draw energy from the cells themselves. If I could figure out a way around this problem then I like the idea of small group or per-cell monitoring with HVC/LVC control.

The idea I like the least is active energy management. That's just too much control of the cell. However, if the system is reliable I can see its merits.


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## honn1002 (Nov 26, 2008)

I used Cell Log 8's to build a BMS and it has been very reliable. Here is my wiring diagram.


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## DavidDymaxion (Dec 1, 2008)

Awesome list, thanks for posting.

I'm not sure how it fits in your list (it's kind of two ways to do most of the items). I think of it as centralized smarts with relays vs. per cell smarts.

With per cell smarts you have the ability to continuously monitor, and individually charge manage all the cells simultaneously, but your failure rate goes up by the number of cells monitored. A failure that draws more current, or shunts more current than expected can ruin a cell or worse. A board that overreports voltage might shut down the charger early, and hopefully the user doesn't flatten the pack. On the other hand, you have a high chance of catching a low or high voltage condition even if one board fails. The per cell smarts can have a constant small draw, bad if the car is stored for an extended period.

The centralized smarts has a central voltmeter, and uses relays to access individual cells. Reliability goes up, but at the expense of only monitoring or charge managing a single cell at a time. If something happens quickly you are likely to miss it, as it might take minutes to cycle through the whole pack. You could keep track of the lowest and highest cells in the pack and check them more frequently, like low/cell0/high/cell1/low/cell2/high/... and replace the high and low when you find a higher or lower cell. Varying currents complicates this!

The ultimate approach might be a fusion of the methods. Central control could open a small relay that electrically removes the per cell monitoring board. The central control could look for a heartbeat and errors on individual boards, and remove those that don't respond. Central control could even check the cell boards are reporting the correct voltage. Of course, now you have a really complicated BMS!

Final thought: BMS boards for each battery, then for pairs of batteries. If the sum of the individual BMS boards don't agree with the parent voltage value, flag an error.


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## crashnfool (Sep 26, 2009)

Overlander23 said:


> If you're going completely BMS-less... What happens if a cell/multiple cells go(es) bad? I mean, manufacturer defect-type of thing.



most manufacture defects are replaceable....if its a bad cell...

If someone decides not to use any kind of protection at all.....Well someone will be losing a certain amount of money.......and someone will be gaining that same if not more......

I've personally seen two cells go bad because of a "bad" bms.....and replaced more from " no bms" problems...

and I'm just a test dummy.....

If you want to spend your money...then study and talk to knowledgeable people and use the advice they will surely give you.....


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## dimitri (May 16, 2008)

Overlander23 said:


> So here we go... from most reliable implementation to least reliable (also keep in mind that in practical use, the range could be tiny, but as with all solutions, crappy implementation of anything is still... well, crappy).


This must be one of the best BMS reviews I have seen that fits on one page. Excellent job Jeff, thanks for taking time to post it.

If moderators read this, can Jeff's post be placed as a sticky in battery section? It deserves to be a Wiki page too, but I suspect few people read those based on usual forum behavior I observed.

BMS discussions suffer the most from lack of proper terminology, lots of confusion about BMS features, etc. Jeff's post is an excellent starting point for anyone trying to sort these out.


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## dimitri (May 16, 2008)

ElectriCar said:


> Well you started it! Thanks for repeating over and over. Someone new will learn something EACH TIME YOU REPEAT IT! And they may buy a BMS.
> 
> And then there's people who think it's an abomination for someone to ask a question before perusing the entire forum in search for answers. If they don't like it they should ignore it and move on.
> 
> I don't mind answering and helping someone if I have a minute or three. Beats the hell out of expecting someone to read for a couple of hours until they get so sidetracked they forgot what they came for! It doesn't cost anything to be nice.


I started nothing, I simply called you on posting a blatant lie you heard elsewhere ( still waiting for you to admit it and retract it ).

Your point of view is common, but it shows utter lack of respect to your fellow forum members. You find it normal not to spend 15 minutes searching and reading existing posts, yet you also expect others to spend their 15 minutes repeating something they already spent 15 minutes posting just a few weeks back. So, in your world, I am expected to double my time spent sharing same info, while you can enjoy immediate results without lifting a finger. This is how I see it and I know for a fact that lack of informed responses to most threads on this forum is due to people who are capable of responding feeling the same way I do.


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## Jan (Oct 5, 2009)

Overlander23 said:


> *De-rating* - Much like Toyota does with Prius batteries, the easiest and most effective path to pack reliability and safety is de-rating. Using 50% of the theoretical capability of a pack will result in longer cell life and larger safety margins. Even as (or if) cell capacities change or resistances grow, you've got room to play in the margins. An entire cell, or groups of cells, could die and you probably wouldn't be in danger of getting into trouble with other cells if you're limiting pack usage to something very conservative in the middle of SOC. *Pros:* Easy and reliable to implement. Cheapest method of management, but not necessarily when you take into consideration... *Cons:* Potentially unacceptable use of available resources. From a "value" standpoint it's not cheap since you're carrying around more battery than you need. If a cell dies in the pack, you won't necessarily know, but since you're not using all of the SOC, it may not be an issue as the safety margins become a little smaller. In this case, money buys you a degree of insurance.


Nice list Overlander. 

But I miss some pros/cons. A important pro in de-rating, is longer battery life. Staying away from the top and bottom improves the number of 'cycles'. At least, that's also a hypotheses. Like so many.

And, if true, that's one of the con's of some BMS's. The ones that always try to top balance during charging.


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## JRP3 (Mar 7, 2008)

Jan said:


> A important pro in de-rating, is longer battery life. Staying away from the top and bottom improves the number of 'cycles'. At least, that's also a hypotheses. Like so many.
> 
> And, if true, that's one of the con's of some BMS's. The ones that always try to top balance during charging.


Not necessarily if they don't try to top balance at a high SOC. If balancing occurs at around 3.45-3.50 for CALB cells then you get the same benefit from undercharging. If the BMS is set to balance at max SOC then yes you are correct.


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## Jan (Oct 5, 2009)

JRP3 said:


> Not necessarily if they don't try to top balance at a high SOC. If balancing occurs at around 3.45-3.50 for CALB cells then you get the same benefit from undercharging. If the BMS is set to balance at max SOC then yes you are correct.


Yep, you're wright. A BMS with de-rating. But is this a theoretical BMS or do they really exist?


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## dimitri (May 16, 2008)

JRP3 said:


> Not necessarily if they don't try to top balance at a high SOC. If balancing occurs at around 3.45-3.50 for CALB cells then you get the same benefit from undercharging. If the BMS is set to balance at max SOC then yes you are correct.


Actually, the whole "stay from the top or bottom" theory is a bit of red herring because we often mix SOC with voltage when referring to top or bottom. If we speak strictly SOC, then anyone who regularly reaches the "knee" in charge voltage, which is most people, then we are all guilty of reaching about 98% SOC every day. My non-expert opinion is that "stay away from top" means top voltage, not top SOC, there is nothing wrong with reaching 98% SOC every day. Reaching top voltage reduces safety margin before we can damage the cell, but most of us have quite significant top voltage margin, about 0.5V or so, plenty to be safe, IMHO.

Same goes for bottom safety margin, considering that voltage drop happens close to empty, we need to allow larger safety margin. Deeper voltage sag under load which some of us use to trip BMS is actually a benefit in keeping wider bottom margin, a feature IMHO, which is widely ridiculed by anti-BMS crowd in their infinite wisdom.

Of course accurate AH counting can be used to truly stay within preset SOC range, but that's another discussion.


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## JRP3 (Mar 7, 2008)

dimitri said:


> Actually, the whole "stay from the top or bottom" theory is a bit of red herring because we often mix SOC with voltage when referring to top or bottom. If we speak strictly SOC, then anyone who regularly reaches the "knee" in charge voltage, which is most people, then we are all guilty of reaching about 98% SOC every day. My non-expert opinion is that "stay away from top" means top voltage, not top SOC, there is nothing wrong with reaching 98% SOC every day.


I look at it a bit differently. Top voltage is only a relative indicator of SOC at that current level, when charging at higher current voltage will appear higher but the SOC will be lower so the cell is not actually full. I think damage occurs from trying to stuff more electrons in than there is room for, not just from voltage. If you put 30 amps into a cell the voltage might hit 4V but if you drop the current down to 10 amps the voltage will also drop. So our knee voltage is dependent on current, (and temperature), as well. The higher current you charge at your knee voltage will be representative of a lower SOC so you actually leave more unused capacity on the table.


> Same goes for bottom safety margin, considering that voltage drop happens close to empty, we need to allow larger safety margin. Deeper voltage sag under load which some of us use to trip BMS is actually a benefit in keeping wider bottom margin, a feature IMHO, which is widely ridiculed by anti-BMS crowd in their infinite wisdom.


It depends. Bottom balancing a pack allows pack voltage to have meaning during discharge. If I see 114V off throttle with my bottom balanced 36 cells I know I'm around 3.17V per cell, if I see 112V off throttle I know I'm around 3.11V per cell, both values well within safe margins. Of course I also use an Ah counter as a fuel gauge and to track real SOC and rarely get near those values unless I'm purposely pushing it, but I did drive around for a while without one just using voltage and a bottom balanced pack.


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## Jimdear2 (Oct 12, 2008)

honn1002 said:


> I used Cell Log 8's to build a BMS and it has been very reliable. Here is my wiring diagram.


honn,

A very nice design using "off the shelf' stuff. A lot of my LVC/LVM rough layout follows what you have.

It's even understandable by a non "electronics" person like myself.

I was wondering how the switched in paralled resistance in the throttle control worked out? Is the reduction enough to bring the batteries up out of the danger zone without being unsafe, is it driver noticable? 

I like the reverse low power adaptation. I wanted to do similar stuff but was going to wait until I had the basics right.

It looks like you have a very complete BMMS (Battery Management Monitoring System) for well unde $600.00.

Congratulations,
Jim


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## Jan (Oct 5, 2009)

I believe (at the moment) that staying away from the top and bottom is not as black and white as you guys seem to believe. I think a Li-Ion cell lives nearly forever charged around 50-60%. Every time you charge it higher or discharge it deeper its life shortens exponential. So at 70% SOC life doesn't shorten much, but often charging to 90% makes a serious difference.


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## Jimdear2 (Oct 12, 2008)

dimitri said:


> This must be one of the best BMS reviews I have seen that fits on one page. Excellent job Jeff, thanks for taking time to post it.
> 
> If moderators read this, can Jeff's post be placed as a sticky in battery section? It deserves to be a Wiki page too, but I suspect few people read those based on usual forum behavior I observed.
> 
> BMS discussions suffer the most from lack of proper terminology, lots of confusion about BMS features, etc. Jeff's post is an excellent starting point for anyone trying to sort these out.


 
You've got my vote on placing it in the WIKI and for sure as a Sticky. 

This would be a nice place for open discussion hopfully "WITHOUT" all of the nasties that seem to pop up with "Things and Ideas" we hold close. 

Probably wishfull thinking there.


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## DIYguy (Sep 18, 2008)

Overlander23 said:


> So here we go... from most reliable implementation to least reliable (also keep in mind that in practical use, the range could be tiny, but as with all solutions, crappy implementation of anything is still... well, crappy).


Thank you Jeff, that is an excellent summary and I second the motion to make this a sticky and a wiki entry. There may be some evolution or further comments to it...but a great read for someone trying to get their head around pack management/monitoring and searching for a solution that fits their needs. Nice job...


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## billmi2 (Nov 29, 2010)

GerhardRP said:


> Do the statistics exist? Of all the fires reported, how many had BMS systems and how many did not? I know stastics lie, but if there are no BMS absent fires, lets think.
> Gerhard


Extending that logic, the cause of EV fires is tires, since 100% of working EVs that have caught fire had tires.

In listening to the show in which Jack rants against BMS technology, he turns around and talks about how individual cell monitoring could be beneficial. Seems to me, he's really arguing more toward manual bottom balancing and against shunt based top balancing than against the LVC and HVC functions - as he certainly makes a case that an LVC monitoring system could have saved the 3 cells he lost while testing manually top balanced packs.


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## Jan (Oct 5, 2009)

billmi2 said:


> Extending that logic, the cause of EV fires is tires, since 100% of working EVs that have caught fire had tires.


I'm not sure your serious. But if you are: You're not extending logic, just twisting it. Tires never cause fires. A faulty BMS however could. 

Since they are designed to prevent just that, burning cars down, it's odd I only know of burnt down cars that had a bms. And 'know of' means here documented in the news media. Not read on a forum.


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## dimitri (May 16, 2008)

JRP3 said:


> I look at it a bit differently. Top voltage is only a relative indicator of SOC at that current level, when charging at higher current voltage will appear higher but the SOC will be lower so the cell is not actually full. I think damage occurs from trying to stuff more electrons in than there is room for, not just from voltage. If you put 30 amps into a cell the voltage might hit 4V but if you drop the current down to 10 amps the voltage will also drop. So our knee voltage is dependent on current, (and temperature), as well. The higher current you charge at your knee voltage will be representative of a lower SOC so you actually leave more unused capacity on the table.


Actually we both say same thing, just looking from different angles. We both speak of how close we get to AH capacity limit. If you get there at lower current, then it simply takes more time, but you still cram same 1-2% AH once you past the knee. So my point still holds, if we reach the knee we all charge to 98% every time and based on above theory we must be shortening our pack's life. However, I don't see a practical way of avoiding it since you must have some reference point on a regular basis and you will never stay in planned range just by AH counting, no matter how good your AH counter is. So, since we need a regular reference point using knee voltages, then we have no choice but bring our packs to almost full charge. Long term effect in real life is yet to be seen, regardless of what we all believe.


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## Jan (Oct 5, 2009)

dimitri said:


> I don't see a practical way of avoiding it since you must have some reference point on a regular basis and you will never stay in planned range just by AH counting.


Yes, and that's the great question. It always comes down to this particular asumption. Or fact. Or whatever.


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## billmi2 (Nov 29, 2010)

Jan said:


> I'm not sure your serious. But if you are: You're not extending logic, just twisting it. Tires never cause fires. A faulty BMS however could.


I'm serious in that being an extension of the logic, and using that extension to show why the logic is flawed. You could substitute any common component that could - connectors, wires, headlights, chargers, but that wouldn't make the flaw in the logic as obvious.

The flaw in the logic is that commonality is not proof of causality.

Just because the EVs that caught fire had a feature in common (BMS, tires, charger, etc.) does not mean that one of those specific feature caused them to burn. 

Now, if a series of EV fires had been investigated and shown that in a significant percentage of them charger failure, BMS failure, tire spontaneous combustion, etc. were the causes of the fire, that would be something.


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## dimitri (May 16, 2008)

Jan said:


> Since they are designed to prevent just that, burning cars down


Actually BMS is designed to monitor/manage battery, not prevent fires. There is no device in the world that I know of that can prevent fires, or we would not have fire stations in every zip code.

BMS *failure* can contribute to a chain of events that can start a fire. Just as much as charger *failure* can, or wiring *failure*, or connection *failure*. This statement is a far cry from saying that "BMS causes EVs to burn down", which is precisely what anti-BMS people say.

In properly designed and implemented system there must be multiple safety checks, such that single failure does not cause catastrophic results. Since there are many BMS systems out there and even more EV designers and implementers, we can't draw any conclusions from 5 reported fires. Only a complete dumbass can make a statement that if EV had BMS and it burned down then BMS *must be the reason.*

Perhaps if those 5 EVs had just one more safety check, the chance of fire could be reduced by magnitude. Unless you are intimately familiar with all details of those 5 EVs, how well they were built and tested, how many people checked them for potential issues, etc etc, you can't possibly draw any conclusions.

When we build our own EVs we take risks. We try to minimize those risks to the best of our ability, but never to zero. Some of us are better at it than others, some are just lucky or unlucky. Can't draw a single conclusion.


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## Jan (Oct 5, 2009)

billmi2 said:


> Just because the EVs that caught fire had a feature in common does not mean that feature caused them to burn.


Yes, that's true. But if they all have a feature installed because of the fear of fire, than it's an odd fact. 



> Now, if 100% of EV fires had been investigated and shown that BMS failure was the cause of the fire, that would be something.


Did you read about the latest fire on the Norwegian ferry? Investigation (by the manufatorer) came to the conclusion the car burnt down due to a wrong extention cable. 

That's really, really hard to believe if you look at the picture. I wonder how objective investigators with money in BMS are.


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## JRP3 (Mar 7, 2008)

dimitri said:


> Actually we both say same thing, just looking from different angles. We both speak of how close we get to AH capacity limit. If you get there at lower current, then it simply takes more time, but you still cram same 1-2% AH once you past the knee. So my point still holds, if we reach the knee we all charge to 98% every time and based on above theory we must be shortening our pack's life.


I don't think you're quite getting what I'm saying. If I'm charging at higher current, say 30 amps, and my cell voltage shows 3.45V, the knee, if I back the charger down to 5 amps it no longer shows 3.45V, it may show 3.4V, just barely in the knee or not even. The actual SOC of the cell didn't change from when it showed 3.45V. Similarly it could go to 4.0V at 30 amps but be at 3.5V at 5 amps. So if I'm charging at 30 amps and shut off the charger when I hit 3.45 per cell the pack is at a lower SOC than if I were charging at 5 amps and shut off the charger when I hit 3.45. I know this is true because if I crank up my charger to 40 amps the voltage rise will cause it to shut down early and the ah counter shows the pack was not fully charged, even though the voltage during charging was higher.


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## Jan (Oct 5, 2009)

dimitri said:


> Actually BMS is designed to monitor/manage battery, not prevent fires. There is no device in the world that I know of that can prevent fires, or we would not have fire stations in every zip code.


There are plenty devices, procedures and precautions that are designed or made up to prevent fires. We all know they only work to some extent. 

I'm prety sure a BMS is also designed to prevent an overcharge. And overcharging is the mother of all battery fires. We all are afraid of a uncontrolled overcharge. Read this topic again, and you will notice some BMS horror stories, about not having a BMS and overcharging.

I don't understand why you want to deny this simple fact.


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## ElectriCar (Jun 15, 2008)

dimitri said:


> I started nothing, I simply called you on posting a blatant lie you heard elsewhere ( still waiting for you to admit it and retract it ).
> 
> Your point of view is common, but it shows utter lack of respect to your fellow forum members. You find it normal not to spend 15 minutes searching and reading existing posts, yet you also expect others to spend their 15 minutes repeating something they already spent 15 minutes posting just a few weeks back.


Utter lack of respect? Talk about drama, lol. No, sorry, you're wrong there. I spend a lot of time reading & searching about many things here. 15 minutes isn't going give you much most of the time. 



dimitri said:


> So, in your world, I am expected to double my time spent sharing same info, while you can enjoy immediate results without lifting a finger. This is how I see it and I know for a fact that lack of informed responses to most threads on this forum is due to people who are capable of responding feeling the same way I do.


I find it odd that you as a business owner would be so hostile to people on this forum who are potential customers, people who may disagree with you or in my case have an opinion on something because of the work and conclusions of others, which could in this case be you, were I on your side and a BMS proponent. 

When I or others ask a question it's not a requirement for you or anyone to reply. It's a courtesy to others and thus I spend a lot of time posting because I enjoy helping people. I also understand how difficult if can be searching for things at times thus my willingness to help people. I don't whine if someone asks for a little of my time. And my time is valuable as is yours.


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## GerhardRP (Nov 17, 2009)

Jan said:


> Did you read about the latest fire on the Norwegian ferry? Investigation (by the manufatorer) came to the conclusion the car burnt down due to a wrong extention cable.
> 
> That's really, really hard to believe if you look at the picture. I wonder how objective investigators with money in BMS are.


This google translate of 
http://translate.google.com/translate?hl=en&sl=da&u=http://folketidende02.armadahosting.com/brand-i-elbil-batteri&ei=XQYmTcL_OYKC8gb65NW_AQ&sa=X&oi=translate&ct=result&resnum=3&ved=0CC8Q7gEwAg&prev=/search%3Fq%3DEkelund%2BSaksk%25C3%25B8bing%2BHejlesen%26hl%3Den%26rls%3Dcom.microsoft:en-us:IE-ContextMenu%26rlz%3D1I7GGIK_en%26prmd%3Divns

It was the battery in electric car from Sakskøbing, who started the fire aboard the Oslo boat. 
It identifies the police investigations.

Electric car owner Søren Ekelund from Sakskøbing-Firm A Future EV themselves believed it was a short circuit in an unoriginal extension cord, which he used to recharge car batteries, which triggered the fire at the ferry Pearl of Scandinavia last week. 


Police technicians has now completed their investigations. These studies would still immediately that it was the extension cord that was causing the fire. Instead, pointing police investigations, the fire started in the car's battery, writes TV2Øst. 


- At present there is every indication that it was the battery. But it is not certain that we will ever be one hundred percent sure, "says Bertel Hejlesen directing the fire section in Copenhagen Police for TV station. 


The theory is that the battery is first burned together and then heat evolution may have started the fire.


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## dimitri (May 16, 2008)

ElectriCar said:


> I spend a lot of time reading & searching about many things here.


If you spent any time reading this forum section you could not possibly have been unaware that every half decent BMS system cuts off the charger on HVC event, its basically the primary function of the system, discussed a thousand times. Few posts above you were completely unaware of it and surprised when someone pointed it out to you. Yet such lack of basic BMS knowledge didn't stop you from proclaiming that BMS causes fires. The only conclusion I draw is that you either don't read or you read wrong stuff.

I have been on this forum over 2 years, everyone who reads my posts can vouch that I am only hostile to liars and bullies. I show support by helping people who are ready to be helped and don't have a veil over their eyes, I also show support by paying for my ad. The business you speak of makes me work 16 hour days, much of which is spend sharing my personal experience with open minded people. I see no point in talking to closed minded people, its a waste of my breath. Stuff I sell I made for my own EV and only started offering to others because they asked for it. I don't push anything to anyone.

I hate to hijack the thread with personal issues, so I will no longer respond on this subject in this thread. If you feel a need to continue, start a new thread on the subject of forum ethics or contact me privately.


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## Jan (Oct 5, 2009)

GerhardRP said:


> This google translate of
> http://sydhavsnyt.dk/wp/?tag=søren-ekelund
> 
> It was the battery in electric car from Sakskøbing, who started the fire aboard the Oslo boat.
> ...


Thanks Gerhard, that makes more sence. And the batteries burned probably together due to overcharging. How a faulty extention cable could cause that is a mistery to me.

p.s. the manufacterer sticks to the faulty cable: http://www.afutureev.com/news.aspx


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## dimitri (May 16, 2008)

JRP3 said:


> I don't think you're quite getting what I'm saying. If I'm charging at higher current, say 30 amps, and my cell voltage shows 3.45V, the knee, if I back the charger down to 5 amps it no longer shows 3.45V, it may show 3.4V, just barely in the knee or not even. The actual SOC of the cell didn't change from when it showed 3.45V. Similarly it could go to 4.0V at 30 amps but be at 3.5V at 5 amps. So if I'm charging at 30 amps and shut off the charger when I hit 3.45 per cell the pack is at a lower SOC than if I were charging at 5 amps and shut off the charger when I hit 3.45. I know this is true because if I crank up my charger to 40 amps the voltage rise will cause it to shut down early and the ah counter shows the pack was not fully charged, even though the voltage during charging was higher.


I perfectly understand you. The "knee" is a moving target, depends on current which is a function of voltage applied to terminals and charger's ability to keep such voltage at the given current or vice versa. My point was to illustrate a general idea that relation between SOC and voltage is not linear, so when saying "stay away from top" you must specify which "top" and how the hell can you tell how far from the top you are at any given time. For any given combination of battery and charger, the knee will be generally known ( in a given range of ambient temps ). Given limited selection of common chargers and limitation of charging circuits we can safely assume that if we reach the general "knee" area then we are at 95%-98% SOC, but definitely far from often reffered 80%. I don't know of any way to stop charging at 80% unless you frequently reference your instrumentation by charging to 95%-98%.


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## GerhardRP (Nov 17, 2009)

Jan said:


> Thanks Gerhard, that makes more sence. And the batteries burned probably together due to overcharging. How a faulty extention cable could cause that is a mistery to me.


And this:



Since an electric car caught fire Wednesday on the ferry Pearl of Scandinavia was not the first time. The same thing happened earlier this year for a second car from the same company.  



On the night of the 18th March broke an electric car from Sakskøbing 'company, A Future EV, namely fire, as it was in a car-house in Aalborg. .​

It writes GT. 
Although both the fire in Aalborg and the Pearl of Scandinavia was in connection with charging the electric car, says Søren Ekelund, which owns electric car company to BT, there were two quite different reasons. 
In Aalborg fire originated in a problem when a cable gland. In the Pearl of Scandinavia started the fire in an adapter between the car's cable and extension cords. Søren Ekelund explains also that type of car from then and till today is far different.


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## ElectriCar (Jun 15, 2008)

Fortunatly dimitri I'm not a liar nor a bully. What you should do instead of calling people names is be a little reserved in your reply and explain why you believe or diebelieve what someone says or not reply at all.

You have made a lot of assumptions about me that are incorrect and resorted to name calling and character assination. That's a little overboard and unwarranted.


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## Jan (Oct 5, 2009)

GerhardRP said:


> ...originated in a problem when a cable gland.


Don't understand what this means.

This I understand:



> Søren Ekelund explains also that type of car from then and till today is far different.


"It was never our fault, but if you doubt that, we changed a lot since then."


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## dimitri (May 16, 2008)

GerhardRP said:


> The theory is that the battery is first burned together and then heat evolution may have started the fire.


But LiFePo4 batteries aren't supposed to burn even from severe overcharge. Do we know exact battery model/type used in that car?

They can deform and even explode if vent's fail, they can melt, they can release gas, but they should not ignite. There must be more to this story.

BTW, if someone thinks extension cords are benigh, think again. I personally observed a spectacular event when poorly crimped charger connection zorched in front of my eyes. I can't say who made that crimp but it was quite shitty job, which goes back to implementors of EV conversions, their safety checks and tests, etc. All it would have taken for someone is simply pull on that crimped wire to make it fall out. Most issues come from stupid human mistakes. I bet that all 5 fires could have been prevented by second pair of eyes checking all the work that was done on that EV.


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## Jan (Oct 5, 2009)

dimitri said:


> ...they can release gas


The gas is, if I recall correct, combustible.


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## tomofreno (Mar 3, 2009)

Yes, the organic solvents, ethylene, propylene, and dimethy carbonates, are combustible, but need something to ignite them upon cell venting or bursting. If so, then I would guess that the burning jet would start the plastic casing of an adjacent cell burning.


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## tomofreno (Mar 3, 2009)

> I don't think you're quite getting what I'm saying. If I'm charging at higher current, say 30 amps, and my cell voltage shows 3.45V, the knee, if I back the charger down to 5 amps it no longer shows 3.45V, it may show 3.4V, just barely in the knee or not even.


 Yes, Jack R. made this point some time ago, even may have had one of his "shows" on it. He charged a cell at very high current to over it's spec'ed voltage limit, then reduced the current to show it was then below the spec'ed voltage limit, and said no damage was done to the cell (no way to prove it immediately). His point was that the spec'ed voltage limit at the spec'ed charging current is just one way to get a fully charged cell. Different charge currents will give different voltages. I always just watch for the knee - where charge current starts to take off, and rise exponentially with time or Ah regardless of charge current value- and stop there or below.


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## dimitri (May 16, 2008)

tomofreno said:


> I always just watch for the knee - where charge current starts to take off, and rise exponentially with time or Ah regardless of charge current value- and stop there or below.


Exactly. In other words, the voltage value of the "knee" when measured at cell terminals simply follow's Ohm's law, no majic here. Jack's demo was a simple demo of Ohm's law, nothing more. But in the context of "stay from the top" theory the "knee" is an event we can easily observe, regardless of its actual value, because we don't look at value, we look at rising delta over short time period. This event tells us that cell is almost full and futher charging is pointless and risky. But we are far past 80% SOC at that point, which means "stay away from top" is an empty theory without practical implications, yet this theory is spreading like wild fire.
Only time will tell if cycle life advertised is real or how far from truth it is.


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## tomofreno (Mar 3, 2009)

> But I miss some pros/cons. A important pro in de-rating, is longer battery life. Staying away from the top and bottom improves the number of 'cycles'. At least, that's also a hypotheses. Like so many.
> 
> And, if true, that's one of the con's of some BMS's. The ones that always try to top balance during charging.


GM would seem to agree with you, with only charging the Volt to 80%. But then some of the Chinese battery manufacturers also sell top balancing bms systems no?


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## tomofreno (Mar 3, 2009)

> But we are far past 80% SOC at that point


 I missed the 80% part. Yes, I don't know how you would ascertain you are at 80% unless you reference it in Ah from the Ah you know you have at the "knee" - only as an approximation.


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## dimitri (May 16, 2008)

tomofreno said:


> GM would seem to agree with you, with only charging the Volt to 80%.


Can we really believe anything GM says in their public releases? 

They kept calling Volt a series hybrid for years, but it turned out to have exact same drivetrain that Prius had for 10 years, with plugin battery being the only improvement. I added 10kw battery to my own Prius and I basically have same car as Volt at half the cost


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## GerhardRP (Nov 17, 2009)

More:
http://translate.google.com/translate?js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&sl=da&tl=en&u=http%3A%2F%2Fwww.comon.dk%2Fnyheder%2Fbatteri-firma-afviser-brandfare-i-elbiler-1.378214.html


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## MN Driver (Sep 29, 2009)

dimitri said:


> Can we really believe anything GM says in their public releases?
> 
> They kept calling Volt a series hybrid for years, but it turned out to have exact same drivetrain that Prius had for 10 years, with plugin battery being the only improvement. I added 10kw battery to my own Prius and I basically have same car as Volt at half the cost


It isn't the exact same drivetrain. It is a planetary drive transmission but GM has incorporated clutches to engage or disengage different planet arrangements. It can connect and disconnect the different motors to allow for different motor speeds and can engage and disengage the gas engine. It provides the ability to prevent the motors from overspeeding which is an issue that prevents the Prius from going to highway speeds without spinning the engine at the same time. IMHO the GM design is better, but the car itself is heavy, expensive, and not as efficient as it could be if it were pure electric.

GM is derating the pack and staying away from the fully charged and discharged end, they have to in order to get the warranty spec they want, they are aiming for EAT-PZEV which requires 10 year 150k mile warranty, once they put that on the car consumers will have more confidence to buy it.

Since someone mentioned this earlier in the thread. GM also is doing cell balancing too, in contrary to what Rickard said. They have wiring running to the cells. It appears Nissan has the same setup with the three connections to every module as well, I think those modules are 4 parallel cells if I'm not mistaken, I haven't gotten any confirmation on whether they are in parallel though.


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## JRP3 (Mar 7, 2008)

dimitri said:


> This event tells us that cell is almost full and futher charging is pointless and risky. But we are far past 80% SOC at that point, which means "stay away from top" is an empty theory without practical implications, yet this theory is spreading like wild fire.


I'm not sure if there was ever an official suggestion that 80%SOC is the sweet spot, just that 100% was not necessary or even desirable. The knee is a curve, not a point, and if you stop charging at the very beginning of the knee I think you end up closer to 90%SOC than 95%SOC. I can usually charge for another 20-30 minutes or so at 20 amps after my charger shuts down if I want more range.


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## jackbauer (Jan 12, 2008)

.........Whether 'tis nobler in the mind to suffer
The slings and arrows of excess voltage,
Or to take arms against a sea of forums,
And by opposing end them?.

Sorry couldnt resist. On a serious note i've just moved to lithium and would dearly love a bms that worked well. I can't exactly define "well" in words. My fears are putting a circuit across cells capable of hundreds of amps or running a big bundle of cable to a bigger circuit. So far from what i've seen the only reasonable system is the minibms. That said i dont exactly like it too much either.........sigh......


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## dimitri (May 16, 2008)

jackbauer said:


> That said i dont exactly like it too much either.........sigh......


Constructive feedback is always welcome


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## Roy Von Rogers (Mar 21, 2009)

dimitri said:


> This must be one of the best BMS reviews I have seen that fits on one page. Excellent job Jeff, thanks for taking time to post it.
> 
> If moderators read this, can Jeff's post be placed as a sticky in battery section? It deserves to be a Wiki page too, but I suspect few people read those based on usual forum behavior I observed.
> 
> BMS discussions suffer the most from lack of proper terminology, lots of confusion about BMS features, etc. Jeff's post is an excellent starting point for anyone trying to sort these out.


 
I agree, we need to change this to BmoS and BmngS, or something like that. There is a big difference between a Battery Monitoring System and a Battery Management System, or whether its active or passive for that matter.

Actually one could monitor/manage a battery pack with three wires if one wants to keep it simple.

I'm thinking if I was going to build an EV, I would stay with a 48 cell pack, one could use the line voltage, rectify it, and use some IGBT's to control line amperage, there would be no way for the pack the ever get overcharged, as long as some basic monitoring is done.


Roy


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## jackbauer (Jan 12, 2008)

No offense meant dimitri i'm still just looking at options. You may well see an order from Ireland in the near future


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## dimitri (May 16, 2008)

jackbauer said:


> No offense meant dimitri i'm still just looking at options. You may well see an order from Ireland in the near future


No offense taken, hence the smiley face. I am honestly interested in constructive feedback, even though I can't promise to act on it short term.


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## jackbauer (Jan 12, 2008)

This looks interesting:
http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1037,C1134,P86662


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## dimitri (May 16, 2008)

jackbauer said:


> This looks interesting:
> http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1037,C1134,P86662


Somewhat old news, looked at this chip year and a half ago. Some people at ES forum made good progress with it, last I read was few months back though, so not sure how far they got with it. Another guy (Method??? maybe the same guy from ES forum now that I think about it) showed a BMS on this forum using this chip last year, but was ridiculed by BMS-jihad crowd and he disappeared, I'm sure you can still find his posts, which had many pics.

I had a couple reasons not to use this chip in large scale EV, but would be perfect for smaller packs.


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## Elithion (Oct 6, 2009)

ElectriCar said:


> I'm really not opposed to "monitoring" per se, just don't want something trying to balance my pack for me.
> 
> I think it's important to know what's going on.


OK.

Then here is a list of all "meters" out there. By "meter" I mean a BMS that doesn't balance, and doesn't do squat if you pack is being abused. All it does is tell you the voltages. If you do not happen to be looking at it at the time, tough.

As you see, only Casa Del Gato's BMS will work for 50 cells (each unit handles 10 cells).


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## Elithion (Oct 6, 2009)

dimitri said:


> BMS discussions suffer the most from lack of proper terminology, lots of confusion about BMS features,


Hence, I have adopted and promoted the following logical breakdown of BMSs based on what they do and how.










For example, Dimitri's MiniBMS and EV-Power's BMS are:"Analog balancer".

Source.

Reference and further reading.


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## frodus (Apr 12, 2008)

gottdi said:


> You know there are a crap load of BMS's on that list. How the hell is anyone supposed to know which is the best and safest to use. One will drown in that sea of decisions. How does one choose? Eeny meeny miny moe catch a ............. you know how it goes. Or do you have a better way for any and all to choose the very best one? Or is it out you go?


same way you chose batteries, charger, motor and controller, DC-DC converter, contactor....etc.

evaluate the options you want/need and chose the best one for your application considering all variables (cost, size, options).


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## Elithion (Oct 6, 2009)

spdas said:


> "What is the function of a BMS?"


This is the best way I can answer your question.


> 1.3.1 BMS Definition
> There is no unique definition of what a BMS is and does, and sometimes other terms [such as voltage management system (VMS) or protection circuit module (PCM)] are used for what is in effect a BMS. Here I take the wide view that a BMS is any product or technology used with the intent of taking care of a battery in one way or another.
> This may include any of the following functions:
> • To monitor the battery;
> ...


Reference: the Li-Ion BMS book


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## Elithion (Oct 6, 2009)

ElectriCar said:


> *For you BMS proponents, don't be shy, here's your chance to make a sale! Describe what your BMS will do for this scenario and if you handle it without a cell level monitoring system
> 
> 
> *As old Sargent Carter used to tell Gomer Pyle...* "I CAN'T HEAR YOUUUUUU!"*


For me to promote ours would be in bad taste.

So, instead, allow me to say that, based on my somewhat deep understanding of Li-Ion BMSs, I would say that the only type of BMS worth using in a vehicle is a "balancer" (either and analog balancer or a digital balancer). 

And from my point of view as a DIY electric person, I would recommend that hobbyists should use an analog balancer (simpler to understand). 

And, that, for my money, the best analog balancer out there is Clean Power MiniBMS, with Rod Dilkes' EV power BMS a close second.

Why? 
1) Because they perform every function that a BMS should perform

HV cutout
LV cutout
Balance
2) Because they are available and priced right


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## JRP3 (Mar 7, 2008)

It seems to me that a BMS without active balancing is a safer product to have installed. Unless your pack is way out of whack the balancing feature will rarely come into play anyway, and the LVC/HVC will signal any problems and protect the pack.


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## frodus (Apr 12, 2008)

JRP3 said:


> It seems to me that a BMS without active balancing is a safer product to have installed.


Why, citation needed.

And BTW, I've seen NO pack, no matter how balanced it was, not use the balancing feature on either Manzanita or Elithion. There are always a few of the cells in a balanced pack that are being actively balanced.


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## JRP3 (Mar 7, 2008)

Balancing means shunting, shunting means heat. I realize it's not much heat as designed, but if something goes wrong it can drain a cell to zero, which has happened to some people.


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## todayican (Jul 31, 2008)

For what its worth, in an age where no one seems to have the data they need with regards to BMS, its the perfect time for BMS builders to sing their own praises.

I may be alone here, and my day job as a marketing guy may show through, but if you built something good, its not in bad manners at all to say so.

Just my 2 cents 

Also, the whole ban cars with tire thing is weak... lol


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## frodus (Apr 12, 2008)

jrp3 said:


> if something goes wrong it can drain a cell to zero, which has happened to some people.


citation needed


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## Elithion (Oct 6, 2009)

honn1002 said:


> I used Cell Log 8's to build a BMS and it has been very reliable. Here is my wiring diagram.


There's a slight problem with solutions that use a single OOB (Out Of Bounds) line, instead of separate LVC and HVC line. (This is also a problem with the Clean Power Auto MiniBMS, and with the EV Power BMS solution). 

The problem is that you can get in a situation you can't easily get out of:
when the pack is left discharged for a long time, the BMS says "No go!", which prevents BOTH charging and discharging, so you can never recover.

This is not a problem with BMSs that use separate LVC and HVC lines: the LVC may be disabling the load, but the HVC is still enabling the charger, so you can recover.

Reference: section 5.2.2.1.3 of the Li-Ion BMS book, "Single bus".

Another problem is that, when the pack is discharged, the relays are turned on, discharging it even further.


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## JRP3 (Mar 7, 2008)

frodus said:


> citation needed


Isn't that what happened with the bad batch of Volt Blochers?


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## ElectriCar (Jun 15, 2008)

Elithion said:


> For me to promote ours would be in bad taste.
> 
> So, instead, allow me to say that, based on my somewhat deep understanding of Li-Ion BMSs, I would say that the only type of BMS worth using in a vehicle is a "balancer" (either and analog balancer or a digital balancer).
> 
> ...


Thanks for your reply. So someone has to convince me of the balancing part. I can't see top balancing, in fact it seems to create a failure in waiting so to speak if you happen to drive the pack dry which people will do if allowed to. 

On the LV cutout. As I understand it, that feature will activate whenever the cell "terminal" voltage reaches 2.5V or whatever point it is set for correct? Since these batteries will sag on hard acceleration, the terminal voltage could drop below 2.5V. Also at that point when the terminal voltage is for example 2V, the SOC of the battery may actually be 2.7 or even 3V maybe, yet the LVC circuit will activate I assume based on terminal voltage, though you could continue if need be as long as the SOC was above empty. Jack Rickard said he did this yet the batteries weren't damaged. I don't know though if he dropped the voltage to 0V or not.

BMS is something I'm still not so versed on as I've not really dug into them. Before I got to that point a lot of people were shying away from them, partly because of info out there about BMS systems damaging cells and burning cars up, others may be looking for a reason to forgo the expense of such hardware. I frankly have no clue what the typical systems costs other than a quote I received for $1700 and I'm not really sure if it monitored or balanced or what.


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## LithiumaniacsEVRacing (Oct 9, 2010)

What a great thread. Since I am in the learning stages of BMS and battery systems, this thread is a wonderful piece for all to learn. Thanks guys!


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## tomofreno (Mar 3, 2009)

> Balancing means shunting, shunting means heat. I realize it's not much heat as designed, but if something goes wrong it can drain a cell to zero, which has happened to some people.


 Not if it has current limiting resistors like the minibms. Some of my cells were drained by one that had a silicon device (voltage supervisor) connected directly between the cell terminals. Some of these had high leakage current...you know the rest. The minibms also has fuses. One of the things that convinced me to purchase it was it was open source. I could see and understand how it worked and that those safety features were there. (Edit: those of you who want to know more about bms operation should do a search and find that thread. Lots of discussion in it on the design) Most others are an enigma to me even though I've read their websites. The shunts are low current and power so should not get hot, and the fuse is there if something goes wrong.

Travis, I don't doubt there are always some cells being balanced, but I do doubt that it is really doing much. Maybe when you get yours datalogging you will convince me otherwise. That would be some nice data to see.

Edit: Well, I should qualify that. If the cells of the pack are as closely matched as mine I doubt the balancing is doing that much. If not, then yes I agree the balancing is necessary. Will they remain well-matched for years? Who knows? If not I'll have to install the shunts on the minibms or find another solution. Davide, you have been at this a while. Do you have data showing this?


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## Elithion (Oct 6, 2009)

frodus said:


> if something goes wrong it can drain a cell to zero, which has happened to some people.
> 
> citation needed


Yes. I have 3.

1) A user damaged a cell board by plugging it backwards. The board still kind of worked, but it started drawing about 10 milliAmps (normally it draws 3 microAmps). Instead of returning the damaged cell board for repair (which we would have done for free), the user used it anyway. Leaving the pack discharged, unattended for a few weeks, that one damaged cell board discharged its cell down to 0.

2) One of our clients absolutely REFUSES to connect the low voltage cutoff to the motor controller. The cells drop to below 2 V. Below 1.9 V, the cell boards stop working (The BMS sounds an alarm, but this client's vehicle ignores the alarm.) Under 1.5 V, the cell board goes into a mode where it draws about 0.5 mA. Leaving the pack discharged, unattended for a few weeks, that one cell board discharged its cell down to 0.

3) This was not an Elithion BMS. The BMS was a hand made prototype. There was a solder bridge across the MOSFET that turned on the balancing load. We didn't notice. The following morning those cells (10 Ah) were dead. (This wouldn't happen with an Elithion BMS, because a) all cell boards are 100 % tested, and b) the LED is lit at the same time as the balancing load is on, so you would see that that particular LED stays on all the time, and know there is a problem.)


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## spdas (Nov 28, 2009)

Aloha, all. Although I am a noobie, I didn't just fall off the turnip truck either. I am hearing very good arguments both pro and con BMS and now even Top vs Bottom vs both balancing and this is GOOD. What turns me off is if that person making these valid/learning/from experience points of view now assumes that all who don't follow their assumptions totally will be guilty of putting their house or family in danger of fire, etc. As Joe friday says: "Just the facts M'am" and let us "not as intelligent or working every day in this EV field", study and make our own conclusions. Thanks for all the great info, keep it up.
Francis


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## Elithion (Oct 6, 2009)

ElectriCar said:


> So someone has to convince me of the balancing part.


I won't.


Balancing is NOT a safety feature.
Balancing is a pack optimization feature.
Please go ahead and drive with a non balancing BMS: you'll be safe. Your range will be less than ideal, and will decrease over time, but you'll be safe.


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## JRP3 (Mar 7, 2008)

Elithion said:


> Please go ahead and drive with a non balancing BMS: you'll be safe. Your range will be less than ideal, and will decrease over time, but you'll be safe.


Could you explain how balancing gives you any more significant range than your smallest cell provides and how it will lessen the reduction in capacity over time?


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## Elithion (Oct 6, 2009)

ElectriCar said:


> Since these batteries will sag on hard acceleration, the terminal voltage could drop below 2.5V. Also at that point when the terminal voltage is for example 2V, the SOC of the battery may actually be 2.7 or even 3V maybe, yet the LVC circuit will activate I assume based on terminal voltage, though you could continue if need be as long as the SOC was above empty.


Correct. Most BMS will shut down due to sag in the cell voltage. Very few top scale BMSs will do IR compensation to calculate the OCV (Open Circuit Voltage), and not shut down, because they know that the OCV is still high enough. (*)



ElectriCar said:


> Jack Rickard said he did this yet the batteries weren't damaged.


He's right. As long as 
1) the terminal voltage stays above 0 V at all times
2) the OCV stays above 2.5 V (or whatever, depending on the chemistry)
3) the cell temperature remains below 60 C
the cell will be fine.

Note: _(*)Yes, the Lithiumate does that._


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## Elithion (Oct 6, 2009)

JRP3 said:


> Could you explain how balancing gives you any more significant range than your smallest cell provides...?


It doesn't. I never said it did.



JRP3 said:


> ... and how it will lessen the reduction in capacity over time?


By making sure that the least capacity cell is, and remains, the limiting factor to both charging and discharging.

Reference: Section 3.2.3 of the Li-Ion BMS book: "Balancing"


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## JRP3 (Mar 7, 2008)

Elithion said:


> Correct. Most BMS will shut down due to sag in the cell voltage.


Good reason to tie LVC to a warning light and/or buzzer instead of allowing it to directly influence the controller.


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## Elithion (Oct 6, 2009)

JRP3 said:


> Good reason to tie LVC to a warning light and/or buzzer instead of allowing it to directly influence the controller.


Our car manufacturing client did that; They lent a vehicle to a potential client, who drove the pack to the ground. Not only they lost the pack, they also lost the client, who thought that their product was unreliable.


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## ElectriCar (Jun 15, 2008)

Thanks Davide for taking the time to answer Q's. We do appreciate it.


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## JRP3 (Mar 7, 2008)

Elithion said:


> It doesn't. I never said it did.


Then what did you mean when you said this:


> Your range will be less than ideal,





> By making sure that the least capacity cell is, and remains, the limiting factor to both charging and discharging.


How would it change? The smallest cell will always be your limit. How does balancing change that?


> Reference: Section 3.2.3 of the Li-Ion BMS book: "Balancing"


The link just took me to a table of contents.


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## JRP3 (Mar 7, 2008)

Elithion said:


> Our car manufacturing client did that; They lent a vehicle to a potential client, who drove the pack to the ground. Not only they lost the pack, they also lost the client, who thought that their product was unreliable.


So what action is reasonable, to cut out or cut back the controller every time LVC is signaled?


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## Elithion (Oct 6, 2009)

JRP3 said:


> Then what did you mean when you said this: Your range will be less than ideal


.

An unbalanced pack is one in which one cell is the limiting factor for charging, and another cell is the limiting factor for discharging. The distance between those two limits is less that the distance between them if the same cell (the lowest capacity) is the limit to both charging and discharging. (That's actually a simplification: when cell resistance variation enter in the equation, the answer is not so simple.)



JRP3 said:


> The smallest cell will always be your limit.


In a pack that is balanced and kept in balance, yes. In an unbalanced pack, no.

Play with this interactive tool for a bit, and you'll understand.



JRP3 said:


> How does balancing change that?


By changing the SOC of individual cells (moving charge out of them, and/or moving charge into them) until the least capacity cell is the limiting factor.

OK, let me be blunt here. You want an education? Buy the book and read chapters 1, 2, 3 and 6. Not because I make 5 bucks from the sale of a book, but because an understanding of Li-Ion packs and of BMSs is the quickest and best way for you to have a reliable pack. (Plus it saves me and Dimitry and Travis hours answering all these questions over and over.) 

Off to bed.


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## tomofreno (Mar 3, 2009)

> Since these batteries will sag on hard acceleration, the terminal voltage could drop below 2.5V.


 The minibms has a built in delay in an attempt to compensate for this. If the sag is just for several seconds during acceleration, it won't trigger LVC on the minibms. It is also temperature compensated so it will tolerate lower cell voltage sag during cooler temperatures without triggering LVC. Mine is connected to a buzzer and resistors to cut the throttle by half. It is very noticeable - I tested it with a momentary switch to interrupt the bms N.C. loop while driving. Not as good as constantly monitoring cell voltage and having logic to tell the bms the cell's unloaded voltage is fine, but it seems to work fairly well.


----------



## Elithion (Oct 6, 2009)

JRP3 said:


> So what action is reasonable, to cut out or cut back the controller every time LVC is signaled?


2 stage:

1) Warning when a cell terminal voltage drops below one threshold

2) Shut down when the terminal voltage (or, better, the OCV) has been below a second, lower voltage for some time.

In a ICE, the first one is equivalent to the blinking reserve light 's fuel gauge, and the second one is equivalent to your running out of gas if you ignored the blinking light too long.


----------



## JRP3 (Mar 7, 2008)

Elithion said:


> .
> 
> An unbalanced pack is one in which one cell is the limiting factor for charging, and another cell is the limiting factor for discharging. The distance between those two limits is less that the distance between them if the same cell (the lowest capacity) is the limit to both charging and discharging. (That's actually a simplification: when cell resistance variation enter in the equation, the answer is not so simple.)
> 
> ...


What you're basically saying is the BMS goes through a lot of effort to make sure you can use 100% of potential capacity. I think it's better to oversize your pack and never get near 100% of capacity since that will prolong cell life.


> OK, let me be blunt here. You want an education? Buy the book and read chapters 1, 2, 3 and 6. Not because I make 5 bucks from the sale of a book, but because an understanding of Li-Ion packs and of BMSs is the quickest and best way for you to have a reliable pack. (Plus it saves me and Dimitry and Travis hours answering all these questions over and over.)
> 
> Off to bed.


I appreciate the offer of an education, and I appreciate all who post their opinions. In spite of what you may think I do have a good understanding of Lithium packs and I do understand what many BMS's do, I'm just not convinced that it's the only or best way to do it. So far an occasional manual balance, undercharging the pack, and conservative DOD, has worked well for me. Even with a BMS I would treat the pack the same way. As I've said, I can afford to kill a number of cells before I reach the cost of even the less expensive BMS's. So far it hasn't happened. Jack Rickard is wrong when he says using a BMS will definitely kill your pack, but those who say not using a BMS will definitely kill your pack are also in error. We've seen cells damaged by BMS's and we've seen them damaged without, no one can claim a definitive answer at this point.


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## ElectriCar (Jun 15, 2008)

gottdi said:


> ...Don't bicker and don't get pissed when we ask questions and question you. If we question you then you need to educate us...
> 
> Pete


You're really going to piss them off with that talk! 

IDIOT, SEARCH THE DAMN THREADS, DO YOUR HOMEWORK! Or thereabouts is what some are thinking unfortunately. It does take an inordinate amount of time to do that. 

It's nice when someone takes a minute or so to type a response, damn nice! I know they are busy, anyone who owns a small business likely is. 

But through all this bitching I've learned a little more. I do want to monitor. HVC and LVC I think are good as well, IF NEEDED. LVC if anything I feel is important due to distractions, other people driving the car etc. but my controller will do LVC, just needs to be sent off to be set. I may do that *and spring for the 1000 or 1200A upgrade *as well to my Curtis 1231C


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## JRP3 (Mar 7, 2008)

It's really better to exchange information without excessive emotion on both sides. We aren't arguing perpetual motion or the miracle of the EVette here


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## Overlander23 (Jun 15, 2009)

EVette FTW!!!! lol


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## Jan (Oct 5, 2009)

JRP3 said:


> What you're basically saying is the BMS goes through a lot of effort to make sure you can use 100% of potential capacity. I think it's better to oversize your pack and never get near 100% of capacity since that will prolong cell life.


No, that's not the same as what he believes will happen. They -the BMS sellers- all believe in cell drift. If you don't regularly balance your pack the cells will drift further apart every charge, every discharge. Making the effective capacity of your pack less and less. If you start with an oversized pack it will take a little longer.

It all boils down to cell drift. If that doesn't exist, or cells will find their own balance somewhere according to their IR and capacity, I'm not so convinced you'll need cell level monitoring. 

I've played around with some data in a spreadsheet. Even in a pack of 100 cells with a max difference of 10% in capacity, you'll still recognize the typical charge/discharge curve for the total pack. The knee's get flatter and less pronounced, but still visible, measurable and at the right location. I mean, you can still use the knees to the determine SOC, witouth killing a cell. 

Do Cells drift, or do cells not drift? That's the question.

I haven't read for a while JR Cell drift results. He was measuering each cell of one of his cars... Maybe I'll ask on his forum the results so far. And piss him off at the same time. Easy.

Edit: I'm not able to post a comment in Jacks blog anymore. Maybe pissed him off one time to many.


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## JRP3 (Mar 7, 2008)

I'm not saying that your pack won't need occasional balancing, just that it seems the frequency is going to be low enough that it may be a once or twice a year event, sort of like an oil change, though not as messy.


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## ElectriCar (Jun 15, 2008)

Here's something I'm inclined to go with. It's called _ EVision_, it's very versatile, gives tons of data to you and is a multi function display. I pasted below a post by DIYguy yesterday from  this thread. It's from a Jack Ricard article. It's a cool looking customizable device that can be mounted on or in the dash or other enclosure. 

_"Now here's one that DOES tell me something. I've got two voltages, the top half of the pack and the bottom. On the Evision these are compared and a little LED gage around the gauge displays top dead center if both half-packs are exactly equal. If one is greater than the other, it moves a dot to the right or left. 
NOW I have an indication I can use. Full acceleration, the dot moves a dot or two left or right. I'm a little out of "balance" between the two halves. But if the dot moves a quarter around the circle, I'm way out. All the cells should be reacting to the same load in about the same fashion, to a tenth of a volt anyway. At the stoplight, I should be balanced between the two halves. At 500 amps, I should be balanced between the two halves. In fact, if it is DIFFERENTLY balanced at the stoplight and under acceleration, by more than a dot or two, that tells me something is wrong."_

This is a much simpler approach than cell level monitoring. It counts Ah and does a ton of things for you, including driving your factory fuel gauge so you can use it for your SOC indicator. Someone posted in the thread linked above all the features it has and the things it can do. Though it is very very useful, it may not be the do all end all solution but I think it provides tons of useful data and is the least intrusive. Three wires tired to your pack I'm guessing is all that's needed to do the above divided pack monitoring. * When fused, it's impossible to destroy individual cells or the pack should it malfunction.*


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## JRP3 (Mar 7, 2008)

Of course it only works if your pack can be divided by 2  I think Jack is using 51 cells in his Speedster rebuild since that's all he can pack in.


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## ElectriCar (Jun 15, 2008)

Yes, but I'm using 50. However if you used 51 you could still connect it up, it would just be off by some amount, likely too much for that function of the gauge to be useful.


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## Jan (Oct 5, 2009)

JRP3 said:


> I'm not saying that your pack won't need occasional balancing, just that it seems the frequency is going to be low enough that it may be a once or twice a year event, sort of like an oil change, though not as messy.


Facts.. Facts, is what we need, JRP3. 

Have you ever done any (re)balancing on your pack? And how much off where the cells? And then again, do you know if they hadn’t found a new balance themselves. I mean: maybe they where out of your original bottom balance. But went to a better '‘mid balance', because some laws of nature tell them to do. And that 'balance' was actually the smartest and best balance you can get, but you didn’t recognize it. No offence. You know what I mean. I hope.


----------



## DIYguy (Sep 18, 2008)

JRP3 said:


> Of course it only works if your pack can be divided by 2  I think Jack is using 51 cells in his Speedster rebuild since that's all he can pack in.


Ya, I was thinking about that. My intentions are 65 cells...although I bought a couple spares, so I could do 64 or 66. I'm thinking that it may still work with an offset? Maybe it's too much difference...ya, likely too much.


----------



## tomofreno (Mar 3, 2009)

> Facts.. Facts, is what we need, JRP3.


 I've given you facts. Evidently you just ignored them.


----------



## Elithion (Oct 6, 2009)

Jan said:


> If you don't regularly balance your pack the cells will drift further apart every charge, every discharge.


Not quite. 
Cell SOC drifts whether you use the cells or not, due to cell self discharge.
Pack balance drifts whether you use the cells or not, due to differing rates of self discharge among its cells. 

These drifts occur when cells are sitting on a shelf. 
They drift when when the pack is in a car (unused). 
They drift under use.

The pack balance drift is higher if cell temperatures are different. Delta temperature is the primary cause of unbalancing a balanced pack, not usage per se. (Though usage often results in temperature differences, which, in turn, results in variations in leakage in the various cells, which in turn results in pack unbalance).



Jan said:


> according to their IR and capacity


Not primarily.
Pack balance is not related to cell capacity.
Pack balance is not related to cell resistance.
Cell SOC drift is primarily due to cell self discharge (leakage).
Pack balance drift is primarily due to cell-to-cell variations in self discharge.
(Though, cell experts tell me that I am oversimplifying this point, so there's more to it than I say here.)



Jan said:


> I'm not so convinced you'll need cell level monitoring.


You do, and you would even if there were no such thing as pack balance drift.

Cell level monitoring is primarily required because of variations in cell capacity. (If starting with a balanced pack, balance drift is only a secondary reason for the need for cell level monitoring.)

Cell monitoring is to detect when the limiting cell (or cells) reach the top and bottom. Even if there were no such thing as SOC drift (i.e.: cells had no leakage), you would still need to know when a cell is at the top, and when a cell is at the bottom.

I know, these are concepts that take some getting used to it. But until you do, you'll be looking at BMSs in the wrong light.

Spend some time playing with the cell balance visualization tool, and understanding these concepts will be a bit easier. Or, get the Li-Ion BMS book and read section 1.4.2. "Balance and balancing".


----------



## Elithion (Oct 6, 2009)

ElectriCar said:


> * When fused, it's impossible to destroy individual cells or the pack should it malfunction.*


Oh?
To destroy a pack with a 100 A fuse, all it takes is 99 A (either in or out) for a few hours. And there's not a darn thing that the fuse can do about it.


----------



## DIYguy (Sep 18, 2008)

Elithion said:


> These drifts occur when cells are sitting on a shelf.
> They drift when when the pack is in a car (unused).
> They drift under use.


Prove it. Please.


----------



## ElectriCar (Jun 15, 2008)

Elithion said:


> Oh?
> To destroy a pack with a 100 A fuse, all it takes is 99 A (either in or out) for a few hours. And there's not a darn thing that the fuse can do about it.


Dude, you're fusing the #24gauge wire or whatever it is, that goes to the gauge, not the battery lead.


----------



## Jan (Oct 5, 2009)

tomofreno said:


> I've given you facts. Evidently you just ignored them.


Not that I'm aware off. I probably missed it. Can you, please, give a page number before I have to search the whole thread again?


----------



## Elithion (Oct 6, 2009)

Jan said:


> They -the BMS sellers- all believe in cell drift.


Cell SOC does drift; due to cell self discharge (leakage).
But that is an argument for balancing. Not an argument for cell level cutout. 

As I said above, if you want a BMS without balancing, I'm fine with it. 
I said:


Balancing is not a safety feature
Balancing is a performance feature
If you want a BMS without balancing, I don't care. As long as you have a BMS with cell level cut out, which makes you safe, I'm fine with it.

You don't believe in cell leakage? Fine. Get a BMS without balancing. But do install a BMS with cell level cutout, and install it correctly, for your safety and for the well being of the EV industry (each EV fire makes us all look bad).


----------



## ElectriCar (Jun 15, 2008)

Re odd number of batteries for Evision split pack monitoring... you can use two 1 Megohm resistors in series across the middle battery. This will split the voltage value of that battery in half. Then you connect the meter lead to the middle of the two resistors. That electronically splits the center battery value for monitoring purposes. The load across the cell is 3.2V/2,000,000 ohms, really nothing practically.


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## Jan (Oct 5, 2009)

Elithion said:


> Not quite.
> Cell SOC drifts whether you use the cells or not, due to cell self discharge.


They seem to self discharge/leak almost unmeasurable. I would like to see some proof of this. Or real objective data. Facts. So to say.



> You do, and you would even if there were no such thing as pack balance drift.


No, not to my humble opinion. If you bottom balance a pack, and there is no such thing as cell drift. You can very well do without cell level monitoring. Count the Ahrs, don't go beyond 90%, or stay even lower when it's not required, with charging. 

And keep track of the pack voltage. Even with cells 10% out of range regarding capacity, you'll still notice the same charge/dicharge curve as if the pack is a single cell. 

You can still use the beginning of the 'top knee' as a important sign. When the knee start, even with 10% out of range, you will not kill a singel cell. And 10% is a lot.

But I'm open for alternative views.


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## Jan (Oct 5, 2009)

Elithion said:


> You don't believe in cell leakage? Fine. Get a BMS without balancing. But do install a BMS with cell level cutout, and install it correctly, for your safety and for the well being of the EV industry (each EV fire makes us all look bad).


Eh.. Elithion, that's somewhat ironical. Considering the fact that EV fires that reach the news are -as far as I know- all equipped with a BMS. And the latest one was done by a professional company. At least, the website looks professional.


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## DIYguy (Sep 18, 2008)

leakage and drift are two different things. All batteries self discharge...albeit at different rates. Drift infers that they do this at different rates...at least for this discussion, in rates that differ significantly enough to cause practical problems.

Please provide data for this discussion.


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## Jan (Oct 5, 2009)

DIYguy said:


> leakage and drift are two different things. All batteries self discharge...albeit at different rates. Drift infers that they do this at different rates...at least for this discussion, in rates that differ significantly enough to cause practical problems.
> 
> Please provide data for this discussion.


Yep.

And what happens to those slightly drifted cells during charing and discharging? Since, I'm a total nitwit about this subject, I'm also able to believe they grow together again during dis/charging. For some odd, complecated but totaly logical, reason. Elithion, only says *that* doesn't drift them apart. There could be more to it.


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## DIYguy (Sep 18, 2008)

Yes, I would like to see the data for this discussion that supports the notion that cells drift apart...particularly during EV-typical charge/discharge cycles, and that this drift is significant enough to warrant management. Thank you.


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## Elithion (Oct 6, 2009)

ElectriCar said:


> Dude, you're fusing the #24gauge wire or whatever it is, that goes to the gauge, not the battery lead.


OK, then.

To destroy a pack with a 1 A fuse, all it takes is 0.9 A (either in or out) for a few weeks. And there's not a darn thing that the fuse can do about it.


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## Elithion (Oct 6, 2009)

Lots of great questions.

However, I have real work to do. 
With your permission, I'll come back to this thread either tonight or Monday, and try to address them.


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## Elithion (Oct 6, 2009)

DIYguy said:


> Prove it. Please.


What will be a satisfactory proof, please?


A scholarly paper?
Web pages? Electropaedia Wikipedia
Cell manufacturer data?
Anecdotal report from users?
A data table from Elithion's own testing?
Confirmation from particular members of this forum whom you trust?


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## Jan (Oct 5, 2009)

Elithion said:


> What will be a satisfactory proof, please?
> 
> 
> A scholarly paper?
> ...


To me: 

Cell manufacturer data
A data table from Elithion's own testing

I trust Elithion enough to take your data serious. Until proven otherwise.

I appreciate your patience. It seems to me BMS (re)sellers have in general a little short of it. And confuse me with BMS haters. I’m just very, very sceptical.


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## DIYguy (Sep 18, 2008)

Elithion said:


> What will be a satisfactory proof, please?
> 
> 
> A scholarly paper?
> ...


 "Arm's length" data is the gold standard. Everyone else has a vested interest.

Theoretical stuff is tough to sell, to me anyways.

We have all read the BMS and non-BMS supporters' claims... 
The BMS guys will warn you of the impending problems if you don't.
The Non-BMS guys that stay away from over/undercharge don't seem to be seeing drift....but I haven't seen data on it.
Unless you are running a pack with monitoring/logging and not balancing... it will be tough to show. 

Based on your simulator.... a few charge/discharge cycles should show some nasty tendencies if balancing is turned off and monitoring/logging is done. In the absence of data...Is this something you could do for everyone?

Please share whatever is available.


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## DIYguy (Sep 18, 2008)

Elithion said:


> Web pages? Electropaedia Wikipedia


ya...I didn't see anything in those pages showing drift within a chemistry subjected to same temps. Self discharge is a well documented fact. 
We need to see something showing drift in a real application that is not being influenced by imposed balance.
Can anyone think of another option to capture this??
Thank you.


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## Jan (Oct 5, 2009)

From the wiki link:

"According to one manufacturer, lithium-ion cells (and, accordingly, "dumb" lithium-ion batteries) do not have any self-discharge in the usual meaning of this word.[24] What looks like a self-discharge in these batteries is a permanent loss of capacity (see Disadvantages). On the other hand, "smart" lithium-ion batteries do self-discharge, due to the drain of the built-in voltage monitoring circuit."

Mmmm....


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## ElectriCar (Jun 15, 2008)

Elithion said:


> OK, then.
> 
> To destroy a pack with a 1 A fuse, all it takes is 0.9 A (either in or out) for a few weeks. And there's not a darn thing that the fuse can do about it.


That is true. If it's parked in the garage. But if I put 50 BMS circuit boards on my 50 cells, what are my odds compared to 3 connections to this thing? 1:17. So that equates to a failure being 17 times more likely with a BMS than with this thing. 

I can set the LVC in the controller, if I lose a cell somehow while driving, I'll notice it on the EVision display by the sudden imbalance the meter will display. 

If I lose it in the garage, well what can you do? How often does that happen. Sure if the charger doesn't stop charging properly and tries to overcharge you may have a problem. So you install a pack HVC device for backup. My thoughts are you should have redundancy in case something fails. I'm researching that now. If I don't find such a device I'll make one.


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## tomofreno (Mar 3, 2009)

> Not that I'm aware off. I probably missed it. Can you, please, give a page number before I have to search the whole thread again?


Sorry, it was on the narrowing prismatic...thread:


> I measure the voltage of ALL cells about every month or less to ensure the HVC cell hasn't changed. It has twice in a bit over one year, 7500 miles. Once when I individually charged some replacement cells - one of them became the HVC cell, and once when I over-charged a couple cells to about 3.95V - one of those then became the HVC cell (Why overcharged? Something took out the Lm339 chip on the minibms main board, the cell temperature was warmer than usual, and at the last minute I decided, well maybe I should check with my dvm just to be sure...). Other than that, the voltage balance of the 32 original cells hasn't changed appreciably. Three of the 4 replacement cells seem to like to stay about 0.02V lower than the others (I discharged the one that was temporarily hitting HVC first a bit, the fourth is staying within about 0.005V. That is checked at 28-30% SOC, which admittedly is not down below the knee where you would see more variation. It is ok for me though, since I never go below that SOC, and usually recharge at 35% SOC or greater (The TBS gauge "empty" alarm is set for 35% SOC). They are also within that range right before end of charge, actually a bit closer.


Below is a map of cell voltages taken on 12/17/10 with a bit over one year and 7500 miles on the pack, at 100*124.7/180 = 30.7% discharge. Eight cells in the front box, twenty in the middle, eight in the rear. They were all at 3.2xxV, so I only wrote the last two, xx, digits on most. The "R" in the lower right corner of four cells indicates these are replacement cells, not part of the original pack. These were charged to match the other cells when installed on 2/16/10, and re-balanced a couple times after that. They have not been balanced since 8/3/10. Three of these have been staying at about 0.02V lower than the other cells, one is within less than 5 mV of the other cells. The other 32 cells have never been balanced, only charged by the Manzanita charger. Yes, there would be more variability in the voltages if I measured them at 20% discharge, but I never discharge that far so don't care. As you can see, the range of voltages is small enough that it does not limit pack capacity when operated from about 97% to 30-50% SOC as I normally do. The HVC cell is the one second from right, in the first row of the middle box. I stop charging when it hits about 3.45V. The pack has over 1600 kWh on it. It takes me less than 10 minutes to generate such a map. Just open each lid measure, write on the clipboard, close. Not such a big chore once a month or so, at least not for me. The voltage range near end of charge, while under charge, is about the same or less than this. If I checked when some cells were above the knee it would of course be larger. I don't care, as I see no point in going there and don't see it as relevant. Edit: in case you can't read them, the voltages range from 3.240V to 3.261V.


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## GerhardRP (Nov 17, 2009)

tomofreno said:


> Below is a map of cell voltages taken on 12/17/10 with a bit over one year and 7500 miles on the pack, at 100*124.7/180 = 30.7% discharge. ... Edit: in case you can't read them, the voltages range from 3.240V to 3.261V.


Thanks for the post, but my eyes will not let me read the numbers.
Could you post a list? Also it would be great to see the matching fully charged [rested] list also.
BTW, if you compare your voltages to JR's discharge curve, you get a SOC of 30% for 3.240 volts and 50% at 3.261, so a 20% imbalance at this point. You have a 30% remaining capacity before you reverse the weakest cell, which is what your fuel gauge says!
Gerhard


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## JRP3 (Mar 7, 2008)

I only did one re balancing of my pack after I had used a cell log8 for a while to watch the behavior of some cells. They were still very close, but this time I used a better DVM and balanced at a lower voltage for greater accuracy. At some point this year I'll do a deep DOD and measure again and report where all the cells are in relation to each other. That will have to wait until summer but I can say that when charging the cells are all in the same relationship to each other, i.e. the smallest capacity cell is still first to reach full. I too have wondered about possible "mid balancing" of the pack on it's own, so if I do see variations at the bottom I may not re balance and just watch and see what the pack does on it's own.



Jan said:


> Facts.. Facts, is what we need, JRP3.
> 
> Have you ever done any (re)balancing on your pack? And how much off where the cells? And then again, do you know if they hadn’t found a new balance themselves. I mean: maybe they where out of your original bottom balance. But went to a better '‘mid balance', because some laws of nature tell them to do. And that 'balance' was actually the smartest and best balance you can get, but you didn’t recognize it. No offence. You know what I mean. I hope.


----------



## tomofreno (Mar 3, 2009)

> Thanks for the post, but my eyes will not let me read the numbers.


 Did you click on the image for an enlarged view?


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## jackbauer (Jan 12, 2008)

Looking at the whole BMS issue I think its fair to say that everyone would like to know what each cell in a pack is doing without the dangers of fire , cell drain and charger problems. Personally , i would very much like to be able to look at a display and see each cell voltage without danger. So as a little side project i'm gonna use the 8 ecity power 8ah cells (with the suicide vent caps) that i have laying around to see if i can get a bms fire going and if i can how and why. Reading around the internet on the whole issue its clouded in mystery and hearsay. Its about time someone ran some small scale tests to generate the problems. 

So can i ask what failure modes are we looking at? Those i can think off the top of my head would be the bms commanding the charger to keep charging , shorts in the wiring , shunt resistors burning up , .............what am i missing? imho reading a bunch of voltages and displaying them on a screen shouldnt be rocket science or have a 50% chance of vehicle inceneration.


----------



## GerhardRP (Nov 17, 2009)

tomofreno said:


> Did you click on the image for an enlarged view?


 Yes, I get a bigger, fuzzier low contrast image.
Gerhard


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## dimitri (May 16, 2008)

Jack,

how many BMSs are you going to run same set of tests against to prove if one is better than the next one? Do you realize that just a handful of common variables will result in dozens if not hundreds test combinations. Each combination might not fail during the test, but not conclusively prove that failure is unlikely long term. How much time will you allocate to testing and how will you draw conclusions? 

I think its great and I am even willing provide free MiniBMS for your testing ( except shipping, Ireland is too far from Florida  ), but I am suspicious that your conclusions will not be accepted by many people as truly valid.

Good luck!


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## spdas (Nov 28, 2009)

jackbauer said:


> Looking at the whole BMS issue I think its fair to say that everyone would like to know what each cell in a pack is doing without the dangers of fire , cell drain and charger problems. Personally , i would very much like to be able to look at a display and see each cell voltage without danger. So as a little side project i'm gonna use the 8 ecity power 8ah cells (with the suicide vent caps) that i have laying around to see if i can get a bms fire going and if i can how and why. Reading around the internet on the whole issue its clouded in mystery and hearsay. Its about time someone ran some small scale tests to generate the problems.
> 
> So can i ask what failure modes are we looking at? Those i can think off the top of my head would be the bms commanding the charger to keep charging , shorts in the wiring , shunt resistors burning up , .............what am i missing? imho reading a bunch of voltages and displaying them on a screen shouldnt be rocket science or have a 50% chance of vehicle inceneration.


Aloha, I would like to see two cells charging without BMS. One at say 50% discharge and the other at 80% discharge and using a GOOD charger, see if it shuts/throttles down or does it push the lower battery to unsafe levels, the one reaching the full charge first? Then discharge and recharge several times to see if the original 50% and 80% come closer or drift farther apart, like 40% 80% or 60%-80%. And at what number of cycles it takes to cause this imbalance.
thanks
francis


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## azdeltawye (Dec 30, 2008)

dimitri said:


> Constructive feedback is always welcome


I would recommend encapsulating the boards in potting compound. I have a real problem with exposed circuit cards in an engine bay environment. 

Take a look at how I potted and fused the first gen MiniBMS boards. It was a time consuming process but well worth it IMO...


----------



## ElectriCar (Jun 15, 2008)

Nice pot job there! Yes any circuits exposed to elements should be potted like that.


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## JRP3 (Mar 7, 2008)

azdeltawye said:


> I would recommend encapsulating the boards in potting compound. I have a real problem with exposed circuit cards in an engine bay environment.


What about a thin spray on coating? Like a silicone spray coating?


----------



## spdas (Nov 28, 2009)

Just wrap a border of thick tape around the board and pour in some fiberglass resin. Pre-Wrap a border on several boards and mix and pour the resin. Or if you want it more fancy, make a border of tongue depressors for a more uniform border,

Fast kine. 
Francis


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## tomofreno (Mar 3, 2009)

> What about a thin spray on coating? Like a silicone spray coating?


 They already have a thin plastic coating on them.


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## tomofreno (Mar 3, 2009)

> Yes, I get a bigger, fuzzier low contrast image


R designates replacement cell:

3.257, 3.247 (R), 3.260, 3.246 (R), 3.254, 3.252, 3.240, 3.243 (R), 3.258, 3.254, 3.255, 3.254, 3.254, 3.261, 3.249, 3.261, 3.259, 3.261, 3.258, 3.252, 3.253, 3.259, 3.253, 3.255, 3.259, 3.250 (R), 3.256, 3.259, 3.253, 3.252, 3.251, 3.252, 3.251, 3.257, 3.252, 3.250

First 8 are in front box behind front bumper, next 20 are in mid box mounted through floor, next 8 are in box totally within the car. So typically have temperature spread from a few F to 10 F from front box to rearmost box after driving.


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## jackbauer (Jan 12, 2008)

I realise i can't test everything and don't even intend to try. Just hit some of the main points. What i want to look at firstly is the wiring. ie can a loom from a pack , brought back to a fixed point be dangerous in itself. If so how can that danger be alleviated. That is step one in my mind.

Dimitri , i'll take you up on that offer! No problem paying shipping. I'll volunteer to small scale test any bms that the manufacturer cares to supply.

Any results i get will be posted on video on youtube and described here for open discussion and sugestions.


----------



## Jan (Oct 5, 2009)

tomofreno said:


> Sorry, it was on the narrowing prismatic...thread:


Ok, thanks Tomofreno. But to see what cells do in a series pack we need lots more measurements. If you have it, I would appreciate it very much if you want to put it online. I want to copy it in a spreadsheet and try to see if I can make up some graphs that show the drift. I think I also need the SOC that comes with the measurements. The picture however was very hard to read.



JRP3 said:


> …i.e. the smallest capacity cell is still first to reach full. I too have wondered about possible "mid balancing" of the pack on it's own, so if I do see variations at the bottom I may not re balance and just watch and see what the pack does on it's own.


That’s exactly what I meant. And nothing you measured ruled the possibility of ‘no cell drift’, or seeking a perfect mid balance, out.

The link in the wiki page that goes to the company that says “There Is No Such Thing As Leaking” is very interesting. But also somewhat indecisive, as if they know our issues, and want to toy with us. 

Here’s the source document: http://www.gpbatteries.com/html/pdf/Li-ion_handbook.pdf

*Self discharge*

According to this document, there is no such thing. It’s just the aging of the cell that seems like self discharge. It also states that aging depends of the SOC. The higher the SOC the faster the aging, and there for capacity loss. 

It advises to store the cells for longer time between the 30-50%. 

The interesting thing is, why not even lower? They say, this limit is chosen, because sometimes they are stored with circuitry that demands a small drain. And this is the most important source of self discharge.

They do NOT say, you have to store them with circuitry. They just write it down as an observation they’ve made.

This fact, about aging and SOC, seems to me a important pro for bottom balancing.

*Cell/string monitoring.*

They also talk of a safety circuit, and its properties. Like a LVS of 2.8 and a HVC of 4.25. They do not write it’s a obligated circuit. They say that it is typically a part of the pack. Not obligated by them, but as if they observed it by their customers. And take it for granted. And if you want it, OK, do what you want, and these are the values you have to set.

But, the thing that intrigues me the most is this sentence:

_“The additional safety chip must be provided for each cell or string of cells connected in series” _

Here they say literally: You don’t need cell level monitoring. 

But I’m confused. Why do they say explicit ‘series’? In parallel a chip per cell is meaningless, they all measure the same. And in parallel cells will balance themselves automatically. So why explicit?

Maybe I’m just searching for problems, and must just accept the simple message of this manufacturer:
•	There is no such thing as cell leakage
•	You don’t need cell level monitoring

*Cell reversal*

Yep. Cell reversal, a great danger to mankind. If I recall correct the professor in the Li-Ion video we all saw, stated: Cells will be damaged if you boil the electrolyte by overcharging then, or if you bring the voltage below zero by discharging them to zero. Also called cell reversal. If I’m not mistaking.

So, you don’t kill the cell by discharging it to zero volts. To empty so to say. But by reversing the current.

How on earth can the current in one cell change direction in a closed series circuit? I don’t get it. In a parallel setup, I can imagine. But most packs are series only. So let’s say you have a series only pack, how could cell reversal actually happen? Does anyone ever experienced it, or has heard of the phenomena? I know JRP3 and JR once drained there pack to the bottom limit with their BMSless packs. And none went in reversal. And none were damaged, like the professor predicted.

Yes, I've been thinking last night.


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## Jan (Oct 5, 2009)

jackbauer said:


> I realise i can't test everything and don't even intend to try. Just hit some of the main points. What i want to look at firstly is the wiring. ie can a loom from a pack , brought back to a fixed point be dangerous in itself. If so how can that danger be alleviated. That is step one in my mind.
> 
> Dimitri , i'll take you up on that offer! No problem paying shipping. I'll volunteer to small scale test any bms that the manufacturer cares to supply.
> 
> Any results i get will be posted on video on youtube and described here for open discussion and sugestions.


Jack, can you proof you will kill cells by over-discharging them?


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## jackbauer (Jan 12, 2008)

Dont see why not. If the cell is part of a string it will get reversed. I have done that experiment and it does happen.


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## Jan (Oct 5, 2009)

jackbauer said:


> Dont see why not. If the cell is part of a string it will get reversed. I have done that experiment and it does happen.


How is that possible? How can the current revere is a part of a circuit?


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## Qer (May 7, 2008)

Jan said:


> How on earth can the current in one cell change direction in a closed series circuit?


No, it's not the current that's reversed, it's the voltage. If you discharge a pack the cell voltage will slowly decrease when SoC drops which ultimately will lead to 0% SoC and 0 Volt over the cell. Since all cells are individuals one cell is bound to reach 0% SoC first, but just because it does doesn't mean that it magically teleports out of the pack. It's still there and as long as the rest of the cells have some charge left the pack can still provide some power.

That's when things go bad. The cell that's already flat will now start to use the current for charging but the current is flowing the wrong way so the cell will start to build up charge with the opposite polarity! That's why you call it cell reversal (plus and minus shifts) and theoretically you could destroy every cell but one in a pack this way, even though it's more likely that the current you can get from the pack will start dropping to unusable levels already with just a few cells reversed.

And that's why I, personally, wouldn't dare spending thousands of bucks on a pack without having some kind of LVC/HVC-monitoring at least, preferably with some kind of display in the dash too. Sure, I can see how manually monitoring and balancing will keep the pack in good shape, but I know myself. The first months, maybe the first whole year, I'll be there with my little volt meter, taking notes and everything, but when nothing changes it'll get boring and in the winter it will be too cold to measure all those durn little cells and I'll procrastinate until I end up stranded on the road with a dead cell.

Whenever I convert an EV it's gonna have a monitored pack, mainly to save the pack from myself.


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## GerhardRP (Nov 17, 2009)

Jan said:


> How is that possible? How can the current revere is a part of a circuit?


It is the voltage that is reversed. Think of the discharge voltage curve that falls off the cliff as you approach zero SOC. If you are using a resistor, it simply goes flat. If you are using a series string, the curve continues into negative territory... a "reversal".
Gerhard

edit: oops, read all replies before replying


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## Jan (Oct 5, 2009)

I just can't get it. I'm not able to understand voltage reversal without current reversal. Or you guys can't explain stuff simple enough, or I'm just to stupid. Start at the beginning. Slowly.


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## JRP3 (Mar 7, 2008)

Jan said:


> I know JRP3 and JR once drained there pack to the bottom limit with their BMSless packs. And none went in reversal. And none were damaged, like the professor predicted.


I had a deep discharge to 1.77V under load, 2.45V after I stopped, and rising, so not really 100%DOD but pretty darn close. Jack has killed some cells with a deep discharge on a top balanced pack without a BMS. I assume those cells that were killed went into reversal.


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## JRP3 (Mar 7, 2008)

Jan said:


> I just can't get it. I'm not able to understand voltage reversal without current reversal. Or you guys can't explain stuff simple enough, or I'm just to stupid. Start at the beginning. Slowly.


Qer explained it quite well I think:


> That's when things go bad. The cell that's already flat will now start to use the current for charging but the current is flowing the wrong way so the cell will start to build up charge with the opposite polarity! That's why you call it cell reversal (plus and minus shifts) and theoretically you could destroy every cell but one in a pack this way, even though it's more likely that the current you can get from the pack will start dropping to unusable levels already with just a few cells reversed.


Think if it as hooking up a charger backwards.


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## GerhardRP (Nov 17, 2009)

Jan said:


> I just can't get it. I'm not able to understand voltage reversal without current reversal. Or you guys can't explain stuff simple enough, or I'm just to stupid. Start at the beginning. Slowly.


Ok, you have a battery. If you charge it the way you are supposed to, you end up with positive voltage on the positive terminal.
Now if you hook up your charger backwards, it tries to make the negative terminal into the positive one. 
[Think of non-electrolytic capacitors which can have either terminal the positive one depending on which way you charge it.]
Batteries and electrolytic capacitors fail if charged backwards.
Gerhard


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## dimitri (May 16, 2008)

gottdi said:


> Question, if the positive wire on the miniBMS shorts or breaks how does the system protect the pack? Will it shut of the charger? Will it limit or shut off the controller if I am driving?


miniBMS is a closed loop system, i.e. any event breaking the optorelay's series string will cause BMS to trip the relay and take action. If positive wire breaks off, module lost power, i.e. optorelay turned off, i.e. broken loop, i.e. relay action.
Relay action is split into HVC and LVC sides, but its technically just one event. If you are charging at the time of BMS event, charger turns off. If you are driving, controller cuts down, buzzer sounds as well in both cases.
Controller part is flexible, its your decision how to wire it. I am proponent of reduced power ( i.e. valet mode ) to get driver attention, yet not just stop in the middle of a road. Driver safety is more important than pack safety, right? User guide provides wiring diagrams for variety of throttle types.


> I'd also like to know if a heavier gauge wire could be used on the +side of the miniBMS?


Yes, but why? That wire never sees more than 0.75 Amp at the peak of shunting. I use high quality AWG18 automotive wire, same wire that controls every ECU function in ICE cars, they don't seem to break. There is no vibration in that wire, your EV doesn't vibrate at frequencies that cause mechanical stress or we would see cars breaking apart on every road. Vibration argument is just silly.



> What about sealing the unit against moisture? Would it hurt if it was encapsulated in clear epoxy?


 miniBMS comes spray coated to protect components, but not enough to be submerged. If you think your battery tops will have puddles of water standing, then yes, further sealing is required. I don't pot them because it would raise cost, only one customer so far managed to do water damage, its been reported on this forum. Module shorts, loop opens, you get alert, no damage to cells at all, just blown BMS module. If you don't care to protect cells from water, then you need to protect BMS from water, its your call. I will still provide warranty if you decide to pot your BMS modules. Just make sure you can still see LEDs and if you use shunting, make sure ceramic resistor can dissipate heat, however little of it there is.


> Also can you use two solid state AC switches together to protect a charger that is being used in a higher amperage setting. We will be using our Elcon in both 120 and 240 mode and the 240 circuit will have at minimum 60 amp circuit breakers. I am not sure if the charger will ever see more than 40 amps but wanted to ask.


Yes, you can parallel SSRs, but you don't need to. Largest Elcon is 5000Watt ( I doubt its the one you have but its worst case scenario). This means max of 20Amp on AC side at 240VAC. My relays are 40Amp, 50% derating, don't need anymore. If charger shorts AC side, relay is not a safety device, breaker is.

Hope this helps.


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## Jan (Oct 5, 2009)

Grmppff. Pff. The pain.

Let me try to rephrase it in my own words.

In a discharging pack, the current is already flowing in the destructive direction. Like a wrongly connected charger. But as long the voltage over the cell is positive, that’s ok. The cell can absorb the electrons. 

But when the voltage drops to zero it immediately changes in a resistor. That’s all what’s left of it's function in the string. Then the voltage over the cell drops a bit, because that's what resistors do. That’s the reversal. But the current keeps flowing in the same direction. And that’s what will kill the cell. The incoming electrons are no longer welcome anymore.

How’s that?


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## etischer (Jun 16, 2008)

Series connected batteries are connected like this:

[+ -] [+ -] [+ -] [+ -]

If one cell goes bad you end up with this
[+ -] [ ] [+ -] [+ -]

When you draw lots of current from the pack, the bad battery acts like an open circuit. 

the (-) from battery 1 is connected to the (+) of the bad battery
the (+) from battery 3 is connected to the (-) of the bad battery. 

this is just like connecting a charger backwards to the bad battery. 





Jan said:


> Grmppff. Pff. The pain.
> 
> Let me try to rephrase it in my own words.
> 
> ...


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## jackbauer (Jan 12, 2008)

The current always flows in the same direction during discharge. If a cell is low and driven down its discharge curve it stop producing energy and becomes a resistor. The other cells now force energy through it and it drops voltage just like a resistor. But this voltage is opposite. Negative to positive.


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## Qer (May 7, 2008)

Jan said:


> In a discharging pack, the current is already flowing in the destructive direction. Like a wrongly connected charger. But as long the voltage over the cell is positive, that’s ok. The cell can absorb the electrons.


Not sure about the "absorbing electrons"-part, but the rest is hunky dory.



Jan said:


> But when the voltage drops to zero it immediately changes in a resistor. That’s all what’s left of it's function in the string. Then the voltage over the cell drops a bit, because that's what resistors do. That’s the reversal. But the current keeps flowing in the same direction. And that’s what will kill the cell. The incoming electrons are no longer welcome anymore.


Um. Nope.

You're pretty much seeing the battery as a bucket of water. When you've filled the bucket to the brim it's 100% SoC and when you've emptied it it's 0% SoC and you can't get any more water from it. The thing is, a battery isn't a bucket and charge isn't water. When you try to drain more "water" from the battery you could actually see it as that you manage to fill it with "negative water", which isn't healthy (especially not for my imagination  ).

Perhaps you should see it as a check balance instead. As long as the balance's positive everything's dandy and fine, but when you manage to overdraw your balance, things go south. Hm. Probably a sucky analogy too.

Hm. We can probably go for wilder and wilder analogies here, but to put it in math it looks something like this:

Ah = A * h

If you have a 100 Ah battery that means that you can draw 100 Ampere from it in 1 hour. If you draw 10 A for 5 hours it means you deplete it with 50 Ah and there's 50 Ah left. No problem. If you keep drawing 10 A for an additional 5 hours it's fully depleted and the voltage will drop to zero. Now, if this is a single cell the story ends here. Since the battery has dropped to zero voltage no current can be created, but in a pack there's other cells that can still hold voltage and as long as the *pack voltage* is above zero, current will still flow.

That's when you kill the battery because Ah is still A * h so when you keep drawing your 10 A current the stored Ah for the cell goes negative! SoC goes negative! If the chemistry was 100% symmetrical this wouldn't be a problem, but since batteries are polar (rather than bipolar) the negative charge (and thus negative voltage) will start breaking down the chemistry and the cell dies.

That's why a pack with many cells in series can get damaged if it's not properly monitored and that's why I personally wouldn't dare running a Lithium pack without at least LVC/HVC-monitoring.


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## GerhardRP (Nov 17, 2009)

Jan said:


> Grmppff. Pff. The pain.
> 
> Let me try to rephrase it in my own words.
> ...
> How’s that?


By George he's got it.
Gerhard


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## JRP3 (Mar 7, 2008)

Qer said:


> That's why a pack with many cells in series can get damaged if it's not properly monitored and that's why I personally wouldn't dare running a Lithium pack without at least LVC/HVC-monitoring.


Coward....


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## dimitri (May 16, 2008)

Absolutely agree that wires must not move on their own, that is not acceptable in a vehicle. All wiring must be secured. However, 2 inch piece of wire attached to solid points at both ends and not tied to other things that can move it, will not move on its own, it simply doesn't have enough inertia to move under its own weight, hence no need to secure it further.

Your case is different. First off, you tied other wires to those little jump wires coming from the contactor and by doing that you created mechanical connection with enough pull to move them. If those were left alone as intended by manufacturer they would not have wiggled on their own and would not break. Other wires must have wiggled them and over time they broke off. So, that's installation mistake. Assuming you tied those together before they broke, not after. However, I agree that Tyco's wires are pretty weak, I had a similar case with Tyco contactor recently where I had to repair those wires because someone else accidentally cut them and it revealed that wires are weaker than I expected.


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## JRP3 (Mar 7, 2008)

gottdi said:


> I have seen wires that look super heavy due to a think outer covering only to find some cheap crappy wire inside.


That's for sure, I had some cheap DVM's that the leads broke from use, the wire inside looked like a few strands of hair


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## DIYguy (Sep 18, 2008)

dimitri said:


> Largest Elcon is 5000Watt ( I doubt its the one you have but its worst case scenario).


A little off topic...but just in case someone is looking at chargers...I have a 6kw Elcon. I think it comes in 8kw also. Actually, I'm not sure I have seen the 5kw...??
Thanks....


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## Qer (May 7, 2008)

JRP3 said:


> Coward....


Yep! Which is a good thing! When you drive your EV you don't want to rely on software from a daredevil programmer.


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## DIYguy (Sep 18, 2008)

I was all excited to come on-line and see some data here today showing what cells do as related to the "drifting" discussion. Tom has a good entry showing one point in time.. but that's the most we have so far. 

Is there anyone else out there reading this right now who has a pack with no BMS? ...or perhaps someone willing to leave the HVC and LVC and disable shunting for a while? (just askin! )... and take some measurements?

Should we throw in some qualifiers? Temperature is probably one. Also, no cells having possible excessive over/undercharge (damage)... what else??


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## spdas (Nov 28, 2009)

gottdi said:


> The manual says I need 12 volts for the BMS with ignition off. I don't have my car set up with an aux battery. Can't depend upon them. I do however have a good dc dc converter. I can set it up to remain on while charging but off when done I think. Any ideas on how to do that?
> 
> Pete


Aloha, Pete....a little off your question, but I have a dc/dc converter too and use it to supply charge to a small AGM 18ah 12v battery to run the accessories. So do most dc/dc rigs run right off the dc ......would that not cause the 12v accessories to dim when you step "on the gas"? Just wondering. 

francis


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## dimitri (May 16, 2008)

gottdi said:


> The manual says I need 12 volts for the BMS with ignition off. I don't have my car set up with an aux battery. Can't depend upon them. I do however have a good dc dc converter. I can set it up to remain on while charging but off when done I think. Any ideas on how to do that?
> 
> Pete


My DC-DC is hardwired always on, I did a poll on the subject few months back, many people do the same thing. Do you have any concerns with hardwiring DC-DC always on?

What you asking can be done, but it complicates things a bit. You'd need a 120VAC coil relay, so it closes when you plug in AC power and relay turns on DC-DC. You'd have to wire it such that it won't interfere with keyswitch ( ignition ) which also needs to turn on DC-DC. Doable, but complicated, IMHO. I would just hardwire DC-DC, it takes very little from the pack without 12V load, just parasitic currents.

Another concern with a relay approach is that BMS needs a reset upon initial power up to start the charger, ignition input is used as a reset normally, but you may need like a push button to start charging, it gets even more complicated then.

Sorry, the system was designed to have always on 12V source, I couldn't do it any other way and keep it simple enough.


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## JRP3 (Mar 7, 2008)

LVC is built in and temperature compensated. Couldn't copy and paste the text for some reason.
http://minibms.mybigcommerce.com/template/files/MiniBMS%20User%20Manual%20-%20Distributed.pdf


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## DavidDymaxion (Dec 1, 2008)

It seems easy enough to test. Get a couple of cells, charge up one, discharge the other. Then wire them in sreies, BMSless. Do a bunch of shallow charge/discharge cycles and see if they grown together in Voltage or apart. When I get some more time I'm have been meaning to try this.


Jan said:


> No, that's not the same as what he believes will happen. They -the BMS sellers- all believe in cell drift. If you don't regularly balance your pack the cells will drift further apart every charge, every discharge. Making the effective capacity of your pack less and less. If you start with an oversized pack it will take a little longer.
> 
> It all boils down to cell drift. If that doesn't exist, or cells will find their own balance somewhere according to their IR and capacity, I'm not so convinced you'll need cell level monitoring.
> 
> ...


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## JRP3 (Mar 7, 2008)

Wouldn't it make more sense to start out with them equal and see if they drift apart? That is the claim after all, that cells will drift apart over time through unequal self discharge. I suppose you could just leave them sitting for a few months and see if they self discharge at different rates.


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## dimitri (May 16, 2008)

gottdi said:


> Well I figured it would have been set lower but guess it will do for now.


The LVC values I set have been derived from lots of real road testing. It was a balancing act between tripping LVC too soon under heavy load, vs. tripping it too late when you are almost empty. First LVC alerts come as the pack nears the end of flat part of the curve, because voltage sags deeper under load in that area. The moment you release the pedal alert stops, but its a first sign to get off the road. 4-5 sec delay on BMS control board is designed to filter out brief bursts of voltage sag under heavy acceleration. LVC values along with delay make it a very practical, yet simple solution, verified by a year of driving. I don't hit LVC daily, but there have been 3-4 cases over past year.

So, when potential customers ask me if I can change LVC for them, the answer is no, because I know they will return the product later to correct it back to original LVC.


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## DIYguy (Sep 18, 2008)

JRP3 said:


> Wouldn't it make more sense to start out with them equal and see if they drift apart? That is the claim after all, that cells will drift apart over time through unequal self discharge.


Yes, this is the way. I agree...

Thanks David also...


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## JRP3 (Mar 7, 2008)

In his latest video Jack shows a 15 month old CALB 180 cell that has never been used sitting at 3.298V next to a brand new CALB 180 cell sitting at 3.300V. He assumes they were both shipped at 50% SOC which is a fair assumption since all cells that he's tested came shipped that way. It might be useful if he discharged both cells to 100% DOD and see if they were indeed both at 50% SOC. It's not a perfect test but I take it as a pretty good indicator that self discharge is not much of an issue at all.


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## DavidDymaxion (Dec 1, 2008)

While that is a good test, I don't think it really answers The Question (with a captial "Q").

The pro-BMS crowd says cells will tend to drift apart, and you should have a BMS to keep them balanced. They'll say if you get away with no BMS, it is because the cells are very well matched, start at the same SOC (as delivered, or via bottom or top balancing), and the drift is slow enough it's tolerable.

The no-BMS crowd (well, actually I've only heard Jack Rickard say it) says the cells have a natural self-balancing tendency.

This is a very key point. If lithium cells are self balancing, they will tend to come together, and stay together, even without a BMS.

Many folks test the idea of starting equal and see what happens -- that's what Jack and others are doing with their cars anyway. What I propose is start with one cell 1/2 drained (or maybe even fully drained), and one full. Do one test with a BMS (seems like it should be a standard type of BMS test, anyway). Test another pair with no BMS. Run a bunch of shallow cycles. See if the no BMS case eventually equalizes in capacity. Then swap roles, and start with the other battery discharged, and see if the result repeats. This would be a great test to see if lithium cells are self balancing or not.

I plan to do this test myself, and would like to see others try it, too. China HiPower or Headway cells are $15 or $19/each + shipping -- I consider it a cheap education. ( http://www.evequipmentsupply.com http://www.manzanitamicro.com )(


JRP3 said:


> Wouldn't it make more sense to start out with them equal and see if they drift apart? That is the claim after all, that cells will drift apart over time through unequal self discharge. I suppose you could just leave them sitting for a few months and see if they self discharge at different rates.


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## GerhardRP (Nov 17, 2009)

This is from the EVDL:
I have 2 ev's in my shop now with Li -ion batteries and shunt
regulators . One pack of 90 100 ah cells now in the bed of my pick up
came from a car that only had the bms set up to shut off the charger
, so when a cell went bad the car could still be driven just not
charged ( batteries ranged from 0v to 2.50) when I got it) . I have
weeded out about 10 cells and can pull 60 ah from the cells that are
left. I did the slow charge after a full charge and have also
individually charged certain cells to get to this point ( first cycle
gave 12ah) . What I think may be happening is this . Some of the cells
have a different internal resistance which makes some cells voltage go
up faster that others when being charged ( The cells that have the
most voltage drop under load seen to go up in voltage faster when
being charged). I am thinking that the shunt regulators start
shunting current across these batteries first and that on every cycle
these cell don't get the same ah as the others . The regulators on
this car come on at 3.65 and stay on till the cell come down to 3.32v
, So I'm thinking that the week sells hit 3.65 first , start backing
off the charger while shunting 1/2 an amp and the good cells keep
soaking up the ah getting ahead , at some point charger shuts off and
every body drops back to 3.32v with the good cells having gotten more
ah then the week ones. I also noticed this same thing on the bike
that's here ( same kind of shunt regs) with a 48v pack that had 3 bad
cells . I now can kind of see why people are thinking that a shunt
reg my not be the best and something that shows batteries voltage of
every cell with lowest and highest cells controlling shut down along
with some way to individually charge/ shunt cells might be better. It
may well be that not much is needed until some kind of abuse has
happened and thin it becomes an on going balancing act that shunt
regulators can't really do .
Steve Clunn

--
Tomorrows Ride TODAY !
Visit our shop web page at: www.Greenshedconversions.com


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## Jozzer (Mar 29, 2009)

LifePo4 cells most definitly do NOT self balance. Those with a BMS can see how much the pack needs balancing each charge (balance currentXtime), those without of course never have a clue (another reason why the "non-bms" crowd perhaps can't see what they are missing, doing an occasional test will never replace getting a visible result every time you charge).

Another important point with LifePo4, is that it does no good for the cells to "nearly" in balance when they come to full charge or full discharge, if they are not 100% spot on then a cell will overcharge/discharge when the knee is reached. The difference between a cell at 2.6v and 0v (or 3.5 and 4v) is very little in terms of AH.
I have datalogging on my BMS's, unfortionatly I don't play much with LifePo4 at the moment (working with Lipo, same principles but less of a "knee" to cause suden overcharging). I will be doing some lifepo4 testing when the next revision of our BMS is ready in a few weeks, but have no hard data to show now. 
When I WAS using 100AH lifepo4 packs, I used an analogue BMS with no data out. It was not unusual to find one cell hit HVC during charge, at which point the charger would cut to trickle charge at 1.2A for the others to catch up (whilst that cell shunted 1.2A). Often it took over 1 hour to come to full balance, especially if the charger had not been run till cutoff during the couple of cycles before. If the cycle was deep, or at high current this became worse, I can recall waiting 3 hours for an 80AH pack to balance correctly at 1.2A on occasion. 

Steve


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## LiFe (May 24, 2010)

Jozzer said:


> LifePo4 cells most definitly do NOT self balance. Those with a BMS can see how much the pack needs balancing each charge (balance currentXtime), those without of course never have a clue (another reason why the "non-bms" crowd perhaps can't see what they are missing, doing an occasional test will never replace getting a visible result every time you charge).
> 
> Another important point with LifePo4, is that it does no good for the cells to "nearly" in balance when they come to full charge or full discharge, if they are not 100% spot on then a cell will overcharge/discharge when the knee is reached. The difference between a cell at 2.6v and 0v (or 3.5 and 4v) is very little in terms of AH.
> Steve


Well described.
Even using the bare minimum of protection hardware; LV Cutoff / HV Clamp, the charger is current limited by the dissipation capability of the shunting clamp current when one or more cells reach the knee ahead of others.

Of course what Steve has described is a result of capacity + impedance variance between multiple modules in series. Capacity reduction can be a result of accidental charging beyond 4.2v, high current discharge below 2v -accompanied by extreme low temperature, or capacity depletion (over discharge). 

Or, they could be poorly manufactured prismatic cells.

Arranging multiple smaller cells in parallel helps to reduce the impact of capacity variation by manufacturing tolerance. It will not help with variations induced by excessive voltage and temperatures.

A combination of high temperature (40c) with an over voltage condition (exceeding 4.2v) will accelerate plating, and manifest as an impedance rise, similar to the appearance of end of life through cycling.

FWIW, if you do the above with LiPo, safety glasses, gloves, and marshmallows are mandatory.


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## ElectriCar (Jun 15, 2008)

There are a few driving with no BMS and say their pack is still balanced pretty well. Jack is one and I can't recall another that has driven quite a bit, maybe 5-7000 miles and the pack is still ok.

It could be that they don't charge theirs to the max like BMSers do and don't discharge as much likewise. Therefore their cells are nearly at the same voltage, as they are in the flat zone and not approaching either knee, I don't really know.

As dimitri pointed out, I have no pack so I can't chime in with results. However I will have a 32Kw Calb pack in a month or so and when the other mods and instruments get installed I'll be reporting my findings if I find them noteworthy. 

I'm thinking I won't balance mine at all initially, only charge them to a level below 3.6 where the first cell begins to spike. Then continue to charge after driving, looking for the pack voltage again where the first cell spikes. 

Though I will get slightly less mileage from a given pack size without a BMS, I feel better about not operating the pack at it's extreme ends which supposedly will pay off with longer life as well.

One thing I haven't settled on is the type of Ah monitoring if I use one at all, whether it's EVision or otherwise. The EVision is very expensive versus the EV display but gives much more information and is much more versatile. It also allows you to divide your pack in half for monitoring and gives you a visual comparison of the two halves, which should indicate if a cell is problematic. 

Do I need all that or not, I don't know so I will drive a while with no counter until I learn a little more about this "cell drift" thing. I'll use my resettable odometer and limit the mileage to a safe % of the estimated available mileage.

I'll be very conservative until I decide on an Ah counter but I think it's a must have if you want to really know how much gas is left in the tank.

The EV Display has a settable "out of gas" point that activates whatever you want to connect it to, whether you want to use a relay to insert a resistor in the pot box circuit to limit demand on the pack, operate an idiot light on the dash, both or whatever you can think of to get your attention. I think EVision also has this feature. So you can have it go off like the low fuel light in your petrol fueled vehicle, at some desired % of remaining capacity.


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## Jozzer (Mar 29, 2009)

"There are a few driving with no BMS and say their pack is still balanced pretty well. Jack is one and I can't recall another that has driven quite a bit, maybe 5-7000 miles and the pack is still ok."

That's my point, how do you know its balanced "pretty" well if you never go near full charge or discharge? It is the only way to get an idea how much capacity a LifePo4 has remaining, voltage can tell you next to nothing until then. Assuming this chap charges to 80% and discharging to 20% on a 100AH pack, all your telling me is that the cells are within 40AH of each other after 5-7000 miles with that statement. When the first cell goes under/over and dies, you'll know that that statement is no longer true, the cells just went a little MORE than 40AH out of balance. Fortionatly, your only trying to make them last some 1-3000 cycles with no mistakes


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## DavidDymaxion (Dec 1, 2008)

Jack says he intentionally ran two of his cars down to the point that neither would move. He says he pulled 183 Ahr out of 180 Ahr batteries. One car had thousands of miles on it, don't know about the other. He says all batteries were close in voltage on the low knee of the curve. He also says both cars then charged up and are now driving fine. He does say he might have hurt the cycle life, but that there appears to be no immediate ill effects. http://jackrickard.blogspot.com/2010_11_01_archive.html

This seems to indicate that either his batteries were very closely matched, and had very little drift, or maybe there is some kind of self balancing effect. My testing idea would rule one of those cases out, and could demonstrate the need for a BMS.

I tested batteries until full (sudden voltage rise) and empty (sudden voltage drop) every cycle. Currents were in the 5C to 11C range, and recharges were 0.5C to 4C. Discharges were 70+% of capacity at 10C. For about 20 cycles they stayed very close in voltage, even at the knees. I still don't know if that was due to close matching and little drift, or not, hence a desire for the definitive test: Will a half full and full battery eventually both deliver full capacity if given enough shallow charge/discharge cycles without a BMS?


Jozzer said:


> That's my point, how do you know its balanced "pretty" well if you never go near full charge or discharge? It is the only way to get an idea how much capacity a LifePo4 has remaining, voltage can tell you next to nothing until then. Assuming this chap charges to 80% and discharging to 20% on a 100AH pack, all your telling me is that the cells are within 40AH of each other after 5-7000 miles with that statement. When the first cell goes under/over and dies, you'll know that that statement is no longer true, the cells just went a little MORE than 40AH out of balance. Fortionatly, your only trying to make them last some 1-3000 cycles with no mistakes


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## DIYguy (Sep 18, 2008)

Like I asked before folks... prove it. Please. 

We have opinions... we still don't have data. Originally, the request was for showing drift on a balanced pack that has not been damaged by over charge/discharge.

If we get additional info regarding cells growing closer together, that's kewl. (actually, more than kewl). 

Thank you.


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## Jan (Oct 5, 2009)

OK. It seems there doesn't exists any convincing data supporting cell leaking. 

And the only thing that drains cells slowly and individual is a BMS. I remember someone who asked here a few months ago, why one of his stored cells was going down. He had a BMS attatched while they where stored. If my memory serves me well, it was a eLithium. But that's not really relevant. 

If eLithium is correct about charging and discharging do not cause imbalance, and only leaking does, then BMS's are causing the imbalance. 

So, it's very well possible people are happy with their BMS because they balance their packs dayly, that's brought in inbalance by that same BMS. Who knows.


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## dimitri (May 16, 2008)

ElectriCar said:


> I'm thinking I won't balance mine at all initially, only charge them to a level below 3.6 where the first cell begins to spike. Then continue to charge after driving, looking for the pack voltage again where the first cell spikes.
> 
> I feel better about not operating the pack at it's extreme ends which supposedly will pay off with longer life as well.


If you don't balance your new cells at all, how will you know SOC of your pack? To configure any AH counter you need to tell it your available AH so it can accurately track the usage. If you charge your pack in series until first cell hits HVC, you have no idea where all other cells are, the difference can be 2% or 20%, you just don't know. You have no SOC refence point on any cell except the one that reached the knee.

Not balancing a new pack is simply irresponsible. At least put them all in parallel for a day , so they equalize somewhere in the middle first, then do first series charge, you have better chance of having most cells at same SOC then, still not good enough IMHO, but better than nothing.


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## JRP3 (Mar 7, 2008)

Jozzer said:


> That's my point, how do you know its balanced "pretty" well if you never go near full charge or discharge? It is the only way to get an idea how much capacity a LifePo4 has remaining, voltage can tell you next to nothing until then. Assuming this chap charges to 80% and discharging to 20% on a 100AH pack, all your telling me is that the cells are within 40AH of each other after 5-7000 miles with that statement. When the first cell goes under/over and dies, you'll know that that statement is no longer true, the cells just went a little MORE than 40AH out of balance. Fortionatly, your only trying to make them last some 1-3000 cycles with no mistakes


I generally charge to around 90% or so, if I know I want max range I'll take the pack up until the smallest cell hits about 3.6V, though I only do that occasionally. I've also occasionally taken the pack down around 3.0V or lower a few times to check bottom balance. I saw no large variation from the initial bottom balancing I did and I have not seen the relationship at the top change either. I'll do a deep DOD again sometime this spring to see where the cells are all sitting and report all voltages, but so far in the first year and about 5K miles of driving I have not seen significant changes.


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## ElectriCar (Jun 15, 2008)

dimitri said:


> If you don't balance your new cells at all, how will you know SOC of your pack? To configure any AH counter you need to tell it your available AH so it can accurately track the usage. If you charge your pack in series until first cell hits HVC, you have no idea where all other cells are, the difference can be 2% or 20%, you just don't know. You have no SOC refence point on any cell except the one that reached the knee.
> 
> Not balancing a new pack is simply irresponsible. At least put them all in parallel for a day , so they equalize somewhere in the middle first, then do first series charge, you have better chance of having most cells at same SOC then, still not good enough IMHO, but better than nothing.


Well I was basing that on info that Calb cells are being delivered with the entire shipment at the exact same voltage down to hundredths of a volt and same SOC, 50%. I understand the need to balance if the voltages are all over the place but if they are identical, there'll be no exchange of current between them when placed in parallel.


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## JRP3 (Mar 7, 2008)

dimitri said:


> If you don't balance your new cells at all, how will you know SOC of your pack? To configure any AH counter you need to tell it your available AH so it can accurately track the usage. If you charge your pack in series until first cell hits HVC, you have no idea where all other cells are, the difference can be 2% or 20%, you just don't know. You have no SOC refence point on any cell except the one that reached the knee.
> 
> Not balancing a new pack is simply irresponsible. At least put them all in parallel for a day , so they equalize somewhere in the middle first, then do first series charge, you have better chance of having most cells at same SOC then, still not good enough IMHO, but better than nothing.


Jack claims that all his CALB cells have come in exactly at 50% SOC and that you can expect the same because it's a computer controlled process that does it. (Don't know if that's a verified fact or not). With the closely matched cells that seem to be coming in these days doing an initial charge through something like a kill-a-watt and watching voltages closely with a DVM should tell you if your cells were at 50% SOC or not. If they all come up to the knee at close to the same time and the pack takes a 50% charge to do it you're probably right on the money. If some cells shoot up well before others then you know they weren't at 50%.


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## tomofreno (Mar 3, 2009)

> This is from the EVDL:...


 This doesn't make sense. First, there are lots of people using shunt balancers and their cells are not going unbalanced. Second, assuming series connected cells, even if the cells have different internal resistance, they all have the same charge going into them due to current continuity, so they all gain the same Ah/time. The cell voltages will be different due to the different work done to move the charge into the cells due to different IR, and more energy will be dissipated as heat in the higher IR cells, but the Ah in will be the same.


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## Overlander23 (Jun 15, 2009)

For the record, I strung my pack together in series and charged off my Elcon 5K while watching cells like a hawk. These were cells that had been sitting in the crates for about eight months. 

They all read 3.31 volts at the beginning, but certainly did not hit the top at the same time. One cell went to 4.2 before I caught it, while the others were still at 3.4v. My Elcon was still going strong in CC mode (set to 3.65v average per cell before switching to C/50 rate to 3.8v).

I pulled the high cell out of the series loop and continued bulk charging. Same thing happened three more times. I pulled cells out three more times. Low cells were still sitting at 3.4v. After that, I just paralleled it all together and let it sit on my Mastech supply at 3.6v for a couple of days. The Mastech delivered 20 amps (max capability) for awhile.

Now that could have just been variances in cell capacity. Or not. I don't have a method of logging capacities of individual cells. If I had let the charger continue until 3.65v average I would have overcharged that high cell. To be fair, I don't know what would have happened at 3.55v average.

The thing is, Jack now seems to be saying he isn't against cell level monitoring... he's just not prepared to trust anything on the market. If he were to spend five years developing and testing his own system, well... But then, I'm probably wrong reading what he wrote.



> Why do I know the BMS is at fault? Because inherent in their design they cannot fail to be. These are amateurs designing systems that have profound real world consequences. And they are doing it poorly.
> 
> IT is NOT that the concept of a cell level BMS is inherently evil. I looked for one for two years. I gave up. The work that is out there is shoddy crap done by morons. It is dangerous, and it is burning cars to the ground.
> 
> ...


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## ElectriCar (Jun 15, 2008)

Overlander what brand were you working with here? 

RE Jack. I guess you also read the ferry fire wasn't caused by any cord but the charger being set too high thus overcharging the cells which the BMS failed to stop handle the situation he says. 

However I'm curious how the fire started other than the fumes from overcharged cells venting and the solvent fumes igniting.


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## JRP3 (Mar 7, 2008)

I'm guessing Overlander has TS cells, which don't seem to have the same QC as CALB.
As for the fire, if the charger keeps charging after they are full for a long time you'll get excessive heat which can melt and burn the casing, and the electrolyte can ignite as well I believe, or the heat could ignite something else nearby. Jack left a cell on a 10 amp power supply I think and forgot about it for hours. It melted down and may have caught fire, don't remember the details.


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## Overlander23 (Jun 15, 2009)

ElectriCar said:


> Overlander what brand were you working with here?
> 
> RE Jack. I guess you also read the ferry fire wasn't caused by any cord but the charger being set too high thus overcharging the cells which the BMS failed to stop handle the situation he says.


I'm using 64 Thundersky TS160 cells. It shouldn't be hard to either control charger shutdown with relays connected to a cell level HVC rather than the CAN-bus, or make sure the charger always shuts down or at least goes to a far lower charge level once a pack voltage has been attained via its internal sensing, instead of having the BMS CAN-bus override the charger all the time. The latter would be up to the BMS manufacturer.


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## tomofreno (Mar 3, 2009)

> As for the fire, if the charger keeps charging after they are full for a long time you'll get excessive heat which can melt and burn the casing


 The C.M prof said above 4.3 to 4.4V the electrolyte solvent breaks down and devolves as a gas, and you get a jet or explosion if it happens at high rate. The solvent is flammable so you get a blowtorch.


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## JRP3 (Mar 7, 2008)

tomofreno said:


> The C.M prof said above 4.3 to 4.4V the electrolyte solvent breaks down and devolves as a gas, and you get a jet or explosion if it happens at high rate. The solvent is flammable so you get a blowtorch.


The videos I've seen do show venting and melting but not what I'd call a blowtorch.


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## ElectriCar (Jun 15, 2008)

JRP3 said:


> ...As for the fire, if the charger keeps charging after they are full for a long time you'll get excessive heat which can melt and burn the casing, and the electrolyte can ignite as well I believe, or the heat could ignite something else nearby.


That's why I'm planning on a HV limiter to shut down the charger in the event of something like this happening.


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## JRP3 (Mar 7, 2008)

ElectriCar said:


> RE Jack. I guess you also read the ferry fire wasn't caused by any cord but the charger being set too high thus overcharging the cells which the BMS failed to stop handle the situation he says.


I don't know much about the Brusa's but Jack claims when the BMS is connected through the CAN bus the BMS overrides any limits of the charger itself. If true this seems like a poor feature, the charger should be able to shut off on it's own at a preset voltage even if the BMS doesn't signal it to do so. That way each system is a backup to the other if one fails.


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## mikep_95133 (May 20, 2009)

Hi Gents,

Jack Rickard is a rookie. There are lots of rookies out there. It's not a crime. We've all been there. They all make the same mistakes, for a while. Usually their wallet forces them to sell their EV or get with the program and stop investing in ignorance. Jack's problem is like so many others that come through this arena. He has preconceived notions about EV's. Most everyone does. So he makes all of the same rookie mistakes. The difference is that he has a lot of cash and a pulpit to preach from. His mistakes are obvious. But as with all new comers, what do you do? Correct everything they say in an effort to keep them between the fence posts or to just watch them go down in flames. In Jack's case, his ego is as grand as his bank account. That's a common trait I've seen between millionaires. But what will eventually catch up with Jack and those that choose not to invest in something to watch over their cells, is that during the end of life phase, the cells will be spreading ever farther apart in capacity and impedance. Watching the end of life phase of any chemistry tells the viewer exactly what to do with the next new pack. Stop guessing and start measuring. We will have to wait a bit longer with lithium since it has a bench rated cycle life that is very long, but not eternal. Since the cost of lithium is so high for an EV, to get a decent return on investment, the pack must last much longer than almost any chemistry before it. The only exception being the EV95 nimh cells that go 200k miles. But you can't buy those.

Today is the wild west for EV's and for BMS technology. Time will sort out the BMS winners and losers. In the mean time designers learn and their customers are the beta testers. We really need to have independent testing of the various BMS systems offered.

When I started looking into a BMS, I always look toward who in the world does it the best/longest. A friend of mine has an AC Propulsion vehicle. It's mind blowing what the BMS in that car taught us both. It was clear that even though his BMS is 17 years old, it's never failed and communicates volumes of info while driving/charging. It's all analog. It turns out to be the best system I've ever seen. ACP didn't stall their research when lithium came along for them around 10 years ago. They developed a BMS for it. If lithium was so self reliant and maintenance free, then they would have figured that out long ago, if it was true. They went on and developed a charge shuttling BMS for their lead and lithium cars. It looks like they wanted the ultimate BMS. Burning off a little heat is a microscopic waste of energy verses all of the kwh's going into and out of a pack. But they wanted to do as they always had. Make the best product possible. They did. 

I've been to their shop. Worked on a few of their vehicles. Learned volumes about the concept of a reliable BMS from them. I have one of their BMS modules on my bench. It's a marvel of simplicity and robustness. These guys use a lot of real life testing to improve their hardware. That is what separates the real deal from the wannabe's. Testing. That's why they are the rock stars of the EV community for all of these years.

I watch Jack's videos. I'll have finished watching all 50 of them in the next few days. He definitely has video taped himself smart. But that's ok. He'll get the education that all rookies get, eventually. I just wonder if his ego will allow him to admit it. I just hate to see his 'flock' loose their investments to ignorance.

I really enjoy this forum. More R & D happens here than any other forum I know. I've learned from you guys and hope to keep on doing so.

Mike


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## JRP3 (Mar 7, 2008)

mikep_95133 said:


> Today is the wild west for EV's and for BMS technology. Time will sort out the BMS winners and losers. In the mean time designers learn and their customers are the beta testers.


That's really the problem that Jack has, people are paying to be product testers and faulty BMS's have cost some people some cells. Cells have died with and without BMS's, so to suggest they are a fail safe protection for cells is misleading. There is also the real matter of cost. Yes lithium cells are expensive, but a BMS that costs 20% or more of pack price does not seem cost effective, especially if it can fail and kill some cells. Not saying they all can but it has happened. Jack has put too many miles on his vehicles to just dismiss his findings. Time will tell but you can kill a few cells and still have a lower lifetime pack cost than one with an expensive BMS.


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## dimitri (May 16, 2008)

JRP3 said:


> I don't know much about the Brusa's but Jack claims when the BMS is connected through the CAN bus the BMS overrides any limits of the charger itself. If true this seems like a poor feature, the charger should be able to shut off on it's own at a preset voltage even if the BMS doesn't signal it to do so. That way each system is a backup to the other if one fails.


This is why I always prefer and recommend to others to use SSR with miniBMS, rather than "BMS enable" input that some chargers have, like REGBUS on Manzanita, etc. Its all about single point of failure. Anything can fail in theory, but there is less chance of failure when 2 components have their independent controls to shut off the power, instead of one relying on the other. If charger fails to stop at CV, there is a good chance it will also ignore "BMS enable input". SSR is as dumb and effective as it gets at cutting power, IMHO. I would never trust CAN bus with my life. Its too intelligent for its own good.


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## mikep_95133 (May 20, 2009)

We've seen Jack's pattern of behavior for many years, over and over. The area I live in has had active EV's for 40 years. The rookie syndrome is old news around here. 

I like his shows. He does have good info when he is not jumping to conclusions or making assumptions. Which he does often. I like seeing what he offers otherwise. A few thousand miles does not qualify him as experienced. Spending loads of cash does not qualify him either. We see that syndrome around here too. The best success stories are the folks that know nothing when they come in the door, and are aware of that fact, but learn. Rich rookies smoke more expensive packs than everyone else. But they always still smoke them. Ego's prevent people from asking what to do to prevent damaging their packs, in the first place.

It's simple to me. I think we now have entered E-Darwinism with a religious fervor. Those that follow one path will have results and those the follow another will have their own results. Both valuable data. In the end it will be the cost that decides the path that wins. The problem becomes as cells die around here, people get embarrassed and slow down or stop their flow of information about them. They stop showing up at EV functions. We see that a lot around here too. Their wallet sees the light before they do.

Every pack of cells that are new behave in unison for a while. But the cells always diverge with time, no matter what chemistry is chosen. Jack has nowhere near the miles he needs to understanding this phenomenon. Even guys with old lead acid packs that died at 10k miles understand that nothing stays the same over time without some external influence. Lithium is no different. The NREL even did testing to show this.

I'm heavily into data. I don't subscribe to beliefs. I'm tracking many lithium owners as we speak. I watch many people with lithium packs looking very fore lorn when their packs have dying cells and they don't know why. When I can, I help them debug their issues. I capacity test their cells for them so they know how much damage is actually done, from their decisions. I want them to succeed. My biggest problem with pack failure is not failure, it's the undeserved black eye that EV's get from uninformed decisions that owners made.

As for bottom balancing it was invented over 60 years ago with the advent of flooded nicads for aircraft and military applications.

The best example of a guy that was a rookie, knew it, and still put together a decent car, is the KIWI EV guy. He video taped his work and it still benefits people who watch it. There are many of his DVD's floating around here. This is the kind of guy that should have an ongoing EV show. His attitude is exemplary. 

Mike


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## mikep_95133 (May 20, 2009)

dimitri said:


> This is why I always prefer and recommend to others to use SSR with miniBMS, rather than "BMS enable" input that some chargers have, like REGBUS on Manzanita, etc. Its all about single point of failure. Anything can fail in theory, but there is less chance of failure when 2 components have their independent controls to shut off the power, instead of one relying on the other. If charger fails to stop at CV, there is a good chance it will also ignore "BMS enable input". SSR is as dumb and effective as it gets at cutting power, IMHO. I would never trust CAN bus with my life. Its too intelligent for its own good.


Hi Dimitri,

The problem with a failure point is due to a lack of testing or even knowing what to test for. In engineering circles to sell something to the public, electroncis have to pass UL/CSA testing. This is one of the steps that separates hobby level hardware from professional. There is also EMI, thermal, and shock & vibration. If some company were to get UL/CSA certs under their belt for their BMS, you can bet their system is far more reliable. The group that does the most testing wins.

The biggest culprit is EMI. Do you ever see info on how someone found EMI with a scope and then solved it? That info is not out there. That's because the hobby level guys don't know to look for it or how to find it. The neat thing about a lot of analog systems is their relative immunity to EMI. Tripping a relay or an SSR, is much easier than hardening a communication protocol that has to fight EMI every step of the way. 

Mike


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## ElectriCar (Jun 15, 2008)

mikep_95133 said:


> Hi Dimitri,
> 
> The problem with a failure point is due to a lack of testing or even knowing what to test for. In engineering circles to sell something to the public, electroncis have to pass UL/CSA testing. This is one of the steps that separates hobby level hardware from professional. There is also EMI, thermal, and shock & vibration. If some company were to get UL/CSA certs under their belt for their BMS, you can bet their system is far more reliable. The group that does the most testing wins.
> 
> ...


Thus why I've had fits with my PakTrakr for 3 years. It's a good idea but horrible at noise immunity. I have chokes all over the place to calm it down. They don't use shielded cable or twisted pairs. 

I don't know if I want a BMS but if I do I want it simple and analog as well.


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## Forse (Dec 21, 2009)

mikep_95133 said:


> Every pack of cells that are new behave in unison for a while. But the cells always diverge with time, no matter what chemistry is chosen. Jack has nowhere near the miles he needs to understanding this phenomenon.


Do you have any data to support this claim?

When will the cells start to diverge? 

How long does it take before the cells are so much out of balance that they start to take damage during use?


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## dimitri (May 16, 2008)

mikep_95133 said:


> If some company were to get UL/CSA certs under their belt for their BMS, you can bet their system is far more reliable. The group that does the most testing wins.


I don't subscribe to this notion. Just because any given system has not been tested by UL/CSA does not automatically make it inferior. Economics bump heads with this ideal engineering approach. DIY is a small market niche, players in this niche can't afford industry testing. Does that mean we have no place at all? How is void benefitting anyone? Same goes for digital vs. analog, why make it more expensive by improving digital protocol when you don't need to. There is whole 1 bit of info that charger needs to get from BMS and there is whole 1 bit of info that BMS needs from cells. No need for CAN bus to exchange 2 bits of info. I am simplifying , of course, but not by much. With a couple of acceptable compromises analog system wins in this area.

Also, what's with labeling people as "hobbyist" vs "pro"? You are lowering yourself to Jack's ignorance level. Last I checked no one is born a pro, everyone has to learn and evolve. Where do you draw a line? What gives you right to draw a line in the first place?


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## DavidDymaxion (Dec 1, 2008)

Jack definitely makes rookie mistakes -- like putting his face near a battery being tested with 100's of Amps, with no safety googles; metal parts too thick or thin; etc. Yes, he does have a big ego (although I think that is independent of wealth).

On the flip side, can you call a guy that has built 3 electric cars, owns 4 other electric cars, and is embarking on his 4th build a rookie? He is also someone with years and 1000's of miles of electric experience now, too.

If you go through all his videos, you'll see he started with the preconceived notion he needed a BMS. The first BMS killed several cells. The 2nd one was on the pack that burned up in transit (shorting to the case, something a BMS couldn't fix). He had a 3rd battery monitoring system but has removed it (not sure why he removed it). Again, not saying I agree with him but the record shows his preconceived notion was to use a BMS.

Love it or hate it, he questioned his preconceived notion and questioned the general wisdom by going BMS-free. He also (to my knowledge) pioneered bottom balancing lithium batteries.

So anyway, I'm not saying Jack is ultimately right -- had he run the AC Propulsion BMS first he could well be singing a different tune -- but thought we should keep the record straight.


mikep_95133 said:


> Hi Gents,
> 
> Jack Rickard is a rookie. There are lots of rookies out there. It's not a crime. We've all been there. They all make the same mistakes, for a while. Usually their wallet forces them to sell their EV or get with the program and stop investing in ignorance. Jack's problem is like so many others that come through this arena. He has preconceived notions about EV's. Most everyone does. So he makes all of the same rookie mistakes. The difference is that he has a lot of cash and a pulpit to preach from. His mistakes are obvious. But as with all new comers, what do you do? Correct everything they say in an effort to keep them between the fence posts or to just watch them go down in flames. In Jack's case, his ego is as grand as his bank account. That's a common trait I've seen between millionaires. But what will eventually catch up with Jack and those that choose not to invest in something to watch over their cells, is that during the end of life phase, the cells will be spreading ever farther apart in capacity and impedance. Watching the end of life phase of any chemistry tells the viewer exactly what to do with the next new pack. Stop guessing and start measuring. We will have to wait a bit longer with lithium since it has a bench rated cycle life that is very long, but not eternal. Since the cost of lithium is so high for an EV, to get a decent return on investment, the pack must last much longer than almost any chemistry before it. The only exception being the EV95 nimh cells that go 200k miles. But you can't buy those.
> 
> ...


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## mikep_95133 (May 20, 2009)

dimitri said:


> Also, what's with labeling people as "hobbyist" vs "pro"? You are lowering yourself to Jack's ignorance level. Last I checked no one is born a pro, everyone has to learn and evolve. Where do you draw a line? What gives you right to draw a line in the first place?


I do UL/CSA testing preparation as part of my profession. Everything I build for my customers, has to pass UL/CSA or by law they cannot sell it. It truly does separate pros from hobbyists. It's not a put down for hobby level developers. The requirements of UL/CSA came about due to people getting hurt and or killed. If I thought that hobbiest level BMS hardware was useless, I would not test it nor study it nor spend time in this and other forums. It's great stuff here! I own some of your hardware, as well as many other brands. People ask me all of the time about what BMS's work. There isn't enough time or resources to find out. It takes thousands of test miles and instrumentation to even begin to do it right.

I didn't draw the line Dimitri. Others did, long before you and I were born. When people died due to electric shock after Edison and Westinghouse sent electricity to our homes, the need was born for some serious standards. We are there now with the damage a failed BMS unit can do to a cell, and with what damage an energy dense pack can do to a car, someones house, garage or ship, when an owner chooses no monitoring or unproven hardware.

Just as with the aftermarket hybrid pack vendors having to look at smog rules in order to sell their hardware to hybrid owners, if there is enough damage done, all BMS vendors may very well find themselves regulated as well, before they can sell their hardware to the public. I design and build BMS hardware too. I only do it for me. The public in general can't tell data from fiction. So I choose not to deal with them. You are a braver soul than I, Dimitri.

Mike


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## mikep_95133 (May 20, 2009)

Good call David. I think that Jack deals in black and white. No room for gray scale. That's another tell for me about him. He tried a little BMS hardware then goes on a rampage through many forums when he has an issue. That yelling and hand waving is just smoke and mirrors to cover up what he doesn't know.

His total time and mileage is not even close for him to qualify as experienced in this arena. He does a great service with his videos, but he only hurts those that don't know what he's doing, when he makes blanket statements that all BMS talk is motivated by dollars. So I dismiss that part of his videos. But the rest I watch and am amused and entertained to see how he solves issues. I still thing the young guy from the KIWI DVD has Jack beat hands down.

Mike




DavidDymaxion said:


> Jack definitely makes rookie mistakes -- like putting his face near a battery being tested with 100's of Amps, with no safety googles; metal parts too thick or thin; etc. Yes, he does have a big ego (although I think that is independent of wealth).
> 
> On the flip side, can you call a guy that has built 3 electric cars, owns 4 other electric cars, and is embarking on his 4th build a rookie? He is also someone with years and 1000's of miles of electric experience now, too.
> 
> ...


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## mikep_95133 (May 20, 2009)

There is a great article in Design News magazine that shows a kit that a fellow carries from job to job. He made all of his own EMI probes. They just attach to his scope. He has written about his many successes because of the probes. After I made a couple for me, everyone at work had me make them sets too. I suspect if you characterize the EMI your system generates, you could just add a simple r-c pair to kill much of it. Twisted wires and ferrite beads are fairly stone age when it comes to really killing EMI. Those ferrites and the twisting of wires is just the most common method for attempting to attenuate it.

If you ever want to try using EMI probes, make sure you use an isolated scope. Battery powered makes it easy. Lots of guys plug a scope into the wall while their EV is charging to probe their hardware, and get a nasty surprise when their scope probe is shorted to 120vac. 

Mike



ElectriCar said:


> Thus why I've had fits with my PakTrakr for 3 years. It's a good idea but horrible at noise immunity. I have chokes all over the place to calm it down. They don't use shielded cable or twisted pairs.
> 
> I don't know if I want a BMS but if I do I want it simple and analog as well.


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## Qer (May 7, 2008)

DavidDymaxion said:


> On the flip side, can you call a guy that has built 3 electric cars, owns 4 other electric cars, and is embarking on his 4th build a rookie? He is also someone with years and 1000's of miles of electric experience now, too.


I'm not going to say whether Jack is a rookie or not, but your conclusions are simplified and thus dangerously close to misguide you (if it hasn't already happened).

Competence doesn't come from what you experience, competence comes from what you learn. It doesn't matter how many cars you convert, how many miles you drive or how much hardware you blow up if you don't take the time to reflect over what you've just experienced. It doesn't matter if you learned by reading, watching or doing, the only thing is if it taught you a lesson or not.

I think one of the best books I've read when it comes to learning things is "Zen and the art of motorcycle maintenance". It's worthless if you want to learn about motorcycles, it's not a very good at explaining Zen either but it made me start thinking and reflecting over a lot of things that I used to take for granted. One of those things were what knowledge really is, because in the end neither a degree nor experience is worth anything if you just collect it without actually taking it in too. There's a lot of people out there that has collected a degree but still are hopelessly incompetent, because they never really understood what they studied, they never learned how to use it, they just collected the prize.



 So can you call someone building his fourth EV a rookie? - Yes, you certainly can.
 Can you call someone building his fourth EV experienced? - Of course you can.
 Does it mean he is a rookie or not? - Mu.


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## dimitri (May 16, 2008)

mikep_95133 said:


> I do UL/CSA testing preparation as part of my profession.


In this case, you are one of the few exceptional cases in public forums where your comments can be taken seriously. I hope you understand where my position was coming from, I meant no personal offense.

I understand the history and public need for UL/CSA and standards, but if kept unbalanced by free market this approach can hurt people as well. Various forms of protectionism and stagnation can result from too much regulation, just look at DIY struggles in Europe.

I believe in natural selection, it should not be a government function to protect people from themselves, it hurts people in a long run. However, wild west is not my preference either. Honestly, this is more of philosophical dilemma and I don't want to hijack this thread with it.

I put my stuff in my own EV before I offer it to others. Still, a day does not go by where I don't think about potential consequences if something goes wrong, no matter how safe I try to make it. I try not to let it get me down, because what is the alternative? Do we give up our dreams and desires to drive EVs in our lifetimes?


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## mikep_95133 (May 20, 2009)

Forse said:


> Do you have any data to support this claim?
> 
> When will the cells start to diverge?
> 
> How long does it take before the cells are so much out of balance that they start to take damage during use?


I wish there was a place to deposit that kind of data. I'm lucky to live in an area where EV's have been active and organized for 40 years. I observe hundreds of EV owners monthly. I watch year after year as failures occur. Like I've said, folks get very shy at speaking up about their pack failures. But it occurs at such a high rate that it's hard to remember it all.

Divergence starts on the first day. When it becomes a problem is related to the dod utilized, cell layout, and owner knowledge. The deeper the depth of discharge utilized, the faster the onset of divergence. On vehicles with a BMS that delivers info on each cell, it's as easy to watch divergence as it is to watch Jack's videos. In fact the ACP car up the street, is very telling. The pack is 14 batts in a row on top of 14 more batts. The upper row of batts always has a higher voltage because they are always warmer. That increases a battery's capacity if it's warm. As the pack heaters thermally equalize the pack, the voltages become closer together. See, more than one way to equalize a pack! Pack installation for a given EV has the same issue. The cells are not all the same temperature, mostly based on where they are located. Cells located in the front of the vehicle always run cooler than those in the trunk due to all of the frontal air flow. That installation is not only very common, it also starts the divergence of cells the very first day of installation.

Assuming that a pack of cells from a vendor all have the same capacity is another fallacy. I always go through my cells my capacity testing them first. Then I know where I've started without any assumptions. Measurements after that are more accurate since my baseline is solid. Capacity differences are how the cell vendors keeps the cost low. Some agencies have their cells especially tested and sorted so they are match at a level that you and I cannot come close to affording. 

Mike


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## etischer (Jun 16, 2008)

DavidDymaxion said:


> Jack definitely makes rookie mistakes --
> 
> The first BMS killed several cells. The 2nd one was on the pack that burned up in transit (shorting to the case, something a BMS couldn't fix). He had a 3rd battery monitoring system but has removed it (not sure why he removed it).


I believe Jack's battery monitoring system failure was the Cell Log 8s he installed. He either pinched a wire or created a short circuit soldering his connectors and claims it almost burned his car down. Lesson learned, everyone should steer clear of CellLog8s. 

I started a thread asking Jack to provide details of his failure and he never responded. The CellLog8s were apparently still functional, so the problem was with Jacks wiring, not the product itself. 

http://www.diyelectriccar.com/forums/showthread.php/cell-log-8-review-43343.html


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## pgt400 (Jul 12, 2008)

frodus said:


> I second that. Sounds risky without something that'l protect the pack from being overcharged or overdischarged. Until I see more empirical data on this, I'm just going to use what I've bought and log.


Agreed, either you use a BMS, you become the BMS or you loose your cells.

Once the cell hits 3.6v it can go to over 4 volts in seconds...so if you are the BMS be prepared to spend allot of time staring at DVM'S!


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## Forse (Dec 21, 2009)

mikep_95133 said:


> I wish there was a place to deposit that kind of data. I'm lucky to live in an area where EV's have been active and organized for 40 years. I observe hundreds of EV owners monthly. I watch year after year as failures occur. Like I've said, folks get very shy at speaking up about their pack failures. But it occurs at such a high rate that it's hard to remember it all.


 
???? Come on, give us a link or something to support your claim. If you "observe hundreds of EV owners monthly" surely it must be on the net, maybe even on this site.​ 


Some of the only data we got on this issue, from JR, shows that divergence is not a problem after 15 months and a few thousand miles.​ 
Brainzel writes earlier in this thread. "After ~40 - 50 charges (Zivan NG3), all cells (SkyEnergy/CALB 121AHA) are still close together in voltage."​ 
JRP3 wrote. "Before I put it up for the winter I had about 8 months and 5k miles on my bottom balanced pack with no BMS. So far no dead cells, even after a limp home event with 1.77 v per cell under load and occasional 5.5C draws. All cells still seem to be in the same relationship to each other at this point, won't know for sure until I do a near 100% DOD again next year. "​


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## DIYguy (Sep 18, 2008)

Ok Mike, I'm glad we finally got the right fellow to talk about this subject. Surely such an accomplished fellow as yourself who has these hundreds of EV's that you watch over...or even perhaps someone that you know.... including all those chaps at AC Pro should have this simple data that would predicate the need for active balancing... I mean, after 60 years of bottom balance and 40 years of EV's (where did the other 20 yrs go?? ) 

Seriously now, I just can't understand why you are not posting it..... ur not typing urself smart are you ??


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## DIYguy (Sep 18, 2008)

Qer said:


> Competence doesn't come from what you experience, competence comes from what you learn.


Brilliant... you have got to be kidding..... if you keep this up, i'm going to have to force you to change that quote about the motors vs Soliton's...


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## JRP3 (Mar 7, 2008)

pgt400 said:


> Agreed, either you use a BMS, you become the BMS or you loose your cells.
> 
> Once the cell hits 3.6v it can go to over 4 volts in seconds...so if you are the BMS be prepared to spend allot of time staring at DVM'S!


I am the BMS, after getting the charger dialed in I spend very little time staring at DVM's. I also don't charge to 3.6, usually aim for 3.45 max on my smallest cells and I avoid extended CV phases since I don't want to put every last electron in the cell. If I'm charging at a substantially different temperature than I set the charger at I will check and readjust if necessary. I don't know how well this would work without a fully adjustable charger, since large temperature swings will change things.


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## Duncan (Dec 8, 2008)

Hi Guys

Somewhere in one of these massive threads was a recomendation to buy a book about the care and feeding of lithium batteries
Can somebody tell me the title and source

Thanks


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## JRP3 (Mar 7, 2008)

http://book.liionbms.com/


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## mikep_95133 (May 20, 2009)

If the data on failure rates of packs were kept anywhere, I'd be all over it. That very problem is contributing to EV lore. People hate admitting they screwed up their packs. Especially $10k-$20k packs. That's why if your are not standing in the room with the owner of damaged pack when they speak, you miss the data. 

If you join with a dedicated EV group in your area, you get to know the other EV owners, and find out what I mean about pack and cell failures. It's so predictable. We just happen to have a high concentration of EV's here due to the weather being so mild relative to the rest of the country.

It's also very important that any cell voltage measurements be made under load. Static voltage is such a poor indication of soc. Jack posted some graphs I'm sure you've all seen in his videos, showing his pulsed discharge performance. The graphs clearly show that from 65% to 100% dod, that the difference between static cell voltage and loaded cell voltage becomes huge. All packs with only a few cycles and a few thousand miles are still matched. It's much easier to get a 'matched' pack when the cells are not under load. If you could watch each cell while driving your opinion of how matched they are would change. 

It's a lot of work to capacity test every cell in a pack. But it's the only way to know how well a pack is doing. This is one place a BMS shines. Instead of taking each cell and capacity testing it one at a time, you can do the same thing while driving the vehicle and watching the BMS data. As the max dod is reached, the first cells that start to drop off of a cliff are the limiting factor in the pack. You just look at the display and know what their capacity is. The rest of the pack obviously has higher capacity. You can't get that info standing their with dvm with your car in the driveway.

The other , almost more important item, is cell impedance. With a BMS displaying each cell's voltage under load, you can see which cells sag more. My friends ACP car showed a slightly sagging battery weeks before replacement was required. He just drove the car to the particular weak battery's soc limit and no further. When a battery dies, you can't feel it. Acceleration does not change. There is no way to tell that it's dead, unless you monitor it. If it's dead shorted, you will find it with a dvm standing in your driveway. Lithium doesn't usually die in a shorted condition. It just becomes so high impedance that it can't conduct enough current to move the vehicle as it once did. It heats up. Eventually it becomes a fire hazard since it's only a giant, expensive resistor at that point.

I've watched BMS systems doing their jobs. Once you see it in action, you are a convert. The other great benefit to a BMS is how it integrates a new replacement cell into the pack. A new cell can be ruined very quickly since it's characteristics are so much different than the rest of the used pack. This is one of those end of life scenarios that Jack doesn't get. Another clue he's a rookie.

I personally don't care what you choose or don't. But I have to know what my pack is doing. So I measure it, under load when I'm in doubt.

Mike


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## mikep_95133 (May 20, 2009)

I'm not offended in the least Dimitri. I watched as you developed your BMS. I read many of threads as others did too. I've been reading here long before I signed up. Same with other forums.

If electrical items kill people or damage property, the free market will gets it's ass kicked. That's a fact. It's happened all over the world. UL/CSA standards are why you can use a hair dryer in your bathroom and not get shocked, etc.

The biggest thing I would watch out for is the DOT. If they determine that an aftermarket BMS is unsafe, they can declare it not road worthy. That makes it illegal to use.

Honestly I think that success of the BMS market will largely depend on foresight. I think the BMS market needs to get themselves organized so standards of operation and reliability can be established.

I also know that most consumers are a serious pain in the butt when it comes to EV's. This doesn't help failure rates any.

Worst case is we just drive naked like Jack does 

Mike




dimitri said:


> In this case, you are one of the few exceptional cases in public forums where your comments can be taken seriously. I hope you understand where my position was coming from, I meant no personal offense.
> 
> I understand the history and public need for UL/CSA and standards, but if kept unbalanced by free market this approach can hurt people as well. Various forms of protectionism and stagnation can result from too much regulation, just look at DIY struggles in Europe.
> 
> ...


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## mikep_95133 (May 20, 2009)

Since Jack came onto the scene, I now advise folks to just do as he does if they are so inclined in that direction. But to keep us informed of their results. The data will generate itself, eventually. In fact I was thinking of passing around DVD's of his shows to those that don't have broadband so they can get a sense of what the stir is all about. I did do that with the Kiwi guy's DVD because I think he's got maybe the best attitude I've ever seen, not to mention his hard work.

Jack is not the first guy to stand up on a podium and preach his values. I had to stop hanging around certain EV venue's because I was tired of guys like Jack spewing lore to those that are not technical. Jack is only one guy in a long string of snake oil salesmen. He does have good info when he is not jumping to conclusions. Remember, Jack is building a business.

No offense to you, but I don't care if you believe me or not. I don't care if I'm qualified to you. It's only important to me to make sure that people that are not technical know that there are good paths to take that will teach them more solid methods to keep an EV on the road. People constantly sell their EV's once they smoke a couple of packs. It's a real heart breaker. That's how I got both of mine.

I tell folks to watch Jack's videos. I also tell them they need to view them with a critical eye. I will have watched all 51 of them here shortly.

ACP has more miles on lithium than any vendor on the planet. They didn't want to speculate. They went out and generated the data. What ever they do, you can bet it came from some serious empirical testing.

Mike




s


gottdi said:


> And what NEW and EXCITING things have you brought to the TABLE? I live in California, a place ripe with 40 plus years of EV building but that does not make me an expert.
> 
> What, besides bashing Jack who actually does do testing and showing his work and will say if it is a mistake, have you done for the EV community?
> 
> ...


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## JRP3 (Mar 7, 2008)

mikep_95133 said:


> If the data on failure rates of packs were kept anywhere, I'd be all over it. That very problem is contributing to EV lore. People hate admitting they screwed up their packs. Especially $10k-$20k packs. That's why if your are not standing in the room with the owner of damaged pack when they speak, you miss the data.


That's the good thing about a forum like this, we post our data. If I kill some cells the first thing I'll do is come here and report it. When Jack has killed some cells he makes a video about it for all to see. He can be obnoxious but that doesn't make him dishonest. 



> It's a lot of work to capacity test every cell in a pack. But it's the only way to know how well a pack is doing. This is one place a BMS shines. Instead of taking each cell and capacity testing it one at a time, you can do the same thing while driving the vehicle and watching the BMS data. As the max dod is reached, the first cells that start to drop off of a cliff are the limiting factor in the pack. You just look at the display and know what their capacity is. The rest of the pack obviously has higher capacity.


If you have one of the really expensive BMS's that display all that, or a handful of Cell Log8's.


> You can't get that info standing their with dvm with your car in the driveway.


Actually you can test capacity with a DVM and ah counter. You bottom balance your pack and then charge it. First cell to fill up is the smallest capacity, the next smallest will start to move into the knee. You can stop there or remove cells and keep charging and track the rest if you want. I found my 4 lowest capacity cells and stopped.


> The other , almost more important item, is cell impedance. With a BMS displaying each cell's voltage under load, you can see which cells sag more. My friends ACP car showed a slightly sagging battery weeks before replacement was required. He just drove the car to the particular weak battery's soc limit and no further. When a battery dies, you can't feel it. Acceleration does not change. There is no way to tell that it's dead, unless you monitor it.


 You don't notice a 3 volt difference in your pack voltage in relation to ah? 


> The other great benefit to a BMS is how it integrates a new replacement cell into the pack. A new cell can be ruined very quickly since it's characteristics are so much different than the rest of the used pack. This is one of those end of life scenarios that Jack doesn't get. Another clue he's a rookie.


That's why he manually balances new cells added into a pack, just as I have done. Even if I used a BMS I wouldn't use it to balance a new cell into the pack, I'd either top or bottom balance it with the rest of the pack manually.


> I personally don't care what you choose or don't. But I have to know what my pack is doing. So I measure it, under load when I'm in doubt.
> 
> Mike


I've occasionally checked my cells with a Cell Log8 when driving to see what they do. Nothing unusual yet. The BMS you describe sounds great, if it were affordable and benign.


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## ElectriCar (Jun 15, 2008)

Got one I've been thinking about Mike as have a lot of others. If the car makers won't do cell level monitoring what do they know that we don't? And how would the Tesla do that with 7000+ cells? With dimitri's miniBMS can you imagine the number of boards that would require? Where on earth would you put them? Obviously, it's not practical. 

If it's not practical then they have to find another way to monitor the pack. String level monitoring? You must see there has to be another way besides cell level BMS monitoring. Have you any details of the OEM's management protocol?


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## DavidDymaxion (Dec 1, 2008)

<shuffles forward with blank look and arms outstretched> All hail Jackton! All hail Jackton! 

Not sure what you are talking about (but would like to know where I'm going off the rails). Don't forget I'm the guy that proposed draining a battery 1/2 way, putting it in series with a full battery, and seeing if a bunch of shallow charges would show a self balancing effect. That's not a matter of belief, and not a conclusion, but asking others to join me in this test I plan to do. I'll post up how it works, whether it helps Jack's cause or not.

I also did one round of lithium testing, just got headways in to test, plus other batteries coming in to test. Once I see cell drift I'll report that, too (haven't seen it yet, once bottom balanced, in very limited testing).


Qer said:


> I'm not going to say whether Jack is a rookie or not, but your conclusions are simplified and thus dangerously close to misguide you (if it hasn't already happened). ...
> 
> 
> DavidDymaxion said:
> ...


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## JRP3 (Mar 7, 2008)

ElectriCar said:


> Got one I've been thinking about Mike as have a lot of others. If the car makers won't do cell level monitoring what do they know that we don't? And how would the Tesla do that with 7000+ cells? With dimitri's miniBMS can you imagine the number of boards that would require? Where on earth would you put them? Obviously, it's not practical.
> 
> If it's not practical then they have to find another way to monitor the pack. String level monitoring? You must see there has to be another way besides cell level BMS monitoring. Have you any details of the OEM's management protocol?


Tesla may not monitor all cells in parallel but they certainly do monitor and balance the units in series.


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## mikep_95133 (May 20, 2009)

I's nice to see you have a plan of action for your pack. It sounds like it's working for you. 

If a cell is dead in a 300v pack, you won't notice it. In fact you won't notice it if several died at the same time. I've watched this happen several times. Even if it's a 144v pack. 3v is too tiny of a change under load, while driving. 

I've characterized and tested a few touch screen BMS systems from China for a customer. They just monitor. Really sweet interfaces. Wish I could remember the brands. Anyway, there are enough of them out there, that it's worth the investment. If a pack does end up getting replaced, the BMS stays. You just reconnect it. So if it does cost some percentage of a lithium packs value, it will amortize itself over several packs. Each time the BMS flags a low or high cell, it just paid you back the cost of that cell. In my mind that makes a BMS dirt cheap.

A $10k lithium pack will have to go 100,000 miles to make it cost only 10 cents per mile. Does anyone really think they can make a pack go for that long, for a few thousand cycles and not know anything other than the max and min pack voltage? I bet many $10k lithium packs won't go 20k miles. That makes them run 50 cents per mile. Might was well lease a Corvette. This all assumes that your electricity cost is free.

Mike






JRP3 said:


> That's the good thing about a forum like this, we post our data. If I kill some cells the first thing I'll do is come here and report it. When Jack has killed some cells he makes a video about it for all to see. He can be obnoxious but that doesn't make him dishonest.
> 
> If you have one of the really expensive BMS's that display all that, or a handful of Cell Log8's. Actually you can test capacity with a DVM and ah counter. You bottom balance your pack and then charge it. First cell to fill up is the smallest capacity, the next smallest will start to move into the knee. You can stop there or remove cells and keep charging and track the rest if you want. I found my 4 lowest capacity cells and stopped.
> You don't notice a 3 volt difference in your pack voltage in relation to ah?
> ...


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## JRP3 (Mar 7, 2008)

It's no secret that Tesla monitors and balances their pack. The user manual even describes the need to not stop the charging process early too often since the pack can't be balanced partially discharged.


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## ElectriCar (Jun 15, 2008)

JRP3 said:


> Tesla may not monitor all cells in parallel but they certainly do monitor and balance the units in series.


I'm certainly not an advocate of cell level monitoring but I may end up that way if we don't come up with an alternative that works. 

I'm sure they do monitor strings but I can imagine how they could balance a string without balancing individual cells which means monitoring individual cells. If it's practical to monitor 7000 cells I'd like to see how they do it just out of curiosity. 

Often I feel like the pioneers and it does feel like the wild west. Lots of questions, lots of people have very different ideas and answers.


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## JRP3 (Mar 7, 2008)

Cells in parallel don't need to be balanced, cells in series do.


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## ElectriCar (Jun 15, 2008)

mikep_95133 said:


> I bet many $10k lithium packs won't go 20k miles. That makes them run 50 cents per mile. Might was well lease a Corvette. This all assumes that your electricity cost is free.
> 
> Mike


I really don't expect it to last that long but if it does, great. If not, I can be greatful I could afford it. I personally don't like sending money to people who want to kill anyone who disagrees with their religion. And I really enjoy not polluting the air around me.


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## mikep_95133 (May 20, 2009)

Tesla, ACP and others that use commodity 18650 cells for their packs, and put many of them in parallel to make a module. They usually have 100-110 modules in a pack. So 60-70 cells per module. I've had ACP modules in my hands. So each module gets monitored and shunted in the case of ACP. I'm fairly sure Testa does shunting as well, but I know they do monitoring of each module. Shunting is only around .3 to .4 amps per module since the charger is throttled back when the first cells hits Max V. Both vendors tie their BMS to the charge hardware and the motor controller. That way when an error is flagged, something automatically gets changed/reduced/shutoff to prevent damage. Keeping the relatively dumb consumer out of the loop.

Most often folks site the factory hybrid packs that don't use any shunting as their source. Hydrids use such a reduced window of soc, that the cells are never pushed far out of balance in normal service. But eventually they do after 100k miles. They do monitor however. The pre-06 Honda hybrids use thermal monitoring since nimh gets hot if it's unhappy. So their system needed some refinement in the form of recalls, but it works. I owned 11 Prius packs for testing in one of my EV's. They monitor. They are so not designed for EV's. Some guys use them in smaller vehicles. But for anything else, they are not the same type of nimh as the robust cells used in EV's. 

I don't know where this comes from about mfr's not using a BMS. It's obvious they do if you just ride in the vehicle and look at the display.

I consider monitoring a subset of a BMS, therefore it qualifies to me as a BMS.

Mike




ElectriCar said:


> Got one I've been thinking about Mike as have a lot of others. If the car makers won't do cell level monitoring what do they know that we don't? And how would the Tesla do that with 7000+ cells? With dimitri's miniBMS can you imagine the number of boards that would require? Where on earth would you put them? Obviously, it's not practical.
> 
> If it's not practical then they have to find another way to monitor the pack. String level monitoring? You must see there has to be another way besides cell level BMS monitoring. Have you any details of the OEM's management protocol?


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## mikep_95133 (May 20, 2009)

David, I like your plan. It will show good data on cells. Drift is such a tiny part of the equation. The reason being that there are other much stronger factors working to diverge a packs cells. If you notice that Tesla uses the most extreme thermal management ever designed for their packs. Their data showed that to keep all of the cells at the same temperature makes them stay in balance with less external intervention. This is besides the fact that overheating a pack is bad.

Since consumers have to just mount cells wherever they will fit, the thermal characteristics of the pack are not even a thought. The cells in the trunk are warmer than the cells under the hood due to frontal airflow. That creates a difference in capacity starting the first day. Cold cells have lower capacity, and due to higher impedance, sag even worse. All of this causes imbalance that you can see while driving and monitoring. Each charge/discharge cycle makes the imbalance worse. These forces will trump any natural cell drift by an order of magnitude. 

The tendencies toward imbalance, can be countered significantly if the pack is charged fully, with each cell reaching the same voltage. This is the definition of equalization, or making them all the same.

Mike



DavidDymaxion said:


> <shuffles forward with blank look and arms outstretched> All hail Jackton! All hail Jackton!
> 
> Not sure what you are talking about (but would like to know where I'm going off the rails). Don't forget I'm the guy that proposed draining a battery 1/2 way, putting it in series with a full battery, and seeing if a bunch of shallow charges would show a self balancing effect. That's not a matter of belief, and not a conclusion, but asking others to join me in this test I plan to do. I'll post up how it works, whether it helps Jack's cause or not.
> 
> I also did one round of lithium testing, just got headways in to test, plus other batteries coming in to test. Once I see cell drift I'll report that, too (haven't seen it yet, once bottom balanced, in very limited testing).


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## JRP3 (Mar 7, 2008)

gottdi said:


> Monitor groups of cells. Like a 12 volt battery is monitored as a 12 volt battery and not on the cell level. Just 12 volts. Plenty of strings of cells to make some groups of like maybe 24 volts. Much easier to monitor those. If a group is out of whack then it's time to fix it. But so far they have not had to do that right? Shows that cells remain pretty well balanced. Sure it's a BMS that is keeping them in balance?


If you're talking about Tesla the groups of cells in parallel are still at 3.7V, so basically just treated like one big cell, each of those is monitored and balanced since they are connected in series. I have no idea if they've had to replace cells or not, but they are actively managing them. Remember they are using LiCo cells, not LiFePO4.


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## mikep_95133 (May 20, 2009)

Agreed!

Mike




ElectriCar said:


> I really don't expect it to last that long but if it does, great. If not, I can be greatful I could afford it. I personally don't like sending money to people who want to kill anyone who disagrees with their religion. And I really enjoy not polluting the air around me.


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## EVfun (Mar 14, 2010)

gottdi said:


> Oh I forgot. Nothing Jack has done and shown is proof. At least not in this realm of the world.


To some extent, that is true. Even his oldest vehicle pack is relatively new compared to the expected life. Proof will required running packs to the end of life and seeing how they fail. The cells will, in time and cycles, get old and start going bad. We cannot say a BMS (either Monitoring or Managing) is not needed until we see packs at the natural end of life.


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## DIYguy (Sep 18, 2008)

mikep_95133 said:


> Each charge/discharge cycle makes the imbalance worse.


Prove it. Please


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## DIYguy (Sep 18, 2008)

mikep_95133 said:


> The tendencies toward imbalance, can be countered significantly if the pack is charged fully, with each cell reaching the same voltage. This is the definition of equalization, or making them all the same.
> 
> Mike


No matter how much you charge, you will not "make them all the same"....cells will not be changed in capacity or resistance as a result of a top balanced full charge. You may balance them at the top or the bottom...or maybe even in the middle....but they are what they are. 

The question is, do they drift as a result of being cycled. Sorry, I can't take your word for it.


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## EVfun (Mar 14, 2010)

gottdi said:


> He has done a great deal and the argument is not with a pack at the end of life but a new or pack even two years old.


That is true only if you don't care if the pack lasts longer than 2 years. You do not know how a 5 year old pack will behave until you have EV packs with 5 years of service. Most types of batteries show changes in internal resistance and capacity as they get old. How will older packs in EVs fare? If you can afford to scrap a pack when it is no longer fresh and new we already know you can go without a BMS. We simply don't know if a 5 year old pack, or a pack with 1500 cycles, needs a BMS. I don't know, Jack doesn't know (yet) and you don't know.


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## EVfun (Mar 14, 2010)

gottdi said:


> The batteries should still be in balance but just not the same capacity.


That is the assumption that I'm not very comfortable with. I want some type of monitoring, not necessarily when new but certainly as they age. That could be as simple as a battery bridge that compares the top half to the bottom half of the pack or as complex as computerized logging. Actually, I'm kinda an analog type of guy so I lean toward a simple cell level high/low voltage alarm. I don't care if it can tell me which cell because I can do the charge or load testing and find out if a problem is noted. I just want to to scream at me if I'm discharging or stop the charger if charging.

I do not trust that the long series string of LiFePO4 cells will all fade away together at the end of life. I haven't seen that with any other battery chemistry since I started building EVs in 1998. You like to ask for proof so surely you can appreciate it when I say "prove it."


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## EVfun (Mar 14, 2010)

gottdi said:


> Yup, prove your claim. I can only provide what is not what might be. It is known that packs two or three years old [...]
> 
> So an educated guess of balanced cells for the useful life of the pack of 3000 or more cycles.


Isn't "prove your claim" what I just asked you to do? Show me the EV packs with 2000 cycles on them. That will take over 5 years if cycled every day. 

The fact that one cell fails before others in most cases has been observed in Lead acid, NiCad, and some early experiments with Lithium cells. We are even seeing this with the Nimh packs in the older Insights (their BMS systems flag the problems and restrict pack use.) Why I should assume that it will not be the end of life for the current crop of LiFePO4 cells as well?


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## mikep_95133 (May 20, 2009)

No worries. I'm not offended if you don't take my word for it. I have observed this phenomenon, so I write about it. 

What happens in a pack of cells when some cells are not at the same soc and or capacity as the others, they get pushed into either a deep discharge because of reduced capacity, or they are overcharged due to reduced capacity. By bringing all cells to top balance, they keep the difference minimized. You could also do this with bottom balancing too, but a BMS would not be equipped to do that deep of a discharge in a reasonable amount of time. So top balancing is just more convenient. This is how equalizing the pack keeps the capacity from going down, by reducing the time in either of the soc two extremes.

Even Jack noted that brand new cells vary several ah's from each other out of the crate. So divergence starts before installation.

What I know about load tests I've performed is that going into just a little overcharge deducted 10% instantly from the cells capacity I was testing. They only went to 4.5v. 

I'm hoping one of these days the NREL will do a cycle test on lithium if they haven't already and show how the cells diverge. They show it with lead. I thin they even showed it with hybrid packs. Maybe that was just hybrid characterization. 

Mike



DIYguy said:


> No matter how much you charge, you will not "make them all the same"....cells will not be changed in capacity or resistance as a result of a top balanced full charge. You may balance them at the top or the bottom...or maybe even in the middle....but they are what they are.
> 
> The question is, do they drift as a result of being cycled. Sorry, I can't take your word for it.


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## mikep_95133 (May 20, 2009)

Disprove it please  

Observing these things is easy. Try it sometime. Find a Tesla or an ACP car with a bms and ask for a ride. Some of the vehicles will always have the same module coming up as either running warmer, sagging more, or coming up first when the pack gets low. 

I went some time ago to the evalbum and looked at lithium vehicles. Maybe the evalbum would be a good source of finding owners with lithium. Maybe with encouragement they would keep their cell info current.

Mike






DIYguy said:


> Prove it. Please


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## mikep_95133 (May 20, 2009)

Ok, now you're not being ignored Mr Gottdi.

The folks without a BMS do not know how their pack is doing. They are driving blind. They are making assumptions. This is not data. It's blind faith. You cannot tell if you have one bad cell in a pack unless you monitor it. 

If you took a known smoked cell and put it in your pack, your car would drive fine, for a while. Try it! You could never tell it had a bad cell. At some point the cell will get too hot and start a self destruction process. If you don't occassionally do a capacity test, you are not generating data. Believing the cells are fine, is not data. Therefore is does not have to be dis-proven. If you did capacity test your pack after xxx miles as a maintenance item, then you'd be giving data to the world to back up your grouchy position.

The problem with people on the no BMS side is that they never have data. No I mean real info derived from doing real work. Capacity testing takes a lot of time. So if you want me to respond to you, demanding proof won't get you there since you can only offer no test data as the argument for your position. Driving blind on a pack for a couple of years does not qualify as data by a mile.

Why not just install a monitoring system? You could still leave all of the cells alone and have it your way too. That way you actually have data to show that no balancing is working perfectly fine. Imagine if all of the non-bms guys found that they were right by having data to back it up. I'd be converted in a minute!

Mike






gottdi said:


> Actually not. He has done a great deal and the argument is not with a pack at the end of life but a new or pack even two years old. The argument is cell drift and the need to keep the cells at the upper most charge with a BMS and say they will live longer and be safer. The proof is showing that you don't need a BMS. Now if you take a balanced or well matched set of cells and toss in a rogue cell then I guarantee you will have troubles. But a BMS won't make it less of a rogue cell. It may put a reign on it but it will limit the rest of the pack. Others are also doing the NO BMS route and showing that the cells are just fine. No drift and not fried out packs either. You must be smart about putting things together but aside from that it is not proven yet that you NEED a battery management system which is the premiss of the issue. If you start out with an unbalanced but generally a pack with lets say 100 AH cells then you can bottom balance to bring them into a matched range. Bottom being below the knee to be sure all are near the SOC needed. Then charge them and watch for a few cycles to be sure all is well. If not rebalance them and go again. Once done you can monitor groups of cells manually and on the go with a couple volt gauges to watch if you so like.


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## Qer (May 7, 2008)

DavidDymaxion said:


> Not sure what you are talking about (but would like to know where I'm going off the rails).


Oh, just that you mix up doing things with learning things. 



DavidDymaxion said:


> On the flip side, can you call a guy that has built 3 electric cars, owns 4 other electric cars, and is embarking on his 4th build a rookie?


As I said, I'm not even going to try to define if Jack's a rookie or not (I leave that to others  ) but yes, someone that has built 4 cars can still be a rookie. If he (hypothetically, this borders to philosophy so I'm not pointing anyone out here  ) do the same mistakes over and over then, yes, that person seems doomed to stay an eternal rookie.

It's like some happy hobbyists I've met that are doomed to stay eternally in the klutz department because they keep repeating the same mistakes over and over again. Somehow they manage to forget about it the next time so they can fail to learn from fucking up a new time!

So, the amount of conversions is not proof of competence. It's just proof of the amount of conversions.


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## Jan (Oct 5, 2009)

Pfff, the thread goes on and on. A lot of repeating. A lot of claims. A lot of asking fo proof. But still no data on cell drift, or a theory that makes sence.

I will also repeat myself:

eLithium states cell drift is not caused by charging and discharging. He must know. He wrote a book. He blames it on leaking. OK. The manufacterer states, there is no leaking. And that the only leaking is caused by BMS's. They both can be wright. In that case imbalance is caused by BMS's. They fortunatly correct themselves.

What's wrong with this reasoning?


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## Qer (May 7, 2008)

JRP3 said:


> You don't notice a 3 volt difference in your pack voltage in relation to ah?





mikep_95133 said:


> If a cell is dead in a 300v pack, you won't notice it. In fact you won't notice it if several died at the same time.


Aaaaand here's a graph over how it'll look in real life in a vehicle with a massive Lithium pack and motor currents all over the place between 0 and 900 Amps.










I think I have to agree with Mike here. Detecting a sudden drop of 3 Volt in that mess will be a challenge, to put it mildly. However, if anyone has an idea how a controller could detect when one single cell drops to dangerously low cell voltage without getting external information from a BMS, I'd be delighted tro try to implement the algorithm in the Soliton software!

Anyone?


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## JRP3 (Mar 7, 2008)

mikep_95133 said:


> What happens in a pack of cells when some cells are not at the same soc and or capacity as the others, they get pushed into either a deep discharge because of reduced capacity, or they are overcharged due to reduced capacity. By bringing all cells to top balance, they keep the difference minimized.


This is the problem I have with top balancing, you are guaranteeing that your smallest cells will be more deeply discharged every time, you can't avoid it. We know the deeper the discharge the shorter the cell life, so by top balancing it would seem you are reducing the capacity of your smallest cells even further with each cycle. With bottom balancing your cells are discharged to the same SOC each cycle. Manufacturers show vastly increased cycles from only 10% shallower discharges but don't mention cycle changes at different charge levels, so it seems DOD at the bottom is more important than SOC at the top. If true the BMS will end up flagging the cells that it prematurely ages, leaving you to think it's doing it's job finding bad cells.


> Even Jack noted that brand new cells vary several ah's from each other out of the crate. So divergence starts before installation.


Recent shipments from CALB have show increasingly closer tolerances. 



> What I know about load tests I've performed is that going into just a little overcharge deducted 10% instantly from the cells capacity I was testing. They only went to 4.5v.


If that was at low current then I'd call that severe over charge. TS has reduced the max charge to 4.0 and CALB uses 3.6.


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## JRP3 (Mar 7, 2008)

Qer said:


> Aaaaand here's a graph over how it'll look in real life in a vehicle with a massive Lithium pack and motor currents all over the place between 0 and 900 Amps.


I was talking about off throttle readings, and I have a much lower pack voltage, 120V full. For example if I'm above 3/4 SOC and saw 117V resting I know I have a problem. I agree it would not show up as clearly under load with a higher voltage pack.


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## dimitri (May 16, 2008)

JRP3 said:


> This is the problem I have with top balancing, you are guaranteeing that your smallest cells will be more deeply discharged every time, you can't avoid it.


Isn't bottom balancing guaranteeing that ALL cells will be as deeply discharged as the smallest cell every time? Smallest cell is the limiting factor regardless of how you balance the pack, you choose to discharge ALL cells as deep as the smallest one every time, aren't you? How does that help your argument?


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## DIYguy (Sep 18, 2008)

JRP3 said:


> This is the problem I have with top balancing, you are guaranteeing that your smallest cells will be more deeply discharged every time, you can't avoid it. We know the deeper the discharge the shorter the cell life, so by top balancing it would seem you are reducing the capacity of your smallest cells even further with each cycle. With bottom balancing your cells are discharged to the same SOC each cycle. Manufacturers show vastly increased cycles from only 10% shallower discharges but don't mention cycle changes at different charge levels, so it seems DOD at the bottom is more important than SOC at the top. If true the BMS will end up flagging the cells that it prematurely ages, leaving you to think it's doing it's job finding bad cells.


I've been thinking about this also.... it's a very significant point. Thanks.


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## JRP3 (Mar 7, 2008)

Dimitri brings up a good point. Bottom balancing should help insure that your pack ages at the same rate which should help keep the cells in closer relation to each other. As the smallest cell capacity is reduced to an impractical level you'd have to replace it. Top balancing means the smallest cell will be cycled more deeply each time than the rest of the pack, but when it's replaced the rest of the pack will have been cycled less deeply, so should have a longer potential life. Dimitri is right.


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## Jan (Oct 5, 2009)

JRP3 said:


> Dimitri brings up a good point. Bottom balancing should help insure that your pack ages at the same rate which should help keep the cells in closer relation to each other. As the smallest cell capacity is reduced to an impractical level you'd have to replace it. Top balancing means the smallest cell will be cycled more deeply each time than the rest of the pack, but when it's replaced the rest of the pack will have been cycled less deeply, so should have a longer potential life. Dimitri is right.


If you -like you do- hardly ever charge higher then 80%, there is no accelerated aging. With a BMS that top balances it must charge more than 80%. Aging is accellerated. Especially if the cells are so close together as CALIB seems to deliver.


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## Jozzer (Mar 29, 2009)

Jan said:


> If you -like you do- hardly ever charge higher then 80%, there is no accelerated aging. With a BMS that top balances it must charge more than 80%. Aging is accellerated. Especially if the cells are so close together as CALIB seems to deliver.


 Except that you don't HAVE to balance every cycle, and at least if you choose to charge to only 90% you can be fairly sure that all the cells ARE at 90%. In fact, by setting max charge to 3.58v per cell (for instance) you would get pretty close to 90% AND balanced at the same time...

Steve


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## Jan (Oct 5, 2009)

Jozzer said:


> Except that you don't HAVE to balance every cycle, and at least if you choose to charge to only 90% you can be fairly sure that all the cells ARE at 90%. In fact, by setting max charge to 3.58v per cell (for instance) you would get pretty close to 90% AND balanced at the same time...
> 
> Steve


That's true, but must also be an available option.


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## dimitri (May 16, 2008)

JRP3 said:


> Top balancing means the smallest cell will be cycled more deeply each time than the rest of the pack


This statement can be easily misunderstood by those with no hands on experience, so let me try to rephrase the same thing:

Top balancing means that larger cells will be cycled less deeply each time compared to the smaller cells ( which are always limiting factor anyway ), hence larger cells should age slower, so when the time comes to replace worst performing cells, hopefully it will not be all of them.

I realise this is all theoretical argument and largely depends on how close your cells are to begin with and how deep you discharge on regular basis, but its worth setting this point straight, IMHO.



> If you -like you do- hardly ever charge higher then 80%, there is no accelerated aging. With a BMS that top balances it must charge more than 80%.


I think I proved somewhere in earlier posts that such statement is a red herring, we all charge to 95%-98% regularly, regardless of BMS or balancing scheme, so lets drop the 80% thing, it just muddies the water.


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## Jan (Oct 5, 2009)

dimitri said:


> I think I proved somewhere in earlier posts that such statement is a red herring, we all charge to 95%-98% regularly, regardless of BMS or balancing scheme, so lets drop the 80% thing, it just muddies the water.


Missed the proof. I'll try to find it. I don't want to mudd any clear water. I actually want to get things clear for myself. I know that annoys a lot of ego's. Sorry for that.


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## JRP3 (Mar 7, 2008)

Jan said:


> If you -like you do- hardly ever charge higher then 80%, there is no accelerated aging. With a BMS that top balances it must charge more than 80%. Aging is accellerated. Especially if the cells are so close together as CALIB seems to deliver.


It seems to me that manufacturer information suggests deeper DOD at the bottom is worse than charging to a higher SOC at the top. So by bottom balancing all my cells are taken down to the same DOD, let's say 80% DOD. With top balancing, for the same distance driven, my smallest cell will go to 80% DOD but all the others will be slightly less. Where it gets bad for the top balanced pack is if that one cell is taken far lower than the rest of the pack and killed, but the BMS should prevent that, or staying well away from the bottom without a BMS.


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## Jan (Oct 5, 2009)

JRP3 said:


> It seems to me that manufacturer information suggests deeper DOD at the bottom is worse than charging to a higher SOC at the top. So by bottom balancing all my cells are taken down to the same DOD, let's say 80% DOD. With top balancing, for the same distance driven, my smallest cell will go to 80% DOD but all the others will be slightly less. Where it gets bad for the top balanced pack is if that one cell is taken far lower than the rest of the pack and killed, but the BMS should prevent that, or staying well away from the bottom without a BMS.


Where did you find that deep discharging is worse that high charging?


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## JRP3 (Mar 7, 2008)

Jan said:


> Where did you find that deep discharging is worse that high charging?


All manufacturers show a large difference in cycle life between 90%DOD and 80%DOD, yet none of them mention any difference between 90% and 80% SOC, they just list maximum charge voltages to prevent overcharging.


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## Jan (Oct 5, 2009)

JRP3 said:


> All manufacturers show a large difference in cycle life between 90%DOD and 80%DOD, yet none of them mention any difference between 90% and 80% SOC, they just list maximum charge voltages to prevent overcharging.


 
Ah, I never read this that way. You might be very right. I read this always, like how much of the capacity you use when discharging. How can I explain? Let me try rephrasing that:

The capacity reduces depending on how much you pull out of the battery. If you drain 90%, it ages faster then 80%. Regardless on how much it's charged. So if you charge it to 100% and discharge it to 10% SOC. Thats 90% DOD. And if you charge it to 80% and discharge it to 0% SOC, that's 80% DOD. And this last discharge was less stessing then the first one.

This could be very well very stupid to see it this way.


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## Qer (May 7, 2008)

Damn. I wasn't gonna take a stance here...



JRP3 said:


> I was talking about off throttle readings


Which means that you won't see the problem until after a cell probably is already irreversibly damaged. Cell monitoring will see it when it happens and might save the cell in time to squeeze out several more charges just by telling the controller to dial down the current in time.



JRP3 said:


> and I have a much lower pack voltage, 120V full.


Which means that the same motor current will cause battery current to fluctuate even more which is (partly) compensated by that the internal pack resistance is lower (fewer cells) even though the cable resistance will be the same.

On the other hand, different brands of batteries will sag differently too, so I doubt you can actually draw any conclusions like that lower pack voltage would be better without having all the facts straightened out. Thin wires will, for example, make a higher voltage preferable...



JRP3 said:


> For example if I'm above 3/4 SOC and saw 117V resting I know I have a problem


No, you had a problem a few miles back. Now you have a dead cell. 



JRP3 said:


> I agree it would not show up as clearly under load with a higher voltage pack.


And I don't think you can draw that conclusion just like that.


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## mikep_95133 (May 20, 2009)

Equalizing a pack can happen with bottom or top balancing. But there is a price to pay.

Bottom balancing: 

1) Requires that the cells be pushed down to near zero dod all at the same time. This reduces cycle life per the mfr's datasheets. Cycle life goes down from 3000 to 2000 cycles just going from 70% dod to 80% dod. There will be a dramatic reduction in cycle life going toward the 100% dod that bottom balancing requires.

2) Bottom balancing will be required many times in the packs life to ensure equalization at the bottom. It's not a one time exercise.

3) With bottom balancing, a BMS is still needed to flag the charger that the highest voltage cell is at it's high voltage threshold, thus the charger has to be throttled back. The data sheets clearly show a hard upper voltage limit from every mfr, or cycle life/capacity takes a hit. 


Top balancing: 

1) When all the cells are at their upper voltage threshold, the cells are at their max soc. Yes of course as the pack is deeply discharged, the cells in the pack are not the same capacity. But that is what a BMS is for. 

2) Flagging the cells as they hit their low voltage threshold, and throttling back the motor controller is how the BMS protects the highest soc cells. 

3) In top balancing, neither of the high or low thresholds of the cell are ever breached.

I choose to top balance. I've done bottom balancing for years with flooded nicads. So I know the benefit, but only with cells that are designed for it.

Mike


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## Qer (May 7, 2008)

JRP3 said:


> All manufacturers show a large difference in cycle life between 90%DOD and 80%DOD, yet none of them mention any difference between 90% and 80% SOC, they just list maximum charge voltages to prevent overcharging.


Ok. I'll bite on this too. I'm bored at work anyway. 

Just to simplify things, let's say we have a pack containing one cell that can do 100 Ah and the rest are 200 Ah to simplify the reasoning.

Scenario #1: All cells are top balanced at 100% SoC and then we drive the car until the 100 Ah cell reach 10% SoC. We get 90 Ah from the pack, the weak cell reach 10% SoC but the strong cells only reach 55% SoC. It's bad for the weak cell but the strong cells are all dandy.

Scenario #2: All cells are bottom balanced at 10% SoC and then charged until the weak cell reach 100% SoC (and the strong cells 55% SoC). When we now drive the car until the weak cell reach 10% SoC we still get the same 90 Ah from it but now all cells has hit 10% SoC in perfect harmony.

If your statement in the quote is correct I can only come to the conclusion that bottom balancing is bad and top balancing is to be preferred. With top balancing the weak cell is hurt the most, that's true, but since the weak cell will be equally abused in both scenarios the only thing I can see we "gain" in scenario #2 is that the average pack life time suddenly is limited by the weak cell.

Or do I miss something here?


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## mikep_95133 (May 20, 2009)

Manufacturers data sheets do not show this accelerated aging, charging above 80% soc. It's a myth. Otherwise it would be on the data sheet. All mfr's show 100% soc for recharging their cells to get the rated cycle life.

It would make way more sense to say that if a pack is operated in a narrow soc range, say 30-80%, then you would get extended pack life, longer than the data sheets show. That's how hybrids get such long pack life by design.

Mike



Jan said:


> If you -like you do- hardly ever charge higher then 80%, there is no accelerated aging. With a BMS that top balances it must charge more than 80%. Aging is accellerated. Especially if the cells are so close together as CALIB seems to deliver.


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## Jan (Oct 5, 2009)

mikep_95133 said:


> Manufacturers data sheets do not show this accelerated aging, charging above 80% soc. It's a myth. Otherwise it would be on the data sheet. All mfr's show 100% soc for recharging their cells to get the rated cycle life.
> 
> It would make way more sense to say that if a pack is operated in a narrow soc range, say 30-80%, then you would get extended pack life, longer than the data sheets show. That's how hybrids get such long pack life by design.
> 
> Mike


It seems you believe what you first call 'a myth'. Or I don't understand what you're trying to tell me.


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## Qer (May 7, 2008)

gottdi said:


> The problem with folks with BMS systems is there is no data. Wheres your data?


No, the problem is that NOONE has any hard data, not Mike, not you, not I, noone. There has been experience shared, experience not backed up with hard evidence, but never the less still experience. Wether you take any sides word for the claimed experience is up to you as long as no side can prove they're right, but I would appreciate it if you stopped attacking Mike over and over again with the same demand for hard data since he's not alone not being able to provide any.



What hard data have we seen in this thread that BMS is the way to go? None.
What hard data have we seen in this thread that no BMS is the way to go? None.

Even if you have decided Mike is selling snake oil I'm interested in hearing what he has to share. If you don't believe him, that's fine, but that doesn't give you the right to turn hostile. So for the sake of the discussion, please stop.


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## Jan (Oct 5, 2009)

Qer said:


> So for the sake of the discussion, please stop.


I my opinion Gottdi is mearly reacting on Mike's very -how do you say that- slightly agressive, full of himself, seeing everyone else as stupid, less then him, way of writing. If Mike would stop that, I think gottdi would stop immediatly.


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## Qer (May 7, 2008)

Jan said:


> I my opinion Gottdi is mearly reacting on Mike's very -how do you say that- slightly agressive, full of himself, seeing everyone else as stupid, less then him, way of writing. If Mike would stop that, I think gottdi would stop immediatly.


There is a difference. Mike is attacking arguments, gottdi is attacking Mike.

But instead of arguing over who argues the foulest I'll gladly leave it to the moderators to sort out. I just didn't want to do that to gottdi just like that so I decided to ask politely instead of just reporting him.


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## Tesseract (Sep 27, 2008)

Jan said:


> I my opinion Gottdi is mearly reacting on Mike's very -how do you say that- slightly agressive, full of himself, seeing everyone else as stupid, less then him, way of writing. If Mike would stop that, I think gottdi would stop immediatly.


We have a saying here in the US that very much applies here: "two wrongs don't make a right"*

Sorry, gottdi, but I think you need to put a sock in it. Mike and Qer's explanations make sense, and I was even leaning towards the bottom balancing side for awhile. One needs to keep an open mind, ESPECIALLY when you are still a "student", as you claim you are. I'm not seeing a whole lot of open-mindedness out of you.


* - but two lefts do! 

(er... three lefts... )


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## ElectriCar (Jun 15, 2008)

Qer said:


> ...I'm bored at work anyway.


What? You have an AC controller to develop. No possibility of being bored with that task! 

BTW, FYI I spoke with Metric Mind about an AC system. Quoted me a 30Kw motor with controller for $10,000 USD. You guys should be able to compete with that. They are a small company too but did move recently into a larger building to produce more. Hopefully you all will get AC systems in place sooner rather than later.


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## mikep_95133 (May 20, 2009)

When someone complains their pack is sagging a bit, or just doesn't feel right, I offer to load test their worst cells for them to get the capacity info that they don't have. These are usually the BMS-less crowd. At least with this testing some data is generated.

I have a rack mount cabinet full of constant current/constant voltage power supplies, and an industrial load tester. This is how I measure capacity, as I hate the guessing game. 

The load tester can be in either, constant current or constant voltage, or constant resistance modes. That way any real life scenario can be replicated on the bench.

Both my trucks have data logging built into the hardware from the factory. The system hardware dumps a text based file onto the hard drive of a laptop. It records an assortment of obvious things like volts and amps. It also records system temp, igbt power efficiency, rpm, time etc. Importing this data into Excel yields great driving info.

When I talk about data, I talk about things actually measured, not guessed at. I'm too much of a cheap bastard to guess at anything. If I know facts, I can make better decisions. The above list is how I sorted fact from fiction.

One of the few freebies with electric vehicles is that with a minimum of an E-meter installed, an owner can measure the vehicles efficiency. Then make possible improvements to it. Then go out and actually measure the improvements. That's real data generation. At least when someone has the equivalent of an E-meter, they can test their pack to some degree. Using a voltmeter and ammeter to 'calculate' efficiency is not generating real data. The very quick and constant variation in voltage and current is why an E-meter or equivalent is required.

I've found that the chase for better efficiency to be very rewarding. Hypermiling an EV in other words. My #1 truck has a best of 178 wh/mi at 4000 lbs. Usually it gets 225-250 wh/mi. Summer is always better for this than winter. Synthetic fluids and a zero toe alignment are great improvements on efficiency, that I've measured with my vehicle.

Having a BMS is just one of the tools available to an EV owner. Chasing efficiency is another. 

Mike




gottdi said:


> I said it because I know that no one can prove it. One can only make an educated guess. The argument is also kind of moot because of the range of lithium chemistries being used. Take one and stick with it. For the case of the folks here most are using large prismatic cells. Now we can focus on a specific type of battery.
> 
> I actually don't want to argue with anyone. What I want to do is learn but you don't learn from just reading what someone types on a page. You must show your DATA or what we call PROOF. It must also be completely reproducible by anyone wanting to get hands on and try it for themselves. So instead of wheres the proof I guess it should say wheres the DATA. I want to become the expert. Not only do I want to become the expert I want to teach it too. Too many hear say this or that and have some excellent hypothesis but no data to go with. No experimenting has taken place to prove or disprove. This is what I am looking for. I don't have a LAB here at my place and if you don't then your not the one to answer the questions. Who ever is doing the work needs to answer. Not the STUDENT in the wings. I can ask questions all day long. I can question the TEACHER all day long. I will until I get the answers needed.
> 
> ...


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## Jan (Oct 5, 2009)

Qer said:


> There is a difference. Mike is attacking arguments, gottdi is attacking Mike.


I've a real hard time to tell the differences in this thread. But I would like to see the thread stay alive. very much.


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## Jan (Oct 5, 2009)

dimitri said:


> I think I proved somewhere in earlier posts that such statement is a red herring, we all charge to 95%-98% regularly, regardless of BMS or balancing scheme, so lets drop the 80% thing, it just muddies the water.


I've found some arguments that imply most charge to 95-98%. But see no proof. The BRUSA or Simons 200$ charger can both charge on AH count. So, I don't see the proof. Only if you charge on voltage, you're right. But it's not a must.


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## dimitri (May 16, 2008)

Jan said:


> I've a real hard time to tell the differences in this thread. But I would like to see the thread stay alive. very much.


With JRP3 being the sole exception on this forum, THE ONLY thing anti-BMS crowd has in their defense is "Jack said so on TV, so it must be true". Other than JRP3, not a single anti-BMS person actively participating in this thread has any meaningful first hand real life experience in subjects they preach. Most have demonstrated utter lack of understanding most basic principles in battery pack design and operation, I am not even talking about BMS operation, just plain "take bunch of cells off the shelf and make them move the car" type of ignorance. Not to offend their intelligence, its just hard to wrap your brain around something you never actually tried yourself. I'm sure every one once tried will come back and say "ahh, that's what you meant back there...I see it now".

Hence, JRP3 is the only one you can exchange meaningful information on this thread subject, everyone else just adds noise. I'm sorry for being blunt, but that is true.

We keep sliding into personal offenses because no one has any new data to offer, all existing data has been posted already, it doesn't seem to help.

I suggest to stop bickering and let 3-4 major supporters of no-BMS approach build their packs and drive for a month or so, then come back with their own data, so we can all compare notes.


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## mikep_95133 (May 20, 2009)

gottdi said:


> You make a mighty big assumption about folks not knowing about the pack with no BMS. You really think they are stupid enough to drive totally blind?


 Please enlighten me. What instrumentation is in your vehicle?



> Who in their right mind would take a smoked cell and put it into a pack? Stupid to even bring that up.


 The smoked cell scenario happens in real life every day. It's cheaper to borrow someone's smoked cell to do the test, than to smoke your own. I was encouraging you to generate you own data with this simple test.



> Actually it is not hard to do a capacity test at all and a good charge with known AH in and a good drive with known AH out and a check of all cells before and after can tell you straight up.


 So you have an ah meter?



> The problem with folks with BMS systems is there is no data. Wheres your data?


 What data would you like? The divergence I speak of is easily witnessed in vehicles with cell monitoring. You can see it for yourself as the passenger in some ones monitor equipped EV. Most people love giving rides.



> Where is your EV? Still never answered that question.


 I just did in a recent post. Sorry for the delay.



> Who made you king of this subject?


 Apparently you just crowned me king? 



> Yes I am calling YOU out.


 Fair enough. Sorry for the offense. 



> I am a student in this field and if your not an educated teacher and have no DATA to back up your information your parroting then your not a teacher and should be ignored.


 True dat.



> I want to learn and teach from those who DO have data to back up what they say. That way if I need to go reinvent the wheel I can go repeat it with accuracy.


 Good point. 




> I will say again to you who keeps ignoring:
> 
> What NEW and WONDERFUL THINGS have you brought to the table in the EV world that will educate and better the advancement of the EV.


 I doubled the efficiency of my truck and passed that data on. I showed how synthetic fluids and a zero toe alignment give a 10% increase in efficiency immediately. I've show people why their packs are dead or dying by load testing their cells for them. I've brought many, many vehicles back into service by rebuilding their 3 phase hardware. I've designed several analog BMS's so I could better understand how they function, their shortcomings, and how to make them reliable. I volunteer my ass off in the EV community to help others understand how to generate their own meaningful data instead of perpetuating lore.

Mike


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## dimitri (May 16, 2008)

Jan said:


> I've found some arguments that imply most charge to 95-98%. But see no proof. The BRUSA or Simons 200$ charger can both charge on AH count. So, I don't see the proof. Only if you charge on voltage, you're right. But it's not a must.


Good, you are making progress. Please go back and read further on issues with AH count as related to real SOC over long time periods. Its all there in same threads.


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## Jan (Oct 5, 2009)

dimitri said:


> Good, you are making progress. Please go back and read further on issues with AH count as related to real SOC over long time periods. Its all there in same threads.


I reckon, you're not in the mood to summerize it again?


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## dimitri (May 16, 2008)

mikep_95133 said:


> I doubled the efficiency of my truck and passed that data on. I showed how synthetic fluids and a zero toe alignment give a 10% increase in efficiency immediately. I've show people why their packs are dead or dying by load testing their cells for them. I've brought many, many vehicles back into service by rebuilding their 3 phase hardware. I've designed several analog BMS's so I could better understand how they function, their shortcomings, and how to make them reliable. I volunteer my ass off in the EV community to help others understand how to generate their own meaningful data instead of perpetuating lore.
> 
> Mike


Mike, none of this matters to people here unless its on TV screen. Only if you organize a TV show to show your experience you might be taken seriously. Trying to communicate in writing is futile. With advancement of TV as primary information medium many people lost ability to comprehend text, I suppose its natural evolution. Sad, but natural.


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## Jan (Oct 5, 2009)

dimitri said:


> Mike, none of this matters to people here unless its on TV screen.


Nice going, Dimitri.


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## mikep_95133 (May 20, 2009)

Good point Dimitri. 

One thing that posting in a forum does, is when someone is gathering knowledge over the years, they can always use the search function to look up things that occur to them. Can't search a video. Video is a lot of fun though. If a forum is even slightly organized, this will happen. I really like the giant faq that the guys at Honda-Tech have. They literally showed me how to repair my fuel injection and everything attached to it through their faq. It's an exceptional faq. The best I've ever seen. I may have missed it but I don't see a faq on the main page here. It's tons of work. I've done it in another forum. But the great thing is, when you have been around long enough and start to forget things, you also can go back and do a search to remind yourself. Works great for me.

In another forum years ago I made a spreadsheet of all 5000 posts. I catagorized them under all kinds of topics like water pump failure, charger failure, start up failure, etc. Each item in each cell of the spreadsheet was linked to all of the posts that it pertained to. Made quick work of answering nube questions and was a repository for my brain fade. Some time later, the dirtbag that owned the forum literally just deleted the entire forum. All of that data lost forever. I even offered him cash for it to no avail. 

Mike




dimitri said:


> Mike, none of this matters to people here unless its on TV screen. Only if you organize a TV show to show your experience you might be taken seriously. Trying to communicate in writing is futile. With advancement of TV as primary information medium many people lost ability to comprehend text, I suppose its natural evolution. Sad, but natural.


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## rwaudio (May 22, 2008)

Here it's a Wiki,

click on it at the top, there is a lot of info there.


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## dimitri (May 16, 2008)

Jan said:


> Nice going, Dimitri.


Thanks, I tell it as I see it. 

Word "proof" has been mentioned a few times here  , but what does it mean in this context? Someone said "show it on TV", I did not make it up.

You mentioned ego earlier, let me respond to that. I consider myself an honest person and value my reputation more than money. Many forum members know me personally in real life, some have been in my EV and my house. I know this means diddly squat to a guy 3000 miles away, I don't blame him, although anyone who finds himself in Tampa area is welcome to my house and drive my EV. I like capitalism ( I actually experienced alternative on my own skin, so I say this with confidence ), so I am not ashamed to be fairly compensated for my hard work. I love helping people as long as they have open mind like I do. I spend hours talking to many people on the phone sharing my experience. Since I know I am honest I expect them to believe me on my word. This does not make me right, I might be totally wrong in everything I preach, but I am not a liar or out to rob anyone. Since I keep an open mind, if/when I see I was wrong I will openly admit it and change my position. So far this has not happened on the subject of BMS.

So, when I am attacked for not having "proof" or "trying to take your money", naturally I am pissed and offended. Can you blame me?


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## Jan (Oct 5, 2009)

dimitri said:


> Can you blame me?


Yes I can. I would like that you tell it to the person who calls you a liar. And ask him to stop. And not against the 'anti-BMS growd'. Although I don't consider myself that way, I can see the way you react on me, that I'm considered by you as one of 'them'. Just becaus I ask questions and try to understand. If *that* pisses you of, then there is something wrong. Somewhere. With someone.


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## mikep_95133 (May 20, 2009)

Oh thanks. I see the part on regen is stated as only being worth 10%. That's the standard wisdom, but far from the truth. Oh well.

Mike

Update: I corrected the wiki where it mentions regen is 10%. Data is clear at 20-40%. Victor @ metric mind even stated that he got 60% on his vehicle using ultra caps. Love to see that data.




rwaudio said:


> Here it's a Wiki,
> 
> click on it at the top, there is a lot of info there.


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## dimitri (May 16, 2008)

Jan said:


> Yes I can. I would like that you tell it to the person who calls you a liar. And ask him to stop. And not against the 'anti-BMS growd'. Although I don't consider myself that way, I can see the way you react on me, that I'm considered by you as one of 'them'. Just becaus I ask questions and try to understand. If *that* pisses you of, then there is something wrong. Somewhere. With someone.


Jan,

I sincerely apologize to you personally. The tone of this thread does tend to set the mood low, so some people might get offended where offense wasn't meant, that was the case with you personally. Yes, I put you in no-BMS crowd, my mistake.

Nothing wrong with asking questions, but try to put yourself in my shoes for a moment, none of your questions are new, every one has been answered within past few months. I know you expect me to repeat it, but I am busy and lazy, please forgive me for not repeating same thing over and over. If you ask very specific questions, with your current understanding of the issue, with some examples, I usually jump to respond, although often others beat me to it. This is what happened when you asked about cell reversal. But you need to show that you at least put some effort in finding an answer on your own and ask for clarification, rather than just take 2 seconds to ask something and expect someone to reasearch it for you. Its just plain etiquette, IMHO.


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## EVfun (Mar 14, 2010)

gottdi said:


> I am a student in this field [...]


and yet you keep teaching that a BMS (either monitoring or managing) is not required. I challenged that assumption because *we do not know* how these batteries will begin failing at their natural end of life. EV duty is pretty tough duty on a long series string of cells. Even Jack doesn't have cells with 2000+ EV cycles on them. I don't know how these cells will fail at the end of life (or how long that will be.) Can you admit you don't know how these cells will fail at the end of life?


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## tomofreno (Mar 3, 2009)

Whew! Wish my pack had the energy density of this thread the last couple days!



> Scenario #2: All cells are bottom balanced at 10% SoC and then charged until the weak cell reach 100% SoC (and the strong cells 55% SoC). When we now drive the car until the weak cell reach 10% SoC we still get the same 90 Ah from it but now all cells has hit 10% SoC in perfect harmony.


 So why not drive the car until the cells are at 30% SOC?



> I've found that the chase for better efficiency to be very rewarding. Hypermiling an EV in other words. My #1 truck has a best of 178 wh/mi at 4000 lbs. Usually it gets 225-250 wh/mi.


 This is not very informative without average vehicle speed and driving conditions such as hilly versus level terrain and traffic versus open road cruising/coasting.



> Manufacturers show vastly increased cycles from only 10% shallower discharges but don't mention cycle changes at different charge levels, so it seems DOD at the bottom is more important than SOC at the top.


 I of course am not certain, but I think this is because they just assume top balancing, i.e. assume all cells are always charged to their spec'ed max charge, so discharge SOC is the only variable. Myself, I would like to know the physical mechanism that causes the exponential rise in voltage with Ah charge near the top (above about 3.45V for CALB cells). Seems it might be some mechanism that induces stress in the anode material, degrading cycle life somewhat. But the manufacturers all seem to spec charging up this exponential part of the curve somewhat (3.6V for CALB), so dunno. That's something that concerns me with top balancing, so in my ignorance of whether it is damaging or not, I would rather be conservative and not charge that high, but you can't top balance well if you don't go to that part of the curve to get significant voltage differences between cells. Just keeps nagging me.

No one I've heard of bottom balances at "zero" as someone said, and you don't balance every charge. You discharge to 20-25% SOC once every several months, so it is not the suggested hit on cell cycle life.

I expect cells to drift apart in capacity as they age due to varying changes in physical structure of the anode and cathode materials. I expect the lattices are under some strain with lithium ions moving in/out each cycle, more so under high discharge currents due to higher E-fields through the materials, so should degrade somewhat with time (broken bonds, trapped charge...), and there is no reason to think they will all degrade the same. I also expect some breakdown of the electrolyte solvent, and attendant loss in capacity due to anode coating over time due to higher temperature operation. The CM video initially said 50-60 C, then 60 C. You can get close to 50 C fairly easily with the prolonged higher currents of highway driving and summer temperatures of 40 C or so and no active temperature control of cells, especially if they are inside a closed up car in the sun or under a hot hood. So I expect to have to balance at top or bottom and count charge to avoid overcharging or over-discharging a cell. Top balancing is definitely much easier as the bms does it for you, and because of that alone, I think more appropriate for many people. 

As far as longer term data, Dave Kois posted a month or so ago on the Yahoo thundersky site that he has several customers driving his Rav4 conversions with over 5 years on the packs, and they report the packs are behaving the same as when new. I believe he used the evpower bms on his earlier conversions, but you would have to check with him to confirm.


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## Jozzer (Mar 29, 2009)

dimitri said:


> With JRP3 being the sole exception on this forum, THE ONLY thing anti-BMS crowd has in their defense is "Jack said so on TV, so it must be true". Other than JRP3, not a single anti-BMS person actively participating in this thread has any meaningful first hand real life experience in subjects they preach.


 More to the point Dimitri, I suspect that many ProBMS folk in this thread DO have a lot of experience with running packs with AND without protection, and that's just why they are bothering to help others understand why the DO need a BMS. 
Steve


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## mikep_95133 (May 20, 2009)

Oh. Can you tell me your vehicle's efficiency and how you would state it?

Mike



tomofreno said:


> I've found that the chase for better efficiency to be very rewarding. Hypermiling an EV in other words. My #1 truck has a best of 178 wh/mi at 4000 lbs. Usually it gets 225-250 wh/mi. This is not very informative without average vehicle speed and driving conditions such as hilly versus level terrain and traffic versus open road cruising/coasting.
> 
> 
> This is not very informative without average vehicle speed and driving conditions such as hilly versus level terrain and traffic versus open road cruising/coasting.


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## Qer (May 7, 2008)

tomofreno said:


> So why not drive the car until the cells are at 30% SOC?


Doesn't change anything, really (except of course that your range just dropped ~20%). All I've read about different kinds of chemistry has told me that the deeper you discharge the batteries, the fewer cycles do you get (and the opposite). If you bottom balance and discharge to 30% SoC it means that all cells reach 30% SoC, but if you top balance the 200 Ah batteries in my example will only reach 65% SoC when the 100 Ah reach 30% SoC and thus live longer than if they too are discharged to 30% SoC.

That means that if JRP3 is right that it's worse for the batteries to get deeply discharged than fully charged it's always better to top balance to lessen the wear and since the cell voltage rush upwards when the battery gets close to fully charged I, personally, wouldn't dare installing an expensive pack without at least LVC/HVC-monitoring.

If it's your pack, feel free to choose the roulette instead if you dare.


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## DavidDymaxion (Dec 1, 2008)

Gottdi, I bow in your general direction, thanks for doing a test.

The most definitive test would be starting with one completely depleted and one full, but I figured that would make it easier to damage a cell and would take many very shallow cycles to get results. Starting with both full is what everyone does on their cars anyway. So I figured 1/2 full is a good starting point. I realize you'd never want to do that on purpose for a car, but it seems like a great starting point for an experiment designed to prove or disprove whether a self balancing effect exists.

It'll take some time, but I'm hoping not too bad. I can charge at 4 C and discharge at about 8 C. Since one battery is 1/2 full you can only discharge 1/2 way, then charge 1/2 way, etc. unless a self balancing effect appears. That would take about 12 minutes per charge/discharge cycle. Hopefully I could see some effect by 10 cycles. If it takes 100 cycles to see any effect it's probably too weak an effect to be useful.


gottdi said:


> I don't think draining by 1/2 is the way to do this. If you start with a well balanced pack in the first place there would never be that large of a difference. But small differences should work just fine. I am game to go along with you on this one. I will have 4 spares to work with. 100 AH batteries. That way I can at lest run a motor to drain my batteries then charge up and discharge again and again and again. When the first gets to the knee I will stop charge. Run the motor and check the cells again and write the numbers down. 12 volts should be plenty to run a 9"motor with no load and amp meter to log the amps. When the pack slows I will stop and charge up again. Easy as punch. It will take some time and must be done during my working on my EV and work. I will start with all the batteries at different levels of charge. I can do that and I can video monitor some of it too. Good enough? Hope so.
> 
> Pete
> 
> Will it prove anything? Maybe. Will it take some time? Yup.


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## JRP3 (Mar 7, 2008)

Qer said:


> Doesn't change anything, really (except of course that your range just dropped ~20%). All I've read about different kinds of chemistry has told me that the deeper you discharge the batteries, the fewer cycles do you get (and the opposite). If you bottom balance and discharge to 30% SoC it means that all cells reach 30% SoC, but if you top balance the 200 Ah batteries in my example will only reach 65% SoC when the 100 Ah reach 30% SoC and thus live longer than if they too are discharged to 30% SoC.
> 
> That means that if JRP3 is right that it's worse for the batteries to get deeply discharged than fully charged it's always better to top balance to lessen the wear and since the cell voltage rush upwards when the battery gets close to fully charged...


Sheesh this thread got away from me, cant keep up  I think Qer and Dimitri, and now me, are correct. Bottom balancing will discharge the entire pack to a deeper level than top balancing, which will only discharge a single cell to that level with all others being slightly less. If you keep your discharge shallow enough it probably won't affect the real world life of the pack in any noticeable way, but the theory makes sense. The main benefit of bottom balancing is protection from over discharge of a single cell.
Regarding top balancing I think you can still limit your maximum charge percentage if you top balance, it should actually be easier since you have all cells coming together at the same voltage which will show a greater change in pack voltage, you can stop charging below 3.45 during the CC stage and don't bother with CV since you don't want to put as much energy in as possible. Stop charging around 3.43 or so (talking CALB cells) without a CV period and you should be around 90% SOC, ish. Current and temperature will change this some.


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## DIYguy (Sep 18, 2008)

I have no problem to run a BMS... if I determine I have to. I still haven't got to that point though. Monitoring I do now, while driving, and I will continue to do. 



mikep_95133 said:


> Equalizing a pack can happen with bottom or top balancing. But there is a price to pay.
> 
> Bottom balancing:
> 
> 1) Requires that the cells be pushed down to near zero dod all at the same time. This reduces cycle life per the mfr's datasheets. Cycle life goes down from 3000 to 2000 cycles just going from 70% dod to 80% dod. There will be a dramatic reduction in cycle life going toward the 100% dod that bottom balancing requires.


you don't need to go to near zero to balance near the bottom... c'mon now. This claim is just a bit extreme. You are comparing the constant 100% DOD with bottom balancing. Just not the case.... you should know that. I don't think anyone has even repeated the bottom balance once yet... unless they were adding in cells. Did I miss someone doing this a lot???



mikep_95133 said:


> 2) Bottom balancing will be required many times in the packs life to ensure equalization at the bottom. It's not a one time exercise.


So far this simply has not been demonstrated. Of all these folks that you help that kill cells everyday... are they running lithium?... and if so, who the heck inspired them to run without a BMS??? Was there another effort in this direction somewhere, sometime?? I'm interested, seriously.

I've read the experience of three users with no BMS and using LifePo and they all have the same results....so far anyways. Maybe the wheels will fall off....


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## Tesseract (Sep 27, 2008)

JRP3 said:


> ...you can stop charging below 3.45 during the CC stage and don't bother with CV since you don't want to put as much energy in as possible.



True, but this requires an Ah counter to keep track of how much energy was used then returned to the pack, and not letting the voltage of all cells go above the knee makes it difficult to "automatically" reset the integrator in the Ah counter to 0 (or, in this case, 100% SOC). Just speaking from an engineering standpoint, here.


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## JRP3 (Mar 7, 2008)

If you aren't charging to 100% SOC why would you want your AH counter to hit 100% SOC?


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## JRP3 (Mar 7, 2008)

DIYguy said:


> you don't need to go to near zero to balance near the bottom... c'mon now. This claim is just a bit extreme. You are comparing the constant 100% DOD with bottom balancing. Just not the case.... you should know that. I don't think anyone has even repeated the bottom balance once yet... unless they were adding in cells. Did I miss someone doing this a lot???


I've done it twice in about 5K miles, once for the initial balancing and second time just to check and correct any imbalance incurred by using a Cell Log8 on a few cells. A third wasn't a bottom balance just a deep DOD when driving.


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## DIYguy (Sep 18, 2008)

JRP3 said:


> I've done it twice in about 5K miles, once for the initial balancing and second time just to check and correct any imbalance incurred by using a Cell Log8 on a few cells. A third wasn't a bottom balance just a deep DOD when driving.


Thanks, and did you see anything of significance on any cells other than what was caused by the Cell Log8 parasitic load?


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## tomofreno (Mar 3, 2009)

> Oh. Can you tell me your vehicle's efficiency and how you would state it?


 Not sure what you mean by vehicle efficiency. I just state Wh/mile like you did, but for some mix of driving like 30% highway at about 55- 60 mph, 70% secondary roads 35-45 mph, some smaller hills. Not very precise either, but gives a little better idea of the conditions. Would be better to state approximate changes in elevation and grades. I've also datalogged pack current, voltage, and Ah used, along with vehicle speed and distance using a gps datalogger. I usually average around 200 Wh/mile at about 50% highway, 55-60 mph, and 50% secondary roads, 35 to 45 mph, on mostly level terrain, a few hills of 300 ft elevation change or so. Car is 2250 lb Suzuki Swift.


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## tomofreno (Mar 3, 2009)

> I've found some arguments that imply most charge to 95-98%. But see no proof.


 I think this comes from the observation by several of us that if you charge to the upper "knee" of the V versus Ah curve, there is very little cell capacity left above that. For example, if I charge my 180 Ah CALB cells to 3.45V, just at the beginning of where V starts to rise exponentially with Ah charge, it only takes about 10 minutes, 1/6 hr, more for it to hit the spec'ed max of 3.6V at 20A charge current, so that is about 20/6 = 3.3Ah, or 100*3.3/180 = 1.8%, or 98.2% SOC. So if you bottom balance and charge your lowest capacity cell to the "knee", you are charging to around 97-98% SOC.


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## Tesseract (Sep 27, 2008)

JRP3 said:


> If you aren't charging to 100% SOC why would you want your AH counter to hit 100% SOC?


I didn't argue otherwise, rather, I asked how your Ah counter can reset accumulated error from, e.g., the shunt being off by 0.1A out of 100A (0.1% error would be really good, if that isn't totally obvious).

See, if you take your pack all the way up to the high knee then the Ah counter can reset because it then knows the pack is at 100% SOC.

You can reset the Ah counter (to 0%) at the other end of the SOC curve, but that seems to be a bit more risky for the cells...


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## ElectriCar (Jun 15, 2008)

tomofreno said:


> I think this comes from the observation by several of us that if you charge to the upper "knee" of the V versus Ah curve, there is very little cell capacity left above that. For example, if I charge my 180 Ah CALB cells to 3.45V, just at the beginning of where V starts to rise exponentially with Ah charge, it only takes about 10 minutes, 1/6 hr, more for it to hit the spec'ed max of 3.6V at 20A charge current, so that is about 20/6 = 3.3Ah, or 100*3.3/180 = 1.8%, or 98.2% SOC. So if you bottom balance and charge your lowest capacity cell to the "knee", you are charging to around 97-98% SOC.


Good info Tom. I didn't check the math though but if your math is right, that's good enough. I was thinking of stopping at possibly 85-90% if that would safely keep me out of the knee.


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## dimitri (May 16, 2008)

Tesseract said:


> I didn't argue otherwise, rather, I asked how your Ah counter can reset accumulated error from, e.g., the shunt being off by 0.1A out of 100A (0.1% error would be really good, if that isn't totally obvious).
> 
> See, if you take your pack all the way up to the high knee then the Ah counter can reset because it then knows the pack is at 100% SOC.
> 
> You can reset the Ah counter (to 0%) at the other end of the SOC curve, but that seems to be a bit more risky for the cells...


To make this argument easier, don't say "100% SOC" , say "full mark", whatever that mark may be for any given pack/person. We discussed this in another thread last week. There is no doubt that AH counter drifts and drifts fast enough not to be trusted unless frequently calibrated to the "knee". Happens to any AH counter, no matter its precision. I had to go thru some compromises to address this in EV Display. However, to JRP3 point, the "knee" is not a point, but rather a set of points across short time period, you can choose earlier point as a mark if you wish, but the spread is not that large to cause much discussion. Even at the earliest detectable knee point you are still over 90% SOC or more.


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## tomofreno (Mar 3, 2009)

> If you keep your discharge shallow enough it probably won't affect the real world life of the pack in any noticeable way


 That was my point with the 30% SOC of the lowest capacity cell. I'm not so much interested in the finer points of a theory as I am in the impact to cell life cycles.




> Regarding top balancing I think you can still limit your maximum charge percentage if you top balance, it should actually be easier since you have all cells coming together at the same voltage which will show a greater change in pack voltage, you can stop charging below 3.45 during the CC stage and don't bother with CV since you don't want to put as much energy in as possible. Stop charging around 3.43 or so (talking CALB cells) without a CV period and you should be around 90% SOC, ish. Current and temperature will change this some.


 Not if the bms doesn't permit you to select the voltage for shunting and is set for a higher voltage. Minibms starts shunting at 3.5V, shuts off charger at 3.6V. Could change out the resistors on all the boards. 

The above scheme wouldn't work very well with a Manzanita charger because it needs to see a 3 to 4V increase in pack voltage for it to cut back charge current to a low value, so the shunts would come on while still charging at near full current, resulting in little balancing before a cell hit hvc. And because you are attempting to end charge on the flat part of the V versus Ah curve you will get quite a bit of variation in charging with variation in cell temperature and charge current level. If you choose to top balance and terminate charging at the knee or a bit above, say at 3.47V on CALB cells, then the change in voltage with SOC around that point is large (0.2V/cell * 36 cells = 7.2V for example), so it is much less sensitive to variations in pack voltage with charge current and cell temperature. I think bottom balancing and targeting 3.45V or lower on the lowest capacity cell, along with the 3-4V rise required for the Manzanita to throttle current back significantly, sets us up for large variation of SOC on that low capacity cell with charge current and cell temperature (I think the effect of different cell temps and charge current is to shift the V versus Ah curve up or down the V axis by +/- a couple volt or so). It wouldn't be near as variable if cells were top balanced and a target for end of charge at 3.46 to 3.48V were used (by setting the charger limit voltage). In that case, the charger would throttle back to low current, or shut off completely (at low cell temps or high charge current) before the shunts come on at 3.5V because all the cells are going through significant voltage rise at that point.


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## david85 (Nov 12, 2007)

BMS seems to be one of those issues that really gets people fired up sometimes. Just try to remember we are all pioneers here and it might not be wise to make absolute statements about what is and is not the best method. Calling some one out might also not be the best way to carry on such a conversation.

Looks like you guys got things back under control but please try to keep things civil, ok?


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## dimitri (May 16, 2008)

JRP3 said:


> Stop charging around 3.43 or so (talking CALB cells) without a CV period and you should be around 90% SOC, ish. Current and temperature will change this some.


This is where Jack would start calling you bad names 

You want to choose lower detectable point in the knee to stop charging to give yourself more safety range at the top, this makes sense. However, the lower knee point will have larger dependency on temp and current variations, than later knee point, so you might be potentially leaving a lot more on the table than you expect. Not saying this won't work, of course it will given the knowledge and tools available with enough precision to impement this approach and keep it stable as cells age and environment changes with seasons. However, its not practical for general population. You trying to balance multiple variables with small safety margin, no way I can sleep at night using this method.


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## dimitri (May 16, 2008)

ElectriCar said:


> Good info Tom. I didn't check the math though but if your math is right, that's good enough. I was thinking of stopping at possibly 85-90% if that would safely keep me out of the knee.


This makes the full circle again in just one week. The whole point of explaining this end of charge process is that YOU CAN'T stop at 85-90% because YOU HAVE NO WAY OF TELLING where that is. You must reach the knee regularly, you have no choice, so you charge to 95%-98% all the time, whether you want to or not. Its not a decision you can make, or argue, or believe, its a fact. Its been proven again and again.


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## tomofreno (Mar 3, 2009)

> I didn't argue otherwise, rather, I asked how your Ah counter can reset accumulated error from, e.g., the shunt being off by 0.1A out of 100A (0.1% error would be really good, if that isn't totally obvious).
> 
> See, if you take your pack all the way up to the high knee then the Ah counter can reset because it then knows the pack is at 100% SOC.
> 
> You can reset the Ah counter (to 0%) at the other end of the SOC curve, but that seems to be a bit more risky for the cells...


I've been using an charge counter, TBS ExpertPro, for a bit over a year now and haven't noticed much problem with this. I did notice at first that it would say the pack was full (defined as lowest capacity cell at 3.45V by me) when it wasn't, until I realized I had not wired the DC/DC through the shunt. After that it has shown very little drift which is easily addressed by charging that lowest capacity cell to 3.45V every couple months or so and manually resetting the gauge to full (push two buttons simultaneously). I find that it remains quite close to the correct reading with very roughly this frequency of manual reset. So in practice it isn't a big deal if you are willing to reset once in a while. If you are top balancing with a bms you could reset to "full" manually each charge if you desired. Then you only need to worry if cell capacity decreases over longer periods time such that the lowest capacity cell is lower capacity it used to be. If you tracked this change you could enter it into the gauge as the actual capacity. If not, then LVC will eventually alert you it has changed.


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## dimitri (May 16, 2008)

tomofreno said:


> After that it has shown very little drift which is easily addressed by charging that lowest capacity cell to 3.45V every couple months or so and manually resetting the gauge to full (push two buttons simultaneously).


Can you elaborate on this? Can you tell every time that gauge is full because it counted itself to full or self reset to full based on voltage while you weren't looking? Could it be that you see little drift because most your charges are full charges? Would it drift more if you often had partial charges and rarely a full charge? I'm just curious how TBS manages the drift.

How can you set the gauge to individual cell voltage? Or is it based on pack voltage?


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## GerhardRP (Nov 17, 2009)

Hi All,
I went back and watched the Jay Whitacre video again http://www.ri.cmu.edu/video_view.html?video_id=60&menu_id=387 
I was listening for what he said about cell damage mechanisms. It seems that the main loss of capacity is related to two causes... electrolysis of the electrolyte at voltages greater tham 4.3V, solvent breakdown at temperatures greater than 60C and depletion of lithium in in the electrolyte by plating out at high overcharge. He says overdischarge is relatively benign down to 1V static. Reversai of the polarity is destructive.


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## DIYguy (Sep 18, 2008)

The other fellow I remember running bms free is Dexion. This is a cut from his blog...from Oct 2009. I don't know if he ever bottom balanced or not.

I have an Rmartin electric scooter which is powered by 21 Thundersky 60 AH Lifepo4 batteries. 
This was my first experience with the WONDERFUL qualities of a lifepo4 battery. I listened to people tell me I need a bms to keep the betteries in check or bad things will happen. Well, I just can't see this. From experience, I have a year and 3000 miles under the belt of the scooter and the batteries are still in ballance. How do I know this, well I check them (often, constantly) trying to find some inbalance or issue with them. I havent found anything yet. I charge them to about 3.7V and I discharge them to 3V.

Other stuff.... I put full synthetics in my trans and differential...but I wasn't able measure any significant improvement. There may have been something...but it was negligible. I tried to find it. I also did an alignment, but did not set toe to zero... I thought about it...but was not too keen on the idea. Depending on factory Camber angle, zeroing toe could actually _increase_ rolling resistance. It also aids steering stability at higher speeds. The most significant impact I found was with tire type (Specifically width) and of course pressure. 178 wh/mi for a 4000 lb truck is ...well, I don't know what to say. . . I just can't see it. I have one also, and have done a lot of stuff. This number is ... I dunno. . pretty much ridiculous.


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## JRP3 (Mar 7, 2008)

DIYguy said:


> Thanks, and did you see anything of significance on any cells other than what was caused by the Cell Log8 parasitic load?


No but results were somewhat muddied because I used a more accurate DVM to 3 decimal places and balanced to a slightly lower voltage for a more accurate baseline. The next check will be telling.


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## DIYguy (Sep 18, 2008)

JRP3 said:


> No but results were somewhat muddied because I used a more accurate DVM to 3 decimal places and balanced to a slightly lower voltage for a more accurate baseline. The next check will be telling.


Oh that's right, I remember that now. Thank you for reminding me.


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## DIYguy (Sep 18, 2008)

I sent the following email to Jay Whitacre. This is the fellow in the video. Jay Whitacre, a Carnegie Mellon professor with a joint appointment in Materials Science and Engineering and Public Policy, gives a quick overview of Lithium-ion batteries. Starting at the chemical level, he explains the properties and mechanics of the battery which give rise to macroscopic behavior, especially focusing on issues relevant to electric vehicles and other high-power systems.

Here was my email.... 

Hello Jay.
> 
> I watched with interest your video on Lithium batteries. It was very informative. It is also very much needed information in the DIY community. (this would be for a series string of batteries in an motive application) There are intense, sometimes heated, discussions regarding many aspects of the current Prismatics in particular. One significant topic is the need for a BMS (management, not monitor). Some say it is a must. Others say, it is not cost justified and if you know how to set up your battery, including charging and use... you may not need one.
> One of the finer points of this discussion is relative to "drift". The BMS proponents say that a well balanced pack of cells with close IR (matched... as close as reasonably possible - I could give numbers) and Ah capacity does "drift" as a result of charge/discharge cycles. That is to say, the cells get further apart with respect to SOC. . and that active cell level balancing is a requirement to prevent usable capacity from shrinking over time and eventually causing catastrophic failure.
> The non-BMS believers, including some real world users..... just aren't seeing this drift in actual practice. They find that if they bottom balance and stay away from top SOC (stop charging at the knee) and not push the bottom on discharge... the cells are fine. No drift. thousands of miles so far, no issues. The BMS guys say... you'll be sorry. The wall will come crumbling down.
> 
> I'm trying to sort my way through it. Can you offer any wisdom in this regard? It would be soooo helpful to this community, which is really trying to do their small part in this thing.
> 
> Thanks in advance.
> 
> Regards,
> Gary


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## DIYguy (Sep 18, 2008)

Here is Jay's reply.....

Hey Gary,

This is pretty easy to answer: well balanced (especially capacity wise) Li-ion strings that are strung up when at the exact same SoC should never drift with respect each other as long as they see the same thermal environment. I'd testify to this in court: there is no mechanism to cause such drift.

I worked at JPL in the group that put the Li-ion batteries on the 2 mars rovers that are still working. No cell level BMS. The Chevy volt, Nissan leaf, and Prius PHEV do not have cell level BMS.

you only need BMS when you have poorly matched cells and you plan on using more than some critical amount of SoC swing (say 80% or so - depends on chemistry and degree of mismatch).


If I were a hobbyist, however, I would monitor cell level voltages to identify failures point and to be safe (to avoid over charging cells in a string where one cell has failed to short or has lost much capacity).


Cheers,

-Jay
It just may be time to get out the "Crow" and put on the bibs....


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## JRP3 (Mar 7, 2008)

dimitri said:


> This is where Jack would start calling you bad names


Wouldn't be the first time 


> You want to choose lower detectable point in the knee to stop charging to give yourself more safety range at the top, this makes sense. However, the lower knee point will have larger dependency on temp and current variations, than later knee point, so you might be potentially leaving a lot more on the table than you expect.


Yes and I've used adjusting the current to compensate for temperature changes. Colder temps obviously drive voltage higher from higher resistance so I lower current, or just live with the undercharge, higher temps lower resistance and voltage so I can use higher current. I find that easier than changing the voltage trim since Rich couldn't put a KNOB on it   If I were better at data logging I could probably come up with a current vs temperature change adjustment factor. Basically I set the charger voltage trim for warm weather and then adjust current if the temperature drops more than 30F or so from that set point if I want more range. If not I'll just leave it and let it shut off early.


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## DIYguy (Sep 18, 2008)

JRP3 said:


> Wouldn't be the first time
> 
> Yes and I've used adjusting the current to compensate for temperature changes. Colder temps obviously drive voltage higher from higher resistance so I lower current, or just live with the undercharge, higher temps lower resistance and voltage so I can use higher current. I find that easier than changing the voltage trim since Rich couldn't put a KNOB on it   If I were better at data logging I could probably come up with a current vs temperature change adjustment factor. Basically I set the charger voltage trim for warm weather and then adjust current if the temperature drops more than 30F or so from that set point if I want more range. If not I'll just leave it and let it shut off early.


Does your charger have temperature compensation? I know there is a temp sensor on mine, but I haven't looked into it since I have been using it on Pb up till now. (Elcon)


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## JRP3 (Mar 7, 2008)

DIYguy said:


> This is pretty easy to answer: well balanced (especially capacity wise) Li-ion strings that are strung up when at the exact same SoC should never drift with respect each other as long as they see the same thermal environment. I'd testify to this in court: there is no mechanism to cause such drift.


Instead of a BMS maybe TMS is more important, Thermal Management System. Maybe worth trying to circulate pack air amongst all packs if possible.



> If I were a hobbyist, however, I would monitor cell level voltages to identify failures point and to be safe (to avoid over charging cells in a string where one cell has failed to short or has lost much capacity).


This is somewhat contradictory. I guess he's differentiating between shunting/shuttling and HVC/LVC signaling.


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## JRP3 (Mar 7, 2008)

DIYguy said:


> Does your charger have temperature compensation?


Just my hand on the current adjustment


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## DIYguy (Sep 18, 2008)

JRP3 said:


> Instead of a BMS maybe TMS is more important, Thermal Management System. Maybe worth trying to circulate pack air amongst all packs if possible.


 I've been thinking about this for a few weeks now. For active cooling/heating... I've been thinking about the spaces in between the cells when strapped. But also when cold, to channel heat. I envision a battery box whereby (on the bottom) I have a 1/2" of SM then, something like the Farnham heating pads...then a thin sheet of Aluminum (to spread heat) then a spacer...like ribs that would allow air flow in one direction under the cells allowing the air to be forced up through the passages. (I'm probably rushing through this ... but whatever lol) This space on the bottom is maybe 3/8" or so. Seal it off all way around and force feed it air in the summer heat or when pushing higher current (thermally controlled) and leave the fan off (plug hole) in the winter ( I live in Canada lol)


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## dexion (Aug 22, 2009)

DIYguy said:


> The other fellow I remember running bms free is Dexion. This is a cut from his blog...from Oct 2009. I don't know if he ever bottom balanced or not.
> 
> I have an Rmartin electric scooter which is powered by 21 Thundersky 60 AH Lifepo4 batteries.
> This was my first experience with the WONDERFUL qualities of a lifepo4 battery. I listened to people tell me I need a bms to keep the betteries in check or bad things will happen. Well, I just can't see this. From experience, I have a year and 3000 miles under the belt of the scooter and the batteries are still in ballance. How do I know this, well I check them (often, constantly) trying to find some inbalance or issue with them. I havent found anything yet. I charge them to about 3.7V and I discharge them to 3V.


 
Scooter is still bms free. The car was until about 13000 miles or so on the pack. I found a small drift on 5 of my cells due to them not being heated as well as the rest. The rest of the cells are directly on a heating pad. The 5 are in the trunk which is warm but not as warm as right on the pads. These 5 cells are colder and fill up about 1% faster (or dont give out quite as much as the others since they are cold) every 15 (40 ah) cycles or so. I have 100 ah cells. Every week I was using a resister to take 1ah out of them over and over. I got tired of it. In the summer they are fine. As soon as the heat is needed they drift. Its repeatable, easy to see and can be measured. But also meaningless. 47 cells are heated to 75F and 5 are at 45F. In the summer they dont drift. So its a design flaw not the batteries. 

The issue with my car is the force is so efficient, I use 40amps rolling down the road at 40mph. I use the 100amp limit on the controller (theres a 50,100 and 200amp limit switch) most of the time and 50 amps the rest. The cells dont heat up. I use about 34 amps from the pack to drive 27 miles in about 55 minutes and the heat is on the whole time. If i had more C discharge instead of .3c i think they wouldnt drift. 

The scooter is fine still it was top ballanced at the 1.5 year mark or so but really didnt need it.


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## DIYguy (Sep 18, 2008)

dexion said:


> Scooter is still bms free. The car was until about 13000 miles or so on the pack. I found a small drift on 5 of my cells due to them not being heated as well as the rest. The rest of the cells are directly on a heating pad. The 5 are in the trunk which is warm but not as warm as right on the pads. These 5 cells are colder and fill up about 1% faster (or dont give out quite as much as the others since they are cold) every 15 (40 ah) cycles or so. I have 100 ah cells. Every week I was using a resister to take 1ah out of them over and over. I got tired of it. In the summer they are fine. As soon as the heat is needed they drift. Its repeatable, easy to see and can be measured. But also meaningless. 47 cells are heated to 75F and 5 are at 45F. In the summer they dont drift. So its a design flaw not the batteries.
> 
> The issue with my car is the force is so efficient, I use 40amps rolling down the road at 40mph. I use the 100amp limit on the controller (theres a 50,100 and 200amp limit switch) most of the time and 50 amps the rest. The cells dont heat up. I use about 34 amps from the pack to drive 27 miles in about 55 minutes and the heat is on the whole time. If i had more C discharge instead of .3c i think they wouldnt drift.
> 
> The scooter is fine still.


Thank you Dexion, this falls inline with what the Prof says. MikeP referred to the issue also. Yours is a bit of an extreme case (which is GREAT for proving a theory) in that you actually heat the one block and not the other, so there is a significant difference in temperature (30F)... and you see a 1% drift per charge..or so. Thank you!


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## DIYguy (Sep 18, 2008)

JRP3 said:


> This is somewhat contradictory. I guess he's differentiating between shunting/shuttling and HVC/LVC signaling.


I asked Jay about this. He was not referring to HVC at all. He was only referring to knowing what is going on with your cells through a visual monitor.


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## DavidDymaxion (Dec 1, 2008)

For the mars rover, this paper says there was cell level current shunting:
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/17736/1/99-1176.pdf

More precisely, Jay's email below says no bms on the "2 Mars Rovers that are still working." So I'm not clear... Was the above link a prototype that didn't fly? I also thought one of them was not responding.


DIYguy said:


> Here is Jay's reply.....
> 
> Hey Gary,
> 
> ...


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## tomofreno (Mar 3, 2009)

> Can you elaborate on this? Can you tell every time that gauge is full because it counted itself to full or self reset to full based on voltage while you weren't looking? Could it be that you see little drift because most your charges are full charges? Would it drift more if you often had partial charges and rarely a full charge? I'm just curious how TBS manages the drift.
> 
> How can you set the gauge to individual cell voltage? Or is it based on pack voltage?


 What I am saying is say I start by charging my lowest capacity cell to 3.45V which I define as "full". I then manually reset the gauge to "full". From then on when I charge it starts off with some Ah used, say 105, and decreases as it charges. If it reaches 0.0 Ah used at the same time my lowest capacity cell reaches 3.45V I say the gauge didn't drift. I fairly regularly measure that cell with my dvm at end of charge out of curiosity of how things are behaving. The gauge is generally quite close to 0.0 when that cell hits 3.45V - many times almost dead on. Of course the charger many times shuts off before that time, with the gauge reading say 2.9 Ah used, or keeps charging past the point when 0.0 Ah is reached. In the later case the times I have checked, the lowest capacity cell is indeed above 3.45V. I usually shut it off at 3.45V, but sometimes I have let it go and watched the gauge out of curiosity, and also to see how fast the cell voltage rises. 

By partial charge do you mean starting at low SOC, charge only partially, say to 70% SOC? Or do you mean starting at fairly high SOC, like 60%, charge to "full"? I do both, but only occasionally. I haven't noticed it making a difference in how well the gauge tracks, but that is fairly useless, since I haven't watched closely for it. I'm not sure what you mean by does it work off cell or pack voltage. I assumed it just counted charge by integrating current through the shunt over time.


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## JRP3 (Mar 7, 2008)

DIYguy said:


> I asked Jay about this. He was not referring to HVC at all. He was only referring to knowing what is going on with your cells through a visual monitor.


When he says this


> If I were a hobbyist, however, I would monitor cell level voltages to identify failures point and to be safe (to avoid over charging cells in a string where one cell has failed to short or has lost much capacity).


A visual monitor won't help you during charging unless you are standing there looking at it, that's why I took it to mean HVC at least. Maybe he's just talking about occasional monitoring as I do.


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## mikep_95133 (May 20, 2009)

DIYguy said:


> Other stuff.... I put full synthetics in my trans and differential...but I wasn't able measure any significant improvement. There may have been something...but it was negligible. I tried to find it. I also did an alignment, but did not set toe to zero... I thought about it...but was not too keen on the idea. Depending on factory Camber angle, zeroing toe could actually _increase_ rolling resistance. It also aids steering stability at higher speeds. The most significant impact I found was with tire type (Specifically width) and of course pressure. 178 wh/mi for a 4000 lb truck is ...well, I don't know what to say. . . I just can't see it. I have one also, and have done a lot of stuff. This number is ... I dunno. . pretty much ridiculous.


Did I mention my system is AC? It has excellent regen, up to 300 amps modified, 250 amps stock. But the 178wh/mi was 95% freeway at 45 mph for 20 miles. Had a couple hundred lbs of cargo too. So regen didn't enter into it much. The ACP car up the street got 154wh/mi at 60mph, 3400lbs, as it's best. Also having a high voltage system helps to limit Peukert's cut too. 225-250 wh/mi is level-ish roads, a few lights per mile.

My toe set to zero did change the handling a tad bit. But at it's 72-74 mph maximum it is steady as a rock. The motor is electronically limited to 9000 rpm. ACP's are limited to 13000 rpm on the old hardware. Wish I could get a little more speed out of mine. Should talk to a motor rebuilder.

Mike


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## mikep_95133 (May 20, 2009)

Trying to compare what incredibly well match cells Jay uses, in a specially engineered thermal environment is not comparable to any EV on this planet. Our costs per cell would double, at least, to get that close tolerance matching. So to me this is not data for anything EV related. The very last thing most EV builders do is a thermal study. Great info, just not relevant to EV's.

Mike




DavidDymaxion said:


> For the mars rover, this paper says there was cell level current shunting:
> http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/17736/1/99-1176.pdf
> 
> More precisely, Jay's email below says no bms on the "2 Mars Rovers that are still working." So I'm not clear... Was the above link a prototype that didn't fly? I also thought one of them was not responding.
> ...


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## mikep_95133 (May 20, 2009)

Great example of a typical cell divergence based on thermal variation. Have you done any recent capacity testing? What kind of heaters did you use? Nice job!

Mike



DavidDymaxion said:


> For the mars rover, this paper says there was cell level current shunting:
> http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/17736/1/99-1176.pdf
> 
> More precisely, Jay's email below says no bms on the "2 Mars Rovers that are still working." So I'm not clear... Was the above link a prototype that didn't fly? I also thought one of them was not responding.





dexion said:


> Scooter is still bms free. The car was until about 13000 miles or so on the pack. I found a small drift on 5 of my cells due to them not being heated as well as the rest. The rest of the cells are directly on a heating pad. The 5 are in the trunk which is warm but not as warm as right on the pads. These 5 cells are colder and fill up about 1% faster (or dont give out quite as much as the others since they are cold) every 15 (40 ah) cycles or so. I have 100 ah cells. Every week I was using a resister to take 1ah out of them over and over. I got tired of it. In the summer they are fine. As soon as the heat is needed they drift. Its repeatable, easy to see and can be measured. But also meaningless. 47 cells are heated to 75F and 5 are at 45F. In the summer they dont drift. So its a design flaw not the batteries.
> 
> The issue with my car is the force is so efficient, I use 40amps rolling down the road at 40mph. I use the 100amp limit on the controller (theres a 50,100 and 200amp limit switch) most of the time and 50 amps the rest. The cells dont heat up. I use about 34 amps from the pack to drive 27 miles in about 55 minutes and the heat is on the whole time. If i had more C discharge instead of .3c i think they wouldnt drift.
> 
> The scooter is fine still it was top ballanced at the 1.5 year mark or so but really didnt need it.


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## ElectriCar (Jun 15, 2008)

mikep_95133 said:


> Trying to compare what incredibly well match cells Jay uses, in a specially engineered thermal environment is not comparable to any EV on this planet. Our costs per cell would double, at least, to get that close tolerance matching. So to me this is not data for anything EV related. The very last thing most EV builders do is a thermal study. Great info, just not relevant to EV's.
> 
> Mike


In the video he says you should have cells Ah matched to 1%, no more than maybe 3%? My cells will be within 1%. I think the performance variation would be trivial if I had them identically matched.

Re thermal issues, I have lined battery boxes, insulated from the environment except the top is currently open. In the swap, I hope to better insulate them so they're all pretty close temp wise and enclose the top as well for winter driving, enough to practically eliminate thermal variation between cells. I don't plan to have any active thermal management but may if it's necessary ie starts getting too cold or warm.

You think this setup will be that far different from his?


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## JRP3 (Mar 7, 2008)

ElectriCar said:


> In the video he says you should have cells Ah matched to 1%, no more than maybe 3%? My cells will be within 1%. I think the performance variation would be trivial if I had them identically matched.


Exactly. We are demanding and receiving more closely matched cells than were previously available. That may be the difference we are seeing compared to those who've been working with older cells.


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## dexion (Aug 22, 2009)

DIYguy said:


> Thank you Dexion, this falls inline with what the Prof says. MikeP referred to the issue also. Yours is a bit of an extreme case (which is GREAT for proving a theory) in that you actually heat the one block and not the other, so there is a significant difference in temperature (30F)... and you see a 1% drift per charge..or so. Thank you!


 
Well not quite. Its a 1% drift over 15 cycles of about 40ah. I have the feeling it would be worse if I went to 80% dod instead of 40ah but ive never really tested it. I really only need 40% out of the pack and I charge at work. So over a month it would be perhaps 4% for the 4 or so months i need the battery heating.


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## dexion (Aug 22, 2009)

mikep_95133 said:


> Great example of a typical cell divergence based on thermal variation. Have you done any recent capacity testing? What kind of heaters did you use? Nice job!
> 
> Mike


Solectria forces came as lead acid with battery heaters. I used the stock heaters but replaced the pack with lithium. Since my cells dont need strapping I put 47 in the rear battery box and 5 on the side in a group 27 box. No lifepo in the front battery box. 

Ive never done any capacity testing. I need 40amps out of the pack at a time. I commute 54 miles a day. I figure in an emergency i could do a round trip if needed but never have. I've always had time charge at work (it only takes 2.5 hours to recharge.) So i pull very little out and very little at one time. I just dont worry about the cells any longer. They just work.

You can spend an awful lot of time and money trying for the best possible outcome but really these cells seems to just work as long as they arent over or under charged however you manage it. I just got tired of being a bms.

I suppose it might be worth mentioning. When I get all 52 pretty red lights (shunting) lit up. The warmest cells are the last. They light up from the outside of the pack to the inside. But the ones that are heated are perhaps .2 amps apart. Its the unheated ones that are 1 amp apart after 15 cycles.

Perhaps i dont even need the heat at all. But my specs say I cant charge under 32F and its under 32f for 3 or so months here.


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## JRP3 (Mar 7, 2008)

dexion said:


> I just got tired of being a bms.


So what BMS are you using now, and why get a BMS for the whole pack instead of just heating the 5 cells that were the problem?


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## dexion (Aug 22, 2009)

JRP3 said:


> So what BMS are you using now, and why get a BMS for the whole pack instead of just heating the 5 cells that were the problem?


 
Minibms. When the cells were in the saturn it was very easy to check them. In the force its not as easy since I built a shelf for the spare tire and a toolbox. Thats part of it. It was the not knowing for sure that made me get the minibms. I couldnt ever walk past it without fluking it. I think it got to be an obsession heh. Now i dont because of the pretty green lights. But, i tighten up the lugs (120inch lbs) every month and check the com loop on the bms. Ive gotten good at it. I can do the whole pack in about 30 minutes now including raising up the shelf (its on hinges.) If i put heat on those 5 cells i still would want to check all the time. Heat would have been a fix as well except for my mental illness


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## GerhardRP (Nov 17, 2009)

dexion said:


> Minibms. When the cells were in the saturn it was very easy to check them. In the force its not as easy since I built a shelf for the spare tire and a toolbox. Thats part of it. It was the not knowing for sure that made me get the minibms. I couldnt ever walk past it without fluking it. I think it got to be an obsession heh. Now i dont because of the pretty green lights. But, i tighten up the lugs (120inch lbs) every month and check the com loop on the bms. Ive gotten good at it. I can do the whole pack in about 30 minutes now including raising up the shelf (its on hinges.) If i put heat on those 5 cells i still would want to check all the time. Heat would have been a fix as well except for my mental illness


Does the heater draw power from the entire pack?
Gerhard


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## mikep_95133 (May 20, 2009)

I thought yours sounded like a Solectria. Great cars to convert to lithium. Heating battery's is one of ACP's secrets to very long battery life. Your shallow discharge drives are going to keep things converged, except for the temperature differences. Ever thought of adding heaters to the other unheated group? 

When you say a 1 amp difference, do you mean 1ah? In only 15 cycles that's a very steep divergence curve considering you may have a 2000+ cycle pack.

I have often thought of trading off one of my trucks for a Solectria.

I know the feeling of watching the BMS light up. My old lead pack had 50 balancers on it, and the flow of current as the cells hit HVC, through the paralleled strings of batts was very telling watching the led's.

Why did your cells not need to be strapped? Those large format cells expand over time I've noticed.

Keep the data coming over time. Your info has the credibility that we can all use.

Mike






dexion said:


> Solectria forces came as lead acid with battery heaters. I used the stock heaters but replaced the pack with lithium. Since my cells dont need strapping I put 47 in the rear battery box and 5 on the side in a group 27 box. No lifepo in the front battery box.
> 
> Ive never done any capacity testing. I need 40amps out of the pack at a time. I commute 54 miles a day. I figure in an emergency i could do a round trip if needed but never have. I've always had time charge at work (it only takes 2.5 hours to recharge.) So i pull very little out and very little at one time. I just dont worry about the cells any longer. They just work.
> 
> ...


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## DIYguy (Sep 18, 2008)

mikep_95133 said:


> Trying to compare what incredibly well match cells Jay uses, in a specially engineered thermal environment is not comparable to any EV on this planet. Our costs per cell would double, at least, to get that close tolerance matching. So to me this is not data for anything EV related. The very last thing most EV builders do is a thermal study. Great info, just not relevant to EV's.
> 
> Mike


Yes, actually it is specifically about EV's on this planet and the prismatics we use. That is what I asked about. He is very familiar with TS Calb and the rest. His video is directly related to electric vehicle applications. Totally relevant. Your facts about drift, other than temp influence are wrong.


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## DIYguy (Sep 18, 2008)

DavidDymaxion said:


> For the mars rover, this paper says there was cell level current shunting:
> http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/17736/1/99-1176.pdf
> 
> More precisely, Jay's email below says no bms on the "2 Mars Rovers that are still working." So I'm not clear... Was the above link a prototype that didn't fly? I also thought one of them was not responding.


Ask him I guess.....


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## MN Driver (Sep 29, 2009)

Keep in mind that some people misinterpreted what was said with meaning that auto manufacturers aren't using a BMS. Chevy Volt is, there are pictures of the voltage balancers online. Tesla has a BMS, plenty of discussion in the blogs about it, they have a different name for it if I remember right though but the discussion is there. Nissan packs have three terminals on each of the 4-pack modules which I think are 4p cell arrange, 48 packs total, third terminal used for?


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## EVfun (Mar 14, 2010)

gottdi said:


> What will happen?
> 
> Take 4 100ah Hi-Power Prismatic Cells. Block them together as a single 12 vlt battery.
> 
> ...


I'll take a stab at it. I have never had any HiPower cells in my hand but list wisdom seems to indicate they have a bit higher internal resistance. 

I'm a bit concerned about the starting voltages. I've never seen any rested cell voltage so high on my TS pack, except for the 3.28 cell. My guess is that cell is fine, just a little low on charge. I don't really know about the condition of the other cells. Provided the other cells are OK (not damaged by overcharging) they should be holding a higher voltage after spinning up the motor. If the other 3 have suffered from increases in internal resistance related to overcharging they may read lower when running the motor, at least until the 3.28 cell starts going dead. 

Either way, the higher resting voltage cells at the start of the test should be the higher resting voltage cells after removing the motor load. If any of the high cells has lost capacity it then it may take the low voltage role after a discharge of sufficient time. Resting voltage speaks to state of charge but not to cell capacity. 

I'm going to guess the motor needs about 20 amps to keep spinning but that the peak starting current is much higher. At those kind of amp levels I would hope all the cells remain above 3.1 volts. Obviously when the lowest cell starts to go flat it will drop a lot more (and countdown fast.) 

If any of the cells start showing an increasing voltage while running such a small load I would be concerned about their internal resistance. Heating a cell will increase its voltage under load and this can be seen while discharging them. With lead it was mostly only seen after recharging and then discharging a second time.


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## mikep_95133 (May 20, 2009)

I never use the word drift, ever, anywhere. That is someone elses notion. You might clarify that a bit. These are observations I've made, so they really can't be 'wrong'. I could accept that you disagree. If you do, please site your experience.

Jay talks to EV guys about their cells and BMS. That sure is a relevent part of the video. But when he talks about using super well match cells, that we can't but at any price, any where, in Mars missions, that is where the commonality with EV's departs. 

Maybe I made too much of a blanket statement about the video to enlicit this reaction?

Mike




DIYguy said:


> Yes, actually it is specifically about EV's on this planet and the prismatics we use. That is what I asked about. He is very familiar with TS Calb and the rest. His video is directly related to electric vehicle applications. Totally relevant. Your facts about drift, other than temp influence are wrong.


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## mikep_95133 (May 20, 2009)

You really cracked me up when you used the word obsession. My pack has 250 1.2v cells. Being the human BMS really bites. I can relate big time! 

Mike




dexion said:


> Minibms. When the cells were in the saturn it was very easy to check them. In the force its not as easy since I built a shelf for the spare tire and a toolbox. Thats part of it. It was the not knowing for sure that made me get the minibms. I couldnt ever walk past it without fluking it. I think it got to be an obsession heh. Now i dont because of the pretty green lights. But, i tighten up the lugs (120inch lbs) every month and check the com loop on the bms. Ive gotten good at it. I can do the whole pack in about 30 minutes now including raising up the shelf (its on hinges.) If i put heat on those 5 cells i still would want to check all the time. Heat would have been a fix as well except for my mental illness


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## EVfun (Mar 14, 2010)

gottdi said:


> Thanks for taking a stab. Too bad the others did not. I figured they would not. Now it's too late.
> 
> Here is where we stand so far.
> 
> ...


Wow, 50 amps to run no load on 12 volts? Is this motor completely new with unseated brushes? Perhaps installed in a vehicle so you are also spinning the tranny?

It looks like those really high numbers where strictly "surface charge." I've never seen a TS cell stay that high, always back down under 3.40 volts after 72 hours. None of mine have ever hit 3.90 volts though. I usually charge to 3.65 volts and hold for one hour. My flat range is roughly between 3.32 and 3.26 volts. The voltage quickly drops to 3.32 after seeing first load (but usually only back from about 3.36-3.38.) 

It is clear the run time is nowhere near their capacity (about 25 amp hour removed) so all the cells should be in the flat land. Perhaps the cell that hit the highest voltage on charge will prove to be the smallest on discharge, though I still think that 3.28 volt starting cell should be at a lower SOC. My TS cells are down quite a few amp hours when they have a 3.28 resting (starting) voltage. If I'm reading that report correctly (the 10:35 numbers are after shutting off the motor) it appears that you are not seeing any significant heating at .5C (good sign.)

My pack is resting right now at 3.32 volts for all 40 cells. The 2 cells that have never been charged or discharged, just sitting as received since they where made in Feb. 2010, are still reading 3.29 volts (down from 3.30.) I have high and low voltage detection (neither have gone off) but have never done any significant running voltage checks aside from pack voltage with my foot in it. I check all the time when charging (I have a BMS and I'm a BMS too .)

I visited your web site today to look at your Buggy. A full length buggy is not commonly seen. It looks like you replaced the pan with a '69 or newer one. Why did you get rid of the '58 pan? My Buggy is on a '64 pan, all those old parts are still easy to get.


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## mikep_95133 (May 20, 2009)

Pete,

Maybe you missed the post, mentioning that I had developed a few BMS's. I have gone line by line and answered your questions and accusations in post # 358 of this thread. That is where I mentioned my BMS work. As for lead, that was long ago. Did you notice any of the other chemistry's tested? Not everything I test makes it to the blog. It goes into a notebook. You have some more catching up to do. Keep reading you'll get there, maybe. 

Please don't be offended if I chose not to respond to the hostile tone in your posts any longer. Maybe we should meet sometime if you are near San Jose. I'm very helpful and a pretty nice guy. But your attacks are just not conducive to helping this BMS thread along.

Maybe if you want to act like Jack Rickard, you could find an outlet for that hostility elsewhere?

Mike




gottdi said:


> Now I know why mikep is so hostile when the issue of bms vs no bms comes up. He's building one himself. Very interesting. Now I am not surprised at this. Ignoring those who promote no BMS. Or at least a minimum of monitoring.
> 
> http://rotordesign.com/blog/
> 
> ...


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## Duncan (Dec 8, 2008)

Hi Mikep

I have been following this thread with interest - I have ordered the lithium book from my library (Did I say I was a Scotsman?)

I have a big problem with your re-gen figures,
the data I have seen is a lot lower, 
- an inner city bus stopping every few meters did not achieve those re-gen numbers (Christchurch Hybrid buses)

There is no way I am using my brakes to absorb 20% - 40% of my motive power

The figures other people have quoted have been more like 5% - and probably less if hypermiling where you drive ahead to avoid braking

These figures I can relate to the amount of braking I do

Have you got some data you can share?


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## mikep_95133 (May 20, 2009)

Hi Duncan,

What lithium book are you refering to? 

The data for ACP cars use to be posted on their website for years. The RAV4 owners that I've spoken to show 25%. These guys love to track their data. I took data for 2 weeks on my truck and got 20-40%. These are all with medium weight vehicles, pure electric. I didn't use the data logger to record the drives. I kept data in my notebook on the energy used getting to work and back home each day from my E-meter. The difference was obvious just in driving the truck when regen was off. I could watch the E-meter count backwards as I regen'd.

You bring up a hybrid bus. I can't comment on the bus as I have zero experience with it. Hybrid's are very gentle on their packs for long battery life by design. So I would expect the regen value to be lower by design.

Max regen current is directly proportional to the systems output capacity. The amount of energy to start and stop any vehicle is far higher than steady state cruising. So if the stopping energy can be captured, it adds greatly to the vehicles efficiency. 

All 3 of the systems I site are professional, well tested, well designed systems. I think that the Curtis AC system that some have is only adding back 10-15%. But that was a design choice.

My regen is so strong that I don't need the brakes to stop my truck, at all. The truck will throw you forward in your seat as it hits zero mph.

I was thinking about heading to where a bunch of RAV4 folks hang out this weekend. I'll try to remember to ask them where they have their data listed somewhere.

It has been common mis-info on EVDL that regen is worth 10%. But once you own an AC vehicle, you can measure the real value.

Mike








Duncan said:


> Hi Mikep
> 
> I have been following this thread with interest - I have ordered the lithium book from my library (Did I say I was a Scotsman?)
> 
> ...


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## JRP3 (Mar 7, 2008)

mikep_95133 said:


> I never use the word drift, ever, anywhere. That is someone elses notion. You might clarify that a bit. These are observations I've made, so they really can't be 'wrong'. I could accept that you disagree. If you do, please site your experience.


That was David Andrea.


> Jay talks to EV guys about their cells and BMS. That sure is a relevent part of the video. But when he talks about using super well match cells, that we can't but at any price, any where, in Mars missions, that is where the commonality with EV's departs.


As previously mentioned he talked about a 1-2% deviation, people are getting new CALB packs within 1% now. Did you know this fact?


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## Tesseract (Sep 27, 2008)

mikep_95133 said:


> What lithium book are you refering to?


Probably Davide Andrea of eLithion's book... I don't have the link handy but it's been posted a couple of times in this thread already.



mikep_95133 said:


> It has been common mis-info on EVDL that regen is worth 10%. But once you own an AC vehicle, you can measure the real value.


I'm sure you realize this, Mike, but the only sources of potential energy that can be recaptured by regen are what it took to accelerate to a given speed or to ascend a given elevation. So, if you do a lot of stop-and-go driving you can recapture a fraction of each _acceleration_ or if you live in a hilly area you can recapture a fraction of energy for every _decrease in elevation_. That's it. As for the argument that it saves wear and tear on brakes - sure it does, but I've gone 79k miles on the original set of pads in my truck and it has an automatic transmission, so very little or no engine braking.

Now, back to the subject at hand... it seems we are sorely lacking in data from destructive testing of lithium, and I don't mean shooting a cell with a .44 Magnum then posting the video on youtube (as entertaining as that may be).

What we really need to know are how the two most common abuses - overcharging and overdischarging - affect cycle life and capacity. The big problem with this kind of testing is that it is expensive. You not only have to buy the batteries, but you also need to build a test rig to do this very tedious testing automatically, and repeatably! Another consideration is the electricity for charging the cells back up: if a single cell has a capacity of 100Ah then at $0.10/kWh it will cost $64 in electricity to charge it up 2000 times. Multiply by the number of cells and/or actual capacity and the dollars really start to add up fast.

So the tester should, ideally, incorporate a dc/dc converter to be able to use the discharge of one cell/battery to charge a second, then vice versa. Only a small amount of additional energy would be needed to make up for losses in the converter and the cells (ie - coulombmetric efficiency, which is supposed to be 98% or so with LFP).

The tester should not only periodically record the voltage, Ah and internal resistance (determined from dV/dI), but also be able to vary the current during charging/discharging over the range of 0.3C to 3C, to better simulate actual use.

The testing regime can be extended (with a sufficient budget, of course) to include cells at different temperatures in the same series string.

This is well beyond the scope of what a small company like Evnetics can afford to do even if we did make a BMS (and believe me, I get asked ALL THE TIME about making one)... I daresay no other company can really justify it, either, though Thomas Cook of LithiumStart is working on a high current load for automated testing so he might be game.

My last $0.02 on this oftentimes idiotic debate is that you either need a very good Ah counter (aka "E meter") or you have to monitor individual cell voltages if you want to have a prayer of reaching even half the promised cycle life LFP. Sorry, but you really can't argue that "not knowing" is ok UNTIL you have accumulated 2000 trouble-free cycles in ignorant bliss. I really don't care that your LFP car is still driving fine after, say, two years ... that's at best going to be 700 or so cycles, and not impressive to me in the least.

The argument that you can buy more cells for the cost of the monitoring system is a red herring, too - that presupposes a) that you have room/GVWR reserve for them and b) that you will, indeed, get as many cycles out of "going naked" as you would if you monitored them. Since no one has yet to do the latter...


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## DIYguy (Sep 18, 2008)

mikep_95133 said:


> I never use the word drift, ever, anywhere. That is someone elses notion. You might clarify that a bit. These are observations I've made, so they really can't be 'wrong'. I could accept that you disagree. If you do, please site your experience.


Oh, sorry about that. I thought you did. My mistake.


mikep_95133 said:


> Jay talks to EV guys about their cells and BMS. That sure is a relevent part of the video. But when he talks about using super well match cells, that we can't but at any price, any where, in Mars missions, that is where the commonality with EV's departs.
> 
> Maybe I made too much of a blanket statement about the video to enlicit this reaction?
> 
> Mike


I don't think it was anything about super matched cells. Current prismatics was the reference. I can ask him for clarification. 
If you folks want to list some specific questions maybe that would be good?


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## DIYguy (Sep 18, 2008)

Duncan said:


> Hi Mikep
> 
> I have been following this thread with interest - I have ordered the lithium book from my library (Did I say I was a Scotsman?)
> 
> ...


I keep thinking about the Moto-mundo couple..whatever it's called. They have been going round the world, a 41,000 km (or Mile?) trip and have been recording everything and have had many days on end to try and maximize their performance. The have an AC system also. They actually found better range by not using their regen at all. It may be possible that regen energy captured looks much better when not trying to maximize range. . after all, you are going through the energy conversion process again as opposed to coasting. 
I do like the idea of regen though, for braking alone I think it is worth it. One of the few things requiring maintenance on an EV (compared to ICE) in many cases is brake replacement.... regen, takes this to another level for sure.


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## JRP3 (Mar 7, 2008)

Tesseract said:


> The argument that you can buy more cells for the cost of the monitoring system is a red herring, too - that presupposes a) that you have room/GVWR reserve for them and b) that you will, indeed, get as many cycles out of "going naked" as you would if you monitored them. Since no one has yet to do the latter...


a) Most packs are budget limited.
b) True, though it's more accurate to say if you will get as many cycles as you *need*. Packs don't have to be worn out to be replaced, if my 50 mile pack only lasts 1500 cycles that's 75,000 miles and about 8-10 years at my usage rates that's more than enough. If prices drop and technolgy improves I may upgrade well before that.


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## JRP3 (Mar 7, 2008)

DIYguy said:


> I keep thinking about the Moto-mundo couple..whatever it's called. They have been going round the world, a 41,000 km (or Mile?) trip and have been recording everything and have had many days on end to try and maximize their performance. The have an AC system also. They actually found better range by not using their regen at all. It may be possible that regen energy captured looks much better when not trying to maximize range. . after all, you are going through the energy conversion process again as opposed to coasting.


Learning to use regen most efficiently takes time, especially if it's tied into the accelerator pedal. It needs to be set up with a decent neutral pedal position that allows easy coasting when possible since that's the most efficient. Obviously if you need to slow the vehicle more than coasting does it's better to use regen than brakes.


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## tomofreno (Mar 3, 2009)

> None of mine have ever hit 3.90 volts though. I usually charge to 3.65 volts and hold for one hour. My flat range is roughly between 3.32 and 3.26 volts. The voltage quickly drops to 3.32 after seeing first load (but usually only back from about 3.36-3.38.)


 "back from about 3.36-3.38" - so are you saying at a few hours or more rest after full charge your TS cells are at 3.36-3.38V, and rest voltage on the flat part of the discharge curve ranges from 3.32 to 3.26V? If so, that is basically the same as my CALB cells.


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## DIYguy (Sep 18, 2008)

Tesseract said:


> Probably Davide Andrea of eLithion's book... I don't have the link handy but it's been posted a couple of times in this thread already.
> 
> 
> 
> ...


Some good points there, Jeff. (overall, I think it was a pretty good debate though). I agree about monitoring for sure... and I would like to have something like the Cell Log8... but on one screen, perhaps not all at once. I think there are some full blown BMS's that have this...but are there any monitors of lesser cost??

I still like the idea of using a representative small group of cells to represent the pack for HVC (and perhaps LVC)... something that does not impart a load on these few cells. Is this possible?

Thanks...


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## tomofreno (Mar 3, 2009)

> Sorry, but you really can't argue that "not knowing" is ok UNTIL you have accumulated 2000 trouble-free cycles in ignorant bliss.


 I wasn't aware anyone had said this. People like JRP3, Dexion, and myself who are running, or ran for a while, without a bms monitor cell voltages with a dvm and use a charge counter. Is there someone here who thinks you don't need to measure anything? The converse is rarely mentioned but is also true of course, you don't know a bms works well until you have accumulated 2000 trouble-free cycles.


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## Tesseract (Sep 27, 2008)

JRP3 said:


> a) Most packs are budget limited.


That's restating the obvious - it is implied that when comparing a pack with a BMS vs. one without it that they both cost the same so, clearly, the naked pack will have more cells because the BMS consumes some of the allotted budget.

If you are budget limited then you just scale down the size of the pack until you once again have two systems to compare that cost the same, differing only in having a BMS or not, with the number of cells adjusted to make the price nominally equal. Now, see how many total miles you get from each pack and THEN you can conclude whether a BMS is worth the money or not.

What I was saying here specifically is that even if you have an unlimited budget there is a maximum number of cells you can cram into a vehicle, so you can't just assume that you can always buy more cells if you skip the BMS... THAT was my point.




JRP3 said:


> b) True, though it's more accurate to say if you will get as many cycles as you *need*. Packs don't have to be worn out to be replaced, if my 50 mile pack only lasts 1500 cycles that's 75,000 miles and about 8-10 years at my usage rates that's more than enough. If prices drop and technolgy improves I may upgrade well before that.


Okay, I'll go with "need" here, but from a strictly economic perspective, it doesn't make sense to go with LFP if the lifecycle cost isn't less than all of the other chemistries, right?

In other words, if a lead-acid pack for a given EV delivers 20 miles per charge and lasts 300 cycles and costs $2000 then a LFP pack has to either: a) deliver more miles per charge for a given weight/volume (they do); or, b) last more than 300 cycles (they *should*); or, c) cost less than $2000 for the same Wh capacity (they definitely don't).

In other words, if you get 6k miles out of a lead-acid pack for $2000 that comes out to 33.3 cents per mile - LFP has to be less than that to be economically justifiable.

Can LFP be justifiable on other merits besides economics? Sure, but that's a whole 'nother argument. It's sort of the same thing with EVs in the first place - if your main motivation for going electric is to save money on gas then gas really has to be $3.50 to $4.00 per gallon and/or you have to get really crappy mileage to start with to have a hope of recovering the cost of conversion. If you factor in other reasons like wanting to reduce pollution or being "energy independent" or you simply want to experience the thrill from having massive amounts of torque at 0 rpm then that might override what is an otherwise economically unsound decision.


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## tomofreno (Mar 3, 2009)

> I keep thinking about the Moto-mundo couple..whatever it's called. They have been going round the world, a 41,000 km (or Mile?) trip and have been recording everything and have had many days on end to try and maximize their performance. The have an AC system also. They actually found better range by not using their regen at all. It may be possible that regen energy captured looks much better when not trying to maximize range. . after all, you are going through the energy conversion process again as opposed to coasting.


 I think if the vehicle is operated in conditions where you don't have to drive in traffic so you can coast to a stop each time, and coast down hills unimpeded at whatever speed the vehicle reaches, then regen would not be used except for possibly adding a small amount of resistance to bring the vehicle to a complete stop after you have coasted to a very low speed. In such a case I agree regen will add negligible charge to the pack. 

I don't see how you can loose energy with regen though unless you modulate between regen and acceleration, modulating the kinetic energy of the vehicle somewhat. In that case you will loose energy each cycle since regen won't recoup 100% of the energy used accelerating (not even close). A jumpy throttle might have this effect. In more typical driving around a city, you have to slow repeatedly in traffic, slow for turns, control speed down hills, etc. Each of these requires dissipating some of the vehicle's kinetic energy as heat in mechanical brakes or using regen. Regen puts some amount of energy into the pack and mechanical braking doesn't, so I don't see how regen can give worse range in normal driving than mechanical braking. 

As for how much you get, that will vary widely with driving conditions, particularly with hills. I can only say that I have datalogged battery current, voltage, and Ah used, and found that I typically get around 10%+/-5%. That is defined as the ratio of energy into pack from regen to energy out of the pack for a given trip, and estimated by summing the product of pack voltage, current, and 1/3600 hour sample interval. Low end if I drive mainly on flat highway, higher end if there are more hills. The highest I have recorded (I've only done it a handful of times) is about 20%. That was when starting at the bottom of a 6 mile 4.5% grade (~1600 ft elevation change), driving up, then back down. (Edit: In this case it was estimated by Ah used going up and Ah gained going down using a charge counter, not datalogging) I would guess it may differ somewhat from one model motor to another, since the motor is not optimized to be a generator. Mine is an HPEVS AC50. Controller is Curtis 1238-7501 with regen upper limit set at 55% of controller full rated current (550A). This is enough to drive the vehicle without using mechanical brakes except for emergency stops, or holding on a hill or at a stop light.


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## Tesseract (Sep 27, 2008)

DIYguy said:


> I still like the idea of using a representative small group of cells to represent the pack for HVC (and perhaps LVC)... something that does not impart a load on these few cells. Is this possible?


Sure - you just need to have the monitoring circuitry powered by something besides the cell being monitored. This adds to the per-cell cost of the monitor, however, because it needs to be an isolated power supply.

I don't know if this has already been done because I don't really keep track of all the BMS (monitoring and management) out there. Not really something I'd like to see Evnetics develop, though we are considering it for, e.g., cylindrical cell packs. I am the main opponent to doing this, mind you, so please no one point an accusatory finger at me saying I am just being greedy, talking my book, etc...




tomofreno said:


> I wasn't aware anyone had said this.  People like JRP3, Dexion, and myself who are running, or ran for a while, without a bms monitor cell voltages with a dvm and use a charge counter. Is there someone here who thinks you don't need to measure anything? The converse is rarely mentioned but is also true of course, you don't know a bms works well until you have accumulated 2000 trouble-free cycles.


That is the inevitable counterargument to running a BMS of some sort - it is not important that someone specifically said it. That said, please look at the title of the thread by the op: "To BMS or not to BMS".

Sorry, but I don't think you can argue you aren't using a BMS if you have an Ah counter; maybe if all you are doing is occasionally checking cell voltages with a DVM, but not if you can keep good track of Ah in and Ah out. Not to put too semantic a spin on the debate, however...

... as what this all really boils down to is if there is an economic benefit to be had from spending money on some form of _automated_ battery [management/monitoring] system. More specifically, whether such a BMS gets you more cycles or more range per charge or even some blend of the two. It's really as simple as that.

Of course, and I made the same statement in a reply to JRP3. The problem here is that neither side has provided data supporting their position, but my specific observation about the BMS-free side is that the only way they can provide data is by surviving the claimed number of cycles, as, by definition, they have no f'in clue as to what is going on otherwise.


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## GerhardRP (Nov 17, 2009)

gottdi said:


> I'd say there are plenty more with lead sleds than lithium sleds.


Maybe that should be "lithium luges"?
Gerhard


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## DIYguy (Sep 18, 2008)

GerhardRP said:


> Maybe that should be "lithium luges"?
> Gerhard


Ha!...that's good!


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## mikep_95133 (May 20, 2009)

JRP3,

I missed that memo  . Please point me to the data sheet stating that the capacity and impedance is 1% matched liked the cells NASA/JPL use, or perhaps the empirical test data showing that the capacity and impedance of the cells is within 1%. Voltage matching at 1% is not what the aerospace world uses, I hope we are not.

Pricey book. I hope any new owners of it give us a review.

Mike



JRP3 said:


> That was David Andrea.
> As previously mentioned he talked about a 1-2% deviation, people are getting new CALB packs within 1% now. Did you know this fact?


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## mikep_95133 (May 20, 2009)

I'm sure my truck is fully informed on all of that 

Mike




Tesseract said:


> I'm sure you realize this, Mike, but the only sources of potential energy that can be recaptured by regen are what it took to accelerate to a given speed or to ascend a given elevation. So, if you do a lot of stop-and-go driving you can recapture a fraction of each _acceleration_ or if you live in a hilly area you can recapture a fraction of energy for every _decrease in elevation_. That's it. As for the argument that it saves wear and tear on brakes - sure it does, but I've gone 79k miles on the original set of pads in my truck and it has an automatic transmission, so very little or no engine braking.


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## mikep_95133 (May 20, 2009)

What I'd really like to know about Professor Jay, is how many miles has he put on an EV? We already have a NASA scientist around here that creates all kinds of theories based on what he reads in published papers. But he does not drive EV's. These guys are great in their fields. But when it comes to EV's, if they don't drive them, then their experience is just theoretical. Jay's group has a budget for test equipment and for developing the perfect operating scenario for lithium cells. What part of driving an EV matches that?? 

A friend of mine nailed it. "Theory and practice in theory are the same, but in practice they are not".

Mike



DIYguy said:


> Oh, sorry about that. I thought you did. My mistake.
> 
> I don't think it was anything about super matched cells. Current prismatics was the reference. I can ask him for clarification.
> If you folks want to list some specific questions maybe that would be good?


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## ElectriCar (Jun 15, 2008)

mikep_95133 said:


> JRP3,
> 
> I missed that memo  . Please point me to the data sheet stating that the capacity and impedance is 1% matched liked the cells NASA/JPL use, or perhaps the empirical test data showing that the capacity and impedance of the cells is within 1%. Voltage matching at 1% is not what the aerospace world uses, I hope we are not.
> 
> ...


Here's where I posted the datasheet from Calb on the batteries i ordered. Post #30.


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## ElectriCar (Jun 15, 2008)

gottdi said:


> What will happen?
> 
> Take 4 100ah Hi-Power Prismatic Cells. Block them together as a single 12 vlt battery.
> 
> ...


Man I woke up this morning thinking about doing something like this to get some answers for myself. Thanks for doing this. Ok it's time for an update too!


----------



## DIYguy (Sep 18, 2008)

And here is mine also....

http://www.diyelectriccar.com/forums/attachment.php?attachmentid=8884&d=1294512331


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## mikep_95133 (May 20, 2009)

Yes, I met those nice people too. They came through our area as well. Got pics and asked questions. They didn't use much regen according to the video from Jack. That was a choice that helped them. 

Just ask someone that owns one of the brands of regen enabled vehicles I've mentioned. As long as they actually track data you'll find the percentages match. 

Here is how my truck is set up. It has a manual transmission locked in 2nd gear. There is a floor shifter that selects different modes of operation that resembles an automatic transmission shifter. It only talks to the system's computer. First gear is set up with 100% regen. Second gear with 50% regen and drive at near 0% regen.

So I too can choose no regen for any particular part of a drive. It's primary use is on the highway. Letting off the throttle in order to coast is why the no regen setting is used. Since I can regen 300 amps into the pack, I don't want that huge amount of deceleration used inadvertently on the highway. So drive has nearly zero regen. The other 'gears' are for all other types of driving.

With regen, theory and fact are separated simply by those that own them and those that don't. If you own one, you have experienced and measured regen's effects. Belief or opinion in this arena is just wasted breath. Data for this is just an owner away. Find one of these individuals and ask them. One of Jack's video's mentions some professor that owns a RAV4 and was getting 26% as a regen value. Now that data point alone should close the debate 

Mike




DIYguy said:


> I keep thinking about the Moto-mundo couple..whatever it's called. They have been going round the world, a 41,000 km (or Mile?) trip and have been recording everything and have had many days on end to try and maximize their performance. The have an AC system also. They actually found better range by not using their regen at all. It may be possible that regen energy captured looks much better when not trying to maximize range. . after all, you are going through the energy conversion process again as opposed to coasting.
> I do like the idea of regen though, for braking alone I think it is worth it. One of the few things requiring maintenance on an EV (compared to ICE) in many cases is brake replacement.... regen, takes this to another level for sure.


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## mikep_95133 (May 20, 2009)

Of the two reports on CALB cells in that thread, capacities were matched at 1%, but impedance was varying 12% in one case and 17% in another. That's significant.

For me it brings another point home for my A123 module project. A123's are 1% in both impedance and capacity.

Mike




ElectriCar said:


> Here's where I posted the datasheet from Calb on the batteries i ordered. Post #30.


----------



## DavidDymaxion (Dec 1, 2008)

Rats, I blinked and missed my chance to put in my guesses! I'll do after the fact guesses. 

50 A * 12.6 V = 630 W. That is much higher than my motor, it takes about 25 A at about 12 V to spin it, 300 W.

I'd guess about 5 milliOhms internal resistance per cell.

50 A * 4 batteries * 5 milliOhms = 1.00 V drop. It looks like it was actually 13.13 V to 12.66 V (0.47 V drop), so your internal resistance is apparently about 1/2 what I guessed (which is really good for a 100 Ahr cell).

The discharge curve is pretty flat, so I wouldn't expect much Voltage drop removing only 8% of the capacity in 10 minutes. I'd guess it'll take about 100 to 120 minutes to suddenly drop Voltage at the lower knee, unless there's a weak cell or cells in the pack (there's a prediction!).


gottdi said:


> Thanks for taking a stab. Too bad the others did not. I figured they would not. Now it's too late.
> 
> Here is where we stand so far.
> 
> ...


----------



## DIYguy (Sep 18, 2008)

mikep_95133;221692I said:


> never use the word drift, ever, anywhere. That is someone elses notion. You might clarify that a bit. These are observations I've made, so they really can't be 'wrong'.


OK, you didn't use the word drift...but you used some other words which inferred the same thing. Any this is wrong according to Jay. So, maybe I didn't owe you an apology...??? 
What did you mean when you said this?


mikep_95133;221692I said:


> "Every pack of cells that are new behave in unison for a while. But the cells always diverge with time, no matter what chemistry is chosen."


and this.....


mikep_95133;221692I said:


> "Divergence starts on the first day. When it becomes a problem is related to the dod utilized, cell layout, and owner knowledge. The deeper the depth of discharge utilized, the faster the onset of divergence."


and this...


mikep_95133;221692I said:


> "Each charge/discharge cycle makes the imbalance worse."


I think you meant drift. I also think you are now taking a few stabs at Jays credibility because it differs with your beliefs. I also think you have overstated several other things like the efficiency of your truck with synthetics and toe, the reclaimed energy from regen, and all of these folks that you oversee with lithium batteries that keep loosing them because they don't use BMS's (a point you have never answered). Yup, it's just my opinion...  Not attacking you, just commenting on what you have written. So.... anyways... back to the discussion...


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## mikep_95133 (May 20, 2009)

Thanks, I'll pass.

Mike




DIYguy said:


> OK, you didn't use the word drift...but you used some other words which inferred the same thing. Any this is wrong according to Jay. So, maybe I didn't owe you an apology...???
> What did you mean when you said this?
> 
> 
> ...


----------



## tomofreno (Mar 3, 2009)

> That is the inevitable counterargument to running a BMS of some sort - it is not important that someone specifically said it. That said, please look at the title of the thread by the op: "To BMS or not to BMS".
> 
> Sorry, but I don't think you can argue you aren't using a BMS if you have an Ah counter; maybe if all you are doing is occasionally checking cell voltages with a DVM, but not if you can keep good track of Ah in and Ah out. Not to put too semantic a spin on the debate, however...


I don't think it is inevitable, and I don't think that most here consider a charge counter a bms. Of course if you frame the debate that way, then any type of monitoring is a bms, the alternative is no monitoring of any kind, and most if not all here would agree that some type of monitoring is better than none at all.

My impression is that people have been debating using a bms with cell level HVC/LVC, or one with that and shunt balancing, versus some type of monitoring such as with a dvm at cell level, some sub-pack module level, and/or using a charge counter. 



> ... as what this all really boils down to is if there is an economic benefit to be had from spending money on some form of _automated_ battery [management/monitoring] system. More specifically, whether such a BMS gets you more cycles or more range per charge or even some blend of the two. It's really as simple as that.


 That is the position JRP3 has steadfastly advocated for a long time. A lone voice in the bmsless wilderness...unless a charge counter is a bms.


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## Jan (Oct 5, 2009)

DIYguy said:


> ...So.... anyways... back to the discussion...




I missed it's nowadays very 2010 to believe in cell drift. Is that a concensus?


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## ElectriCar (Jun 15, 2008)

mikep_95133 said:


> Of the two reports on CALB cells in that thread, capacities were matched at 1%, but impedance was varying 12% in one case and 17% in another. That's significant.
> 
> For me it brings another point home for my A123 module project. A123's are 1% in both impedance and capacity.
> 
> Mike


At first glance I thought "wow, these range from .25-.31 mohm, that's a lot of variation" but then I whipped out the calculator (actually the computer calc) and when charging, the difference will vary from .00075-.00093V when charging at 30A. While that's not identical you're talking a fraction of a millivolt difference. When driving I will seldom go over 200A and even less over 300A, which could happen on hills. Most will be around 30-50A I'm thinking on flat ground. 

With the data, I should probably group cells in areas by IR with the higher IR in the center of the pack and lower IR on the edges. Though the pack will be well insulated it will sit outside my office in winter. I may also line the boxes with radiant barrier as well to retain heat in the winter, removing it in summer.


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> At first glance I thought "wow, these range from .25-.31 mohm, that's a lot of variation" but then I whipped out the calculator (actually the computer calc) and when charging, the difference will vary from .00075-.00093V when charging at 30A. While that's not identical you're talking a fraction of a millivolt difference. When driving I will seldom go over 200A and even less over 300A, which could happen on hills. Most will be around 30-50A I'm thinking on flat ground.


I think Jay mentioned that a close Ah capacity was the more important factor also.... 


ElectriCar said:


> With the data, I should probably group cells in areas by IR with the higher IR in the center of the pack and lower IR on the edges. Though the pack will be well insulated it will sit outside my office in winter. I may also line the boxes with radiant barrier as well to retain heat in the winter, removing it in summer.


Placement is definitely worth considering... more thought required here...(by me lol)

No heating planned?

Any one care to comment on what they think the Farnham heaters will take wrt DC voltage? (meant for 120VAC)


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## DIYguy (Sep 18, 2008)

Jan said:


> I missed it's nowadays very 2010 to believe in cell drift. Is that a concensus?


+ 1.  ( I had to add this.. was too short to post...lol)


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## ElectriCar (Jun 15, 2008)

DIYguy said:


> No heating planned? ...


 Normally only gets down to around 20-25F here, only occasionally going below that and warms up in 30-40's during the day. But I'll probably add some heat underneath. Have info at home about what someone else was using that worked well, some type soil heater with thermostat.


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## mikep_95133 (May 20, 2009)

It occurred to me that the BMS or no BMS debate is very old. As I look back, it never did matter about the chemistry. The debate has been around forever. I'm fairly sure that it started after folks started moving away from flooded cells. With floodies, the cells that reach 100% soc first just boil off water while the rest of the cells catch up. With the use of non flooded packs, there was nothing to boil off.

So this debate is fueled from many types of sources. That's why it's not resolvable now. Over time we will know more. I can tell you that the folks that bought the first gen of Thundersky cells, got burned in a big way. These current lots of cells have a much better life span. So they will take much longer to find out in real life, how long they can last. 

As for regen, I will keep that noise to a minimum since this is a BMS thread. But I have sent emails to good sources asking for url's that show the data many of us have already taken. As for my vehicle, the pack is being tested often. If my spot welder project or other factors don't cloud my path, I'll do a test drive with my truck, with and without regen, to show the data. I'll post the url's and my own data when possible. My notebook is MIA. So I can't quote the regen data for the 2 weeks I took it on my work commute. Some will still deny the data is not real.

For me, it's everyone's personal responsibility to educate themselves on EV's. Those that don't work at it, waste everyone's time. Those types stand out in any crowd. I go to EV meetings all the time for many years. Those that don't know, but want to know, do research to find out. Those are the types that I like to connect with, no matter what their level of experience. I generate data through R & D both professionally and as a hobby. 

As a hobby, EV's have the highest proportion of misinformation I've ever experienced. When I raced R/C heli's, BS was easily sorted out because bad technology or uninformed opinions, resulted in splattered heli's. That's a quick and harsh process. Competing in combat robotics was the same thing. Reality was separated from opinion many times. We all watched many scientists from NASA and all over, or teams with huge budgets, get their butts whipped by a folks without the education or money but with more combat experience. In EV's, especially with lithium and it's long cycle life, fact from fiction will take longer to sort out. 

For some people, they will never be satisfied. Data is always suspect. That's fine with me. I want to learn so I do. I go out and find the data. I travel to the sources because I really enjoy research, of nearly any type. When possible I generate my own data.

We should be comparing data, not opinions. The problem is not all of us are equipped or even willing to generate data. So sources are limited. Opinions are unlimited. More opinions don't make for a conclusion. A consensus is also not data. We should measure everything and assume nothing.

Mike


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## JRP3 (Mar 7, 2008)

Tesseract said:


> Sorry, but I don't think you can argue you aren't using a BMS if you have an Ah counter; maybe if all you are doing is occasionally checking cell voltages with a DVM, but not if you can keep good track of Ah in and Ah out. Not to put too semantic a spin on the debate, however...


Sorry but you're way off base on this one. BMS obviously refers to a cell level device, either measurement or active management, or both. Your logic could lead one to say a pack voltage meter is a BMS system. Strictly true since it is monitoring batteries, but it has no relevance to this thread or the BMS debate. No one is suggesting driving with nothing, though as mentioned I drove quite successfully for a while with nothing but pack voltage and a trip odometer. The Ah counter makes it easier.
Your basic premise that we don't really know what we are doing in the long term to our pack life is correct, but we do know the mechanisms of failure. Over charge and discharge, excessive C rates, and overheating. If you can avoid those conditions it doesn't matter how you do it. A cell level monitoring system increases the frequency of monitoring over occasional manual checks but if the manual checks occur frequently enough to find differences before they become problematic then the pack is in no greater danger. Obviously "if" is the big unknown.


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## Tesseract (Sep 27, 2008)

JRP3 said:


> Sorry but you're way off base on this one. BMS obviously refers to a cell level device, either measurement or active management, or both.


I really didn't want this to devolve into semantics (and said so) but you took it there, anyway.

Look, the quintessential metric of a cell is it's ability to store charge. A series pack of cells with nominally similar capacity can, indeed, be monitored quite accurate with just a charge counter.

A voltmeter doesn't cut it (or, at least, not until it is way too late).

Also, it is BATTERY monitoring/management, not CELL... BMS, to me, simply refers to a way to monitor a pack of cells. You think it means cell level monitoring, but I don't.

A charge counter/Ah meter/E meter whatever you want to call it is, in fact, a BMS. A pretty good one, too, IF you have a reliable means of resetting it every cycle. The only assumption it makes is that the lowest capacity cell be known, or at least be accurately estimated.

*unsubscribing*


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## jackbauer (Jan 12, 2008)

Ok. As far as i'm concerned the purpose of a bms is to report cell voltages , temps , soc etc. Some top balance cells some don't. Thats it in a nutshell. As far as i'm concerned that's a good thing. Nothing seems to be more of a contentious issue in the ev community. The internet is full of opinions from one extreme to the next. Quite frankly i couldn't care less for any of them. Either side. I just want to be able to safely monitor 48 series connected lifepo4 cells without a)burning my car b)spending money i'd rather spend on more cells. 

Some simple failure analysis would indicate that the first area of concern would be the big bundle of wire leading from the pack to the bms pcb. Forgetting about the composition of the circuits , i decided today to find out just how easy or difficult it would be to cause a wiring fire. I employed 8 ecitypower 8ah 38120 cells. Connected in parallel and charged to 3.60v by a 20v 10a psu. The wire was the cheapest crap i could find. Six core stranded alarm wire. I started with a piece 15ft long and connected two core to the 3.2v 64ah cell block. I bashed the hell out of it with a hammer. Nothing. A direct short yielded a whopping 2.5amps of current. I guess thats cable resistance eh? Took the cable back to 6ft. Higher current. Some heating. Down to 2ft. Typical bms length. Shorted. 7.5amps. Left on for 20 minutes. Hot? yes. No fire. 

Wired the pack 4s2p for nominal 12.8v and wired up the 6 cores. Hammered and bashed the cable until it parted. Nothing. Spent 15 minutes shorting it , cutting, bashing , more cutting , bashing and eventually got it to melt. For a second or two. Then it fused near the cells and went open circuit. 

Had each wire been fitted with a 1a or 2a fast blow fuse at the cell this would have been an even more boring test. Yes i know a few cells on a bench does not constitute a traction pack. I did a video on this. Only problem is its 30 minutes long. Very boring. I was even bored. I started singing. Never a good idea. I'll upload it if anyone is interested. Can't think why. 

Make of this what you will. I hope to continue testing the various failure points.


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## Overlander23 (Jun 15, 2009)

I've asked this before and haven't really gotten any responses. What happens if you run BMS-less, you monitor once a year, twice a year, <insert preferred duration here>, and a *cell goes bad due to simple product failure*?

By BMS-less I mean no monitoring or management short of manually using a DVM once in a while and being conservative with the pack usage?

I don't intend this as a "pointed" question. It's just, with all the "real-world" scenarios everyone's discussing this particular failure mode never comes up. There's a lot of talk about whether or not drift exists, what happens when you over/undercharge, etc... What about simple, random, cell failure?

I'm including battery monitoring in with the term BMS (see my previous list for my ideas of what a BMS can do).

I find posting on this subject to be very hard, because it seems impossible not sound like I'm taking a side when I don't think the question has clear sides. And I also feel the sidelines (the ones I don't believe in, ironically) keep moving. I've heard the anti-BMS crowd seem to move from, no BMS of any kind meaning no extra wiring at all (not even for monitoring), to maybe monitoring is OK (or absolutely the way to go) but no charge management (shunting).

Unfortunately, or fortunately, depending on your perspective, the pro-BMS crowd remains fairly consistent... though again, there are varying degrees of necessary implementation opinions. Some think that charge monitoring with automatic intervention is all that's necessary. Others believe you need the full monty with active charge management at the cell level.

This is what it all seems to boil down to. You either have faith in the system, or you monitor/manage it because it can't be trusted all the time. That is to say, you trust the data you see and believe it will work for you all the time (anti-BMS)... or you trust the data and don't believe it will work the same all the time (pro-BMS).

Ironically, if you look at this way the data is almost irrelevant. You either trust in the consistency and reliability of the chemistry. Or you don't. You either trust nothing will go wrong below the BMS level... or you trust nothing will go wrong at or above the BMS level.

Personally? I find it difficult to trust that everything will always be OK even if I never push the bounds of the chemistry, even if it were to perform consistently all the time. I would like a peak under the hood. I would like to know when reality steps in and does something *random*. 

I don't have any opinion on existing monitoring solutions except that I don't think any would work for my situation since I need an externally powered voltage monitoring scheme.

I also think that you can design a BMS that, if it were to randomly fail, would alert the user that it has failed while not taking drastic action on a cell. Why? Because every consumer product on the market that uses lithium chemistry (cell phones, ipods, laptops, etc) has a monitoring system that works.

It's really about information.


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## GerhardRP (Nov 17, 2009)

Is it still true that the PakTrakr draws power from the first monitored battery, leading to an uneven drain? Do any voltage reporting systems draw power uniformly, or from the accessories battery? [I know the MiniBMS does.]
Gerhard


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## dimitri (May 16, 2008)

GerhardRP said:


> Is it still true that the PakTrakr draws power from the first monitored battery, leading to an uneven drain? Do any voltage reporting systems draw power uniformly, or from the accessories battery? [I know the MiniBMS does.]
> Gerhard


Yes, Paktrakr causes severe pack imbalance over couple of months period. I verified it, measured it, proved it. One of the main reasons my Paktrakr is in a trash bin (rendered useless by EMI being the 2nd reason). The only correction to your assumption is that Lithium version of Paktrakr draws power from first 3 cells in a group of 8, where Lead Acid version draws from 1st battery in a group of 6.


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## ElectriCar (Jun 15, 2008)

Tesseract said:


> I really didn't want this to devolve into semantics (and said so) but you took it there, anyway.
> 
> Look, the quintessential metric of a cell is it's ability to store charge. A series pack of cells with nominally similar capacity can, indeed, be monitored quite accurate with just a charge counter.
> 
> ...


Having a means to split the pack and compare one half to the other is a way around this cell level monitoring IMO as far as finding a cell issue developing. While you don't have cell level details, you have a visual comparison of the two halves of a pack. 

Think of it this way. You start with a new pack. Everyone here pretty much is in agreement I believe that with a new pack everything is pretty much the same. So you monitor each half of the pack voltage and contrast the two. All cells being virtually equal, the two halves voltage is virtually equal until you have a cell issue. 

Whether you're stopped or accelerating the display should stay in balance. I know some will say "well when you lose a cell yea it will be apparent but too late". Can't argue with that. However, what causes cells to go bad? 

If I only charge my 3.6V rated Calb's to 3.5 or whatever yields a safe level such that no cell voltage spikes, I'll not overcharge them until something changes over time, which I should catch with periodic DVM monitoring I think... That's how some are charging. 

I'll still monitor them with a DVM when charging occasionally after initially doing it a lot to get a better understanding of their qualities. Also I'll limit the discharge to a safe level with a warning when it's getting low and another limit to kill the controller so as to not allow continued driving and kill a cell.

I may toast a cell along the way but I'm ok with that. So be it if that's the price of piece of mind.


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## Qer (May 7, 2008)

Overlander23 said:


> I've asked this before and haven't really gotten any responses. What happens if you run BMS-less, you monitor once a year, twice a year, <insert preferred duration here>, and a *cell goes bad due to simple product failure*?


If Mikep is right and the internal resistance goes up when a Lithium cell starts to die (which doesn't sound unreasonable to me, I've seen it happen with other kinds of batteries) then forcing hundreds of Amps through that cell will definitely turn it into a fire hazard. A system that either detect the under voltage or the raising temperature will be able to either alert the driver or shut off the power in time to hopefully avoid a fire.

A BMS measuring voltage could even react in time to make it possible to avoid being stranded beside the road. Unless, of course, the cell instantly goes from 100% ok to completely dead...



Overlander23 said:


> I also think that you can design a BMS that, if it were to randomly fail, would alert the user that it has failed while not taking drastic action on a cell. Why? Because every consumer product on the market that uses lithium chemistry (cell phones, ipods, laptops, etc) has a monitoring system that works.


Of course you can. Most micro controllers do, for example, have a watch dog that can be used for resetting the CPU in case there's a fatal software bug and all micro controllers I've encountered boot with all the IO-pins in a known state (usually inputs). That means that properly designed a dead BMS-module will fail in a state that can be detected.

Now, there's nothing that can be 100% certain, but you should at least be able to reach a very high 99.99...% probability that a failure will be benigm if you know what you're doing and don't compromise.


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> Having a means to split the pack and compare one half to the other is a way around this cell level monitoring IMO as far as finding a cell issue developing. While you don't have cell level details, you have a visual comparison of the two halves of a pack.
> 
> Think of it this way. You start with a new pack. Everyone here pretty much is in agreement I believe that with a new pack everything is pretty much the same. So you monitor each half of the pack voltage and contrast the two. All cells being virtually equal, the two halves voltage is virtually equal until you have a cell issue.
> 
> ...


Hey Electricar,

If you are referring tot he Evision meter... ya, and it takes it's power from the entire pack, which I think is another good idea.


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> Normally only gets down to around 20-25F here, only occasionally going below that and warms up in 30-40's during the day. But I'll probably add some heat underneath. Have info at home about what someone else was using that worked well, some type soil heater with thermostat.


I had the soil heaters in mind also... however, after some more thinking and searching. I believe the Farnham heaters will spread the heat more evenly and they are actually pretty inexpensive. I found some others similar also for RV water tank heating...adheasive with foam cover.

I still like the idea of (from the bottom up);
- First layer, 1/2" SM (dense foam)
- Farnham heaters or equivalent (even better if off of pack voltage, even better if off of pack voltage and 120VAC)
- Aluminum sheet metal ( to evenly spread heat)
- grating of some kind to allow air flow (for active cooling)
- feed space with grating with forced air, (blank off other sides) thermo controlled for cooling. Air to come up through spaces in clamped prismatic cells. (ribs)
- cover box in winter, uncover or vent top in summer.

Edit...oh ya sorry, you may not need heating with your ambient temps....


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## JRP3 (Mar 7, 2008)

Has anyone heard of a SE/CALB cell failing on it's own out of nowhere? I know some have been killed by a faulty BMS, I have not heard of anyone getting a bad one. Not saying it hasn't happened, just that I'm not aware of it.


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## DIYguy (Sep 18, 2008)

no, haven't heard that. I heard of a few TS that went bus-bar...


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## JRP3 (Mar 7, 2008)

Tesseract said:


> I really didn't want this to devolve into semantics (and said so) but you took it there, anyway.


You started it 



> A voltmeter doesn't cut it (or, at least, not until it is way too late).


I've done it, repeatedly. 


> *unsubscribing*


Sheesh T, thought it would take more than that to drive you away. I didn't even start calling you names.


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## Overlander23 (Jun 15, 2009)

JRP3 said:


> Has anyone heard of a SE/CALB cell failing on it's own out of nowhere? I know some have been killed by a faulty BMS, I have not heard of anyone getting a bad one. Not saying it hasn't happened, just that I'm not aware of it.


I think my point is more that in the real world where random things happen, one method allows you to know if something has happened while the other doesn't.

I, of course, think everyone's particular situation is different and requires different solutions. My own is that my battery boxes are sealed and located under the vehicle. I can't monitor them just by manually using a DVM. Yet I still don't have a solution.

Does your situation warrant the use of a BMS? Probably not... since it's been working for you and have the ability to manually monitor your cells. You're also doing the most effective form of management, as far as I'm concerned, which is a form of de-rating which gives you wiggle room.

Ask anyone, though, would they use a BMS if it was reliable and cost 10 cents per cell to implement. Who would say no?

Cut through all the arguments and it comes down to reliability and cost. 

I've heard a lot of people call for the testing of cell behavior. But no one seems to want to test the reliability of the BMS systems, rather there's an assumption out there that they will all fail... all the time... horribly.... with fire... and brimstone. And there's nothing you can do about it. And while fire is usually cool, not so much in this case.


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## Tesseract (Sep 27, 2008)

ElectriCar said:


> Having a means to split the pack and compare one half to the other is a way around this cell level monitoring IMO as far as finding a cell issue developing. While you don't have cell level details, you have a visual comparison of the two halves of a pack...


Yep - this is another good example of a BMS that doesn't work at the cell level but provides reasonably useful info about the pack's balance. It does require that the cells in each half experience reasonably similar thermal environments, however.




JRP3 said:


> I've done it, repeatedly.


Surely you aren't arguing that measuring the resting voltage of a cell after a drive or a charge tells you anything useful? Correction: it tells you something useful, but not BEFORE the damage is done.

Once again, you can do this if you like, but you need to be extra careful to stay well inside the middle of the pack's capacity (i.e. - 20% to 80%, max). 

As Dimitri correctly noted, however, it is very difficult to know when you are approaching either end without an Ah counter. The SoC function inside the Soliton1 proved that to us - it works reasonably well with lead-acid packs, even NiCd, but not with LFP.



JRP3 said:


> Sheesh T, thought it would take more than that to drive you away. I didn't even start calling you names.


It's mostly because I got tired of there being 20 freaking e-mails in my mailbox with updates every time I turned around. However, it's also because some participants in this thread have failed to be civil and once a thread goes down the tubes I tend to lose interest in it real fast. Same with Ron's twin motor thread (now that I think about it, same with pretty much all of Ron's threads).


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## JRP3 (Mar 7, 2008)

I'm less concerned with fire and brimstone than with a faulty or damaged BMS module killing some cells. Certainly if a BMS were cheap enough and could in no way harm a cell if it failed then I'd use it for monitoring, probably not management though.


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## JRP3 (Mar 7, 2008)

Tesseract said:


> Surely you aren't arguing that measuring the resting voltage of a cell after a drive or a charge tells you anything useful? Correction: it tells you something useful, but not BEFORE the damage is done.


My 36 cell pack sits at about 120V after a charge, normal use takes it to 115 or so under load, springs back to around 118 off throttle after some use and stays in that range for most of the SOC. When I see 116 off throttle I know I'm getting closer to the bottom and should be nearing a charger, 114 means I need to be within a couple miles or so, 108 means I better see the plug up ahead or be ready to pull over. Before that actually happens voltage sag under load will trigger the controller to cut back current and put me into limp home mode, which I did once. Since my pack was bottom balanced no damage was done and the cells were at 2.45 and climbing when I got out and checked them all, that's 88V for the pack. So I'm dealing with about a 30V spread. It's not ideal but it is workable when used with your trip odometer if you know your pack mileage and don't push it. I pushed it because I'm that kind of guy. Sometimes you just have to do something to see what happens.


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## Jimdear2 (Oct 12, 2008)

JRP3 said:


> I'm less concerned with fire and brimstone than with a faulty or damaged BMS module killing some cells. Certainly if a BMS were cheap enough and could in no way harm a cell if it failed then I'd use it for monitoring, probably not management though.


JRP3,

You mention Module failure, modules can certainly be made that are reliable enough. The charging modules we are going to use for charging on our battery maintaince/monitoring system have MTBF of around 5 million hours. The unit cost on these things is about $5.00. I know they were built for another purpose and are now surplus. But they are also a 10 year old design. New equivalents are probably pretty inexpensive.

I don't know what the MTBF is for the Cell Logs, the monitoring half of the system. But if they wern't pretty robust I think we would all hear about it pretty fast. 

I'll bet a dedicated generic charger/monitoring module and a centeral diagnostic, power supply system for the charger could be built by the battery OEMs for much less then the total cost of even the most basic BMS and lithium ready bulk charger. Remember the quantities of batteries they are building. The modules would have only two variables, charge voltage and amprage.

The system, properly designed would not allow the battery to be over charged above 95% because it phisically could not, since it would only put out a set voltage matched for that type cell. If each module had a unique ID then the central unit woud monitor condition balance of each battery on a CAN type buss and warn ofout of balance and LVC events. It would work like the familiar OBD and OBD II and flash warnings. The codes could be used to diagnose problems. Since the chargers can only reach a set voltage, each full charge would be a battery balancing event.

Now I've opened up a whole new set of things to discuss. 

I've always believed it was the lithium battery OEMs responsibility to provide some level of protection for these VERY expensive and fairly fragile products. An agressive mfg. might a real selling advantige for something like this.

Would you pay a few dollars more for your cells, if you knew you would get a matched module that charged it correctly, monitored it and you also got a central data unit that was also the power supply for your batteries.

Let the battery OEM know if you would be pleased with something like this. I like it enough I'm building my own.

Jim


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## JRP3 (Mar 7, 2008)

Jimdear2 said:


> I don't know what the MTBF is for the Cell Logs, the monitoring half of the system. But if they wern't pretty robust I think we would all hear about it pretty fast.


I had one fail within a few days of getting it. The replacement was fine, but I know others had similar issues. Maybe just problems with early production units.
As for CAN bus control, Jack Rickard claims that faulty CAN signals from a BMS overrode the charger programming and caused the fire on the Norwegian ferry. I don't know if this is true or not as it is his speculation.


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## tomofreno (Mar 3, 2009)

> The system, properly designed would not allow the battery to be over charged above 95% because it phisically could not, since it would only put out a set voltage matched for that type cell.


 The SOC of the cell will then vary with cell temperature, since internal resistance and cell voltage while charging will vary with temp. If you imagine the charging curve, voltage versus Ah, I think cell temperature moves that curve up and down the vertical (voltage) axis since that is the effect of changing Rs, so at lower temperature you will charge to lower SOC.


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## EVfun (Mar 14, 2010)

JRP3 said:


> Sorry but you're way off base on this one. BMS obviously refers to a cell level device, either measurement or active management, or both. [snip]


So using a Lee Hart battery bridge (comparing the voltage of the top half and bottom half of a pack) wouldn't be considered a BMS? It would be a lot easier to discuss "BMS or not to BMS" if we are talking about the same thing.


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## EVfun (Mar 14, 2010)

tomofreno said:


> "back from about 3.36-3.38" - so are you saying at a few hours or more rest after full charge your TS cells are at 3.36-3.38V, and rest voltage on the flat part of the discharge curve ranges from 3.32 to 3.26V? If so, that is basically the same as my CALB cells.


Basically. A couple hours after the charge is complete they are in the 3.39-3.42 volt range. The next day they are back to 3.36-3.38 volts. Once they fall back to 3.32 volts from a little use they will sit there, even if left a week.


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## JRP3 (Mar 7, 2008)

OK, I'll concede the point that BMS does not have to mean cell level, though I think it would be useful if we used the term to at least mean sub pack level monitoring/managing.


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## mikep_95133 (May 20, 2009)

Dimitri,

I've heard that noise issue from Paktrakr owners a few times. It really smells of EMI. Did the EMI damage your units or did you just remove them? Do you have an isolated or portable scope Dimitri? It's not too much work to make an E field and an EMI probe from coax to hunt down the EMI. Simple r-c across the vcc on each board is often a partial solution. An Xprize team here in town had that exact issue and solved it exactly that way.

I'd be willing to sniff them for EMI on my truck if you don't want to.

Here is the article on how to make the EMI probes. I've made a bunch of them. You won't believe what you'll learn from them.

http://electronicdesign.com/article...emade-sensors-solve-tough-emi-problems74.aspx

Mike



dimitri said:


> Yes, Paktrakr causes severe pack imbalance over couple of months period. I verified it, measured it, proved it. One of the main reasons my Paktrakr is in a trash bin (rendered useless by EMI being the 2nd reason). The only correction to your assumption is that Lithium version of Paktrakr draws power from first 3 cells in a group of 8, where Lead Acid version draws from 1st battery in a group of 6.


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## mikep_95133 (May 20, 2009)

Overlander23 said:


> I've asked this before and haven't really gotten any responses. What happens if you run BMS-less, you monitor once a year, twice a year, <insert preferred duration here>, and a *cell goes bad due to simple product failure*?


You can't tell if a single goes bad by just watching a voltmeter as you drive. It's too small of a portion of the total. The voltage swing in the pack from loaded to unloaded is enough to swallow the voltage of one cell easily. 




> "...And I also feel the sidelines (the ones I don't believe in, ironically) keep moving...."


Yep. That does happen.



> Unfortunately, or fortunately, depending on your perspective, the pro-BMS crowd remains fairly consistent... though again, there are varying degrees of necessary implementation opinions. Some think that charge monitoring with automatic intervention is all that's necessary. Others believe you need the full monty with active charge management at the cell level.


The pros make each BMS module control the charger and motor control to help avoid failures. Makes ya wonder why...



> Ironically, if you look at this way the data is almost irrelevant. You either trust in the consistency and reliability of the chemistry. Or you don't. You either trust nothing will go wrong below the BMS level... or you trust nothing will go wrong at or above the BMS level. Personally? I find it difficult to trust that everything will always be OK even if I never push the bounds of the chemistry, even if it were to perform consistently all the time. I would like a peak under the hood. I would like to know when reality steps in and does something *random*.


"Trust but verify" works for me.



> I don't have any opinion on existing monitoring solutions except that I don't think any would work for my situation since I need an externally powered voltage monitoring scheme.


You could always buy a Vicor, dc-dc that runs off of your pack and supplies 5v or 12v to your BMS. They are isolated power modules.



> I also think that you can design a BMS that, if it were to randomly fail, would alert the user that it has failed while not taking drastic action on a cell. Why? Because every consumer product on the market that uses lithium chemistry (cell phones, ipods, laptops, etc) has a monitoring system that works.


Your point here is good, but the difference is that you don't find consumer electronics pulling .5c, 1c, 2c, etc, values from the battery. EV's are the premiere way to test batteries.

Mike


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## EVfun (Mar 14, 2010)

gottdi said:


> I'd say don't concede because the premiss is that a BMS is both a monitor system and cell level manager to keep the cells in balance according to preset voltage levels which include a HVC and LVC to shut off the charger in case of a malfunction to protect the pack and any single cell.


By that definition the Toyota Prius doesn't have a BMS. It doesn't act on the cell level; it measures short series strings of cells. Still, it limits power to the drive system, limits regen to prevent overcharging and manages equalization when it senses the need. It displays SOC on request. I'd call that a pretty active BMS (even though it doesn't have any shunts.)

I don't think this is a matter of conceding. It is a matter of talking about the same thing. It is real hard to have a rational discussion if we are writing about different things while calling them the same name. 

One example is that you seem to feel that BMS means battery *management* system. I always thought it included battery *monitoring* systems because it was up to the user to hook it to something. If the user fails to do that it doesn't effect the hardware installed. My cell regs where hooked to nothing but my eyes for a while. I don't feel cell level is required either, but feel it must be broken down to something smaller than the whole pack level (in other words, an amp hour counter by itself is NOT a BMS IMHO, no matter if it controls the charger and controller or not.) The Lee Hart Battery Bridge is the simplest thing that I would consider a Battery Monitoring System because it looks within the pack to provide results. Feel free to disagree, but we should figure out what we are discussing. Perhaps this is partly at the reason for overheated BMS debates.


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## mikep_95133 (May 20, 2009)

I'd like to discuss BMS and cell failure modes. These are my experiences and observations over the years. It's long so I won't be offended if you don't read it. Someone will benefit from it. I know I sure have.

IDLE: Pro BMS's usually bypass .3-.4 amps for those that use shunting and control the charger/motorcontroller. If the BMS module failed to a shorted condition, it would pull .4 amps max. On a 100ah cell that's 250 hours or 10.41 days until the cell is dead from fully charged. Some where in that 10 days you would think an owner would notice the led is not lit on that module, or the lcd is showing very low voltage for that cell. SOC is what determines how long the cell survives. Lower SOC, fewer days.

DRIVING: Most DC conversions pull 100-600 amps during driving. Is a .4 amp load on one cell going to even be noticed during a week of driving? Nope.

CHARGING: If your vehicle charges at 5, 10, 20, 50 amps, is .4 amps going to be noticed? When the pack is fully recharged, one cell might be at 2 volts instead of 3.6v or 4.0v. Will that be detected on the voltmeter? It can't be detected. The charger only knows that it has to hit it's target. It does not care what tries to get in it's way. If your 50 cell pack charges to 200v, the charger will push the pack to 200v. It has no way of knowing that one cell is dying. So it hits the 200v just as it's suppose to. That means all the rest of the pack is charged a tiny bit more than normal. One cell in this scenario will not overcharge the rest of the pack. But as more cells fail, the rest of the pack has the potential to be overcharged if the cells fail in a low impedance state, or the pack gets very undercharged when they fail in a higher impedance state. 

This previous scenario in my experience, happens when a cell is freshly damaged. As the damaged cell keeps moving current, it starts to become weaker. Higher and higher impedance occurs. As impedance goes up, so does temperature. If a new cell is at .030 ohms with a load of 300 amps, it's dissipating .030 x 300 = 9 watts. When the cell gets to .300 ohms at 300 amps we are talking 90 watts. When the cell gets to 30 ohms at 300 amps, we arrive at 9000 watts of heat generation.

A dead or dying cell can cause a fire without a BMS even being attached with enough time and heat. As they fail they just become a better heat source.

Even worse, the charger will not know of the bad cell. It just keeps pushing the pack to it's goal of 200v. The charger can get to 200v, and the pack will only be at 66% soc. The bad cell, acting as a resistor, or a voltage drop, prevents the rest of the pack from fully charging, even though the pack hit 200v. The current didn't flow at a high enough value, or long enough to fully charge the pack.

When I say cell, it could very well be 5 cells or 10 cells in a 50, 100, or 250 cell pack.

This has happened to me something like 10 times over the life of the 250 cell nicad pack. This scenario I'm describing is part of the end of life phenomenon. All chemistry's do it. My pack is exhibiting it's end of life. The most recent last week was 2 shorted cells and one that was low on water. The pack would only go 15-20 miles before reaching the LVC for the control system. After I found the 2 shorted cells, and watered the 3rd one, I suddenly had a 30 mile range. Just 3 cells made my truck far less useful.

Sometimes the cells get so hot, they melt together. When I'm doing the human BMS thing with a DVM, it's easy to find a shorted cell. It's near zero volts without a load. Often as I try to pull the cell out, it will pull up another one with it. The tough outer case is melted to the unlucky cell next to it. Both are trashed. This latest case is in my blog.

These are not your garden variety cells. These are from the military. They are used in all turbine aircraft. They are tested to over 100,000 feet, and sub zero temps, per the military spec. The cell's 10mm studs are nickel plated copper as are all of the nuts and bus bars per military spec. These cells are not available to the public, except through rare gov't auctions. I was lucky and quick.

This is one of several times I've watched the end of life phenomenon of a pack. Several of my own and many other packs of other owners. The pattern repeats perfectly regardless of the chemistry. 

You can tell yourself that it won't happen to you because you have lithium. I am watching it with lithium as we speak. I hope to see one of the owners this weekend to help him with his lithium powered vehicle. The other owner I have not seen in a while. He had failing cells and asked if I would capacity test them for him. These two guys I see and have access to fairly easily. Others cycle through over the months. I will start taking notes and asking them if I can document their experience. 

Mike

PS Seriously, if you don't believe any of this, then spare me your opinion. I don't collect opinions, I generate and collect data. If you want to know more as the data arrives on the lithium pack owners I know, I'll be happy to share it. Just let me know. For the benefit of everyone, please post publicly your experiences. Some of the PM's I've gotten are so valuable to everyone that it's a shame they get wasted just being sent to me. Some of you had cell failures. How did you find them? How were you notified?

If you have real failure experience on any chemistry, counter to what you've read here, I'd love to hear it! Just spewing your opinion, won't get you a response.


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## JRP3 (Mar 7, 2008)

gottdi said:


> I'd say don't concede because the premiss is that a BMS is both a monitor system and cell level manager to keep the cells in balance according to preset voltage levels which include a HVC and LVC to shut off the charger in case of a malfunction to protect the pack and any single cell.


You could still use a split pack monitoring system to actively manage charge and discharge if either half of the pack is out of spec, so it still fits the strict "management" definition. If your pack is divisible by four you could even do a quad split system to increase the "resolution" without going to the cell level. I'm not against using "BMS" to mean both monitor and/or management as long as the meaning is specified. Even management has different forms, HVC/LVC signalling is one, shunt balancing is another, and charge shuttling another.
Terms could be:
Split pack monitor/management
Cell level monitor
Cell level HVC/LVC management
Cell level shunt management or balance
Cell level shuttle management or balance.


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## mikep_95133 (May 20, 2009)

gottdi said:


> Granted you can't see single cells but you can monitor pack health. I sorta get that you guys think cells just crap out all of a sudden.
> 
> So your saying Lithium cells just crap out all of a sudden!


Pete,

If you are pulling 300 amps through a cell that is reversed, it's no longer contributing capacity to the pack. It's just a resistor, moving current. Reversing lithium will wreck it so badly it actually becomes a hazard to the remaining good cells. 

The good news about lithium is it is so power/energy dense. The bad news about lithium is it is so power/energy dense. 

Mike


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## JRP3 (Mar 7, 2008)

mikep_95133 said:


> IDLE: Pro BMS's usually bypass .3-.4 amps for those that use shunting and control the charger/motorcontroller. If the BMS module failed to a shorted condition, it would pull .4 amps max. On a 100ah cell that's 250 hours or 10.41 days until the cell is dead from fully charged. Some where in that 10 days you would think an owner would notice the led is not lit on that module, or the lcd is showing very low voltage for that cell. SOC is what determines how long the cell survives. Lower SOC, fewer days.


So a 50% SOC pack could have dead cells after 5 days, that could be missed.




> I will start taking notes and asking them if I can document their experience.


That would be most useful, especially noting the brand of cells.


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## ElectriCar (Jun 15, 2008)

OK Mike, open your mind for this one and please give your unbiased commentary. I know you've read the comments about split pack monitoring but you've not had a response. It would address the failures in your above post. 

Assuming a 50% pack split, and you can split an odd number of cells with a simple voltage divider across the last cell and center tap it there. The display is a dot bar unit of say 15 segments. *Left side of the display is first half of your pack, right side is the second half.* Assume this monitoring device has a resolution of 1V per led. With all new cells the center led is lit in your garage or while driving.

Here's two scenarios: 

1. As the pack ages you have a cell develop higher ir which causes the voltage drop to increase, the display will show that. As the imbalance over time grows, the imbalance starts peaking at 1V, you begin to see the 1st led flicker to the right side, then jump back to center. Eventually it worsens and that led begins to stay on more and more while driving. As you increase current, voltage drop increases across the cell and once it hits 2 volts, the led display moves to the second led. 3V and the third led illuminates. When you stop, the pack balance is restored and the center led it lit again. You know the cell problem is located in the second half of your pack. Now you know where to look for it. Once it's bad enough, a hand held IR sensor such as this will likely point it out to you. Same thing with a bad connection.

2. For whatever reason, you just lose a cell. It shorts out. Immediately you have a 3.2V imbalance in the pack on one side. When you get in the car to drive the display has the 3rd led lit on one side. Immediately you know you have a problem Houston, before you ever hit the throttle. Or if you're driving along at 35Amps and suddenly the display jumps 3 places to the right, same thing and you know where to find it.

Again, much more simple and you don't need a wiring harness to implement it. No current running through it so if you leave it a month to go to Tahiti when you win the lottery, when you get back your pack is still charged and no lost cells due to a shorted BMS module.

If you've been following my posts here and there, you know I've figured on a separate HV/LV cutout and a low fuel warning to supplement this, along with an Ah counter and SOC meter.

I know it's hard for you to think outside the box as you're an old head like me and are set in your ways a bit too!


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## spdas (Nov 28, 2009)

mikep_95133 said:


> I'd like to discuss BMS and cell failure modes. These are my experiences and observations over the years. It's long so I won't be offended if you don't read it. Someone will benefit from it. I know I sure have.
> 
> DELETED DUPLICATING MIKE'S QUOTE ABOVE ^^^^^
> 
> If you have real failure experience on any chemistry, counter to what you've read here, I'd love to hear it! Just spewing your opinion, won't get you a response.


Great post Mike, thanks. 

 I will be getting 40 used/tested assorted TS 160ah and 200ah cells in 10 days so this noobie needs all the sound advice he can get. 
I plan to charge them all up to 3.55 or 3.6 and using the CBA that was suggested to use to find the strong cell from the wimps, I will sort/evaluate them. 
I ordered 5 cellog8's to monitor each cell on charge and discharge, (yes I know you guys have been using them for over a year, some good some bad stories). 
This will be a higher ah pack than what i need for my Toy 2,100 pound Yaris, but I will treat the pack gentle and use them at 30% to 85% SOC. So time will tell and I will be able to draw my own conclusion when I decide to go for the $12k of new Lithium later on.
Thanks again to all you pioneer contributors and especially to Dave K and several others whom have given me advice in my quest.

Francis


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## mikep_95133 (May 20, 2009)

I've seen so many ways to 'BMS' a pack that didn't work, I've lost track. It's not that I'm closed minded, it's the rate of failure of cells that has made me understand that there are zero shortcuts. Pay now for the extra cost of a BMS or pay later when you only get some seriously reduced percentage of your packs rated life. 

If I understand this 1/2 pack scenario, it came from Lee Hart. I really like the work he has done for so many years. With you adding LVC and HVC that makes it more viable. But I don't see every cell being covered. 

Depending on the gain for the bar graph, every time you accelerate, the bar graph could move. As cell groups are at different temps, you find that the bar graph moves. Great concept. High voltage precautions should be taken. The bar graph has to fed from an opto coupler or equivalent to isolate it from the pack. Pack voltage should never, ever enter the passenger compartment.

Since this does not cover each cell, it won't qualify in my mind as a BMS. It's another cool toy. If there were any shortcuts to watching over a pack full of cells, the pros would have figured it out by now. 

What we should be doing is homework on the various monitoring systems around the world and work on a group price. That way those that are paranoid about shunting could still have monitoring to guide them. Although I know a guy that ignored his monitor to the death of a few cells. Excuses galore. That's why the BMS needs to be tied to the motor controller and the charger.

Peter Perkins in the UK designs his own BMS hardware. Great stuff. Tons of people have his BMS. Get's hammered with EMI. I have his hardware. But by just taking out the bypass resistor you get a monitoring only system. So if not him, maybe we find someone that can design a monitor that we either build from a kit, or buy complete. Could very well be the cheapest route is to DIY your own BMS. It could drive a touch screen display that always shows the highest and lowest cell. That way there is very little for the driver to do. All of this with the understanding that we duplicate UL/CSA, thermal, electrical, and mechanical tests so that it's reliable.

Mike




ElectriCar said:


> OK Mike, open your mind for this one and please give your unbiased commentary. I know you've read the comments about split pack monitoring but you've not had a response. It would address the failures in your above post.
> 
> Assuming a 50% pack split, and you can split an odd number of cells with a simple voltage divider across the last cell and center tap it there. The display is a dot bar unit of say 15 segments. *Left side of the display is first half of your pack, right side is the second half.* Assume this monitoring device has a resolution of 1V per led. With all new cells the center led is lit in your garage or while driving.
> 
> ...


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## EVfun (Mar 14, 2010)

ElectriCar said:


> Assuming a 50% pack split, and you can split an odd number of cells with a simple voltage divider across the last cell and center tap it there. The display is a dot bar unit of say 15 segments. *Left side of the display is first half of your pack, right side is the second half.* Assume this monitoring device has a resolution of 1V per led. With all new cells the center led is lit in your garage or while driving.


Do you have an example circuit in mind? I've used the simple design by Lee Hart using 3 LEDs and I've considered versions where the red LEDs where replaced with the LEDs inside a couple of optical isolators. This is also the kind of circuit that could be suited to some type of comparator. The thing is, each of these simple designs places a load on the pack similar to the cell level BMS systems available. 

I also have a serious concern with "split an odd number of cells with a simple voltage divider across the last cell and center tap it there." The resistor divider across this cell will be a load on that cell not present on the other cells. Even one additional milliamp is over 8 amp hours per year for a fixed load. Also, if you place a voltage divider across the center cell it isn't being monitored by the system. The answer with Lee's LED design was to use slightly different resistors on either side of the bridge. With 13 Optimas that might be something like 7000 ohms on one side and 6000 ohms on the other side. You would "center tap" the pack 7 cells down from end with the 7000 ohm resistor.


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## mikep_95133 (May 20, 2009)

Wow, the first I've ever heard of a used lithium pack. You have the right idea about monitoring each cell. Not sure if you know the history of the cells or even if the history is credible. Since the cells each have serial numbers, then make a spreadsheet of the pack and keep it updated. 

30-85% is a commendable goal. It can really help cell life. But the real question is how will you know what the soc is? Using voltage alone is insufficient. Cells go up in voltage as the get warm, down when cold. Not good to try and shoot at a moving target.

If your cell monitors are ok, you should be fine. In addition, something in your vehicle needs to count the wh's (watt-hours) in and out. There is a very good reason not to use ah counting on an EV. As the pack voltage goes down, the amps have to go up to hold the same speed/acceleration. So the ah's/mile will be better with a fully charged pack, and worse with one at 25% soc. Every time your pack sags, the ah's become inaccurate. This is why wh's are used. They take into account pack voltage and the ah's at the same time. If you want to compare efficiency of your vehicle to all of the data out there, you need wh's.

The only time using ah's are ok is with constant current charge/discharge. While driving around, amps and volts are all over the place in addition to the volts sagging over time. So, make sure you have a gauge that can count wh's.

Mike



spdas said:


> Great post Mike, thanks.
> 
> I will be getting 40 used/tested assorted TS 160ah and 200ah cells in 10 days so this noobie needs all the sound advice he can get.
> I plan to charge them all up to 3.55 or 3.6 and using the CBA that was suggested to use to find the strong cell from the wimps, I will sort/evaluate them.
> ...


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## ElectriCar (Jun 15, 2008)

EVfun said:


> Do you have an example circuit in mind? I've used the simple design by Lee Hart using 3 LEDs and I've considered versions where the red LEDs where replaced with the LEDs inside a couple of optical isolators. This is also the kind of circuit that could be suited to some type of comparator. The thing is, each of these simple designs places a load on the pack similar to the cell level BMS systems available.
> 
> I also have a serious concern with "split an odd number of cells with a simple voltage divider across the last cell and center tap it there." The resistor divider across this cell will be a load on that cell not present on the other cells. Even one additional milliamp is over 8 amp hours per year for a fixed load. Also, if you place a voltage divider across the center cell it isn't being monitored by the system. The answer with Lee's LED design was to use slightly different resistors on either side of the bridge. With 13 Optimas that might be something like 7000 ohms on one side and 6000 ohms on the other side. You would "center tap" the pack 7 cells down from end with the 7000 ohm resistor.


No I've thought about building one but haven't found appropriate circuits. I'm likely to purchase the EVision. It has about 22 leds on the bar display. It's built in and does a ton of other things including allowing you to export data to a PC, Ah counter, will drive your fuel gauge for an SOC meter, not sure about wh as Mike mentioned. It just displays a multitude of things with the changing of a switch.

re the splitting of a cell, at 3.2V, two 1 Megohm resistors in series will be nothing of a load on a cell. 3.2V/2,000,000ohm= your current draw, 1.6 micro amps. Nothing!


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## DavidDymaxion (Dec 1, 2008)

I had predicted 100 to 120 minutes for 50 amps.

The Voltage jumped up at the end? Did your cells stay cool? I see a Voltage rise effect when the cells start to get hot.

Many thanks for testing and posting! I'll be very interested to see if the 2nd cell Voltage and overall capacity go up or not with some cycles.


gottdi said:


> Discharge test done. 4 Hi-Power 100 AH Prismatic Cells.
> 
> 2 hours 10 minutes run time at 45 to 50 amps running a GE 9" motor. Checked every 10 minutes and logged.


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## mikep_95133 (May 20, 2009)

When I evaluate a BMS, my own or from a vendor, I look for a few things. Here's an important one.

How much idle current does it draw? One design that floated around for some time and was built by many drew 7.5ma (.0075 amps) when it was off. 

.0075 x 24 hours = .18 ah's. 
.18ah x 365 days = 65.7ah's per year.

I optimized the circuit and got it down to 0.75ma (.00075 amps). 
That's only 6.57 ah's per year. 10x improvement.

Considering this is an analog shunting circuit, the new idle current was good. Compared to some processor based units it's still high.

Mike


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## EVfun (Mar 14, 2010)

ElectriCar said:


> re the splitting of a cell, at 3.2V, two 1 Megohm resistors in series will be nothing of a load on a cell. 3.2V/2,000,000ohm= your current draw, 1.6 micro amps. Nothing!


You still won't be checking the center cell if you do it that way. It will also mean a very high impedance measuring system will be required and that tends to increase noise error issues. If would be easier to use unequal resistors for an off-center point. For example, if you had a 51 cell pack and wanted the measurement loop current to be 100 microamps you would want the upper and lower resistor to add up to about 1.5 megohms. You would want the resistance on one side to be 764,700 ohms and the other side to be 735,300 ohms. The center tap would be 26 cells from the end with the larger resistor.

I think this idea has merit because I've used it with lead acid. I've actually been doing these measurements on my Datsun and know that the pack half difference at any point while charging, resting or under moderate load is always less than 0.10 volts. I would be inclined to use a 2 channel opto-isolator to replace the red LEDs and a TLV431 as a 1.24 volt zener diode in place of the green LEDs. This would provide an isolated output for monitoring. I could use a double pole switch to disconnect this circuit from the pack + and - if I wanted to park the pack for several months (like in my beach buggy over the winter.)


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## EVfun (Mar 14, 2010)

gottdi said:


> Jump at the end is after I shut it down and let is set a few minutes. Cells stayed cool. Now that the cells are discharged I am going to charge up the lower of the batteries to match. In other words I am going to bottom balance them. Then charge them up. and do the run again.


Well, I called cell #2 right. Overall, that group looks good in the low current test. Of course, suitable for our purposes will depend on what they think about 2C or greater peak discharges for short bursts but I think you may have gotten yourself a deal.


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## JRP3 (Mar 7, 2008)

mikep_95133 said:


> If your cell monitors are ok, you should be fine. In addition, something in your vehicle needs to count the wh's (watt-hours) in and out. There is a very good reason not to use ah counting on an EV. As the pack voltage goes down, the amps have to go up to hold the same speed/acceleration. So the ah's/mile will be better with a fully charged pack, and worse with one at 25% soc. Every time your pack sags, the ah's become inaccurate. This is why wh's are used. They take into account pack voltage and the ah's at the same time. If you want to compare efficiency of your vehicle to all of the data out there, you need wh's.
> 
> The only time using ah's are ok is with constant current charge/discharge. While driving around, amps and volts are all over the place in addition to the volts sagging over time. So, make sure you have a gauge that can count wh's.
> 
> Mike


Dimitri should chime in but I'm pretty sure he tested wh counting and ah counting with his EV display and found almost no difference at all.


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## dimitri (May 16, 2008)

JRP3 said:


> Dimitri should chime in but I'm pretty sure he tested wh counting and ah counting with his EV display and found almost no difference at all.


Mike is absolutely correct if the goal of this excersise is to know precise energy efficiency of the vehicle during every drive. However, as a daily driver trying to get from point A to point B, I could care less about such data. I actually care only about how many AH I used and have left in the "tank". LFP battery *useful* capacity is measured in AH , not in WH. WH will vary based on C rates due to voltage sag, but AH stays almost perfect ( within normal C rates of course ). I am perfectly content with approximate WH figure based on nominal voltage, which I proved to be within 7% error margin. Anyone here needs better error margin for their WH data? I don't think so.


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## Qer (May 7, 2008)

gottdi said:


> Discharge test done. 4 Hi-Power 100 AH Prismatic Cells.
> 
> 2 hours 10 minutes run time at 45 to 50 amps running a GE 9" motor. Checked every 10 minutes and logged.


Good, good. Now you only have to repeat this test a few hundred times after bottom balancing the pack and we'll have some hard core data.


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## DavidDymaxion (Dec 1, 2008)

Got it, thanks.

How about doing a few cycles without a bottom balance? I would like to see if they naturally grow closer together or not.


gottdi said:


> Jump at the end is after I shut it down and let is set a few minutes. Cells stayed cool. Now that the cells are discharged I am going to charge up the lower of the batteries to match. In other words I am going to bottom balance them. Then charge them up. and do the run again.


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## mikep_95133 (May 20, 2009)

dimitri said:


> Mike is absolutely correct if the goal of this excersise is to know precise energy efficiency of the vehicle during every drive. However, as a daily driver trying to get from point A to point B, I could care less about such data. I actually care only about how many AH I used and have left in the "tank". LFP battery *useful* capacity is measured in AH , not in WH. WH will vary based on C rates due to voltage sag, but AH stays almost perfect ( within normal C rates of course ). I am perfectly content with approximate WH figure based on nominal voltage, which I proved to be within 7% error margin. Anyone here needs better error margin for their WH data? I don't think so.


Dimitri,

Have you tried taking your ah/mile readings at 95-100% soc and then again at 20-25% soc, or lower, and compared them? They won't be the same. Why is that? 

Wh's can also tell you what you have left in your tank. The E-meter has both ah's and wh's. I don't know about the later version or other brands. Most I would think, have both. 

I show new drivers wh's so they are universal with the rest of the world's measurements. I don't read in magazine articles any ah/mile figures. Just wh/mi. That way I can compare my 16 year old technology to brand new as it arrives 

Mike


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## dimitri (May 16, 2008)

mikep_95133 said:


> Dimitri,
> 
> Have you tried taking your ah/mile readings at 95-100% soc and then again at 20-25% soc, or lower, and compared them? They won't be the same. Why is that?
> 
> ...


Mike, I am not arguing with you, you are 100% correct. If you take your scientific hat off for a moment and put on a regular EV driver hat on. You drive a car from point A to point B, all you really need to know is how much fuel you have left. Not even exact numbers since we have 20% derating typically when we size our packs, just a percentage bar going from full to empty. As you might know, I designed my own EV Display. My goal was to make simple, practical, affordable device. I know I have to read current to get AH and I need both current and voltage to get WH. However, since discharge curve is flat, I can just assume nominal pack voltage for WH calculations and keep my device simpler and cheaper. I don't have to deal with voltage scaling and high voltage circuits, I can make the device safer and cheaper.

I hope you see now why I said what I said. I am just trying to be practical.

BTW, it takes the same WH to move the car regardless of SOC. It takes more amps at less volts as voltage sags, obviously, so AH rate will be higher at low SOC all other things being the same. But none of this really matters with LiFePO4 battery in practical terms, my AH gauge is just as practical as your WH gauge and my WH calculation is approximately the same as your real WH reading, which was my goal to start with.


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## mikep_95133 (May 20, 2009)

dimitri said:


> Mike, I am not arguing with you, you are 100% correct. If you take your scientific hat off for a moment and put on a regular EV driver hat on. You drive a car from point A to point B, all you really need to know is how much fuel you have left. Not even exact numbers since we have 20% derating typically when we size our packs, just a percentage bar going from full to empty. As you might know, I designed my own EV Display. My goal was to make simple, practical, affordable device. I know I have to read current to get AH and I need both current and voltage to get WH. However, since discharge curve is flat, I can just assume nominal pack voltage for WH calculations and keep my device simpler and cheaper. I don't have to deal with voltage scaling and high voltage circuits, I can make the device safer and cheaper.
> 
> I hope you see now why I said what I said. I am just trying to be practical.
> 
> BTW, it takes the same WH to move the car regardless of SOC. It takes more amps at less volts as voltage sags, obviously, so AH rate will be higher at low SOC all other things being the same. But none of this really matters with LiFePO4 battery in practical terms, my AH gauge is just as practical as your WH gauge and my WH calculation is approximately the same as your real WH reading, which was my goal to start with.


It didn't occur to me that we were arguing Dimitri. 

I am a daily commuter with my EV as well. No science involved. Just not burning gas. All good.

Please tell me why wh's don't matter with LiFePO4?

If 7% variation is what you came up with. I believe you. 7% would easily be the difference between getting home and reversing a cell. 

Mike


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## dimitri (May 16, 2008)

mikep_95133 said:


> Please tell me why wh's don't matter with LiFePO4?
> 
> If 7% variation is what you came up with. I believe you. 7% would easily be the difference between getting home and reversing a cell.
> 
> Mike


Because discharge curve is flat and I derate my pack capacity 20%, so my fuel gauge is empty when pack still has 20% to go.

You are wrong about one thing though. Battery capacity is not in WH, its in AH, so 7% error margin does not apply here. As voltage drops current goes up, which means current rate goes up, but since I am counting A over T, I am still at correct AH count, no matter the rate. This means, theoretically, my fuel gauge will reduce at faster rate towards the end, but it will still have correct AH value, which is the only thing that matters because battery is not rated in WH, its rated in AH.

Error only applies in measuring WH. We both know that WH is all over the place as you drive, so I could care less about its accuracy. My AH counter is surprisingly accurate, however, proven by many months of service.


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## mikep_95133 (May 20, 2009)

dimitri said:


> Because discharge curve is flat and I derate my pack capacity 20%, so my fuel gauge is empty when pack still has 20% to go.
> 
> You are wrong about one thing though. Battery capacity is not in WH, its in AH, so 7% error margin does not apply here. As voltage drops current goes up, which means current rate goes up, but since I am counting A over T, I am still at correct AH count, no matter the rate. This means, theoretically, my fuel gauge will reduce at faster rate towards the end, but it will still have correct AH value, which is the only thing that matters because battery is not rated in WH, its rated in AH.
> 
> Error only applies in measuring WH. We both know that WH is all over the place as you drive, so I could care less about its accuracy. My AH counter is surprisingly accurate, however, proven by many months of service.


Cell capacity is provided from mfr's in ah's. By simply multiplying by the cell voltage you get wh's. But pack ratings are always in wh's from car mfr's, electricity generators, etc, because it takes into account, volts, amps and time.

I can see that you saved $$ by making a gauge that uses just ah's and time. So the end user benefits by paying less. Adding in a 20% cushion keeps the errors of using just ah's and time out of daily use. So the end user has some level of protection. 

Mike


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## dimitri (May 16, 2008)

mikep_95133 said:


> Cell capacity is provided from mfr's in ah's. By simply multiplying by the cell voltage you get wh's. But pack ratings are always in wh's from car mfr's, electricity generators, etc, because it takes into account, volts, amps and time.


Yes, but those are all *nominal* ratings, using *nominal* voltages, which is exactly the same as my WH calculation using *nominal* voltage. There is no sense in communicating real every day WH data in real numbers, it would confuse the hell out of everyone because they integrate voltage over time and could be different every time due to randomness of outside conditions. Its easier and simpler to communicate in nominal WH numbers. This is my entire point. If I was after scientific lab grade data, then I need to track voltage along with amperage. If I want useful simple fuel gauge, I don't need to track voltage.

With LFP battery ( assuming I have HVC/LVC cell level BMS ) voltage is most useless piece of data for day to day drive. I haven't bothered to look at voltage in my EV in many months.


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## mikep_95133 (May 20, 2009)

dimitri said:


> Yes, but those are all *nominal* ratings, using *nominal* voltages, which is exactly the same as my WH calculation using *nominal* voltage. There is no sense in communicating real every day WH data in real numbers, it would confuse the hell out of everyone because they integrate voltage over time and could be different every time due to randomness of outside conditions. Its easier and simpler to communicate in nominal WH numbers. This is my entire point. If I was after scientific lab grade data, then I need to track voltage along with amperage. If I want useful simple fuel gauge, I don't need to track voltage.
> 
> With LFP battery ( assuming I have HVC/LVC cell level BMS ) voltage is most useless piece of data for day to day drive. I haven't bothered to look at voltage in my EV in many months.


I see your economics. I see your philosophy. I choose differently. 

The instrumentation that I've owned and observed that measures wh's is does not have to be lab grade, but it's accurate. I measure my pack in wh's as well as my truck's efficiency, so I can have good accuracy and to be able to compare notes with all the auto mfr's and other EV owners. Wh's make my measurements accurate and universal with the rest of the world. When I ask an auto mfr what their efficiency is, I can compare their multi million dollar car directly with my own truck. When the weather changes, I can see easily what the rain or the temperatures do to efficiency. When I make changes to the lubricants or tires on my truck, I can easily see the difference. These are the reasons I choose to measure wh's. I didn't pay much for my E-meters either. Granted they were not new.

Mike


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## ElectriCar (Jun 15, 2008)

Mike, is your E meter same as the TBS meters? Just curious.


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## electricmobile.ru (Jan 14, 2011)

spdas said:


> Aloha, I am trying to plan my Lithium purchase. Probably 50 Calb cells @200ah. But I am hearing conflicting heated, (even namecalling) arguments about weather to use a bms or not. So will the person with the most Lithium-use-hours experience stand up and give me the "skinny"? thanks
> Francis


My max. run-out per one charge is 80km at 35C temp., 40-50km at -10C. I use TS-LFP90Ah cells, 32 pcs (110V). I tried to talk to australian EV owners, but some do not believe in my words. 
I had run 19500km till today, from may 2009. I do not use BMS, but I use "balancers". The detailed description of balancers' work principle is described in http://electricmobile.ru/balansiry/


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## ElectriCar (Jun 15, 2008)

electricmobile.ru said:


> My max. run-out per one charge is 80km at 35C temp., 40-50km at -10C. I use TS-LFP90Ah cells, 32 pcs (110V). I tried to talk to australian EV owners, but some do not believe in my words.
> I had run 19500km till today, from may 2009. I do not use BMS, but I use "balancers". The detailed description of balancers' work principle is described in http://electricmobile.ru/balansiry/


So these balancers are attached to the cells but you have no wiring to a control board correct to stop the charger when necessary?


And you drove 80km (49 miles) on a 9500 watt pack? That's like <200wh/mile! Do you drive very slow or is it a very small vehicle?


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## mikep_95133 (May 20, 2009)

ElectriCar said:


> Mike, is your E meter same as the TBS meters? Just curious.


Xantrex Link-10 and E-meter are equivalent. The original E-meter was sold from Cruising Equipment to Xantrex as I understand it. It's had a few more iterations after that. Hope that answers you question. I don't know the TBS meter.

Mike


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## DIYguy (Sep 18, 2008)

electricmobile.ru said:


> My max. run-out per one charge is 80km at 35C temp., 40-50km at -10C. I use TS-LFP90Ah cells, 32 pcs (110V). I tried to talk to australian EV owners, but some do not believe in my words.
> I had run 19500km till today, from may 2009. I do not use BMS, but I use "balancers". The detailed description of balancers' work principle is described in http://electricmobile.ru/balansiry/


I do this with AGM batteries, but mine do not waste excess energy as heat. Mine shuttle up to 5 amps between batteries. As long as they are balanced, charger shuts down at correct voltage HVC... and programmed LVC is set in controller. As most ppl know, AGM's are also very sensitive to over charge/discharge. Unfortunately, I don't think the controller (Soliton, or any) will work well for Lithium LVC since the discharge curve is so flat. .. perhaps, but I kind of doubt it.


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## DIYguy (Sep 18, 2008)

Regarding the AH vs WH I use the Cycle Analyst (high voltage model). It's under $200. In addition to Volt/amp/watts, it does AH (including regen), WH, speed (so also does WH/mile) and other stuff....and also has outputs for speed limit, current limit and LVC. Not bad really.
Here's the list. (Sorry, this is a little off track for the thread)


*Volts, Watts, Amps:* The instantaneous electric power being drawn from the battery.
*Amp-Hours, Watt Hours:* The net energy that has been pulled from the pack since the meter was reset. The accumulated amp-hours let you know the remaining energy in the battery pack with far greater accuracy than a voltage or LED indicator.
*Speed, Distance, Time:* All of the basic features of a bicycle computer, including the average and maximum trip speeds, plus a total distance odometer.
*Regen, Wh/km:* There are several quantities this meter will calculate that you don't get with other instrumentation, such as the % extra range that was gained from regenerative braking, as well as the vehicle's average energy use in Watt-hours per kilometer or mile.
*Peak Currents and Voltage Sag:* Records the maximum forwards and regenerative currents as well as the minimum voltage on the battery pack.
*Total Battery Cycles and Amp-Hours:* Retains life cycle information on the vehicle's battery pack, such as how many charge and discharge cycles the pack has experienced and the total amp-hours that were delivered over its entire life.
 Furthermore, the Cycle Analyst has the ability to over-ride the user's throttle and regulate the power delivered to the motor, turning an otherwise dumb ebike into an intelligent device with a user programmable speed limit, current limit, and low voltage cutout. 


*Speed Limit:* This has the utility of providing legal compliance to the speed cap imposed on ebikes in most jurisdictions. When used with a full throttle, it serves as a cruise control on the electric bicycle. It can also be beneficial to riders who want to increase their torque and power by using a higher voltage battery, without simultaneously increasing their top-end speed.
*Current Limit:* An adjustable amps limit is useful to prevent damage to the batteries from excessive current draw, to increase the range that you'll get on a charge, and to protect the motor controller and motor in setups that draws too many amps.
*Voltage Cutout:* A low voltage cutout is used to protect a battery pack from being discharged too deeply, which can cause cell reversals in NiMH/NiCad packs, permanent cell damage in Lithium packs, and sulfation in Lead Acid batteries. The programmable low voltage rollback allows you to set an appropriate low voltage point tailored to your pack.


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## ElectriCar (Jun 15, 2008)

Wow DIY that thing does a lot! I looked at it briefly once but isn't it rated for lower voltages? I plan to be at 165V resting once charged. Maybe not that much if I limit charging to 3.45 or so.


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> Wow DIY that thing does a lot! I looked at it briefly once but isn't it rated for lower voltages? I plan to be at 165V resting once charged. Maybe not that much if I limit charging to 3.45 or so.


My truck is 192 volts nominal. 208 charged. Charger cycles up to 250 volts at the top. They had to do some mods for my CA. Justin was good about this. One mod req'd for the display (too much in-rush @ higher voltage) and another for the code I believe. He has it worked out now. Just make sure he knows the application first.

cheers.


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## EVfun (Mar 14, 2010)

electricmobile.ru said:


> My max. run-out per one charge is 80km at 35C temp., 40-50km at -10C. I use TS-LFP90Ah cells, 32 pcs (110V). I tried to talk to australian EV owners, but some do not believe in my words.
> I had run 19500km till today, from may 2009. I do not use BMS, but I use "balancers". The detailed description of balancers' work principle is described in http://electricmobile.ru/balansiry/


I like your web page. I see you are using your shunt regulators similar to the way I have been using my EVworks regs. That is, just a little nudge to help keep the pack lined up near the top. My regs are set a little lower (3.65 volts) and I do have HVC and LVC functions hooked up but neither have been tripped so far. 

Thanks for sharing.  I'm interested in those little regs. Are they still available for sale as indicated? Do they come in sizes for different cells? How much current do they shunt? About what is their off-state current? I am a big supporter of putting cell management at the cell and not running wires that are at pack potential around the vehicle (except for the most positive and most negative terminals, of course. )


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## tomofreno (Mar 3, 2009)

Mike, here is a link to a summary of some data I posted on Ah and Wh datalogged on a 58 mile run back in October/2010:

http://www.diyelectriccar.com/forums/showpost.php?p=208464&postcount=621

The net energy used was 11571 – 1199 = 10372 Wh. The net Ah used was 91.3Ah. Multiplying this by the nominal pack voltage of 36 * 3.2V = 115.2V gives 10518 Wh , and 100*(10518-10372)/10372) = 1.4% difference from that calculated by summing the product of pack voltage, current, and 1/3600 hr sample interval. I think I would have to discharge to an SOC below 30% to see more significant difference because the V versus Ah curve is fairly flat down to there for typical current draw while cruising in my car. The voltage sags more of course very briefly during acceleration, but that is a very small part of the overall driving time so doesn’t affect the calculation that significantly. I agree with Dimitri that the product of Ah used and nominal pack voltage is good enough for most purposes.

The raw data is given in post #618, in the same thread. Some comments on the summary I gave: I “assumed” 94% charger efficiency because that was what I measured previously at four different current levels. The data should of course agree with the “Ah used” displayed on the gauge since that is what generated it. I simply meant that gave some confidence I didn’t make an error in the calculation.

The gauge is a TBS ExpertPro. They make the LinkPro for Xantrex. Xantrex was the only U.S. dealer back when I purchased it (confirmed with Daniel at TBS), but did not sell the voltage adapter, so I bought both from evworks in Australia. They both, and the datalogging software/adapter for the gauge, are now available at evolveelectrics and others in the U.S.


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## Jozzer (Mar 29, 2009)

FYI, the new version of the Cycle Analyst will be good to 400v. Very fine and affordable bit of kit, am always amazed when I see an EV without one! That said, it is NOT easy to track AH day in day out with one, one mistake about when you zero the counter and youve got false data (happened to almost all of the TTXGP racers this year at one time or another).

Right, fed up of there being no real data in this discussion, I set up a 5 cell LifePo4 pack yesterday (10AH LifeBatt cells) and left it cycling. I will continue with these experiments, if anyone has any requests for the test to be altered please let me know.
The tests are being performed on a Cellpro Powerlab 8, the software is freely downloadable and doesn't need the hardware for you to open the file and check out the other saved info (IR, pack capacity etc).
Here is a JPG of the cell voltage output and the zipped data file.
The link to the software is here. http://www.revolectrix.com/pl8_software_v2.html

It's tricky to set up a test showing how cells unbalance in use with a device that is constantly trying its best to balance the cells, the unit starts shunting at 3.3v, then throttles back current to balance levels at HVC. I've turned the balance current down and increased the balance tolearance to slow down any balancing in the charge portion of the curve.
CHarge current was 15A, discharge 20A.

Steve

PS, it should be noted that the cells are balanced every cycle, so we are not seeing the accumulated effect of cycling with no balancing. I've just started a test with balancing turned off (hopefully) and will leave it running overnight..


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## JRP3 (Mar 7, 2008)

Had a thought that better terminology might be CMS, Cell Management/Monitor System, if talking about cell level devices. Probably won't catch on.


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## mikep_95133 (May 20, 2009)

That's amazing. I agree with you that keeping dod above 30% is helpful for accuracy, not to mention cycle life. 

Mike




tomofreno said:


> Mike, here is a link to a summary of some data I posted on Ah and Wh datalogged on a 58 mile run back in October/2010:
> 
> http://www.diyelectriccar.com/forums/showpost.php?p=208464&postcount=621
> 
> ...


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## Tahoe Tim (Feb 20, 2010)

JRP

I suggested the same idea in a new thread I started yesterday. I considered cell monitoring and pack monitoring but PMS was taken


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## mikep_95133 (May 20, 2009)

I have confirmation of a local EV guy who's going to bring some of his 90ah TS cells and the BMS modules with them. His issues are a bit muddy. So I don't know if this case is going to be decent data either way in the BMs debate. In fact I don't know yet what issue he has other than rain water leakage. That's what I mean by muddy.

So I'll cap test the cells and play with a brand of BMS that I've not yet reviewed. That is right after I get the spot welder finished. Ya right.

Mike


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## mikep_95133 (May 20, 2009)

gottdi said:


> By golly I think you got it correct. Works for me. Cuts confusion. Cuts arguments on terminology and those that want BMS and those that want CMS can talk till their hearts content.
> 
> Could use PMS for those of us who want monitoring of the pack. You know it's been nothing short of PMS anyway. Headaches, Bitchy attitudes and just all around pissy at each other. Sounds like PMS to me.
> 
> Pack Monitoring System (PMS) I've had my bowl of bitchy today, Have you?


That was funny!!

Mike


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## EVfun (Mar 14, 2010)

gottdi said:


> Second run on pack at 45 amps for 2hr 16 minutes. Running a 9” GE Motor as load. 100 AH Hi-Power Cells. All logs are running voltages of both pack and cells.


It is interesting to see how cell 4 is generally the low voltage one on discharge until the end where number 2. It looks like number 2 is the smallest, but only by a small amount. I guess the numbers mean cell 4 has slightly higher internal resistance, since the resting voltage seems in line.

Thanks for your efforts.  Now just do that 2000 more times and we will have some life data.


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## ElectriCar (Jun 15, 2008)

gottdi said:


> Wish I had a way to check internal resistance. Know of a way to tell.
> 
> Pete


Yes, on your next discharge, note the resting voltage then load it up. Immediately note the voltage of that cell again and the current draw from it. Deduct the loaded voltage from the static voltage and that gives you the voltage drop. E/I=your Ir in ohms. 

If you're pulling 30A, 0.1V drop/30A=.0033 or 3.3mohms.


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## Tesseract (Sep 27, 2008)

ElectriCar said:


> Yes, on your next discharge, note the resting voltage then load it up. Immediately note the voltage of that cell again and the current draw from it. Deduct the loaded voltage from the static voltage and that gives you the voltage drop. E/I=your Ir in ohms.
> 
> If you're pulling 30A, 0.1V drop/30A=.0033 or 3.3mohms.


Not quite... you have to compare the cell voltage at two different currents to get an accurate internal resistance measurement. For example, measure the voltage at 0.5C and 1C, then divide the difference in voltage(dV) by the difference in current dI) to get the resistance.

E.g. - 3.00V at 100A (0.5C) and 2.90V at 200A (1C) gives a dV of 0.1V over a dI of 100A, or 0.1/100 = 10 milliohms.

This was just an example, and not an actual test result, btw.


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## tomofreno (Mar 3, 2009)

There was some concern about needing to synchronize a charge counter with the actual SOC of the pack regularly. Thought it might be worth mentioning that the TBS gauge (and maybe others) allows for manually synchronizing this way, and it also will automatically sync. You give it a pack voltage and a charge current, and when those conditions are met it sync's and displays "Full". It would be easy to have it autosync this way with a top balancing bms. You could set the voltage at number of cells times the cell voltage when shunts turn on, and charge current at a value close to that when the shunts come on, say maybe 3A. It would then autosync and display "full" when those conditions are met, which should be about every charge.


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## JRP3 (Mar 7, 2008)

EV Display also allows you to reset it.


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## mikep_95133 (May 20, 2009)

The guy didn't bring his cells or bms modules. Not sure why. But the other fellow that's kept me informed was there. His pack is currently BMS-less. Total mileage about 9k on 90ah TS cells. He had an analog BMS for the first 1000 miles. He has since removed it and thrown the BMS modules away. He had a cell go dead was why he tossed them. He was told it was the BMS module. But since the module was not examined by anyone, it's speculation. So it's not really a credible data point. He said it was not obvious that the one module had failed or if it was a cell only failure. 

Jon is the owner. I told him I'd be using him as data as several of us are looking and watching more carefully at lithium owners to see how the failure rates are. He has a small car with a 72v system. He told me of some pack sagging that he experiences after driving for just a very short time. We thought it might be that much of the grille is still unblocked and the cells are experiencing some wind chill factor. Regardless, I think that his vehicle looks like a good source of data to add to the pile. I've got one other fellow looking into sources from his end as he is very well connected in EV circles.

Mike

PS I entered some data on regen values in the regen thread.


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## GizmoEV (Nov 28, 2009)

I don't get the EVA Newsletter but if you go to http://jackrickard.blogspot.com/2011/01/first-show-2011.html#comments and read comment #85 posted on January 19, 2011 you will read where Jack posted someone's experience with a BMS caused fire.


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## EVfun (Mar 14, 2010)

GizmoEV said:


> I don't get the EVA Newsletter but if you go to http://jackrickard.blogspot.com/2011/01/first-show-2011.html#comments and read comment #85 posted on January 19, 2011 you will read where Jack posted someone's experience with a BMS caused fire.


It sounds more like a fire caused by unsafely running pack potential spaghetti, rather than by the BMS itself. I believe this was also the cause of Jack's BMS fire. I would be curious to learn more about the causes of this currently reported "thermal event." 

This is a good time to point out (again), *it is very important that pack spaghetti be fused at the cells!* Proper fusing is a serious fire safety issue. I wouldn't allow any car with unfused BMS spaghetti to charge in my garage without my constant presence.


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## mikep_95133 (May 20, 2009)

This lithium pack fire story Jack Rickard just posted stinks like all his other BMS failure examples. I wrote him my honest opinion of it in his blog. We need to find this guy that had the fire, and see if pics are available of his pack. 

Any idea from the description what brand it is? Something about self adhesive to the cell top?

I swear, this whole BMS-less thing is a religion! Jack deserves yet another convert.

Mike


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## ElectriCar (Jun 15, 2008)

Yea Mike a lot of people are gettin' religion when they lose a $250 battery and it turns out the "manager" that is supposed to protect them is the one who toasted it. I want to just skip that part and take the next step. 

To be fair though I'm sure some issues are due to faulty installations by unskilled installers but really how many in depth investigations have there been of these fires? If I were to place a bet I'd put my money on non-engineers designing these things and unqualified installers who've never been schooled in electrical practices thus don't know how to do it safely, ie fusing wires, enclosing wiring in wire looms or other protective raceways to prevent shorts etc.


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## mikep_95133 (May 20, 2009)

ElectriCar said:


> Yea Mike a lot of people are gettin' religion when they lose a $250 battery and it turns out the "manager" that is supposed to protect them is the one who toasted it. I want to just skip that part and take the next step.
> 
> To be fair though I'm sure some issues are due to faulty installations by unskilled installers but really how many in depth investigations have there been of these fires? If I were to place a bet I'd put my money on non-engineers designing these things and unqualified installers who've never been schooled in electrical practices thus don't know how to do it safely, ie fusing wires, enclosing wiring in wire looms or other protective raceways to prevent shorts etc.


Actually they are getting religion based on fear, not facts. 

Two great points you make. Zero in depth investigations on all fires. Or at least not publicly disclosed. 

The funny thing about unqualified 'installers' is that engineers are the worst offenders. Bar none.

Please keep us informed of your BMS-less pack's life as it ages. 

Mike


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## ElectriCar (Jun 15, 2008)

mikep_95133 said:


> Actually they are getting religion based on fear, not facts.
> 
> Two great points you make. Zero in depth investigations on all fires. Or at least not publicly disclosed.
> 
> ...


RE engineers, I don't doubt that. They have the atomic level of understanding how electricity works but some don't have the application part under their hat, the manual labor part, wiring the stuff up!

Oh yea on mine I think I'm going free and must decide soon. I'm about ready to order some things, the Cycle Analyst for 200V systems with the new large in dash type display is very thorough with a lot of data gathering and low voltage signal. They've also upped the max ah, and the wh tracking was bumped to 100kw, well almost, it's 99,999wh but who's counting...


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## GizmoEV (Nov 28, 2009)

mikep_95133 said:


> Actually they are getting religion based on fear, not facts.


With out conclusive verifiable data your statement works either direction. I bought my CManS (AKA cell level management system) based on the fear that if I didn't top balance them I would kill them. It was the "religion" that "every body" was preaching to me over a year ago. I quit top balancing my cells back in August 2010. I charge my pack to an average of 3.458vpc and have so far not seen cell drift/divergence/moving apart/or what ever other term you want to call it. If you want to see my data I posted it on my blog. The direct link to the file is here. I'm still on the fence but heavily leaning toward no CManS. Right now I'm essentially using my CManS as a CMonS (cell monitoring system). As I find other sources of information about theses particular cells it looks less and less like a cell level system is needed.



mikep_95133 said:


> Two great points you make. Zero in depth investigations on all fires. Or at least not publicly disclosed.


And no clear data on how different packs have been treated so there are too many variables to come to a conclusion about things. I think it all comes down to what one thinks is the lowest risk. Again, it probably is a decision with out sufficient evidence.

I would like to see pics of both the before and after the fire. It sounds like maybe the boards are connected to the posts with pigtails and then held in place by double sided sticky foam. I seem to remember seeing some pictures of boards mounted like this. Maybe I can find it again.


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## mikep_95133 (May 20, 2009)

GizmoEV said:


> With out conclusive verifiable data your statement works either direction. I bought my CManS (AKA cell level management system) based on the fear that if I didn't top balance them I would kill them. It was the "religion" that "every body" was preaching to me over a year ago. I quit top balancing my cells back in August 2010. I charge my pack to an average of 3.458vpc and have so far not seen cell drift/divergence/moving apart/or what ever other term you want to call it. If you want to see my data I posted it on my blog. The direct link to the file is here. I'm still on the fence but heavily leaning toward no CManS. Right now I'm essentially using my CManS as a CMonS (cell monitoring system). As I find other sources of information about theses particular cells it looks less and less like a cell level system is needed.





> And no clear data on how different packs have been treated so there are too many variables to come to a conclusion about things. I think it all comes down to what one thinks is the lowest risk. Again, it probably is a decision with out sufficient evidence.





> I would like to see pics of both the before and after the fire. It sounds like maybe the boards are connected to the posts with pigtails and then held in place by double sided sticky foam. I seem to remember seeing some pictures of boards mounted like this. Maybe I can find it again.


That would be helpful if you could find it.

This shuttle term that's been floating around is Peukert's Exponent. He figured that out 113 years ago or so. All chemistry's have it. Lithium has it far less. So your charging or AC efficiency is better. Also depends on the efficiency of the charger quite a bit too.

Be careful what you take from the EVDL. They are just a prone to 'beliefs' as EVTV. 


Mike


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## DIYguy (Sep 18, 2008)

GizmoEV said:


> With out conclusive verifiable data your statement works either direction. I bought my CManS (AKA cell level management system) based on the fear that if I didn't top balance them I would kill them. It was the "religion" that "every body" was preaching to me over a year ago. I quit top balancing my cells back in August 2010. I charge my pack to an average of 3.458vpc and have so far not seen cell drift/divergence/moving apart/or what ever other term you want to call it. If you want to see my data I posted it on my blog. The direct link to the file is here. I'm still on the fence but heavily leaning toward no CManS. Right now I'm essentially using my CManS as a CMonS (cell monitoring system). As I find other sources of information about theses particular cells it looks less and less like a cell level system is needed.


This is excellent information (the data particularly). It is exactly what we have been talking about. Very solid. Good on ya. Thank you!


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## EVfun (Mar 14, 2010)

mikep_95133 said:


> This shuttle term that's been floating around is Peukert's Exponent. He figured that out 113 years ago or so. All chemistry's have it. Lithium has it far less. So your charging or AC efficiency is better. Also depends on the efficiency of the charger quite a bit too.


What? Peukert's formula describes the discharge curve of a Pb acid cell by predicting how long you can discharge at a given amp level until the cell gets down to 1.75 volts. Peukert's formula has nothing to do with charging. Charging is replacing the amp hours removed plus a little because no battery chemistry is 100% efficient (though modern LiFePO4 cells seems very close below 3.5 volts.)

I've done the Peukert's test on Optimas. I can run them down to 10.5 volts at 100 amps in 20 minutes and it takes only about 35 amp hours to recharge them no matter what my recharge rate. In addition, I can pull 100 amps out for 20 minutes then switch to a smaller load and the cell will supply the lower current while staying above 10.5 volts. Charging amp hours is always a little more than removed amp hours no matter what rate I discharge or charge the battery.


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## GizmoEV (Nov 28, 2009)

mikep_95133 said:


> This shuttle term that's been floating around is Peukert's Exponent. He figured that out 113 years ago or so. All chemistry's have it. Lithium has it far less. So your charging or AC efficiency is better. Also depends on the efficiency of the charger quite a bit too.


The Peukert's Exponent is a derived value independent of the chemical reactions going on in the cell. The formula derivation is exactly the type of thing I did as an undergraduate Physics physics student. Nothing about the chemistry is needed, only the raw data of the result. The research I found on Peukert bared this out.

The shuttle reaction is an actual chemical process and directly affects self discharge.

The amount of energy entering the battery has no bearing on the efficiency of the device converting the wall energy into something the battery can handle. I don't put my shunt in the AC line to count Ah into the battery. I put it just before the negative terminal of my battery pack. 

If I want to know the cost of the electricity for driving my car then I measure at the wall since the loss between my house meter and my wall plug are negligible for my purposes. If you read my blog on efficiency of my car going to LiFePO4 you will see I'm talking about wall energy. The amount of energy it takes to move my car down the road didn't change significantly but the amount out of the wall did.

Anyone who has worked with Pb, NiMH, NiCd batteries and had them for a while has found that even when they start out at the same state of charge that it is common to have two of the same type of cell or battery have different self discharge rates. LiFePO4 cells don't appear to behave this way. The 4 cells I left on sitting before adding them to my Gizmo pack acted this way. I only wish I wrote down the data to present here. JR showed a 15 month old unused cell that was within 0.001v of a new one from the factory. I only wish he had taken the time to measure the voltages when new and then again later so there was a good start value. Other research I've read confirm the same thing. Looking at the chemical reaction in a LiFePO4 cell it is clearly different than in other batteries so one has to learn the characteristics of this battery, not apply the characteristics of other batteries to this one.


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## GizmoEV (Nov 28, 2009)

I think this is the BMS I was thinking of with short pigtails on the board with it stuck to the center of the battery. It looks smaller than I remember and I think I first saw some in a photo of someone's EV conversion.

http://electricbluemotors.com/balancer.html


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## Kendrick57 (Jan 23, 2011)

Hi 
Right near the start of this thread jozzer posted about a guy who sells cheap boards that can protect a battery pack from over discharge. It was created for the electric cycle market with a small percentage of electric motorbikes using them as well.
It has taken some time for me to decide to join this forum but I decided to to let you all know about what it is I have and do.
Now that lithium batteries are becoming used more and more on electric cycles some form of BMS was required,now LiFePO4 BMS boards are available from china, I don't know how good they are with some of the latest cells I have not tested them. A lot of them are going for LiPo cells which are a lot more difficult to get charged and manage. One member on out forum worked out how to use simple electronics to protect the cells from over discharging and later on over charging as well. The circuit used less lower than the cells natural discharge rate so could be put on to the cells and left there, his boards had only one problem they were DIY you get a board and a either a list of components or a full kit components included, I decided to take this circuit to the next stage by making a SMD version as I considered that having to put all the components on was too much for many of the Ebikers to do. I therefore got in touch with someone in china and with their help made a version of his board that was a dedicated LVC board suitable to usenwith the favoured LiPo cells that we are using with one component change it could be used with LiFePO4 the favoured type on this forum.
I am in the process of designing a second run of boards to be made in china these will include a HVC part to help with charging and a few other bits and pieces, I am always open to ideas I have no strong background in electronics what I do have is a the ability to convert a schematic circuit diagram to A circuit board design with as many SMD components as possible, my other ability is that I can deal with my guy in china which takes a lot of time with the translation problem and the time difference.

Kendrick


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## mikep_95133 (May 20, 2009)

It sure seems to me that there could be a workmanship issue here from the description. I can see that having a bms module wired to a cell as being more universal to various cells sizes. But I cannot imagine that it would be more reliable than a full length circuit board. I found the email of the guy that reported this latest car fire, that he kept driving anyway, and got no response.

It's occurred to me that there is a short and long term 'religion' developing with lithium. The easiest is to do nothing, have faith, and compel others to do the same thing. As with any chemistry, the pack works great while it's new. I've noticed it creates a 'high' with owners around here. The big downer is when cells start to die. I think the longer term view of buying a BMS does the obvious of watching over the pack. But I've also watched it give information to the owner that cannot be obtained otherwise. It's a great training device. Cell voltages vary with location in the pack due to cooling differences etc. during charging or driving. Easy to see with a BMS. Also any cell that has an issue will show that well in advance of a sudden failure. I have watched these occurrences for years on BMS equipped vehicles. Granted, with so many hobby level designs for sale, there is no central standard they are tested to, or an organization that does their own independent testing. But I think it's a short term over reaction when one brand of BMS has a failure, then all of them are sworn off as bad. Especially from those that have never owned a BMS. 

I have 3 40ah lithium cells here. They are 2 years old. I only tested and characterized them for full capacity when I got them brand new. I was going to do driving tests with them, when a vendor asked me to use his cells instead. Once the data was generated, I gave back his cells and mine still sit, in a box at 70 degrees day in and day out in my lab, which is a converted bedroom. A few days ago I checked them for voltage and one cell was dead. I charged it for several hours but it's self discharge rate has climbed out of site. It goes dead again in minutes. This cell never gave any clues that it ever had a problem from the tests that I did. Never overcharged or over discharged. Nonetheless, the one is dead. I can't imagine trusting a pack of 50-100 cells with nothing but faith.

I'm off building a spot welder so that I can assemble A123 cells into a module for testing in my truck. The tough parts will be the mechanical design of the case that holds the cells and a BMS module. It has to handle 300 amps in and out. The BMS module will have very little room. The cells are 65mm long. The module will have to fit between the 10mm studs atop the module. I'm well versed with surface mount parts. This design will have to make good use of the available volume. The A123's should do well with the 300 amp regen bursts.

If you have cell spot welding experience, I like to hear from you.

Mike

PS Peukert Exponent and Faraday efficiency are worthy study material.



GizmoEV said:


> I think this is the BMS I was thinking of with short pigtails on the board with it stuck to the center of the battery. It looks smaller than I remember and I think I first saw some in a photo of someone's EV conversion.
> 
> http://electricbluemotors.com/balancer.html


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## JRP3 (Mar 7, 2008)

> This cell never gave any clues that it ever had a problem from the tests that I did. Never overcharged or over discharged. Nonetheless, the one is dead.


Brand please?


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## DIYguy (Sep 18, 2008)

mikep_95133 said:


> It sure seems to me that there could be a workmanship issue here from the description. I can see that having a bms module wired to a cell as being more universal to various cells sizes. But I cannot imagine that it would be more reliable than a full length circuit board. I found the email of the guy that reported this latest car fire, that he kept driving anyway, and got no response.
> 
> It's occurred to me that there is a short and long term 'religion' developing with lithium. The easiest is to do nothing, have faith, and compel others to do the same thing. As with any chemistry, the pack works great while it's new. I've noticed it creates a 'high' with owners around here. The big downer is when cells start to die. I think the longer term view of buying a BMS does the obvious of watching over the pack. But I've also watched it give information to the owner that cannot be obtained otherwise. It's a great training device. Cell voltages vary with location in the pack due to cooling differences etc. during charging or driving. Easy to see with a BMS. Also any cell that has an issue will show that well in advance of a sudden failure. I have watched these occurrences for years on BMS equipped vehicles. Granted, with so many hobby level designs for sale, there is no central standard they are tested to, or an organization that does their own independent testing. But I think it's a short term over reaction when one brand of BMS has a failure, then all of them are sworn off as bad. Especially from those that have never owned a BMS.
> 
> ...


You know, it's ok to be wrong. We all take our turn at it. Just don't profess to have all the answers .... and u keep gettin it wrong. Who would fly with blind faith? (other than these couple of hundred guys ur watching over? ) . . and it's not self discharge...obviously.

Now spot welding is something I have experience with. Never had anything to do with welding battery tabs though.


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## DavidDymaxion (Dec 1, 2008)

Mike: BYU used A123 cells on their eletric land speed car http://explodingdinosaurs.com/byugarage . They put about 50 Amps through each cell with the stock interconnects. Caveat: I think the longest the car ran was about 2 or 3 minutes. So just a thought, if you have enough cells in parallel you might not need to spot weld.

What would be really cool is some tests on the stock connections and on your own spot welds. You could plot terminal temperature vs. current and that should show your welds are much better.

BTW the BYU "BMS" was to use one RC charger for each parallel block of cells.


mikep_95133 said:


> ... I'm off building a spot welder so that I can assemble A123 cells into a module for testing in my truck. The tough parts will be the mechanical design of the case that holds the cells and a BMS module. It has to handle 300 amps in and out. The BMS module will have very little room. The cells are 65mm long. The module will have to fit between the 10mm studs atop the module. I'm well versed with surface mount parts. This design will have to make good use of the available volume. The A123's should do well with the 300 amp regen bursts.
> 
> If you have cell spot welding experience, I like to hear from you. ...


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## ElectriCar (Jun 15, 2008)

mikep_95133 said:


> ...It's occurred to me that there is a short and long term 'religion' developing with lithium. The easiest is to do nothing, have faith, and compel others to do the same thing.


I haven't heard of anyone doing this, have you? 



mikep_95133 said:


> As with any chemistry, the pack works great while it's new. I've noticed it creates a 'high' with owners around here. The big downer is when cells start to die.


And what causes that? I wasn't aware of any Lifepo4 cells reaching end of life due to old age. Only that some have lost a little capacity and internal resistance was up a bit.


mikep_95133 said:


> I have 3 40ah lithium cells here. They are 2 years old. I only tested and characterized them for full capacity when I got them brand new. I was going to do driving tests with them, when a vendor asked me to use his cells instead. Once the data was generated, I gave back his cells and mine still sit, in a box at 70 degrees day in and day out in my lab, which is a converted bedroom. A few days ago I checked them for voltage and one cell was dead. I charged it for several hours but it's self discharge rate has climbed out of site. It goes dead again in minutes. This cell never gave any clues that it ever had a problem from the tests that I did. Never overcharged or over discharged. Nonetheless, the one is dead. I can't imagine trusting a pack of 50-100 cells with nothing but faith.


 That's interesting. Never heard of anything like that either.


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## JRP3 (Mar 7, 2008)

Some people have gotten cells that were DOA, or only survived a single cycle. I'm not aware of anyone getting CALB cells that failed.


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## MN Driver (Sep 29, 2009)

gottdi said:


> Three? Been sitting for two years. Self discharge? hardly. What are the other cells? If it was self discharge all three would have been flat. Period. The one cell is dead because of a different reason and you tested a few times then put them away. I'd have to say without a doubt that the cell was already crap when you got it. Yes, cells can come from the factory like that. It is expected and to have one that is dead as an argument for a BMS is quite BULL.
> 
> Now if you had done daily or weekly voltage readings on those cells for that year then I'd be more inclined to believe you but with out that data it's just bull.
> 
> It is not because of SELF DISCHARGE.


Three years doesn't pull self discharge to zero. I've got NiMh around sitting for years that don't self-discharge flat. Whether small 1800-2500mAh AA cells sold for $10 for a 4 pack or professional 30amp rated Panasonic D cells that manage to push 100 amps. Generally inactivity isn't great for these and some fail from dendrite failure but others will hang onto 1v to 1.2 volts and have close to nothing left but not zero volts, charge and discharge 3 times or so and they are back in the game. Makes pack building tough since the self-discharge and memory issues don't match from cell to cell but NiMh is a whole 'nother monster.

For what its worth I've got cell phones and laptops with LiCo batteries that have been unused that I pull out once a year and mess with, generally have power left to run for awhile. I usually discharge them at least halfway before storing though.


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## Overlander23 (Jun 15, 2009)

I think one of the points here is not about self-discharge rate, but about information. I've mentioned it before. There's certainly merit in a monitoring system that informs you of a bad cell... or bad behavior, for whatever reason.

As far as those that don't run a monitoring system it seems that they, at the very least, periodically manually check the status of their individual cells. Same thing.

I, for one, can't do that easily. It would necessitate dropping 150-300 lbs boxes from under the truck. 

Can you run without a BMS? Sure... you just have to be one yourself.

Now if only I could find a way of building a monitoring system that didn't always draw current from the cells... I suppose that's for a different thread.


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## JRP3 (Mar 7, 2008)

I think split pack voltage monitoring takes care of informing you of what's going on with your pack, and can use a separate power source to run the volt meters.


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## EVfun (Mar 14, 2010)

I think the split pack Lee Hart style battery bridge could work and the most positive and most negative connections could be made through a double pole relay. That way even the small load from the bridge need only be present when charging or discharging. Shut off the relay when neither is happening and there will be no load.


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## ElectriCar (Jun 15, 2008)

JRP3 said:


> I think split pack voltage monitoring takes care of informing you of what's going on with your pack, and can use a separate power source to run the volt meters.


I've looked into building a multi LED unit with a 2V per led sensitivity. Just haven't found a chip to do this. I even emailed National Semiconduct who have helped people solve issues in the past but they've not responded. I've been out of electronic work for over a decade so things don't click to me like they used to unfortunately. Maybe someone here can help us out. It can be done as Metric Mind did it.


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## JRP3 (Mar 7, 2008)

As has been mentioned the Lee Hart Batt Bridge does it pretty simply with 3 LEDs, one green means balanced, one of the two red ones means imbalance and tells you which half of the pack has a problem. Different resistor values can compensate for odd number packs.
http://www.evdl.org/pages/battbridge.html


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## Overlander23 (Jun 15, 2009)

Yes, at the very least I will be monitoring both sides of the pack. 

What I'd like is a master->slave monitor that combines sub-boards which interface with a master board via optical. Each sub-board would monitor 8-16 cells by switching FET pairs to feed voltage to an MCU (per sub-board.) The cells would be polled sequentially rather than simultaneously, with the FETs turning on and off for each cell. The sub-boards are powered via isolated 12v which would run the MCUs and FETs. That way if the the BMS power dies or is intentionally shut down, the FETs just shut off. No current flow out of a cell. If a FET goes bad the MCU will detect voltage when there shouldn't be. Could even have re Wouldn't have to worry about multi-cell, voltage potential since voltage is controlled by the sequencing of the FETs. Fuses at the cells for safety. Optical communication between sub-boards and master should take care of some EMI issues.

But then, I'm not an EE. And what I wrote above could be a recipe for instant fail...


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## Tahoe Tim (Feb 20, 2010)

LM3914 chip
http://www.national.com/mpf/LM/LM3914.html#Overview

I built an air fuel ratio meter out of it that my brother retails on the internet. It's basically a 10 LED volt meter that allows you to set the span and the end points. The air fuel meter spans 0.1 volt across 10 lights in a very specific range of the ox sensor.

I have thought about using one to watch the knee area of my cells. It's like zooming in on a small voltage area.

Plenty of info on line on how to design one for your needs.


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## ElectriCar (Jun 15, 2008)

JRP3 said:


> As has been mentioned the Lee Hart Batt Bridge does it pretty simply with 3 LEDs, ...


Yea I know about this circuit but I'm thinking ahead to a point that you get a couple of cells developing higher resistance on one half than the other then you have a light on all the time when driving then back to green when stopped. If this could be trimmed with a trim pot or such periodically then it would still work. Also with a certain sensitivity you could spot something more significant than just a little higher resistance. 

I'll probably integrate this thing in an enclosure with the new Cycle Analyst in-dash display I ordered Friday if I can't find a way to get it inside the factory dash board. 

I really like the idea of knowing the status of each battery though. I still may put in a cell level monitoring system with an HVC cutoff just to know what's happening if I can be convinced it will do no harm. I've not even looked at such equipment though and have no idea about any of it. The Cell log 8 may be the path to go from what little I've read from those using it.


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## ElectriCar (Jun 15, 2008)

Tahoe Tim said:


> LM3914 chip
> http://www.national.com/mpf/LM/LM3914.html#Overview
> 
> I built an air fuel ratio meter out of it that my brother retails on the internet. It's basically a 10 LED volt meter that allows you to set the span and the end points. The air fuel meter spans 0.1 volt across 10 lights in a very specific range of the ox sensor.
> ...


OK let's see a circuit for this thing to operate on 160V pack. I just can't get something in my head but I did look at this thing.


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## rochesterricer (Jan 5, 2011)

MN Driver said:


> Three years doesn't pull self discharge to zero. I've got NiMh around sitting for years that don't self-discharge flat. Whether small 1800-2500mAh AA cells sold for $10 for a 4 pack or professional 30amp rated Panasonic D cells that manage to push 100 amps. Generally inactivity isn't great for these and some fail from dendrite failure but others will hang onto 1v to 1.2 volts and have close to nothing left but not zero volts, charge and discharge 3 times or so and they are back in the game. Makes pack building tough since the self-discharge and memory issues don't match from cell to cell but NiMh is a whole 'nother monster.
> 
> For what its worth I've got cell phones and laptops with LiCo batteries that have been unused that I pull out once a year and mess with, generally have power left to run for awhile. I usually discharge them at least halfway before storing though.


IIRC, the natural voltage at rest for a fully discharged LiFePO4 battery is about 1 volt. So you are right that it shouldn't naturally discharge to 0 volts. Assuming I am remembering that correctly, of course.


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## ElectriCar (Jun 15, 2008)

Now that's interesting to note. 1V when discharged. *Hmmm so there's the explanation of how Jack R. ran his all the way down yet didn't damage any cells. * Bottom balancing makes them all even down there so they split the load evenly so when one is discharged and can't move any current they all are. When Jack ran his down I suspect the car would hardly move. I wonder what his pack voltage was after letting the batteries rest.

Had he top balanced by hand and did this, he likely would have reversed a cell or lost the lowest capacity one. Has anyone else had this experience? I think JRP3 ran his very low once with no damage, I don't think as low as Jack did.

*I wonder if Gottdi or anyone else is willing to do this on a small testing sample? *That would be great news if someone did and nothing bad happened. It would need to be a good load though, like an EV. Maybe 30A minimum would work as most Ev's can still go 30-40mph on that many amps on flat terrain.


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## JRP3 (Mar 7, 2008)

I was at 1.77 under load but popped back up to 2.45 unloaded and climbing. I wish I had waited longer and see how high they climbed back but I put it on the charger.


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> Now that's interesting to note. 1V when discharged. *Hmmm so there's the explanation of how Jack R. ran his all the way down yet didn't damage any cells. * Bottom balancing makes them all even down there so they split the load evenly so when one is discharged and can't move any current they all are. When Jack ran his down I suspect the car would hardly move. I wonder what his pack voltage was after letting the batteries rest.
> 
> Had he top balanced by hand and did this, he likely would have reversed a cell or lost the lowest capacity one. Has anyone else had this experience? I think JRP3 ran his very low once with no damage, I don't think as low as Jack did.
> 
> *I wonder if Gottdi or anyone else is willing to do this on a small testing sample? *That would be great news if someone did and nothing bad happened. It would need to be a good load though, like an EV. Maybe 30A minimum would work as most Ev's can still go 30-40mph on that many amps on flat terrain.


This is exactly what happened. No need to test. JR did it three times consecutively. . . granted, he may have had one cell purposely lower, who knows. The guy in video says the same thing about low voltage.


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## Qer (May 7, 2008)

ElectriCar said:


> Bottom balancing makes them all even down there so they split the load evenly so when one is discharged and can't move any current they all are.


Which is the whole point in bottom balancing, yes. It will work as a charm as long as the cells are in a (close to) perfect balance. If they ever drift out of that balance you'll risk killing a cell pretty quick since you "know" it's safe to run down the pack deep into DoD.

Also, this means you run the cells repeatedly into a very deep DoD since that is the feedback you have; that pack voltage prummet when the pack is depleated. If it's true that it's deep DoDs that really make the cells age fast you'll effectively shorten the life span of the whole pack. A top balanced pack with cell individual LVC-detection won't drive all the cells equally deep down and this the average wear will be lower.

But bottom balancing sure beats running without a LVC-BMS on a top balanced pack. 

EDIT: Tried to make my explanation more clear since people by some odd reason thinks that I somehow claim that a bottom balanced pack magically has less Ah than it otherwise would have.


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## MN Driver (Sep 29, 2009)

I thought the guy in the video(professor) said that below 2 volts that problems happen with the electrolyte.

I don't know where the 1 volts fully discharged is coming from, if you pull them down to zero volts at a low current, they will stay there. I wouldn't assume that just because a battery can still hold voltage that it isn't damaged. After all, we might never know how long Rickard's pack would otherwise last, he didn't have much mileage on it and he is already replacing the whole thing with a bigger CALB pack right after he drew all of those cells down to varying voltages low enough yet scattered enough to show they weren't quite bottom balanced as equally as he originally said they would remain.

I don't see a reason of why there would need to be a situation that these ever need to be below 2 volts except under extreme conditions such as racing, heavy draw under very cold temperatures, or discharging lower than you would probably want to for cycle life. These things get hot when you pull enough amperage to pull them down to 2 volts, including when they are at low SOC with a little less amperage. Watch Rickard's video of the mostly constant 4C discharge of CALB, at 4C I personally would have stopped before 30% SOC at that rate based on the temperature profile versus SOC in his chart. He might not have vented and destroyed the cells if he had stopped there.


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## JRP3 (Mar 7, 2008)

Qer said:


> Also, this means you run the cells repeatedly into a very deep DoD and if it's true that it's deep DoDs that really make the cells age fast you'll effectively shorten the life span of the whole pack instead of individual cells.
> 
> But it sure beats running without a LVC-BMS on a top balanced pack.


I didn't realize running a bottom balanced pack means you have to run the cells repeatedly to a deep DoD. You mean like once or twice a year? The horror


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## ElectriCar (Jun 15, 2008)

Qer said:


> Which is the whole point in bottom balancing, yes. It will work as a charm as long as the cells are in a (close to) perfect balance. If they ever drift out of that balance you'll risk killing a cell pretty quick since you "know" it's safe to run down the pack deep into DoD.
> 
> Also, this means you run the cells repeatedly into a very deep DoD and if it's true that it's deep DoDs that really make the cells age fast you'll effectively shorten the life span of the whole pack instead of individual cells.
> 
> But it sure beats running without a LVC-BMS on a top balanced pack.


Hi Qer. I don't see the correlation between bottom balancing and repeatedly deep discharging cells. It's not just going to happen. I "can" do it now with my lead but I'm smart enough not to, knowing it shortens the life. Occasionally I do run it low but only on rare occasion. Maybe 4 or 5 times in 7500 miles. And I know it won't kill my batteries if I do. 

My point is if you bottom balance it properly and they won't die then you could get down in the bottom if you wanted to, unwise though it is.


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## Jan (Oct 5, 2009)

Qer said:


> ...deep DoDs that really make the cells age fast...


I wonder if that's really or completely true. Aging depends on higher voltage and higher temperature. That's what a manufaturer says.

http://www.gpbatteries.com/html/pdf/Li-ion_handbook.pdf

I wonder what is worse: Charge and discharge between 20 and 100% SOC or between 0 and 80% SOC. And why.


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## Qer (May 7, 2008)

JRP3 said:


> I didn't realize running a bottom balanced pack means you have to run the cells repeatedly to a deep DoD. You mean like once or twice a year? The horror


I guess this was an attempt at being sarcastic. Since you apparently misunderstood me and thus your attack were uncalled for I'll try to be civil and explain again what I mean rather than bitch back (except for this sentence which I, quite frankly, think you deserved  ).

All packs have to be protected from being depleted so deep that you risk to reverse individual cells. How you protect them doesn't matter but somehow you have to protect your investment no matter if it's done purely manual or with the help of a BMS. I'm sure we can agree on that, right?

Bottom balancing protects the individual cells by making sure they hit fully discharged at the same time, so if you manage to suck them dry all the cell voltages will drop more or less simultaneously, thus avoiding that the other cells keep the pack voltage up while one single cell gets reversed. This is the advantage of bottom balancing; IF you discharge the pack close to 100% DoD and IF the pack is still in proper balance no cell will be destroyed since there's not enough voltage left to force a cell into reverse.

The disadvantage of this is that if you have a pack where some cells have a noticeable lower Ah than the rest you still force the whole pack to use the same amount of Ah. This means that IF you run the pack deep into DoD you will wear all the cells instead of just the weakest while, in a top balanced pack, only the weakest cells will be deeply DoD and thus excessively worn.

However a top balanced pack without LVC will probably kill the weakest cells where a bottom balanced pack without LVC won't. If you top balance your pack the average cell MTBF will probably be longer (at least if the BMS doesn't break in a harmful way) than if you bottom balance it but instead you NEED a BMS that at least can signal LVC to either shut down or dial down the controller.

Pros and cons.


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## Qer (May 7, 2008)

Jan said:


> I wonder what is worse: Charge and discharge between 20 and 100% SOC or between 0 and 80% SOC. And why.


That is a very good question. From what I've read it seems that the amount of cycles decrease the deeper into DoD you go and my reasoning is based on that that is correct. If that's NOT correct and the level of SoC doesn't matter, then bottom balancing suddenly sounds a lot more beneficial.


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## Jan (Oct 5, 2009)

Qer said:


> That is a very good question. From what I've read it seems that the amount of cycles decrease the deeper into DoD you go and my reasoning is based on that that is correct. If that's NOT correct and the level of SoC doesn't matter, then bottom balancing suddenly sounds a lot more beneficial.


It's not about NOT correct, but about interpretation. What does one mean with '80% DoD'. 

Most seem to think that DOD and SOC have exactly the same meaning. DOD is just the reverse of SOC. A little pointless to use two terms for the same thing.

I wonder if that's the case. Why advise to store a battery at or below 50% SOC. If going low is bad. It all seems to contradict to me.


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## ElectriCar (Jun 15, 2008)

Qer said:


> The disadvantage of this is that if you have a pack where some cells have a noticeable lower Ah than the rest you still force the whole pack to use the same amount of Ah. This means that IF you run the pack deep into DoD you will wear all the cells instead of just the weakest while, in a top balanced pack, only the weakest cells will be deeply DoD and thus excessively worn.
> 
> However a top balanced pack without LVC will probably kill the weakest cells where a bottom balanced pack without LVC won't. If you top balance your pack the average cell MTBF will probably be longer (at least if the BMS doesn't break in a harmful way) than if you bottom balance it but instead you NEED a BMS that at least can signal LVC to either shut down or dial down the controller.
> 
> Pros and cons.


Lots to debate right there. You know how it is with established thinking on a subject, it's hard to change ones thinking. On a well matched pack like it appears we're now getting from Calb, some of the "issues" in the past, ie large variations in actual cell Ah aren't an issue anymore. If so then other problems arising from such variation will be less as well thus moving the balance scales in the direction of "no BMS needed". If we bottom balance but stop the charge at 95-98% we gain life as well, however little that is. 

I think the idea that "you will wear all the cells instead of just the weakest" will become insignificant as the % variation is reduced to a trivial number. My cells are within 1% which is trivial itself IMO.


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## Qer (May 7, 2008)

ElectriCar said:


> My cells are within 1% which is trivial itself IMO.


Then the big question is; after how many cycles?


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## ElectriCar (Jun 15, 2008)

gottdi said:


> If you pull with a load a battery to like .5 volts and then remove your load the battery will pop backup and more than likely pop back up beyond 1volt. If you keep a sustained load and bring the battery into a .01 volt situation then the battery may only pop back to under 1 volt. Want to see one?
> 
> Pete


If you draw it down low then put a low power load on it, say 5 amps it could die. Then again it may not. I think it should have a load that approximates an ev typical load. Probably 30A would be on the low side but not unrealistic. At some point the cell voltage is low enough it can't force "usable" current through the motor so your vehicle is pulling over! That's the magic of bottom balancing IMO.

gottdi I Vote "Yay" in favor of you testing yours with a load of 30A or more and see what happens.


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## Jan (Oct 5, 2009)

Qer said:


> Then the big question is; after how many cycles?


Yes. In other words is there cell drift? No one seems to know.

Bottom line: The facts of these kind of cells are very unclear. And especially about the properties that should tell us "To CMS Or Not To CMS".


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## Jan (Oct 5, 2009)

After searching in google books and reading some more. There seem to be two causes of aging. One that has nothing to do with SOC, and one that depends on Voltage and Temperature. It confirms what I already 'knew'.

The higher the temp, and the higher the voltage, the faster the aging. Fast is a relative term here. Nothing about DoD. 

But since cell temperature depends on internal resistance, and IR on SOC. There is a indirect connection. But this connection has more to do with the amount of amps you draw, then SOC. I reckon.


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## Qer (May 7, 2008)

Jan said:


> Yes. In other words is there cell drift? No one seems to know.


My post was pointing out that ElectriCar had managed to pin point the main advantage with bottom balancing when he wrote:



ElectriCar said:


> *Hmmm so there's the explanation of how Jack R. ran his all the way down yet didn't damage any cells.*


but also that if deep discharges decrease the amount of cycles it also means that you'll wear the whole pack rather than just the weakest cells. Now, if your pack is within 1% it's all fine and dandy, but I wouldn't go so far to expect all packs to automatically be that closely matched or that they stay that closely matched when they start to age.

And it's that question about age that led me to ask about how many cycles you've had your pack. If it's just a few hundred cycles old it's rather brand new still and the cells are likely to still be rather close to each other, but will they be that when they reach 1000 or 2000 cycles? Or if you happen to abuse them a few times?

My experience from other kind of chemistry tells me that the older or more abused the batteries get, the more they will turn into individuals. Will it be the case for your pack as well? It'll probably take a few years before we know, right?


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## rochesterricer (Jan 5, 2011)

MN Driver said:


> I thought the guy in the video(professor) said that below 2 volts that problems happen with the electrolyte.
> 
> I don't know where the 1 volts fully discharged is coming from, if you pull them down to zero volts at a low current, they will stay there. I wouldn't assume that just because a battery can still hold voltage that it isn't damaged. After all, we might never know how long Rickard's pack would otherwise last, he didn't have much mileage on it and he is already replacing the whole thing with a bigger CALB pack right after he drew all of those cells down to varying voltages low enough yet scattered enough to show they weren't quite bottom balanced as equally as he originally said they would remain.
> 
> I don't see a reason of why there would need to be a situation that these ever need to be below 2 volts except under extreme conditions such as racing, heavy draw under very cold temperatures, or discharging lower than you would probably want to for cycle life. These things get hot when you pull enough amperage to pull them down to 2 volts, including when they are at low SOC with a little less amperage. Watch Rickard's video of the mostly constant 4C discharge of CALB, at 4C I personally would have stopped before 30% SOC at that rate based on the temperature profile versus SOC in his chart. He might not have vented and destroyed the cells if he had stopped there.


I'm getting this info mostly from the video of the Carnegie Mellon prof. He said that the voltage at rest when the anode is empty of lithium is 1 volt. I think the point at which the electrolyte starts splitting is 0.1 or 0.2 volts, but I don't remember for sure. If I have time today, I will try to watch the vid again and give you some time markers for when in the vid these things are said.


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## DIYguy (Sep 18, 2008)

Jan said:


> Yes. In other words is there cell drift? No one seems to know.
> 
> Bottom line: The facts of these kind of cells are very unclear. And especially about the properties that should tell us "To CMS Or Not To CMS".


Earlier in this thread, or was it the other thread.... they seem to be a blurr now.. it was established by this leading expert that there is no such thing as "drift" ...NO DRIFT. 

Qer, your experience with other chemistries is not applicable to LiFePo.

Edit, post 396 and 397. There was also data posted which demonstrates this.....


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## Jan (Oct 5, 2009)

DIYguy said:


> Earlier in this thread, or was it the other thread.... they seem to be a blurr now.. it was established by this leading expert that there is such thing as "drift" ...NO DRIFT.
> 
> Qer, your experience with other chemistries is not applicable to LiFePo.


Sweeds (scandinavians in general) have a lot of experience with 'other chemistries'. Especially when they're out of their country.


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## Jan (Oct 5, 2009)

DIYguy said:


> Edit, post 396 and 397. There was also data posted which demonstrates this.....
> 
> "This is pretty easy to answer: well balanced (especially capacity wise) Li-ion strings that are strung up when at the exact same SoC should never drift with respect each other as long as they see the same thermal environment. I'd testify to this in court: there is no mechanism to cause such drift."


'Thermal environment' is not clear to me. As long they are exactly the same temperature? And if they're not, they start to drift?


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## DIYguy (Sep 18, 2008)

If you have some in a heated battery box and others not... .that's a different thermal environment. It wasn't really quanitified ...however... temperature effects just about everything  If you push the extremes, you can change state of matter.  lol

My take was that the useful capacities are affected. This is well established and posted by all the battery companies.


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## JRP3 (Mar 7, 2008)

Qer said:


> I guess this was an attempt at being sarcastic. Since you apparently misunderstood me and thus your attack were uncalled for I'll try to be civil and explain again what I mean rather than bitch back (except for this sentence which I, quite frankly, think you deserved  ).


Really? You're going to play sarcasm police, after this statement?


> Originally Posted by *Qer*
> _Also, this means you run the cells repeatedly into a very deep DoD and if it's true that it's deep DoDs that really make the cells age fast you'll effectively shorten the life span of the whole pack instead of individual cells.
> 
> *But it sure beats running without a LVC-BMS on a top balanced pack.* _


_
I detected sarcasm and responded in kind, it didn't seem uncalled for and I reject your attempt to chastise me. So there.
_


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## Jimdear2 (Oct 12, 2008)

It seems to me there is some real reluctance in the DIY EV community to size a battery for real world conditions. All I am seeing are a lot of the people that look at buying a battery just a bit wrong.

Kind of like buying a ICE vehicle with an X gallon gas tank, since they normally only drive Y miles a day that all they need.

The very first thing is they have to realize the pack needs to be oversized just to protect itself (untouchable excess). Then they have to add a bit more for the time in slow traffic with the wipers and headlights on.

From what I've been reading, for prismatic cells, it seems to me that the best *Battery Management System* is actually a *Battery Monitoring System *that controls what you put into and take out of the pack as a whole, not adjusting the in and out of individual batteries. 

The BMS has to become transparent to the operator.

That is it needs some way of keeping your cells from terminal low or high voltage and damage. This is the desired result and is a real world requirement. By the KISS principle the best method is to never go where the damage can happen.

Normally, people who drive ICE never even come close to using the maximum fuel available. I.e. they don't fill the tank until it runs over or drive around until they run out of fuel, this id the ICE KISS principle. 

Now we get to my questions about how and if. 

Mostly this is addressed to Tesseract and QER as the only EV hardware and software experts that I know of and who know each other and have an understanding of what they each can do. I know there are others out their please jump in.

I'm thinking that for prismatic cells to come into there own, they need two things, just like the cylinders of a modern engine. 
One) NEVER be taken into the area that potential damage could occur.
Two) Each cell needs a positive identifier so if damage does happen, you know where to look.

Tess, is it possible to make a really reliable voltage sensing device that would have a (this is where QER comes in) unique code assigned and then be potted to the point of indestructibility? These would need to be attached to each battery as it was installed.* Then, can each unit be polled over the existing traction battery cables?* I know that you can buy intercoms that use the existing wiring in a house to transmit and receive, I would think this would be somewhat similar.

Then, (TESS and QER) could a central processing unit be made that would look at these signals from each battery and could watch during charging and shut things down at chosen percentage, say 80 or 90% charge for the highest voltage battery in the pack. Then identify that battery if it were consistently more then X% out of balance. Thus preventing any single battery from ever being driven too high, and allowing quick positive location of a bad or damaged cell.

This CPU would give a full FUEL gauge reading if the all batteries in the pack successfully reached the 80 or 90% chosen to be a full pack. It would also give a less then full FUEL reading at the end of charging, if not all batteries reached a balanced full charge. The system would identify any battery that was consistently out of balance by a set percentage (by the unique number of the sensing unit). 

The converse of the above would protect the pack at the low end. The system would show a empty gauge *and to protect the battery actually shut down the vehicle* (_with a couple of shakes and judders first, just like running out of gas_) at a safe 10 or 20% of pack capacity. Again if one or more batteries were out of balance above a set percent consistently, the CPU would identify that battery. 

So we would have a monitoring system that manages the pack as a whole. Never allowing an individual battery to become damaged, and giving each individual battery a bit of wiggle room to come back into line without ever actually adding or subtracting from a specific battery. Finally it gives the operator, by monitoring the voltage of th pack as a whole a reasonable full to empty fuel gauge.

There would need to be some pretty fancy programming in there to say that if 1 or if 10 out of twenty batteries reached full charge voltage before the rest, it would affect the overall percentage or the rate the gauge went from full to empty.

I don't have the skills to know if this is possible I await your comments


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## JRP3 (Mar 7, 2008)

Jan said:


> I wonder if that's the case. Why advise to store a battery at or below 50% SOC. If going low is bad. It all seems to contradict to me.


Manufacturer data clearly shows higher cycle life by staying away from 100%DOD, progressively longer to 70%DOD usually showing more than 3000cycles. After that additional cycle life gains are basically meaningless so presumably any possible benefits from storing at a higher SOC than 50% are probably outweighed by the benefits of staying around 50%. If you mostly discharge to 70-80% on a regular basis projected cycle life should allow the pack to outlast the vehicle, even with the occasional 100% DOD event.


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## JRP3 (Mar 7, 2008)

Jimdear2 said:


> Finally it gives the operator, by monitoring the voltage of th pack as a whole a reasonable full to empty fuel gauge.


Voltage is not a great indicator of SOC through the middle discharge range so ah counting is better. I've used voltage as a monitor but it does fluctuate a lot under load so you really have to get a feel for how your pack behaves. Ah counting takes the guesswork out.


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## Jan (Oct 5, 2009)

DIYguy said:


> If you have some in a heated battery box and others not... .that's a different thermal environment. It wasn't really quanitified ...however... temperature effects just about everything  If you push the extremes, you can change state of matter.  lol
> 
> My take was that the useful capacities are affected. This is well established and posted by all the battery companies.


Grm. Why is it all so unclear? 

The temperature affects the capacity in two ways:

Low temperatures decreases the capacity temporarily. Simply because the chemical processes in the battery need a certain minimal temperature, and operate better at higher temperatures

But higher temperatures, speed up the aging process. What decreases the capacity in the long term. 

The cells heat up, according to their IR under load, and cool down according to their position in the car/pack. Both are different per cell.

Which effect causes permanent drift? And how serious?

Anyway. So far I know now, deap DoD ansich doesn’t do anything bad to a cell. On the contrary, higher SOC (high voltage) is the bad guy. But most of all: temperature. 

The only correlation between DoD and aging is the temperature: The low SOC mean higher IR, which mean higher temperature under the same load. Combined with the fact a deap DoD defacto means a lot of amps for a long time. Which in its turn means higher temperatures for a longer time.

Deap DoD => high temps for a relative long time. It doesn’t much matter if you come down from 100% to 20% SOC, or from 80% to 0% SOC. The same time period, the same amps, only a little higher IR in the last one. I doubt that will be measurable. 

At no load, the higher voltage has a much better documented and noticeable aging effect on the cells.

Conclusion so far: Bottom balance and keep them cool. Keep them all just as cool. But not to cool. 

Oh, and CMS? 
Inconclusive.


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## Jan (Oct 5, 2009)

JRP3 said:


> Manufacturer data clearly shows higher cycle life by staying away from 100%DOD, progressively longer to 70%DOD usually showing more than 3000cycles. After that additional cycle life gains are basically meaningless so presumably any possible benefits from storing at a higher SOC than 50% are probably outweighed by the benefits of staying around 50%. If you mostly discharge to 70-80% on a regular basis projected cycle life should allow the pack to outlast the vehicle, even with the occasional 100% DOD event.


I disagree. 0% is better than 100% SOC for a li-ion. All books, handbooks, and other online literature I read confirms this. 

It’s just HOW you go from 100% to 0%. Or from 80% to 20%. 

What is the temperature of your cells and how long do you punish them with this? Of course going to 100% DoD or to 50% DoD, under the same circumstances, the first one will be worse for your cells. 

But I believe (at the moment) that going slowly, with proper cooling from 80% SOC to 0% SOC is better for the pack then from 100% to 20% SOC without proper cooling and with a higher load. 

Temperature is what will kill them finally.


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## ElectriCar (Jun 15, 2008)

I wish the good doctor would get on this thread. He seriously could answer some questions and put other notions to bed! JRP3 maybe you or DIYguy could invite him, whichever one of you has been conversing with him. He would only need to subscribe to a few threads and answer anything contrary to the truth, which on this site is quite a bit.


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## JRP3 (Mar 7, 2008)

Jan said:


> It’s just HOW you go from 100% to 0%. Or from 80% to 20%.


None of the manufacturers show this. They use the same C rates in their test at 100%, 90%, 80%, 70%, and clearly show longer cycle life with shallower discharge. At constant C rates the cells reach a temperature during use but if it's within the capacity of the cell to shed that temperature a cell shouldn't get any hotter discharging to 100% than 70%, so I think you are jumping to conclusions that may not exist. Manufacturers do allow higher C rates with more aggressive cooling.


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## ewert (Sep 5, 2009)

You know, I was thinking about the whole CMan/CMon/BMan/BMon thing. Has anyone done intentional high/low cell monitoring setup?

Say 40 cells. Bottom balance. Charge one cell say 3% of capacity. Charge whole pack to knee (with the high charged as marker). Discharge one cell say 3% of capacity. Do cell level monitors on just these two cells (now that's only 5% of the cost and much-o-less wiring of something like dmitri's CMon's instead of using one on all cells).

Now, during charging HVC trips on high cell and leaves rest mostly un-kneed. During discharge, LVC trips on low cell and leaves rest again mostly un-kneed. Beware though, you really REALLLLLLY do not want to go past that LVC, or the designated marker cell is gonna buy the farm.

This same system could very easily be made into a cheap and effective middle SoC running system by increasing the top and bottom differences. Maybe even do split pack voltage monitoring of the "base cells", so that cell #1 LVC, cell #40 HVC, and cells 2-39 are split into 2-20 and 21-39 with voltage monitors for splitpack monitoring, so you will see if your main pack ever goes into imbalance. Add a switch to bypass the #1 LVC cell for emergencies, so you can go to super deep DoD if a true emergency?

Sounds good to me ...


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## DavidDymaxion (Dec 1, 2008)

Real data alert!

It's not much, but here are some torture testing runs I did:

http://explodingdinosaurs.com/9electric/celltest

Some high level observations:


Cells were delivered out of balance
Cells stayed close after bottom balance (until vented)
Did high current and deep discharges
After venting, 2 cells showed 0.1 V / day self discharge
Vented cell was 93 Celsius
No more venting staying below 70 Celsius
1 cell wept a little electrolyte but has continued to work fine
Caveat city: This is just a small number of cycles. My cells seemed to be very well matched. This is a small number of cells, obviously it'll be harder to see the knees on the curve by observing overall voltage of longer series strings of cells.

I think my data generally agrees with Jack Rickard, for the small number of cycles I did. Where it definitely disagrees is he states cells are delivered in "middle balanced" condition, and to just use them straight out of the box with no initial balancing. My data showed conclusively my cells were not!

The next goal is to look for the presence or absence of a self balancing effect.


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## MN Driver (Sep 29, 2009)

Interesting results. I haven't come across the spec sheet on these, what are they rated for charging amperage? Are these prismatic cells like the rest of HiPower cells or not? I thought I read about HiPower planning or producing cylindricals, are these the cells?

If these can repeatedly support 50 amp charging bursts with solid 100 amp discharges to 20 or 30% SOC, I would be very happy. How hot do they normally get with a 10C continuous discharge before you ran them over their specs and damaged them? I'm not looking to exceed about 60 degrees C.


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## JRP3 (Mar 7, 2008)

DavidDymaxion said:


> I think my data generally agrees with Jack Rickard, for the small number of cycles I did. Where it definitely disagrees is he states cells are delivered in "middle balanced" condition, and to just use them straight out of the box with no initial balancing. My data showed conclusively my cells were not!


I don't know if Jack ever tested newly shipped HP cells, that might be the difference.


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## Jan (Oct 5, 2009)

JRP3 said:


> None of the manufacturers show this. They use the same C rates in their test at 100%, 90%, 80%, 70%, and clearly show longer cycle life with shallower discharge. At constant C rates the cells reach a temperature during use but if it's within the capacity of the cell to shed that temperature a cell shouldn't get any hotter discharging to 100% than 70%, so I think you are jumping to conclusions that may not exist. Manufacturers do allow higher C rates with more aggressive cooling.


I believe the cycle life data in the battery specsheets is simplified, yet very usable data. But not exactly what makes a li-ion cell age.

Found another very difficult document:

http://www.che.sc.edu/faculty/popov/drbnp/website/Publications_PDFs/Web26.pdf

Very hard to read for me as a non scientific, non native english speaking stupid person.

What I understand is that the aging and DOD correlation, is the time a 'parasitic reaction' is able to do its destructive work. It's the time, not the exact final SOC. 

Maybe someone with brains can translate the document for people like me.


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## Jan (Oct 5, 2009)

Maybe the conclusion is enough for someone with brains:

_*Conclusion*

A charge-discharge capacity fade model was developed based on the loss of active lithium ions due to solvent reduction reaction. The rise in the surface ﬁlm resistance at anode due to the precipitation of insoluble product of the parasitic reaction was also considered in the model. The model considers process parameters such as CR, DOD, and EOCV and controls the required DOD by controlling the discharge time and estimates the discharge voltage as a function of cycle number. The results indicated that both the dimensionless loss of lithium and the surface ﬁlm resistance increase with the increase of the overpotential and the duration of the parasitic reaction. The loss of the active lithium Qs also increases with the increase of the exchange current density of the parasitic reaction. The total parasitic reaction time increases with an increase of EOCV or DOD. The overpotential of the parasitic reaction at the negative electrode increases with an increase of EOCV and shows a maximum at the transition point from CC to CV charging._

EOCV=end-of-charge voltage
CR=charge rate


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## JRP3 (Mar 7, 2008)

Jan said:


> _The total parasitic reaction time increases with an increase of EOCV or DOD. The overpotential of the parasitic reaction at the negative electrode increases with an increase of EOCV and shows a maximum at the transition point from CC to CV charging._
> 
> EOCV=end-of-charge voltage
> CR=charge rate


I would take that to mean that higher charging and deeper discharging damages the cell.


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## Jan (Oct 5, 2009)

JRP3 said:


> I would take that to mean that higher charging and *deeper* discharging damages the cell.


I would say: longer.


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## JRP3 (Mar 7, 2008)

That's not what was written. Additionally, a longer discharge at a slower rate is better than a shorter discharge at a higher rate to the same DOD, as we have seen. Cell life is extended by limiting C rates, since that's what causes overheating. You don't overheat a cell by discharging it to 90% DOD verses 80% DOD.


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## Jan (Oct 5, 2009)

JRP3 said:


> That's not what was written.


No, not specific. But the way DOD is interpreted here on this forum, I think that also is not what is meant.



> Additionally, a longer discharge at a slower rate is better than a shorter discharge at a higher rate to the same DOD, as we have seen. Cell life is extended by limiting C rates, since that's what causes overheating. You don't overheat a cell by discharging it to 90% DOD verses 80% DOD.


I never said overheating. I understand from other articles, that aging increases with temperature. Not all of a sudden at some limited temperature. But the aging process goes faster at 30C than at 20C. Not much, but noticable. 

Overheating, is more like boiling the electrolyte. That's murder, not aging.


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## JRP3 (Mar 7, 2008)

Higher temperatures that are still below boiling do seem to affect cell life. You seem to be making an assumption that a deeper DOD is a longer continuous event and therefore will keep cell temperatures elevated, longer, but for me at least a deep DOD takes more than one continuous trip to reach, so the cells cool down in between.


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## DavidDymaxion (Dec 1, 2008)

It is important to note these are the old cells, and the new cells China HiPower is coming out with are supposed to be better. I have some on order to test. (I also ordered and have received some Headways that I'll be testing.)

The spec sheet I was furnished said they can discharge at 10C and recharge at 5C. That's true for one cycle, but I found they went to 73 Celsius if I did 10C, 2 min out and 4C in for 3 cycles.

100 A for 5.5 minutes got them up to 73 Celsius also.

A single 100 A burst for 2 minutes would get them up to about 45 Celsius.

Caveat: It's been very cold here, so those temps could go up in summer.

Spec said to not exceed 80 Celsius. To be more conservative I now limit that to 70 Celsius for testing. I have verified they will spit out a ruinous amount of electrolyte at 93 Celsius. Per the Rice professor's talk, I think I'll plan to limit to 60 Celsius as the long term plan.

The newer cells are supposed to have about 20% less internal resistance, so they should run a bit cooler.

These are little 10 Ahr cylindrical cells. I bought them here:

http://www.evequipmentsupply.com/CylindricalCells.html

Here is an interesting white paper on their construction:

http://www.evequipmentsupply.com/media/HiPower/HiPower_Advantages.pdf

Disclaimer: I am getting some sponsorship from Carl at http://www.evequipmentsupply.com .

Regarding Jack and HiPower cells and initial balancing. I don't remember him qualifying just using lithium cells right out of the box, but on his comments section he amended that to that was his experience with the CALB cells.


MN Driver said:


> Interesting results. I haven't come across the
> spec sheet on these, what are they rated for charging amperage? Are these prismatic cells like the rest of HiPower cells or not? I thought I read about HiPower planning or producing cylindricals, are these the cells?
> 
> If these can repeatedly support 50 amp charging bursts with solid 100 amp discharges to 20 or 30% SOC, I would be very happy. How hot do they normally get with a 10C continuous discharge before you ran them over their specs and damaged them? I'm not looking to exceed about 60 degrees C.


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## Jan (Oct 5, 2009)

Just found another one, more focused on automotive:

http://mtrl1.me.psu.edu/Document/ZhangY_JES_2009.pdf

The only problem is understanding this shit. The answers are here, but...


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## JRP3 (Mar 7, 2008)

DavidDymaxion said:


> The spec sheet I was furnished said they can discharge at 10C and recharge at 5C. That's true for one cycle, but I found they went to 73 Celsius if I did 10C, 2 min out and 4C in for 3 cycles.


One thing to watch out for is sometimes they say "continuous" on one sheet and then another sheet for the same cell says "continuous for 30 seconds" or some such qualifier. I think some things get lost in translation at times.


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## Qer (May 7, 2008)

Jan said:


> Sweeds (scandinavians in general) have a lot of experience with 'other chemistries'. Especially when they're out of their country.


Oho? You sure you don't mix us up with he Dutch? Up here it's just hard liquor.



JRP3 said:


> _I detected sarcasm and responded in kind, it didn't seem uncalled for and I reject your attempt to chastise me. So there._


Dude, you definitely have to dial down your sarcasm detector. It hardly reaches cheeky on my scale... 

As for jimdear2's questions in post #612, still pondering it but I have to dash off to work now...


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## rochesterricer (Jan 5, 2011)

Ok, I watched it again and found the spots I was talking about.

The discharged voltage of 1 volt is brought up when he first talks about the voltage profile at about the 9:30 mark.He brings it up again at about the 55:30 mark when talking about over-discharge. He also mentions the electrolyte not being stable below 0.1 or 0.2 volts shortly after that at about the 56:20 mark.

He starts talking about the effects of temperature at the 33 minute mark. He says the electrolyte starts to break down at a local temp. of 50 or 60 degrees Celcius.

Here is think link if any of you don't have it yet:

http://www.ri.cmu.edu/video_view.html?video_id=60&menu_id=387


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## Jan (Oct 5, 2009)

Qer said:


> Oho? You sure you don't mix us up with he Dutch? Up here it's just hard liquor.


We are hard working non drinking calvinists, with no sense of humor. 

With a totaly wrong, on nothing based, bad reputation.


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## Jan (Oct 5, 2009)

Jan said:


> Just found another one, more focused on automotive:
> 
> http://mtrl1.me.psu.edu/Document/ZhangY_JES_2009.pdf
> 
> The only problem is understanding this shit. The answers are here, but...


 
Low temperatures are also bad for the aging process.. Pfff...


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## Qer (May 7, 2008)

Jan said:


> We are hard working non drinking calvinists, with no sense of humor.
> 
> With a totaly wrong, on nothing based, bad reputation.


I see. Well, better watch that lack of humour if you ever visit Scandinavia, it might be unhealthy. Or you could simply visit Finland, they share the same complete lack of humour so you'd fit right in. Just don't stand between a Finn and his sauna...


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## Jimdear2 (Oct 12, 2008)

Qer said:


> I see. Well, better watch that lack of humour if you ever visit Scandinavia, it might be unhealthy. Or you could simply visit Finland, they share the same complete lack of humour so you'd fit right in. Just don't stand between a Finn and his sauna...


QER,

I'm a Finn and do you realize where you are standing? Worse don't be between the sauna and the snow bank.

Jim


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## Qer (May 7, 2008)

Jimdear2 said:


> Worse don't be between the sauna and the snow bank.


Oooo. Do that and you'll never realise what hit you...


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## JRP3 (Mar 7, 2008)

Qer said:


> Oooo. Do that and you'll never realise what hit you...


A hot naked dude?  Hmmm, that didn't sound right.


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## Jimdear2 (Oct 12, 2008)

JRP3 said:


> A hot naked dude?  Hmmm, that didn't sound right.


Come on give us a break, It could be a dudette. At least half of us are female, thats why there are still Finns.


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## rochesterricer (Jan 5, 2011)

JRP3 said:


> A hot naked dude?  Hmmm, that didn't sound right.


I like where this thread is going....... Wait, what?


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## JRP3 (Mar 7, 2008)

Jimdear2 said:


> Come on give us a break, It could be a dudette


That would be welcome, but....


> Just don't stand between a Finn and *his* sauna


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## ElectriCar (Jun 15, 2008)

gottdi! Are you doing the discharge testing to verify the cells won't die when run down to 0V under a 30A or so load?


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## Jimdear2 (Oct 12, 2008)

JRP3 said:


> That would be welcome, but....


 
Enough Enough Enough. 

You guys keep on with the Finn jokes and I might think about maybe, possibly, kind of getting offended . . . maybe.

*Now You Naughty Boys Get Back to BMS Where You Belong*

(And QER brought in gender so it his fault . . . so there)

Jim


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## dexion (Aug 22, 2009)

I think gizmoev postulated about what if the cells were the same temp would they come up at the same time. I waited for them to be off (15 cycles) and then brought them all to the same temp (about 50F) they all came up at nearly the same time (perhaps .05amps apart rather than 1ah.) Repeated it again the next week. So they dont like 30F difference (but not by much.)


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## GizmoEV (Nov 28, 2009)

That is interesting. So if I understand you right you let the cells drift apart. Then you warmed them all up to about 50°F and charged them and they were off by only 0.05Ah rather than the typical 1Ah? That sounds quite small but it could accumulate over a longer period of time.

It appears that in my 1 battery box Gizmo I won't have to worry about it much but it might be worth checking on when I finally get to do a full sized EV conversion.

BTW, at least on a Windows computer holding the Alt key and typing 0176 (Alt+0176) on the key pad will generate the degree symbol.


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## ElectriCar (Jun 15, 2008)

gottdi said:


> I will be doing so. I have 4 cells to use for the testing.


You ARE THE MAN! 

Well I've decided I'm going FREE. Should conditions WARRANT further monitoring I will do whatever I feel is needed. For now I'm planning to use four devices to help protect and notify the driver of pack status and developing faults. 

I think it will give ample protection coupled with not charging to the max and not discharging below 80-90% DOD with a bottom balanced pack. Even that deep discharge will be VERY INFREQUENT. 

1. I've already ordered the Cycle Analyst large in-dash display to track Ah, display volts and a host of other things. Nearly worthless PakTrakr is going in the trash. It has a bad module now and is the 3rd one of 3 to fail in 3 years. Horrible noise issues three years later are NOT being addressed by these people. Hopefully this is my last instance into pack wiring to each battery.

2. ABB voltage relay for a backup HVC cutoff in case my Zivan NG5 fails to stop at the appropriate voltage. IMO it's worth a measly $135 and a few minutes wiring to prevent pack destruction should that happen. These batteries SHOULD HAVE REDUNDANCY to protect them from charger failure IMO. Also should I want to charge to a lower level than initially planned, I could adjust this thing instead of returning it to Zivan again for reprogramming if a trim pot inside won't do it.

3. Lee Hart battery bridge, home built to compare each half of the pack. This simple device should show any significant development on an individual cell by displaying an imbalance in the two halves of the pack. With all good cells and aging equally this thing should do a pretty good job of showing a high resistance connection, shorted cell etc. It could be duplicated so you could further divide the pack into smaller portions if warranted but that means more intrusion into the pack to make the connections. 

4. The Zeva fuel gauge driver plus converts most fuel gauges to an SOC gauge, provides a settable "low battery" indication feature and with the flip of a switch it will display up to 600 amps on my newly installed Auto Meter 3707 tach. If it doesn't work on your fuel gauge they will refund your money. 

With all of this I'll have ONE wire running to the middle of the pack with the other wiring under the hood. My batteries I think will all be in the back of the S10.


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## Roy Von Rogers (Mar 21, 2009)

I also highly recommend that instead of using bolts to hold down the battery connectors, use studs with nuts and nord-lock washers, so as to leave some of the stud exposed above the main hold down nut, for the purpose of aux/monitor connection(s).

This way there are no other connectors between your main connection to cell, and only the connection above is being used for auxuilliary purposes, and will therefore not interfere with the main amperage connection.



Roy


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## GizmoEV (Nov 28, 2009)

ElectriCar said:


> Well I've decided I'm going FREE. Should conditions WARRANT further monitoring I will do whatever I feel is needed.


Most of the "complaints" with going without a CMS of some sort is what happens at the end of life of the pack. Well, since it has been demonstrated that a 2-year old pack has done fine without a CMS of any sort it appears that you will be fine for at least 2 years. Second, if the pack is at the end of life and it has a problem, well...it is End Of Life! Doesn't that mean it is time to replace it any way?

Hopefully it will be easy for you to get to your cells to get end of charge voltages with a meter. It would be great to have you get data on them regularly and keep a spreadsheet of them to see what happens over time. After bottom balancing your pack maybe you can get a set of voltages at the end of charge as a benchmark. At first I'd recommend taking readings at least once per week to see what the batteries do when new.

The only data I have when mine were new is that I could go about 6 miles/kWh out of the wall. Right now my average is just over 5 miles/kWh. Still better than 4 mi/kWh with lead but low. I don't know if it is lower because of the pack aging or if it is because the pack is much colder right now. We'll see as the weather warms up. FWIW, I've attached a chart of mi/kWh from the wall and %DOD vs full charge #. A full charge is defined as letting the charger complete its charge cycle. There are a couple of outliers but there is a trend. The data starts with January 18, 2010 and continues through January 27, 2011. There is a yellow line at charge #128 where I installed all 40 cells for a 2p20s pack and one indicating Jan 1, 2011. Sorry, I was too lazy to remove the remaining days for 2011 which are at zero right now. This is also where I quit charging to 4.00vpc. Last winter was much warmer than this winter, too.



ElectriCar said:


> With all of this I'll have ONE wire running to the middle of the pack with the other wiring under the hood. My batteries I think will all be in the back of the S10.


Are these going in the bed or under the bed? How big is your pack going to be in kWh using 3.2vpc as the nominal voltage?

Edit: Oh, and can you explain how that ABB voltage relay works? The site you linked to didn't give any specs on it. How sensitive is it and how accurate is it?


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## ElectriCar (Jun 15, 2008)

GizmoEV said:


> ... if the pack is at the end of life and it has a problem, well...it is End Of Life! Doesn't that mean it is time to replace it any way?


Haha yea I guess it would be postponing the inevitable to keep running. 



GizmoEV said:


> Oh, and can you explain how that ABB voltage relay works? The site you linked to didn't give any specs on it. How sensitive is it and how accurate is it?


It's a voltage monitor with an adjustable set point, time delay and hysteresis. In your case you adjust it to 70V? and if your charger exceeds that it will shut it down. The hysteresis is adjustable 3-30% so once it is tripped it won't release charger control until the voltage drops at least >3%. (Note to Microsoft: A greater than or equal to key would be very nice!) Here's the spec sheet.


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## ElectriCar (Jun 15, 2008)

GizmoEV said:


> Are these going in the bed or under the bed? How big is your pack going to be in kWh using 3.2vpc as the nominal voltage?


All under the bed which frees up space under the hood. Pack voltage 160, Kw 32 at 3.2V. Should have them in about 3 weeks so I'm probably going to tear it down in a week or so and start installing all the new equipment. I may have new battery boxes made when I get some time to consider the weight and what I can do for insulation. I'm thinking of using radiant barrier foil faced bubble insulation. It's 5/32" thick and is R 3.4 if I recall correctly. I'd like to be able to remove it in the spring and replace it in the fall. It reflects heat like a mirror reflects light with 95% efficiency. I've used it or the foil only type for years under the floor, attic and walls. This stuff works great to keep heat wherever it is. I think Nasa developed radiant barrier for space suit lining to allow space suits to be thinner and lighter.


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## GizmoEV (Nov 28, 2009)

Thank you for the spec sheet for the ABB voltage monitoring unit.

I was just thinking about the CA. When I had mine hooked up continuously it would record a drain on the pack greater than what it actually was because with a 500A 50mV shunt the CA only has a 0.1A resolution. I decided that the parasitic load on my pack was small enough that I wasn't going to worry about it. I didn't like having to manually switch on the CA every time I drove and then remember to turn it off so I built a relay which would come on when the key was turned on which would turn on the CA and then turn it off on key off.

The next thing I did was use the two relays in the Zivan NG1 charger. Each has a NO and NC contact. One relay switches when power is applied to the charger and the other switches when at the end of charge. What I did was run a wire to the first relay's NO contact and jumper over to the next relay's NC contact. This was wired in parallel to the relay operated by the key. When power is applied to the charger the first NO relay closes completing the circuit so I can see the Ah count down on the CA. When the end of charge comes the NC relay switches open, turning off the CA. It works great. The resistance of the CA is high enough that the inrush current is quite small and stays under the charger's relay contact ratings. Maybe the NG5 has the same set of relays.


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## ElectriCar (Jun 15, 2008)

So the CA doesn't lose data when powered off? I have the same two relays I think. I have one so that it locks out the control when charging. I just know that one day I'd try and drive off while charging!


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## GizmoEV (Nov 28, 2009)

Right. The manual talks about not drawing too much power from it's output when creating a serial output circuit because it can drain the capacitors too fast for the info to be saved to non-volital memory or something along those lines.

It is the positive line being controlled by the relays so if you are using them for a lockout you might want to consider a setup to isolate the HV. I didn't want to switch the negative line because there are 3, IIRC. One for the most negative line and power and the other two for measuring the shunt voltage.


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## tomofreno (Mar 3, 2009)

Let me see if I understand the ABB relay Electricar. The measuring terminals, B, C, would be connected across the battery pack to read pack voltage, and the supply terminals, A1, A2, would be in the AC supply line to the charger. When the pack voltage hit the threshold setting, the timer turns on and if the pack voltage is below the threshold voltage minus the hysteresis setting at that point, the relay re-connects power to the charger, if not, the charger remains disconnected - that is if operated in the over voltage mode of course. Correct? Looks like it works with both 120 and 240AC. If I understand it correctly, I agree it would be a good backup. 

Of course, what average SOC the pack is at when the ABB hits its threshold voltage will vary with cell temperature and charging current magnitude, same as with the Manzanita chargers. Then you would get more repeatable SOC if you operate top balanced and set the threshold voltage to the pack voltage value when all cells are just below the bottom of the knee (about 3.45V/cell for CALB cells, so say set at 3.44V) at the lowest temperature at which you expect to charge. Because then the increase in voltage with SOC from that point on will be very large compared to the variation in pack voltage with cell temperature or charging current magnitude - since all the cells will be starting up the knee, rather than only one if the pack is bottom balanced.

Edit: I should add that if the pack is sized large enough and you have a charge counter, the variation in SOC with charge current magnitude and cell temperature won't matter of course. You will still have plenty range even if you charge 10 - 20 Ah less when the cells are colder or you charge at higher currents.


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## JRP3 (Mar 7, 2008)

If his cells are within less than 1% of each other I'm not sure it would matter. Enough of them should come up together even with bottom balancing.


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## ElectriCar (Jun 15, 2008)

tomofreno said:


> Let me see if I understand the ABB relay Electricar. The measuring terminals, B, C, would be connected across the battery pack to read pack voltage, and the supply terminals, A1, A2, would be in the AC supply line to the charger. When the pack voltage hit the threshold setting, the timer turns on and if the pack voltage is below the threshold voltage minus the hysteresis setting at that point, the relay re-connects power to the charger, if not, the charger remains disconnected - that is if operated in the over voltage mode of course. Correct? Looks like it works with both 120 and 240AC. If I understand it correctly, I agree it would be a good backup.
> 
> Of course, what average SOC the pack is at when the ABB hits its threshold voltage will vary with cell temperature and charging current magnitude, same as with the Manzanita chargers. Then you would get more repeatable SOC if you operate top balanced and set the threshold voltage to the pack voltage value when all cells are just below the bottom of the knee (about 3.45V/cell for CALB cells, so say set at 3.44V) at the lowest temperature at which you expect to charge. Because then the increase in voltage with SOC from that point on will be very large compared to the variation in pack voltage with cell temperature or charging current magnitude - since all the cells will be starting up the knee, rather than only one if the pack is bottom balanced.
> 
> Edit: I should add that if the pack is sized large enough and you have a charge counter, the variation in SOC with charge current magnitude and cell temperature won't matter of course. You will still have plenty range even if you charge 10 - 20 Ah less when the cells are colder or you charge at higher currents.


 I think it can be powered by and monitor the pack at the same time. The relay NC contacts are in the AC line of the charger. If the relay setpoint is reached it opens the contacts and won't close them until the voltage drops below the hysteresis setting.


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## GizmoEV (Nov 28, 2009)

Unless I missed it, it looks like the control current is only 4A. It appears that this then would need to control an AC relay in the charger line. Am I reading it right?

Also, I would think that the hysteresis would need to be sufficiently large so that the charger would not be turned on again if/when the pack voltage dropped after the charger shuts off.


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## ElectriCar (Jun 15, 2008)

Yea I haven't looked at the contact current rating but it may be that I can put a signal on the charger via that contact. If not I'll have to use a relay. I'm not concerned about how to connect it up, just that it will do the job I need it to. If it has a NC it can be wired to stop anything. The hysteresis setting I'll figure out too. 3% is the minimum so that's about 5V at 172V charging @ 3.45V. That thing would have paid for itself by now as much as I've allowed my charger to shut down on it's on. Mine will equalize every charge so I usually unplug it as soon as the AC amps hits about 10 or around 173V.


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## tomofreno (Mar 3, 2009)

> Unless I missed it, it looks like the control current is only 4A. It appears that this then would need to control an AC relay in the charger line. Am I reading it right?


 That's how I read it. Didn't read that far before.


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## ElectriCar (Jun 15, 2008)

It's being delivered tomorrow. I hope to have it installed in a temp fashion tomorrow evening. I hate having my charger do a equalization charge every single charge. Wastes a ton of electrons!


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## JRP3 (Mar 7, 2008)

Cells killed by a CMS
http://electric-vehicle-discussion-...-report-at-16-6K-miles-tp3247230p3247230.html


> I've replaced about three of the cells. This seems to be come from
> malfunctioning EVPower cell modules that allowed the cells to over
> charge (and swell). The EVPower modules probably failed due to getting
> zapped with high voltage on installation. That is, improper
> ...


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## GizmoEV (Nov 28, 2009)

ElectriCar said:


> I hate having my charger do a equalization charge every single charge. Wastes a ton of electrons!


At least with LiFePO4 the "equalization" phase on my NG1 draws only ~5W from the wall. It looks like it runs a little under 45 minutes after its first current turn off so that is less than 4Wh of "extra" electricity on each charge. That is about 1.4kWh/year extra.


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## ElectriCar (Jun 15, 2008)

Ordered my Zeva plus tonight. I tried to order it over the weekend but something wouldn't let it go through. I like the fact I can wire it and flip a switch and have the tach display amps. 

I think this setup will work pretty well with proper feeding of and not over working the batteries. No need for them to become gluttons and cram in that last amp hour or two! As the bible says "moderation in everything". They must have known about these things!


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## EVfun (Mar 14, 2010)

JRP3 said:


> Cells killed by a CMS
> http://electric-vehicle-discussion-...-report-at-16-6K-miles-tp3247230p3247230.html


I read that. I'm wondering how many of those 10 where initially zapped and how many failed without provocation. One problem is very clear, the owner was relying on the BMS to shut the charging off. The charger and controller should both be programmed to take care of the pack with the BMS only there to back it up by shutting things down if something has gone wrong. 

I've had 40 on my pack since spring. None have had any issues but great care was taken to not zap any with high voltage, reverse voltage, or allow any of the optical isolator outputs (signal loop) make contact with the pack at any point. I also haven't driven any cell out of range, though I have taken the pack up to the point where I can see all the shunts turn one briefly. I'm using the EVworks regs with the Clean Power Auto head end board. I wonder if he has had any of the Clean Power Auto cell modules fail? 

For the Buggy I'm looking into some type of Lee Hart style battery bridge so the car can be shut down easily with no parasitic pack loads. Just disconnecting the bridge pack + and pack - connections would remove the entire load from the system. I've been thinking about 2 different approaches to this. 

One would be a 2 comparators forming a voltage window detection circuit. If the common input was the center of the pack and the references where about 1/4 volt above and below the virtual center of the pack the voltage window would be exited if any one cell swung 1/2 volt out of line. The output of the comparators would drive a optical isolator and then a typical 12v system control setup could drive the alerts. My Clean Power Auto BMS head end board could be used. 

The other idea is to build the system with diodes like Lee designed it but instead of red LEDs use the LEDs in a 2 channel optical isolator. Then the isolated output of those LEDs could drive the warning/shutdown systems. Since this would operate the isolator output transistors is a more analog mode I would guess each channel would require a trim pot to adjust an output stage that would most likely be a TLV431.


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## spdas (Nov 28, 2009)

gottdi said:


> Electrons = Money.


I have one megawatts of solar power/panels per 3 weeks at my shop, so I can burn electrons.

Francis


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## GizmoEV (Nov 28, 2009)

EVfun said:


> For the Buggy I'm looking into some type of Lee Hart style battery bridge so the car can be shut down easily with no parasitic pack loads.


What about starting a thread for something like this. I have a couple of emails from Lee Heart about two other ways to do this. One of them is to use a zero centered ammeter in with a +-50 uA range. The meter could be calibrated to represent any voltage difference desired. The other circuit would be some sort of comparison circuit. A couple of designs could be created with possible source of components for each one.

What do you think?


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## ElectriCar (Jun 15, 2008)

GizmoEV said:


> What about starting a thread for something like this. I have a couple of emails from Lee Heart about two other ways to do this. One of them is to use a zero centered ammeter in with a +-50 uA range. The meter could be calibrated to represent any voltage difference desired. The other circuit would be some sort of comparison circuit. A couple of designs could be created with possible source of components for each one.
> 
> What do you think?


I second that. This thing needs some discussion.


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## GizmoEV (Nov 28, 2009)

The thread is here: http://www.diyelectriccar.com/forums/showthread.php/battery-balance-monitoring-system-54845.html


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## ElectriCar (Jun 15, 2008)

GizmoEV said:


> Unless I missed it, it looks like the control current is only 4A. It appears that this then would need to control an AC relay in the charger line. Am I reading it right?
> 
> Also, I would think that the hysteresis would need to be sufficiently large so that the charger would not be turned on again if/when the pack voltage dropped after the charger shuts off.


Ok tonight we got the ABB HV cutout relay installed and somewhat tested. Hopefully this description isn't confusing! It is controlling a 3 pole 50A contactor with a 208-240V AC coil. The ABB relay is connected to the wall power feeding the charger. Once plugged in, the ABB begins monitoring the Pack V. The contactor coil is powered through an NC relay on the ABB . Once the pack V reaches the setpoint of the ABB, it opens the contact killing power to the contactor, killing power to the charger. 

Once the voltage drops to around 142V OR I pull the plug, the ABB is reset. The way I have it configured this setup consumes no power unless the truck is connected to the power cord for charging. The two parts are installed in a 6x6x6 PVC electrical junction box behind the seat adjacent to the charger. 

I did this now with my lead pack to keep the Zivan from boiling the heck out of the batteries EVERY CHARGE wasting power trying to equalize. That is totally unnecessary and wastes probably about 2.5kw per recharge! 

My Calb batteries are supposed to be delivered around Monday the 21st or so. Once installed, the ABB setup will be adjusted to shut down the charger in case it fails to stop charging where it should. With 50 cells I am thinking I'll want it to trip around 175V or about 3.5 V/cell which is about where I want to shut down now for my 144V lead pack. That is the point that the charger goes into CC mode. 

Initially I'll set it for a lower voltage while I study the pack behavior and increment it upwards as I go. After I reach the voltage where the first cell begins to spike, I'll back the setting down a bit for a safety margin then send the Zivan out for reprogramming. So far it seems that setting is about 3.45V or 172.5 for 50 cells.

The Zeva Plus arrived today and the Cycle Analyst arrived last week. I'll be "getting the lead out" any day now to get the party started!


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## tomofreno (Mar 3, 2009)

> The ABB relay is connected to the wall power feeding the charger.


 It is connected to both wall AC and to the 50A contactor?
I was thinking the contactor coil would be connected to terminals A1, A2 on the ABB, and the contactor would be in the AC line from the wall, no? 


> Once plugged in, the ABB begins monitoring the Pack V.


 The pack is connected to terminals B, C of the ABB?


> It is controlling a 3 pole 50A contactor with a 208-240V AC coil.


 Got a part number and/or source for this contactor?

Thanks for the info. Sounds like a good safety measure. With an ABB in place, the minibms with HVC, and the charger limit voltage and timer set correctly, I may even be willing to try charging at night unattended - maybe.  

I would definitely do as you said and start with a lower cutoff voltage until you get to know your pack better. I don't see any reason to charge CALB cells above 3.45V or so unless you are top balancing with shunts - and that would likely only be required intermittently.


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## ElectriCar (Jun 15, 2008)

tomofreno said:


> It is connected to both wall AC and to the 50A contactor?
> I was thinking the contactor coil would be connected to terminals A1, A2 on the ABB, and the contactor would be in the AC line from the wall, no?
> The pack is connected to terminals B, C of the ABB?
> Got a part number and/or source for this contactor?
> ...


Yea Tom, the ABB has 240AC on A1,A2. The relay contact controls the coil power to the 50A contactor. Correct B&C is the pack power connection. 

The contactor was a used one I picked up, just a 3 pole 50A contactor. I think it's made by Allen Bradley, probably a little old too but it works great.

The only issue I may have with it is not being able to set the voltage as precise as I want but with such a high voltage I think it will be fine. Would be good if it were a multi turn pot but it's not. And it's very small. So far so good though. It's easy enough it appears to get the setting within 2V or so of what you're looking for. It may be easier still if I worked at it some. It's REALLY NICE knowing your pack is SAFE as it will take over should the charger fart and start overcharging!


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## tomofreno (Mar 3, 2009)

Oh I see, the ABB requires AC power to operate. The AC to the charger goes through the contactor. Nice.


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## spdas (Nov 28, 2009)

Aloha, I am installing my calb 180 batteries and for the first part will be monitoring only and no official BMS. Bottom balance and celllog8 to start off and go from there. Anyways, what voltage will I have to lead the pack with mostly full amperage to end up with resting voltage of 3.35? I will want to lead the pack voltage high enough so I will not be depending on hours of charging with diminishing amperage. To clarify, to end up with 3.35 Voltage and the current just starting to drop off, do I need to use 3.8v, 3.9v, 4.0v??? I know if I use for example 3.5V charging voltage, the amperage will start to throttle down at 3.25 or so and it will take ages to come up to 3.35 resting voltage. But I do not want to set the charger to 4.0v as I know I really need 3.35 in the end, but do not want to wait a long time getting the cells up to 3.35. Makes sense?

Francis


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## EVfun (Mar 14, 2010)

If you charge to 3.60 volts and then hold at 3.60 volts for 1 hour the charged and rested voltage will be right about 3.35 volts. Remember, there is no harm in undercharging so you have all the time and cycles you need to work up to a suitably full charge. My Manzanita Micro PFC-20 charger is set to 144 volts and the timer is set to run for about one hour after reaching that voltage. My pack is 40, 60 amp hour TS cells.


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## spdas (Nov 28, 2009)

EVfun said:


> If you charge to 3.60 volts and then hold at 3.60 volts for 1 hour the charged and rested voltage will be right about 3.35 volts. Remember, there is no harm in undercharging so you have all the time and cycles you need to work up to a suitably full charge. My Manzanita Micro PFC-20 charger is set to 144 volts and the timer is set to run for about one hour after reaching that voltage. My pack is 40, 60 amp hour TS cells.


Wondering....... what is your current at the three points.
1: starting current, 
2: current when you reach 3.6v
3: current after one hour?

thanks
francis


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## EVfun (Mar 14, 2010)

1: Usually set to 12 amps, sometimes 15 amps. I only have 120 volt service in the garage. 

2: When the charger first reaches 3.60v it is still at full current. The charger runs at full output current all the way to target voltage and then hold the target voltage as the amps decline until the timer shuts it off.

3: No easy accurate way for me to tell. I only have the 500 amp shunt in the system. Tenths of a millivolt are at the measuring limits of my best meter. Its tolerance means the current is in the range of 0 to 3 amps. I'm pretty sure it is in the lower half of that.


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> The only issue I may have with it is not being able to set the voltage as precise as I want but with such a high voltage I think it will be fine. Would be good if it were a multi turn pot but it's not. And it's very small. So far so good though. It's easy enough it appears to get the setting within 2V or so of what you're looking for.


Thanks Electric for your work on this. I'm interested to do something similar, but was a bit worried about the above statement when I looked at that ABB unit. Wondering what else may be out there...even digital would be great.


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## ElectriCar (Jun 15, 2008)

tomofreno said:


> Oh I see, the ABB requires AC power to operate. The AC to the charger goes through the contactor. Nice.


No the pack CAN power it but it only needs to work when the charger is connected as I have an onboard charger. I chose to use AC so that when unplugged it doesn't draw ANY power off the pack.


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## ElectriCar (Jun 15, 2008)

spdas said:


> Aloha, I am installing my calb 180 batteries and for the first part will be monitoring only and no official BMS. Bottom balance and celllog8 to start off and go from there. Anyways, what voltage will I have to lead the pack with mostly full amperage to end up with resting voltage of 3.35? I will want to lead the pack voltage high enough so I will not be depending on hours of charging with diminishing amperage. To clarify, to end up with 3.35 Voltage and the current just starting to drop off, do I need to use 3.8v, 3.9v, 4.0v??? I know if I use for example 3.5V charging voltage, the amperage will start to throttle down at 3.25 or so and it will take ages to come up to 3.35 resting voltage. But I do not want to set the charger to 4.0v as I know I really need 3.35 in the end, but do not want to wait a long time getting the cells up to 3.35. Makes sense?
> 
> Francis


I'm not experienced with the new batteries yet but my "plan" is to charge them with a voltage at 30 amps that will charge them sufficiently but not overcharge them. I'm expecting the batteries to be completely charged when the voltage averages 3.45 or so per cell.

Here's something that comes to mind that I teach my employees about electricity. For current to flow in a circuit, there must be a difference in potential. That's the definition of voltage. In this case, the charger is creating a voltage higher than the pack voltage. Because the pack resistance is extremely low, it will accept a charge as long as the voltage is only slightly above the cells terminal voltage.

Here's an example. The batteries I ordered were measured at around .00025 ohms. Multiplied times 50 batteries that I'm running and that's a total of .0125ohms for the pack. So in order for 30 amps to be able to flow into it I only need .375V more than the pack resting voltage using the formula E=I x R. E is voltage, I is current and R is the resistance in ohms. So you can see it doesn't take much voltage to charge one of these batteries. 

That's how it's possible to bottom balance the cells all at once by simply tying them in parallel before you install them in the vehicle.


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## ElectriCar (Jun 15, 2008)

DIYguy said:


> Thanks Electric for your work on this. I'm interested to do something similar, but was a bit worried about the above statement when I looked at that ABB unit. Wondering what else may be out there...even digital would be great.


 Well I found four units I think. It may be on my "narrowing my selection" thread if I posted them all. One is a Crouzet, one is a Binder, one was possibly Schneider/Telemechanique. I ruled them all out but the Binder. The Binder will give you a HVC and LVC function in one unit but it's more expensive. Since my Zeva and Cycle Analyst both can alert you of LV I decided to get the ABB which is only single point capable but it will do over or under voltage function, dip switch selectable. 

I think it will work fine though but I've not tinkered with it much. I have it stopping now at 174.5 and that's close enough. I only set it once and didn't overshoot my goal but by a teeny bit. I didn't touch it again because at this voltage it's only a matter of a couple of minutes of charging because the voltage is rising rapidly at this point. 

I noted the voltage and amps yesterday on one charge and it took several minutes to rise .1 volt until it was about 173.4V. After that it increases pretty quickly.


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## GizmoEV (Nov 28, 2009)

spdas said:


> Anyways, what voltage will I have to lead the pack with mostly full amperage to end up with resting voltage of 3.35? I will want to lead the pack voltage high enough so I will not be depending on hours of charging with diminishing amperage. To clarify, to end up with 3.35 Voltage and the current just starting to drop off, do I need to use 3.8v, 3.9v, 4.0v??? I know if I use for example 3.5V charging voltage, the amperage will start to throttle down at 3.25 or so and it will take ages to come up to 3.35 resting voltage.


Francis, it all depends on how your charger is programmed. When I was trying to use a charger programmed for lead acid batteries it would take for ever to charge up. When I got it programmed for LiFePO4 batteries it charges full current until about 3.45vpc and reaches 3.485vpc in about 15-18 minutes. I have a resting voltage of around 3.4vpc after several hours. I have TS cells in a 200Ah pack. Charging current is only about 15A into the batteries since I only have 120V charging in my case.

My point is that if you have a properly programmed charger it won't take hours because the charger started cutting back too early. I'd strongly recommend ending at 3.5vpc since this will not stress your cells and you will not be leaving much capacity un-used. Maybe 1% at most according to my testing.


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## spdas (Nov 28, 2009)

GizmoEV said:


> Francis, it all depends on how your charger is programmed. When I was trying to use a charger programmed for lead acid batteries it would take for ever to charge up. When I got it programmed for LiFePO4 batteries it charges full current until about 3.45vpc and reaches 3.485vpc in about 15-18 minutes. I have a resting voltage of around 3.4vpc after several hours. I have TS cells in a 200Ah pack. Charging current is only about 15A into the batteries since I only have 120V charging in my case.
> 
> My point is that if you have a properly programmed charger it won't take hours because the charger started cutting back too early. I'd strongly recommend ending at 3.5vpc since this will not stress your cells and you will not be leaving much capacity un-used. Maybe 1% at most according to my testing.


I want to end up at resting 3.35v, I am not about trying to get the last 5% or the first 5% of the cell. I need to travel up to 60 miles and have new calb 23x180(actually 195ah) (just arrived) and 23 used TS160's (actually tested at 165ah). I will be limited to the output of the TS and since I did not pay a lot for them, they will act as my "canary in the mine" or fuse. 
But I will be using my charge controller run off my solar panels. I can charge 80v at a time and voltage is adjustable in .1v increments so 79.1 or 79.2, etc. I will get 3.48 per cell charging voltage output for the 23 cells. If that is not enough lead voltage then I will drop a cell and go to 22 @ 80/22=3.63 each. I also may add some more cells if I do not like the range.....maybe to 180v+ and then charge at 60v for 3 banks. I can set time of charging at the max output and will need to play around. I will not be going anywhere near 3.8 charging and will have to pay close attention to the whimpy used TS 160 as the rate determining step. I have celllog 8's ready to hook up to each battery. Charger will (depending on the sun) charge up to 80amps, but I can limit current if needed.

Should be interesting.


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> Well I found four units I think. It may be on my "narrowing my selection" thread if I posted them all. One is a Crouzet, one is a Binder, one was possibly Schneider/Telemechanique. I ruled them all out but the Binder. The Binder will give you a HVC and LVC function in one unit but it's more expensive. Since my Zeva and Cycle Analyst both can alert you of LV I decided to get the ABB which is only single point capable but it will do over or under voltage function, dip switch selectable.
> .


Ya, I was looking at these also. I kinda like the look of this Bender unit...

http://www.bender.org/documents/VME420.pdf

More documentation.... http://www.aktifmuhendislik.com.tr/documents/179_VME420_DB_en[1].pdf

Like u say, will be more money. Not sure how much. Has upper and lower limits, digital 0.1 volt resolution 0 - 40% hysteresis, programmable...memory on alarms etc... 

Anyone come up with a price??


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## EVfun (Mar 14, 2010)

Oh, you have the mixed pack of TS and CALB cells. I would consider putting a single TS in the CALB group (and the opposite) because you plan to split charge as well. The idea is, if the newer CALB cells don't get charged while the other half does (for whatever mechanical or electrical failure situation) then you have a sacrificial cell mixed with the new pack. You loose a single cell, but just one older and smaller TS cell.


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## spdas (Nov 28, 2009)

EVfun said:


> Oh, you have the mixed pack of TS and CALB cells. I would consider putting a single TS in the CALB group (and the opposite) because you plan to split charge as well. The idea is, if the newer CALB cells don't get charged while the other half does (for whatever mechanical or electrical failure situation) then you have a sacrificial cell mixed with the new pack. You loose a single cell, but just one older and smaller TS cell.


Actually I have 28 new Calb 180's and 18 used TS 160's. I do not see a problem of not getting the both packs exactly equally stuffed with amphrs. I have a lot of settings on the computerized charge controller to ensure this. 
So maybe putting 9 TS in with each pack of 14 Calbs. (is there any reason to think one end of the pack gets hit harder than the other)....ie the Neg or Pos end? Any reason to go 180, 160, 180, 160. or just go. 160 160 160 etc then 180 180 180 etc?

Francis


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## ElectriCar (Jun 15, 2008)

DIYguy said:


> Ya, I was looking at these also. I kinda like the look of this Bender unit...
> 
> http://www.bender.org/documents/VME420.pdf
> 
> ...


They said around $250 IIRC. The ABB unit was about $150 delivered. Re the Binder resolution, it says 1V in the range we use. .1V was up to 49V.


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## DIYguy (Sep 18, 2008)

Here is another one. This one looks ideal. It's actually designed for this application. You could monitor pack temperature as well and shut down with this signal as well as voltage. Accurate to 0.1% of range which would be 0.5 volts on the 500 volt scale. Digital, alarms.. all the goodies.... Need to find price.

http://www.brodersencontrols.com/docs/UDC-35 2009.pdf


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## spdas (Nov 28, 2009)

DIYguy said:


> Here is another one. This one looks ideal. It's actually designed for this application. You could monitor pack temperature as well and shut down with this signal as well as voltage. Accurate to 0.1% of range which would be 0.5 volts on the 500 volt scale. Digital, alarms.. all the goodies.... Need to find price.
> 
> http://www.brodersencontrols.com/docs/UDC-35 2009.pdf



Is pack temperature will charging relevant or measurable? On my charge controller (from solar voltaic panels) I have an AUX feature that will monitor the battery temp while charging and will switch off charging if temp becomes an issue.

francis


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## DIYguy (Sep 18, 2008)

spdas said:


> Is pack temperature will charging relevant or measurable? On my charge controller (from solar voltaic panels) I have an AUX feature that will monitor the battery temp while charging and will switch off charging if temp becomes an issue.
> 
> francis


Hey Francis,

Yes, temperature is relevant when charging. Some chargers are temperature compensated while others just use an upper limit to protect. This, however, is not my point for this device.

This device is meant for those who may opt to go BMS-less (actually, more I think about it.... it may benefit BMS users even more...lol ... never mind... lol) and want redundancy for charger control. To allow good sleeping patterns for EV owners who park their cars in attached garages especially. 
The idea is to monitor pack voltage with a separate system/device and disconnect charger through a relay if this upper voltage threshold is reached. I was just suggesting that a temperature probe could be used as one more level of protection for a "runaway" charging situation. It does have separate contacts so, it does offer some additional level of protection I suppose.

Knowing that you have normal charger shutdown, redundant voltage monitor shutdown, and a temp probe for shutdown should prevent sleepless nights in EV-land.  Heck, u may as well put a wall timer on also and go for the whole belt and braces approach.


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## spdas (Nov 28, 2009)

Yah, too bad the sun does not shine at night so my solar panels will charge. If I can measure the heat increase, then I will hook up the probe to the Aux of my charger to monitor. But so far I feel no heat coming off the charging batteries......maybe it will be noticeable if overcharging occurs.

I just charged up some uneven cells (mostly 3.1 and 3.2) and left it for a bit .... 15 minutes at "full 20a current". When I got back some cells were 4.35 and 3.9, and a couple were 3.2. Yes got to be more on top of it!!!
Francis


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## ElectriCar (Jun 15, 2008)

Didn't look at the specs closely but where can you buy it? I've been out all day looking for another S10 newer, possibly Extreme package with extended cab. I'm going to take the new truck and really take the time to do it right so this may be an upgrade to the current unit. I spent a lot of time looking when I found the ABB but I never saw one that had temp monitoring though I didn't look for that either.


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## cyclops2 (Feb 12, 2011)

*The best battery control system is.............*

You.

Nothing is more reliable.

Expanded voltmeters for charging & discharging. 
Ampmeters. 
A hand operated cell refiller.
Using the same connecting bar material as the battery terminals.
Enough correct sized & tripping class fuses.
Use them within the stated limits of the WEAKEST part of the vehicle.

You ARE supposed to know the weakest part in any DIY project. What ?? Why ??

Who else is going to know more than you ? You designed it. 

Take care.


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## JRP3 (Mar 7, 2008)

WTF was that?


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## GizmoEV (Nov 28, 2009)

*Re: The best battery control system is.............*



cyclops2 said:


> You.
> 
> Nothing is more reliable.


Lets all go back to the ICE days where timing and air/fuel mixture were hand controlled then.



> Expanded voltmeters for charging & discharging.
> Ampmeters.


Have fun standing around for hours at a time watching voltages on the battery pack.



> A hand operated cell refiller.


Why in the world would I want one of those with a LiFePO4 cell that is sealed? In fact, distilled water will murder my cells let alone the opening up of the cell.



> Using the same connecting bar material as the battery terminals.


Please explain to me how to do this when the positive terminal is aluminum and the negative terminal of the next battery is copper.











> Enough correct sized & tripping class fuses.


How does a cell in an over voltage condition trip a fuse?

It looks like you need to do more reading and research so that your response fits the topic.


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## EVfun (Mar 14, 2010)

*Re: The best battery control system is.............*

I think it's just a chat bot experiment. The general goal is trying to imitate human conversation. In this case, FAIL.


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## GizmoEV (Nov 28, 2009)

*Re: The best battery control system is.............*

That is possible. The other post made by cyclops2 wasn't very helpful either.


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> They said around $250 IIRC. The ABB unit was about $150 delivered. Re the Binder resolution, it says 1V in the range we use. .1V was up to 49V.


I have a quote of $222 Cdn for the Bender unit, and I can order direct. 
I'm still interested in the Brodersen one though.


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## ElectriCar (Jun 15, 2008)

For any of you with the Zivan chargers that want to equalize EVERY charge, this thing is awesome! It's stopping the charge just as the CC phase just finishes and is rapidly paying for itself! I'm averaging about 470wh/mile now where before due to me having to unplug it at just the right time which was hardly ever, I was averaging over 500. For January and December it was around 600! Yesterday I drove it with no heat and averaged 414. Even though I'm stopping it at about 2.42V/cell in the lead I haul around, my SOC indicates a normal charge and the range is normal.


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## DIYguy (Sep 18, 2008)

DIYguy said:


> I have a quote of $222 Cdn for the Bender unit, and I can order direct.
> I'm still interested in the Brodersen one though.


I also have a quote for the Brodersen unit. No Distributor in Canada, but can order direct from Germany. $479 Euro each, "ex-Factory". Nice unit...but not happening.....


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> For any of you with the Zivan chargers that want to equalize EVERY charge, this thing is awesome!


I think u meant "For any of you with the Zivan chargers *Who DON'T *want to equalize EVERY charge, this thing is awesome!" 

Yes, no??


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## dexion (Aug 22, 2009)

Thats a nice unit. I may have missed it but why not just use a timer? I use a 220vac air conditioner timer as a backup (it was about 15 bucks) it cuts the charger off when I want it to (aside from all the other safetys built in that cut off the charger its an ng3) I have the benefit of an amp hour counter and lithium batteries so 30 ah our is 30 ah in. I charge at 16.2amps an hour. I dont see why you couldnt use a timer for lead acid as well. Perhaps its necessary since there are times a charger doesnt shut off and boils the batteries. Its a good safety to have.


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## DIYguy (Sep 18, 2008)

dexion said:


> Thats a nice unit. I may have missed it but why not just use a timer? I use a 220vac air conditioner timer as a backup (it was about 15 bucks) it cuts the charger off when I want it to (aside from all the other safetys built in that cut off the charger its an ng3) I have the benefit of an amp hour counter and lithium batteries so 30 ah our is 30 ah in. I charge at 16.2amps an hour. I dont see why you couldnt use a timer for lead acid as well. Perhaps its necessary since there are times a charger doesnt shut off and boils the batteries. Its a good safety to have.


Ya, timer is a good backup....but you have to keep figuring out how long to set it for. If you drive 10 miles one day and 50 miles the next, and 32.5... and... u get the idea. There is something to be said for redundant controls that are completely disconnected from the primary system (of course the timer is also) AND they don't need human input each time (room for error). = Better sleeping


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## ElectriCar (Jun 15, 2008)

DIYguy said:


> I think u meant "For any of you with the Zivan chargers *Who DON'T *want to equalize EVERY charge, this thing is awesome!"
> 
> Yes, no??


Well I guess it was an interpretation thing. My charger "wants to equalize" every time it charges. I don't want it to. Now it doesn't.


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## ElectriCar (Jun 15, 2008)

dexion said:


> Thats a nice unit. I may have missed it but why not just use a timer? I use a 220vac air conditioner timer as a backup (it was about 15 bucks) it cuts the charger off when I want it to (aside from all the other safetys built in that cut off the charger its an ng3) I have the benefit of an amp hour counter and lithium batteries so 30 ah our is 30 ah in. I charge at 16.2amps an hour. I dont see why you couldnt use a timer for lead acid as well. Perhaps its necessary since there are times a charger doesnt shut off and boils the batteries. Its a good safety to have.


I want to plug it in then have a beer and supper and not be bothered with it. I'm "bothered" at work all day, I don't need anything else to be doing. When I get lithium batteries next week, they require specific charging & they're not very forgiving if you push them far. My charger will be programmed properly for them and this relay will be a redundant control should the charger fail to shut down properly.


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## cyclops2 (Feb 12, 2011)

ElictriCar

I have used LIFEPO4 almost since day 1 when Saphion started releasing engineering samples to us.

They have a extremely fast end of charge, voltage increase. I was using 600 mahr samples. I was using a Delta C NIMH charger at 1 C rate. The pack was at about 3.0 volts. No problem I thought. I will run upstairs, a quick pee & back down to watch the charge continue.

SURPRISE !!
All 6 cells had pressure vented & released the sweet smelling white powder. The voltmeter now reads 4.3 volts. It was over in 2 to 3 minutes.
To this day I know there is no way to beat the risk of a overcharge if the fully automatic charger has a problem.
You can run the LIFEPO4s to 0 % & they come back fine. You overcharge them above maybe 3.8 & depending on the chemicals used, they may be damaged or ruined.

That is the ONLY bad thing of LIFEPO4 batteries. I have been retired for several years so some changes may have occured.

I just purchased a bunch of A123 1100 mahr LIFEPO4 cells that have sat on BLACK & Deckers corporate parts depot since 2007. A slow .3C charge and all 20 cells came up to full capacity. All 5 recharges are doing the same power levels.
With your investment. I would be there watching the final 20 % the first couple of times to be sure the charger is doing the job correctly.

Good luck


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> Well I guess it was an interpretation thing. My charger "wants to equalize" every time it charges. I don't want it to. Now it doesn't.


Oops, I get it..


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## GizmoEV (Nov 28, 2009)

cyclops2 said:


> They have a extremely fast end of charge, voltage increase. I was using 600 mahr samples. I was using a Delta C NIMH charger at 1 C rate. The pack was at about 3.0 volts. No problem I thought. I will run upstairs, a quick pee & back down to watch the charge continue.
> 
> SURPRISE !!
> All 6 cells had pressure vented & released the sweet smelling white powder. The voltmeter now reads 4.3 volts. It was over in 2 to 3 minutes.
> ...


From my experience with the Zivan NG1 it will shut down if it can't control the voltage. It is very quick at cutting current down to a few mA but will shutdown if needed. This is one of the things I really like about it.

As for 0%SOC remember that this does not equal 0V it is more like 2-2.5V ocv. As for over charging there has been one report of a cell getting overcharged while it was held at 3.65V for an extended period of time. The CALB spec sheet lists 3.4V as float voltage so I assume that at this voltage you won't over charge but it might take a while to get a full pack. Charging to 3.485vpc has been working fine on my pack and filling it in a relatively short period of time.


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## JRP3 (Mar 7, 2008)

I briefly hit 4.0V on a couple of my CALB's with no noticeable issues.


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## ElectriCar (Jun 15, 2008)

I plan to do just that. I'll keep an eye on them to find the lowest capacity cell or two and at what pack voltage they begin to climb. I'll likely back off the setting of the charger for .05 V/cell or so for some cushion. 

However if you were charging at 1C that explains why they got torched so quickly. With our prismatic cells it's highly unlikely anyone approaches 1C charging. I have 200Ah cells so I'll be charging at .15C or 30A. It should take much longer to climb quickly. Even if I were charging 40Ah cells I'd only be at .75C with a 5kw charger.


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## cyclops2 (Feb 12, 2011)

The A123 cells .....original LIFEPO4 .....Will take massive over charge rates. I have been doing the 4 amp. rate on the 1.1 amp cells for years every year. Still a 98% charge when settled after 1 hour. A123 cells are absolutly high C bullet proof. 

The RC helicopter guys do pull 60C discharge rates & recharge at 5C rates.

Only bad / good feature is that pressure release valve & the white powder discharge. All the power is gone forever. Still the safety from acid or fires is terrific in any moving object.

I do not think I would have the guts to do a full battery load of them from a overcharge risk of that much money. Not sure if any EV charger company would show up, look at all the blown pressure valves & poweder & say. OK here is a check for a new set, less some depreciation value.

Edit

NEVER disconnect the battery charger from its power source till the charger inspector SEES the recordered over charged voltages that was used on each cell. Just another piece of charger error evidence. Hope it never comes to that.

Yes. That is my real experienced industrial backround trying to help someone.

All of you guys are TRUE pioneers in the EV field. My best wishes to all of you.


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## ElectriCar (Jun 15, 2008)

cyclops2 said:


> NEVER disconnect the battery charger from its power source till the charger inspector SEES the recordered over charged voltages that was used on each cell.


Huh? What are you trying to say? Sorry but I can't comprehend what you're saying here.


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## JRP3 (Mar 7, 2008)

I think he's talking about some charge balancing, but yeah I'm confused as well


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## cyclops2 (Feb 12, 2011)

I am try to tell you that .....IF.....you were to check your finished charging voltages on your battery pack & see that any cells were definately damaged by overcharging............
DO NOT lose the cell voltage data on the charger. Keep it for a actual record of the damage by the charger to the battery cells. I would take pictures of the charger screen voltages. 
Most companies are not about to admit that their equipment damaged your cells. Then instantly write a check, to buy new cells or a complete battery in a worst case
YOU will need to have proof. Hang on to it.

My medication makes getting a thought out difficult sometimes.
Do not get old. It can really " suck " at times.


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## ElectriCar (Jun 15, 2008)

Already there cyclops. Well over the hill but not under the ground yet lol.


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## cyclops2 (Feb 12, 2011)

Everyday I read the paper I never see my name in the obituary.


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## spdas (Nov 28, 2009)

ElectriCar said:


> Already there cyclops. Well over the hill but not under the ground yet lol.


Yeah, I'm one of those 61 year olds going on 29

Francis


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## JRP3 (Mar 7, 2008)

cyclops2 said:


> Do not get old. It can really " suck " at times.


Of course it's better than the only alternative, which is death


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## Roy Von Rogers (Mar 21, 2009)

I was declared death once....
And then I resurrected myslef...

​ 

Roy​ 



cyclops2 said:


> Everyday I read the paper I never see my name in the obituary.


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## JRP3 (Mar 7, 2008)

BMS opinions from Bob Stempel:


> .... battery makers are paying more attention to cell-to-cell variation: "Once you get those cells where each one is virtually identical to the next one, the pack process becomes a lot less complicated. And people are working on the controls. When we started with li-ion, you literally had to measure the temperature and the voltage drop in every cell, so the complexity of the controls was horrendous. Now it's getting much simpler."


http://green.autoblog.com/2011/02/16/gms-bob-stempel-talks-about-lithium-batteries-and-what-will-ma

Matched cells for the win.


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## EVfun (Mar 14, 2010)

JRP3 said:


> Matched cells for the win.


Except there are "people are working on the controls." I don't think you will find a production Lithium EV without some method of detecting a failing cell. It may not involve single cell level measurement; Nimh has tended toward small block monitoring. I would also point out that GM is talking about using only 60% of the available range ("20 to 80 percent range.")


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## JRP3 (Mar 7, 2008)

Right but the only way it is "getting much simpler" is they are moving away from a CMS setup because the cells are getting better. They may indeed be doing some form of block monitoring but probably not active cell level management.


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## EVfun (Mar 14, 2010)

Most likely it will be a move away from cell level up to blocks of cells. One other possibility is to move away from shunting and to very low current sensing with off the shelf watchdog chips. They may try to go with "smart software" to track expectations at the whole pack level. Their work may or may not apply to home builders.

I don't know what is in GM's and Nissan's labs. I'm pretty sure the results will be cheap and just enough to be safe most of the time. That's the nature of the modern disposable automobile.


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## spdas (Nov 28, 2009)

Aloha, after reading and posting and listening to many of the BMS, charging, (top and bottom). I still come away with these conclusions:

1: If you believe in BMS then just hook it up and hopefully you never fry a cell

2: If you do not BMS, then either top or bottom balance and check your cells periodically. Develop a theory of which cells remain strong and which become weak in each cycle and watch them

3: So I think monitoring the cells after balancing may be the best way to go, sooooooo. 

a) Put a cellog 8 on each cell or every 2 or 3 cells to watch their voltage at critical times.

b) Is there any "smart" method to charge cell individually ie (economical 3-4 v 20ah individual charger?)

c) Is there any electronic device that when you have your 45 cells in series for running your EV, you then hit a magical switch and series gets disconnected and parallel gets hooked up? Then you charge and balance?

Francis


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## GizmoEV (Nov 28, 2009)

spdas said:


> 3: So I think monitoring the cells after balancing may be the best way to go, sooooooo.
> 
> a) Put a cellog 8 on each cell or every 2 or 3 cells to watch their voltage at critical times.


A word of caution that if you are not balancing your cells regularly that you not put a cellog 8 or any other monitoring device which takes cell energy on only a few cells. Doing what you describe will unbalance them.


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## spdas (Nov 28, 2009)

GizmoEV said:


> A word of caution that if you are not balancing your cells regularly that you not put a cellog 8 or any other monitoring device which takes cell energy on only a few cells. Doing what you describe will unbalance them.


No I was thinking of having all cells monitored, whether I go every 2 (~6.6v) every 3 (~9.9v) or each one (~3.3v). Watching them will alert me to get'em into balance. 

Any comments on using celllogs? Seems like a good monitoring solution, but rarely discussed.

Also any magical series/parallel switch or individual charger that is small/light enuf to make sense?

Francis


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## Jimdear2 (Oct 12, 2008)

spdas said:


> No I was thinking of having all cells monitored, whether I go every 2 (~6.6v) every 3 (~9.9v) or each one (~3.3v). Watching them will alert me to get'em into balance.
> 
> Any comments on using celllogs? Seems like a good monitoring solution, but rarely discussed.
> 
> ...


Try to get a run through of the operating manual. I don't know if it is copywrited so I won't post it, but Hobby King has the units on sale right now and they* may* have a location where the manuals can be downloaded.

http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=10952.

The units are prouced by 
SHENZHEN JUNSI ELECTRONIC CO.,LTD, 
they *may* post the manual.

I'l attach a copy of one persons diagram showing his application that incorperates low voltage and high voltage cut off as well as cellog shutdow with the key switch.

Below are some of the features listed in the manual.

It can be set Individual Voltage Alarm and Pack Voltage Alarm, Overvoltage Alarm, Low Voltage Alarm, Differential Voltage Alarm and Time Over Alarm. What​​​​‘s more, the extra alarm output can be linkage controlled by the users.

It has 8 sets default monitor alarm settings, which can be selected for different battery packs.

CellLog 8M has been 100% calibrated before it enters to the market, at the same time, it supports the calibration by users themselves.

We are building our own individual cell chargers, (I just finished the last one, of 50 total) patterened on somthing RWaudio is also building. They are based around isolated DC to DC converters with, output that can be adjusted from 3.3 to 3.65 volts with a minor modification.

Hope this helps,
Jim​


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## algea07 (Oct 1, 2010)

i decided a while a ago that i was one of those people that was going to need a BMS of some kind, i don't trust my self to monitor my batteries, i can barely be trusted to check the oil.

i was just going to go for a nice simple shunt system like the mini bms, that would do the job. i saw this on the thundersky page but it's more of a battery monitoring system so i'd still need the a shunt BMS.

i saw this active cell management system the SKU: EHUG BMS for $2000 it looks good, it alows me to watch what what each cell is doing while it actively balances the cells. It's always on which means it has a parasitic load but thats not a huge downside.

personally i like the EHUG but i was just wondering what you guys thought i should do?

does anyone have any experience with this company or porduct?


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## JRP3 (Mar 7, 2008)

Wow, $2K for a BMS? Do you really need to watch the cells charge? I promise you it's really boring. I'd stick with the MiniBMS if you're going to use a BMS, anything more doesn't make much sense.


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## algea07 (Oct 1, 2010)

JRP3 said:


> Wow, $2K for a BMS? Do you really need to watch the cells charge?


it's more to make sure the cells don't fail, as far as i'm aware the the mini bms wont alert me if any thing goes wrong. if a cell fails i wouldn't know, if i can see the voltage of every cell then i know if one fails, and i can remove it or prevent over charging.

For a 300v car the mini bms still cost over $1000, and it seems that for an extra $1000 i get a much better BMS.


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## JRP3 (Mar 7, 2008)

The MiniBMS will signal if a cell drops below a safe voltage. It will also shut off the charger on high cell voltage or power down your controller on low cell voltage, and note which cell has triggered the fault. What else do you need? There is no way you will be visually monitoring all your cells while driving and be able to see the problem as it happens with the EHUG so I'm not sure that feature is really useful.


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## algea07 (Oct 1, 2010)

yes your right, the mini bms will suit my needs.


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## bmentink (Apr 22, 2011)

Jimdear2 said:


> We are building our own individual cell chargers, (I just finished the last one, of 50 total) patterened on somthing RWaudio is also building. They are based around isolated DC to DC converters with, output that can be adjusted from 3.3 to 3.65 volts with a minor modification.


Hi Jim,

I have been reading this thread with much interest as I too have reservations in charging cells in series, and like the individual DC-DC converter for each parallel pack approach.

I have decided on building my own pack out of 440 16Ah Headway's, grouped in packs of 110 x 4 parallel cells.

I am thinking of 110 50W DC-DC converters and wonder if they can be had/built cheap enough to make it economic. I intend incorporating these converters in the packs.

Can you point me to a supply of DC-DC converters that you are modifying for 3.65V ?

I had thought of maybe building a 360v DC (rectified 240v RMS) to 3.65v isolated converter, as I don't see anything suitable out there.

Love to have some pointers, don't want to re-invent something that you guys have done allready ..

EDIT: An update. I have found a source of 50W and 75W 240vAC to 3.3V DC (Adjustable to 3.6v) AC/DC converters at $25US and $28US respectively.
I will use one of these on every "cell" (I have 110 cells (4 cells parallel)) , also I will monitor the cell voltage of each "cell" with a micro controller built into the cell packs, this will report back via CAN bus
or 1-wire bus to my main inverter/controller to report out-of-range condition in cell voltages. The AC/DC converters will be set to charge the cell to 3.55v which I believe is just over the knee.
With this method I have protection for both charge and discharge without a BMS, ...and for a cheaper cost than a high-voltage charger+BMS combo .... my 2c.
oh, and I will be using the main controllers built in coulomb counter (Ah's) to measure SOC which won't be allowed to fall further than 20%. The counter will be reset automatically when all cells have
reached there EOC.


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## mszhao (Oct 17, 2009)

apparantly BMS is quite neccessary for the lithium batteries.
if you want your lithium battery pack safer,and has longer lifespan,
please using an effective BMS which can monitor and manage the batteries.


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## GizmoEV (Nov 28, 2009)

mszhao said:


> apparantly BMS is quite neccessary for the lithium batteries.
> if you want your lithium battery pack safer,and has longer lifespan,
> please using an effective BMS which can monitor and manage the batteries.


The key word here is "apparently." There are many variables to consider in using a lithium battery pack including the specific type of lithium battery. A long pack life can be achieved with no BMS just like some have found that cells have been damaged by having a BMS. It isn't as simple as saying a BMS is required for long pack life.


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## icec0o1 (Sep 3, 2009)

mszhao said:


> apparantly BMS is quite neccessary for the lithium batteries.
> if you want your lithium battery pack safer,and has longer lifespan,
> please using an effective BMS which can monitor and manage the batteries.


SPAM. Go away.


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## bmentink (Apr 22, 2011)

mszhao said:


> apparantly BMS is quite neccessary for the lithium batteries.
> if you want your lithium battery pack safer,and has longer lifespan,
> please using an effective BMS which can monitor and manage the batteries.


Well that is a ridiculous statement if ever I heard one  Obviously aimed at starting a flame war. 

Well, BMS's come in all flavours, from just pure monitoring to trying to balance your pack for you, or some combination between, and those that promote BMS's are most likely trying to sell the stupid things ..

In my mind, serial charging is a flawed concept and your cells will always at some point be out of balance. If you parallel charge, your cells are being top balanced EVERY time you charge the pack to EOC. The alternative to this (serial charge) is to monitor your cells and do a manual labour intensive charge when they are out of balance (because even the most expensive BMS still doesn't do a good enough job balancing the pack).

With parallel charge (top balanced), you only have to monitor the cell voltage at the end of discharge to make sure you don't get in the danger area at that end of discharge, keeping a reserve 20% in your "tank" makes that just a precaution, you may even get away with no monitoring at all ....

I know of people who series charge and use expensive BMS's and still have to balance there pack every few months ... they are the ones that endanger the life of there pack, not those that parallel charge ... I will say no more on the matter!


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## pgt400 (Jul 12, 2008)

not ridiculous at all, all li batterys require either a bms or that you be the bms....from cell phones, laptops to ev's. after just a few cycles without a bms the need became clear....walk away from a charging pack without a cell level HVC is a huge risk. parallel charge? i guess you mean separate isolated 3.6v dc-dc chargers? great way to charge, but you would need one for every cell....could be pricey. i just put the mini bms on my bike, after 5-6 cycles the charger now turns off at 86v without an HVC alarm from the BMS turning off the charger.....all balanced. 





bmentink said:


> Well that is a ridiculous statement if ever I heard one  Obviously aimed at starting a flame war.
> 
> Well, BMS's come in all flavours, from just pure monitoring to trying to balance your pack for you, or some combination between, and those that promote BMS's are most likely trying to sell the stupid things ..
> 
> ...


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## spdas (Nov 28, 2009)

Aloha, all. Good points in the last 2 posts for no-bms and bms. So the bottom line, cells need to be monitored by human or by BMS, BMS either either down and dirty $8.00 each or $2000.00. Parallel charging may be the way to go, but who has a 3.6v charger x48 cells capable of 30-50 amps? 

So.... 
1: do the series charge and monitor every couple of months 

2: Install a BMS and do not monitor, wing it and have a couple spare cells and never go below 20% or above 90%.

3: Install no BMS, wing it and have a couple spare cells and never go below 20% or above 90%.
or 
4: Wait for someone to invent a 30amp x 48 output x 3.6v charger.

Francis


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## bmentink (Apr 22, 2011)

spdas said:


> Parallel charging may be the way to go, but who has a 3.6v charger x48 cells capable of 30-50 amps?
> 
> 4: Wait for someone to invent a 30amp x 48 output x 3.6v charger.
> Francis


Like I said in an earlier post. You can purchase an AC/DC module (1/2 brick) for $25US for the 50W version, or $28US for the 75W version. These are 240v/110v in, 3.3v (adjustable to 3.65v). There are 100W versions too. But a 75W version will charge 100Ah cells in <5hrs anyway. Try out Google, you will like it .. 

No one has to "invent" them, there are hundreds of suppliers of these, they are standard industrial power supplies ... hence the low cost.
In your situation that would be 48 x $28 = $1344, how much do you pay for a charger + BMS?


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## bmentink (Apr 22, 2011)

pgt400 said:


> not ridiculous at all, all li batterys require either a bms or that you be the bms....from cell phones, laptops to ev's. after just a few cycles without a bms the need became clear....walk away from a charging pack without a cell level HVC is a huge risk. parallel charge? i guess you mean separate isolated 3.6v dc-dc chargers? great way to charge, but you would need one for every cell....could be pricey. i just put the mini bms on my bike, after 5-6 cycles the charger now turns off at 86v without an HVC alarm from the BMS turning off the charger.....all balanced.


It's not balanced, you can fool yourself into thinking it is balanced, but unless your "BMS" is doing the balancing, and minBMS doesn't, you will still need to balance your cells in a few months time ..

And no, as per my previous post, these isolated AC-DC power supplies are cheap, and there is the added advantage of being able to build them into the pack, as I am doing.


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## JRP3 (Mar 7, 2008)

pgt400 said:


> after just a few cycles without a bms the need became clear....walk away from a charging pack without a cell level HVC is a huge risk.


This statement sort of ignores the reality that a number of us are doing exactly that for a few thousand miles over the last couple of years with no problems.


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## ElectriCar (Jun 15, 2008)

mszhao said:


> apparantly BMS is quite neccessary for the lithium batteries.
> if you want your lithium battery pack safer,and has longer lifespan,
> please using an effective BMS which can monitor and manage the batteries.


Look zhao, if you have something to sell, advertise it on this site. That is a false statement and you should not make statements like that. Either you think people are stupid on this site or you don't know very much about the subject. Obviously you've not read about alternatives to BMS systems. 

Many ev'ers are successfully doing just that *and I suspect BMS free batteries will actually last longer than those charged to the max and shunted with a BMS system*. That's because we non BMS people don't charge them to the max and don't discharge them completely which supposedly extends the life. I charge mine to 3.41V and have a safety device to shut down the charger if it fails to shut down properly on its' own.


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## bmentink (Apr 22, 2011)

gottdi said:


> Uhhh! NO. My cells are not going out of balance. Neither are the cells from others who don't use BMS systems.


Really! How can you tell, have you tested each cell? Normally you will only find out when it is too late.



gottdi said:


> These cells do not drift out of balance. Period.


So you are saying that you got "perfectly" matched cells when you bought them (i.e their impedance was exactly the same, and you are making the assumption that their impedance does not change with age .... ding! wrong!

Take this scenario, one cell has impedance of 8mOhm and one has impedance of 7mOhm. What do you think is going to happen when you pull a sudden load from them, like >300A, as in acceleration or hill-climbing, those cells will discharge at a different rate and therefore charge to a different capacity ... think about it. 

One cell will have a lower voltage because it discharged greater than the others. When you charge the pack again to the "same" voltage, some cells will be "overcharged", some will be undercharged 

The only real way around that is to parallel charge .. end of story.


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## EVfun (Mar 14, 2010)

bmentink said:


> Take this scenario, one cell has impedance of 8mOhm and one has impedance of 7mOhm. What do you think is going to happen when you pull a sudden load from them, like >300A, as in acceleration or hill-climbing, those cells will discharge at a different rate and therefore charge to a different capacity ... think about it.


They will not discharge at a different rate. They will be at a different voltage under load. Cells store amp hours not watt hours (ions move across the electrolyte while electrons go through the circuit.) The cells we are typically using have 10% to 20% of that resistance.

Lead acid batteries drift because of self discharge and charging inefficiency. They vary from cell to cell even when new. If either of these are happening on LiFePO4 it must be pretty slight. Charge efficiency seems to be right at 100%, at least below 3.6 volts. I've got cells that have sat for over a year with no change in terminal voltage so self discharge must be minimal.


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## GerhardRP (Nov 17, 2009)

bmentink said:


> So you are saying that you got "perfectly" matched cells when you bought them (i.e their impedance was exactly the same, and you are making the assumption that their impedance does not change with age .... ding! wrong!


For a series string, the salient parameter is capacity. Impedance is most important in a parallel setup.The thing about lithium batteries is that they are essentially perfect with regard to Coulombic charge efficiency: this means that if you start with a battery at a certain state of charge, say 90%, and remove a certain number of Ahr from it; then recharge with exactly that number of Ahr, you WILL return to the initial SOC. In a series string, EXACTLY the same number of Ahr will be removed from and returned to EACH battery.[


> Take this scenario, one cell has impedance of 8mOhm and one has impedance of 7mOhm. What do you think is going to happen when you pull a sudden load from them, like >300A, as in acceleration or hill-climbing, those cells will discharge at a different rate and therefore charge to a different capacity ... think about it. One cell will have a lower voltage because it discharged greater than the others. When you charge the pack again to the "same" voltage, some cells will be "overcharged", some will be undercharged


If you are using individual cell terminal voltage monitoring under a heavy load, what it will tell you is which cell has a higher impedance. The SOC is related to resting voltage.


> The only real way around that is to parallel charge .. end of story.


I vote for careful occasional bottom balancing then Ahr controlled charge and discharge with accurate charging voltage monitoring, timer shutoff, maybe pack temperature or pressure safety cutoffs.
Gerhard


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## GizmoEV (Nov 28, 2009)

It has been over 4300 miles since I top balanced my pack and I'm not seeing the supposed cell drift. I check about once per month regardless of miles traveled. I charge to 3.485vpc average. Time will tell what happens but I can assure you that the cells do not diverge "in a few cycles".


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## steven4601 (Nov 11, 2010)

I do not want to go with a BMS either, probably have to. I am doing cell cycle testing. they diverge eventually. 
Think I will use an LM431 / shunt balancer or similar solution to provide some way of balancing above 3.4V per cell when assembling the traction pack.

About your finding on non-diverging cells.
Do you measure the cell voltage under regular load every month?
I noticed with my cell cyclin testing the cells start to diverge when almost full and almost depleted. the big 'flat' spot in the middle not really gives a sign of what is going on. Also the voltage at rest is even more of a constsant rather than an indicator.


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## bmentink (Apr 22, 2011)

steven4601 said:


> I do not want to go with a BMS either, probably have to. I am doing cell cycle testing. they diverge eventually.
> 
> I noticed with my cell cyclin testing the cells start to diverge when almost full and almost depleted.


Exactly, hey people, this is from someone who actually tested his cells.

The sooner everyone realizes that parallel charging is the way to go, the sooner that the extra demand for 240v/110v -> 3.3v converters will push down price even further. Just think, when these things get down to $10 per unit and everyone starts incorporating them into cell packs....

To me that is ideal ... but until that happens, I am happy to pay $25 for a 50W converter per cell and I have 110 cells, so for me that is $2750 for my "charger" ... but remember, that is 5500 Watts of charge .. use 100W converters and that is 11Kw of charge ... if your power supply can handle it.


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## steven4601 (Nov 11, 2010)

Each to their own. I do not preach for individual chargers at all.

Here is a bit of perspective.
A 3kW PFC is about 300 euro. Technically this is also a battery charger , just needs a microcontroller to turn it into a current souce and taper off the current output at a specific voltage.

A 100mA LM431 cell balancers are perhaps 1 euro the piece? I would need about 130 units. 

430 euro for value of products sounds like feasible for the industry. Extra costs are connectors wires labour interest & marketing 

Going with individual chargers require Hi-potted DC-DC transformers. This automatically requires more components, test-time & costs. I don't think series charging is flawed as cheaper components with the same results can be used. 

The Headway 38120 I tested diverge about 600mAh per 154Ah worth of charging/discharging in the course of 2 weeks cycling. This translates to 3mAh worth of balancing required per charge.  That is not much at all. 
I would not invest in high power balancers, it would be more useful if the balancer can report it starts shunting to indicate which cell/group has the lowest capacity.

edit: the 'status' flag that starts shunting can be a simple optocoupler part of the energy dissipation circuit. A little more expensive but less wiring required would be to use a microcontroller which sends a code of the cell voltage. This may need some protocol tinkering as there are 100 to 130 co-microcontrollers trying to tell their status on the same 'open collector' bus. A random delay generator and a fixed length packet with a crc comes to mind  The receiver end can be a simple USB Uart & embedded / pc software


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## Coulomb (Apr 22, 2009)

bmentink said:


> The sooner everyone realizes that parallel charging is the way to go, the sooner that the extra demand for 240v/110v -> 3.3v converters will push down price even further.


There are downsides to using individual chargers.

There is the efficiency issue; medium power 3.3 V power supplies are typically 75% efficient, compared to perhaps 93% for a 2 kW charger.

There is also the power factor; small power supplies would probably not have power factor correction. So with a current limit imposed by opportunity charging, not much more than 50% of the capacity of an outlet would be available for charging.

Finally, there is the turn-on surge, typically 20 A. With 45 to 110 chargers starting at once, the turn on surge could be enormous, and could trip the breaker. If you're using power from a commercial source (say a coffee shop) and the lights go out due to the turn-on current surge, you may be politely refused next time you ask if you can charge there. Of course, you can modify each power supply to make the turn on softer, but it's more work.

On top of all this, there is mounting / installation. You need to make all that mains wiring safe and waterproof, and keep it away from all those DC terminals.

So maybe not everyone will be jumping onto the "parallel charging" bandwagon, even if the price comes right down.


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## steven4601 (Nov 11, 2010)

Good point about efficiency.
Low voltage output converters require synchronous rectifiers to be mildly efficient and still more lossy than higher voltage output converters. 

A PFC/charger of 97% would be excellent already! I am going to invest if there are cheap bridgeless PFC's are available for the diy market to convert. Those can do 98 to 99% without components made from 'unobtanium'.


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## JRP3 (Mar 7, 2008)

bmentink said:


> Exactly, hey people, this is from someone who actually tested his cells.


Your results contradict many of us who actually use their cells every day. What cells are you using and how closely matched were they? That might be your problem.


> The sooner everyone realizes that parallel charging is the way to go, the sooner that the extra demand for 240v/110v -> 3.3v converters will push down price even further.


I wouldn't count on that happening. Along with the efficiency issues mentioned you are also mounting a potentially cell destroying charger connected to each cell, raising the likelihood of component failure. Parallel charging is not the way to go, no manufacturer is doing it that way and very few individuals will either. Plus the fact that cells are coming in more closely matched these days than in the past, I see a manual pack balance as a simply occasional maintenance issue, not something that needs to be done at every charge. Think of it as an oil change, only much cleaner.


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## steven4601 (Nov 11, 2010)

JRP3 said:


> Your results contradict many of us who actually use their cells every day. What cells are you using and how closely matched were they? That might be your problem.


Hi, are you referring to my measurements or Bmentink his statements? 

Incase you referring to mine I am still cycling them. More results next week I hope. Currently testing the reject anr26650m1a cells for their capacity.


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## JRP3 (Mar 7, 2008)

Bmentink's statements about testing his cells.


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## ElectriCar (Jun 15, 2008)

steven4601 said:


> I do not want to go with a BMS either, probably have to. I am doing cell cycle testing. they diverge eventually.
> Think I will use an LM431 / shunt balancer or similar solution to provide some way of balancing above 3.4V per cell when assembling the traction pack.
> 
> About your finding on non-diverging cells.
> ...


Typically we don't charge to 100% and don't discharge below 70-80% unless testing so it isn't an issue unless you do. However to charge the last 2-3 % is unnecessary IMO and actually degrades the cell life. 

Now on my first charge I had a few cells spiking but I balanced them to 1/1000V at around 3.3V which may have been too low as I had to do it again later. After getting them closer at around 3.4V they are much better behaved. I'm leaving about 5-10Ah out of the 50 cells when I recharge out of 200+ but I'm still getting over 100 mile range on a 3300 lb 1991 S10 truck, not exactly an aerodynamic masterpiece.


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## steven4601 (Nov 11, 2010)

I respect the fact you have your car up and running already! Im still halfway. 

Not charging it full or discharging to the roll of leaves you in the big fat section in the middle It is a "Blindspot" regarding soc. Using prismatic cells which actually are many paralleled batteries in a box. Perhaps that already lengthen the edges a bit vs single cells. As each cell has a slightly different internal resistance and capacity.


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## JRP3 (Mar 7, 2008)

Repeatedly taking your cells to a higher SOC just to assure that they are balanced will reduce the number of cycles you get from them in the long run. The important thing to remember is that cycle life is what we are really after. Some degree of balancing is necessary to ensure that but the best way to get the most cycles is to stay as near as possible to the middle of the SOC range. A perfectly balanced pack that's charged to 98% SOC every time won't last as long as a pack with a 5% imbalance that's charged to an average of 90% SOC. If you don't take your pack to the extremes a slight imbalance doesn't really matter. And of course "balanced" is relative, a perfectly top balanced pack is unbalanced at the bottom, and vice versa.


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## Jan (Oct 5, 2009)

Yes JRP3. That's what all the scientific literature online tells me too. 

And they will not get easily out of the 'balance' you put them in. Unless you use a BMS. Or put a load or charge on every individual cell. Which is a BMS. 

The only thing that can make them drift is aging. Not a very rapid process. Maybe a BMS is needed by then. Maybe. 

The sad part is the aging and therefor the drifting apart emerges at the bottom of the discharge curve. Since I want bottom balancing, that's a bit of a bummer.


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## EVfun (Mar 14, 2010)

steven4601 said:


> The Headway 38120 I tested diverge about 600mAh per 154Ah worth of charging/discharging in the course of 2 weeks cycling. This translates to 3mAh worth of balancing required per charge. That is not much at all.
> I would not invest in high power balancers, it would be more useful if the balancer can report it starts shunting to indicate which cell/group has the lowest capacity.


What are you using to monitor the cells during this test? The reason I ask is that if it is an attached cell level device *that* may be the divergence you are seeing. I measured a bunch of EVpower regs and noticed that they vary in current drawn by about 0.1 milliamp (2.8 to 2.9 ma.) That doesn't sound like much but is almost 1 amp hour per year. I think if you have cell regs you will needs shunting (20 milliamps might be enough for a balanced pack) and you will need to bring all cells up until they are shunting to equalize just to compensate for the BMS.


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## steven4601 (Nov 11, 2010)

EVfun said:


> What are you using to monitor the cells during this test?


A cheap RC balancer discharger. Reason I bought it is its current rating. It can do 30A charge & discharge. The discharge is regenerative. Using a 12V car battery as the buffer for cycling. 

I keep forgetting its name, its the iCharger 3010b. Good for 1kw. 32hours of internal log memory. Was afraid id had to run the laptop next to it but the log memory is handy for many charge - discharge cycles. The only negative is that their using an usb-rs232 bridge with a NON standard baudrate & semi propritairy drivers. I cannot use it in Linux (yet). So i have to read the logs in windows. 



EVfun said:


> (20 milliamps might be enough for a balanced pack)


That is what I was thinking. Balancers shouldn't need much at all. If your pack is okay the drift is small. If something is out of order regarding self-discharge it will turn pear shaped sooner or later.


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## GizmoEV (Nov 28, 2009)

steven4601 said:


> I do not want to go with a BMS either, probably have to. I am doing cell cycle testing. they diverge eventually.
> Think I will use an LM431 / shunt balancer or similar solution to provide some way of balancing above 3.4V per cell when assembling the traction pack.


Why not just parallel the whole set and charge to 3.6-3.8V and hold them there for an hour or so?



steven4601 said:


> About your finding on non-diverging cells.
> Do you measure the cell voltage under regular load every month?
> I noticed with my cell cyclin testing the cells start to diverge when almost full and almost depleted. the big 'flat' spot in the middle not really gives a sign of what is going on. Also the voltage at rest is even more of a constsant rather than an indicator.


Unfortunately I don't have a way of measuring cell voltage under load. The most I can draw while sitting still is about 6A but then the SOC is just under the steep part of the voltage curve. At the end of December 2010 I discharged 179.6Ah from my 200Ah pack and put my 6A load on the pack and the voltage difference was only 0.015V from the two extremes.

The Zivan NG1 will turn off and on current during the last stage of charging to keep the voltage from going above its set point. I can both see on my wall meter and hear when this happens. I take voltage readings immediately after the current stops and then stop taking measurements when it starts again and wait for the next time it stops. What I have found is that the relative positions of the cells in a voltage lineup changes but that the high and the low cells haven't changed since October 2010 at the 12,810 mile mark on the odometer. My last measurement was the 5th of May at the 15,737 mile mark.

So, while you are seeing some change, are the cells "trading places?" Also, as I think some one else noted, is your shunt balancer putting an imbalanced load on the cells? Another thing to consider is that there may be enough difference in how the Headaway cells are made and the WB (TS) and CALB cells are made to cause the Headaways to be different. Also, for those reading, it is important to note that we are only talking about LiFePO4 cells. Others may be different but the literature I've found implies that they behave very similar with respect to "cell drift" or the lack there of.


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## tomofreno (Mar 3, 2009)

> I do not want to go with a BMS either, probably have to. I am doing cell cycle testing. they diverge eventually.


 What fraction C were your charge and discharge currents?


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## JRP3 (Mar 7, 2008)

GizmoEV said:


> Another thing to consider is that there may be enough difference in how the Headaway cells are made and the WB (TS) and CALB cells are made to cause the Headaways to be different.


My impression is that the Headways don't have the same quality control as CALB or TS.


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## tomofreno (Mar 3, 2009)

> the big 'flat' spot in the middle not really gives a sign of what is going on.


 That's exactly where you want to operate. Regularly driving cells to the exponentially increasing V versus Ah part of the curve while charging or the exponentially decreasing part during discharging shortens cell life. Cells behaving the same over the flatter part of the curve is all you need care about. The charge gained by extending operation to the exponential regions is a few Ah. Deviations in voltage amongst cells on these exponential regions corresponds to negligible differences in charge. The voltage differences are larger due to the higher cell resistances there, but it doesn't really tell you much. Most of the charge transferred during charging on the exponential part of the curve will diffuse back when the charger is shut off, which is why the cell voltages "relax" to a lower value. Btw, another source of variation is in the turn on voltages of the shunts. I measured a spread of 0.03V in the turn-on voltage of the shunts on my 36 minibms modules. That is larger voltage variation than I see between cells when charging at 20A charge current (0.11C), with them top balanced and at voltages at the bottom of the exponential part of the curve, ~3.45V. They of course start diverging as some climb higher on the exponential part than others. I'm guessing that resistance increases because intercalation sites are becoming scarce, and a larger E-field is required to force charge into the electrode material to get to those sites. If so, this isn't representative of the operation of the cell over most of it's SOC so who cares? Eighteen month old CALB cells with a bit over 10k miles on them. I think operation over the flatter part of the curve is what matters, and examining differences on the exponential parts is a waste of time.


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## tomofreno (Mar 3, 2009)

> Not charging it full or discharging to the roll of leaves you in the big fat section in the middle It is a "Blindspot" regarding soc.


 Only if you are trying to estimate SOC with voltage rather than a charge counter. Most of us use charge counters for that reason.


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## bmentink (Apr 22, 2011)

Coulomb said:


> There are downsides to using individual chargers.
> 
> There is the efficiency issue; medium power 3.3 V power supplies are typically 75% efficient, compared to perhaps 93% for a 2 kW charger.
> 
> ...


All good points:

1. Efficiency of the converters I sourced were in the 88% order .. but as you say, could be better.
2. Not sure on the power factor ... will check that out.
3. Turn on surge I was going to manage by ripple starting the converters, the inverters have enable pins, so the 1st one would come up which would bring the next one up after a delay, and so on ..
4. Managing the AC connections legally/safely is not that hard .. 

Thanks for the comments.


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## bmentink (Apr 22, 2011)

steven4601 said:


> Each to their own. I do not preach for individual chargers at all.
> 
> Here is a bit of perspective.
> A 3kW PFC is about 300 euro. Technically this is also a battery charger , just needs a microcontroller to turn it into a current souce and taper off the current output at a specific voltage.


Can you elaborate on where to get a 3Kw PFC power supply from, for that price ... I am very interested.



steven4601 said:


> edit: the 'status' flag that starts shunting can be a simple optocoupler part of the energy dissipation circuit. A little more expensive but less wiring required would be to use a microcontroller which sends a code of the cell voltage. This may need some protocol tinkering as there are 100 to 130 co-microcontrollers trying to tell their status on the same 'open collector' bus. A random delay generator and a fixed length packet with a crc comes to mind  The receiver end can be a simple USB Uart & embedded / pc software


A simple solution at $2 per cell is to use a Maxim 1-wire Li-Ion battery monitor chip .. something like the DS2762 which would report back to the controller the faulty cell and can light an LED near the cell as it has a GPIO line ..

Cheers,


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## steven4601 (Nov 11, 2010)

For a PFC, this could happily be hacked. http://www.deltapowersolutions.com/en/732.htm


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## bmentink (Apr 22, 2011)

steven4601 said:


> For a PFC, this could happily be hacked. http://www.deltapowersolutions.com/en/732.htm


So, that price you quoted was from these guys? Can I buy direct, or did you get them from a distributer ..

I presume these are PFC rectifiers, do you know what voltage they go upto? I can only see normal telecom voltages of 48v nominal.
I am running 110 cells so need final charge voltage at 390..410v from input of 240v RMS.


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## bmentink (Apr 22, 2011)

Maybe you guys who want to make your own BMS should look at this cheap option from Linear Tech. ... the LTC6802-1. It can monitor and shunt regulate upto 12 cells with the one cheap (<$10) IC. For me I am building 10 cell packs(for a manageable 20Kg weight) so add a bi-directional isolator chip for the SPI data bus and you have monitoring and shunt regulation in a two chip solution(for upto 12 cells) .. I would think this a better solution than the LM431.

The chip also has some GPIO lines, so I imagine them driving a BCD 7-segment display so you can see which cell(s) are faulty by a casual look down the battery pack.

Hope that helps ..


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## steven4601 (Nov 11, 2010)

About the Delta telecom rectifier. Those are fixed (48V) voltage. But it is the PFC you'd be after. 
I didn't see the quote on paper but i recall what as being said was in the 300-400 range. 
Before digging further into hacking these units, there are off the shelf PFC too. Ill do my utmost best to find an example. 
The only thing that the PFC has to be modified is the end voltage, normally 400V reducing that to 390 wouldn't cause too many problems, maybe slightly worse PF. Also the current limit has to be added to provide a CC/CV instead of tripping current limit.


About the balancers, wrong with the LM431C? it can do 100mA, its 0.08cents. Their variations in accuracy, I think their shunt voltage is less than/better than 0.4% accurate.


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## bmentink (Apr 22, 2011)

steven4601 said:


> About the Delta telecom rectifier. Those are fixed (48V) voltage. But it is the PFC you'd be after.
> I didn't see the quote on paper but i recall what as being said was in the 300-400 range.
> Before digging further into hacking these units, there are off the shelf PFC too. Ill do my utmost best to find an example.
> The only thing that the PFC has to be modified is the end voltage, normally 400V reducing that to 390 wouldn't cause too many problems, maybe slightly worse PF. Also the current limit has to be added to provide a CC/CV instead of tripping current limit.


Appreciate you dig out the off the shelf PCF's.



steven4601 said:


> About the balancers, wrong with the LM431C? it can do 100mA, its 0.08cents. Their variations in accuracy, I think their shunt voltage is less than/better than 0.4% accurate.



Well, for one to get the cell info back to the microcontroller, you will need an isolated interface to each LM431, with the chip I just recommended, you only need one isolator for the whole PACK, and isolation is expensive.

Two, the accuracy is only as good as your resistive divider ..

Also the chip does over-voltage, under-voltage warning, temperature measurement, etc ....


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## bmentink (Apr 22, 2011)

You know guys, there is a better way.

What needs to happen is that all the cell voltages need to be equalized.
I.E The charge on cells with too high a voltage needs to be shifted to ones with too low voltage, this way you don't expend energy in shunting.

This is quite easy to achieve.

Attached is a diagram of how to do this.

These switches could be CMOS analog switches capable of 100ma current. The switches are driven by a simple clock which switches each capacitor to the cell above or the cell below. What happens over time is that the charge is equalized over all the cells. It works in the background with no monitoring and no software needed. It can work during charge and discharge.

No energy is wasted. Seems like you can do this very cheaply .. one capacitor plus one switch per cell.

What do you folk think?


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## Elithion (Oct 6, 2009)

bmentink said:


> You know guys, there is a better way.


I hate to tell you, but, of all the various non-dissipative balancing topologies, this one performs the worst.



bmentink said:


> No energy is wasted.


Capacitive balancing is in theory, only 50 % efficient (half the energy transferred is wasted in heat), in reality, it is even less efficient.

In addition, as in any cell-to-cell balancing scheme, when used with large packs, this topology is pretty much unable to transfer energy between cells at either end of the pack, because so much is lost at each stage.

For a more detailed explanation, see section 5.4.5.1.2.1.1 of the Li-Ion BMS book.


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## bmentink (Apr 22, 2011)

Elithion said:


> Capacitive balancing is in theory, only 50 % efficient (half the energy transferred is wasted in heat), in reality, it is even less efficient.
> 
> For a more detailed explanation, see section 5.4.5.1.2.1.1 of the Li-Ion BMS book.


I find it hard to believe that you loose that much energy in capacitors ... what type and quality cap are you talking about.
(I have designed switch-mode power supplies that switch around 20Amps with capacitors and they don't heat at all, in this application we are only moving around mA's)


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## Elithion (Oct 6, 2009)

bmentink said:


> what type and quality cap are you talking about?


Ideal capacitors.
Then the loss is only 50 %.

The loss is not in the capacitors, it is in the act of tranfering energy between 2 voltage sources: the cell is a voltage source, and the capacitor is a voltage source. Whenever you do that, 1/2 the energy is transferred, 1/2 is dissipated in heat. It's just physics.


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## Coulomb (Apr 22, 2009)

bmentink said:


> You know guys, there is a better way.


It's an interesting idea. Thanks for sharing it.



> ... No energy is wasted.


That's not true. You're connecting a small capacitor, with perhaps 0.1 ohms of equivalent resistance (wild guess), across a cell with milli-ohms of internal resistance, with a CMOS switch with tens or perhaps hundreds of ohms of resistance. So the difference between the cell and the capacitor voltage will be charged via the resistance of the switch. The switches themselves will dissipate energy as heat.

It's hard to say how efficient this would be at transferring charge. If the highest- and lowest- voltage cells happen to be far apart, the losses could be substantial; I'd guess of the order of 90% (loss, not efficiency) at times. Overall, it might be 50-75% efficient (another wild guess) at moving around some charge. [ Edit: as others have posted, the theoretical maximum efficiency is 50%, and the practical efficiency will likely be much less. ]

Of course, bypass resistors are 0% efficient (100% loss, no energy is recovered), so any gain is a slight bonus (basically, saving you a little energy when charging, slightly quickening charges, and warming the vehicle and its battery pack slightly less).

My concern would be how much current you could transfer with this. Even if the switches were rated at say 500 mA average, I'm not sure that you could guarantee "bypassing" (really shuffling charge, but it amounts to much the same thing) anything like 500 mA. When a LiFe cell approaches 100% SOC, its voltage rises very rapidly. To save the cell from damage, that voltage needs to be capped. So you need something to tell the charger to reduce its output to a low level, say 500 mA. But then, assuming you don't want to terminate the charge right there (i.e. you have chosen to top balance), you need to reduce the current to the cells that have a high terminal voltage, to next to zero. Bypass resistors will do this. If the cell with the highest voltage happens to have a neighbour that is almost as high in voltage, then there is little voltage difference to work with to shuffle charge.

The continued need to throttle the charger back when one cell reaches a voltage threshold means you still need the main complexity of a BMS (some means for measuring the voltage of each cell, and transmitting that information to the charger). If you could shuffle enough charge fast enough (i.e. bypass enough current) that you could just let the charger continue at its normal charge rate (which near the end of charge might be tapering off), then that would be a significant saving. But sometimes one cell will be reaching a high voltage when the average is still low enough to warrant full charger output. Without a full BMS, you won't know if and when this is happening.

It's possible that this could be made to work well, but the devil is, as so often is the case, in the detail.


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## GizmoEV (Nov 28, 2009)

bmentink said:


> You know guys, there is a better way.
> 
> What needs to happen is that all the cell voltages need to be equalized.
> I.E The charge on cells with too high a voltage needs to be shifted to ones with too low voltage, this way you don't expend energy in shunting.
> ...


I can't speak to an abused pack or one at the end of life but watching my LiFePO4 pack of 18 cell pairs of LFP-100AHA cells top balance it took less than 5 minutes to balance at a 200mA current. That is less than 66mAh between the highest cell and lowest cell. That is so little energy it isn't worth trying to "save" because it will cost more to save it than to "waste" it.

EDIT: FWIW, I now have 20 cell pairs and only charge to 3.485vpc. No balancing for 10 months and no drifting cells.


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## yarross (Jan 7, 2009)

The charge travel distance issue could be resolved by arranging such BMS in a hierarchical way. Why not arrange let's say 36 cells in 6 cells banks and do balance cells inside banks and the whole banks themselves? For large cell number, this approach will yield log distance, effective enought even for high voltage batt packs.


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## bmentink (Apr 22, 2011)

yarross said:


> The charge travel distance issue could be resolved by arranging such BMS in a hierarchical way. Why not arrange let's say 36 cells in 6 cells banks and do balance cells inside banks and the whole banks themselves? For large cell number, this approach will yield log distance, effective enought even for high voltage batt packs.


That's what I was thinking, in my case 11 packs of 10 cells. I think 10 cells would still balance up quite quickly, especially given GismoEV's experience with balancing .. 

I think a trial is on the menu ...


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## steven4601 (Nov 11, 2010)

Hi Bmentink,

you could turn it into a cuk converter by adding two inductors and a diode. That will increase efficiency. Eff. results are limited by the low voltages & using regular diodes.


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## yarross (Jan 7, 2009)

steven4601 said:


> Eff. results are limited by the low voltages & using regular diodes.


So, synchronous rectifiers are welcome.


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## bmentink (Apr 22, 2011)

steven4601 said:


> Hi Bmentink,
> 
> you could turn it into a cuk converter by adding two inductors and a diode. That will increase efficiency. Eff. results are limited by the low voltages & using regular diodes.


My understanding of cuk inverters are that they invert the voltage, so not sure how that would wire up .. maybe you could draw a picture 
EDIT: Sepic would be better maybe ..


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## ElectriCar (Jun 15, 2008)

I spoke to Greg at Electric Conversions in Sacramento today about reprogramming my Zivan NG5. I had asked him to set my maxV to 170.7 or about 3.41V/cell. I told him that is only a little, <10Ah shy of fully charged. He disagreed and said he thinks that's a mistake for 50 cells as he's talked to numerous knowledgeable people and they all say the batteries will be nowhere near fully charged at that voltage, said most energy is added between 3.5-3.6V or 175-180V for my pack so I'll be leaving a lot out. I told him I've already gotten over 100 miles on a recharge with probably 10+ miles remaining, which is better than I expected. Also told him I was counting Ah and that what I'd removed was being added back with the charger shutting down at 171V. He then was scratching his head I'm sure.

He also was urging me to get a BMS as inexpensive as I can afford. What? Cheap BMS gear with all the concern about them shorting and destroying batteries? No if I were to get one, I'd want one with a track record of no shorting and a very high regard in the EV world, not cheap.

I was just amazed to listen to him trying to convince me to get a BMS. And they don't sell BMS gear!


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## GizmoEV (Nov 28, 2009)

Maybe I should email him my data on the amount of energy between 3.45V and 4.00V then. I don't think he understands that the lower the ending current the lower the cutoff voltage should be to not over charge the cells. If you talk to him again ask him if he personally has tested the amount of energy between 3.5 and 3.6V.

Even if he programmed your charger for 175V there would likely be enough turns of the voltage pot available to turn down the ending voltage.

What you ran into is why I told them I need the charge profiles so I could determine the number of cells to put in my pack because my DC-DC had an upper voltage limit. My charger is programmed for 19 cells but I installed 20 cells and turned up the voltage from 69.3V to 69.7V and lately have been considering turning it down to 69V or 3.45vpc.


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## steven4601 (Nov 11, 2010)

Sepic is possible too. Cuk might lend itself better for cheaper components.

If it produces negative voltages, look around the voltages in your pack if you have more than 1 cell.... there is a negative voltage somewhere


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## JRP3 (Mar 7, 2008)

ElectriCar said:


> I spoke to Greg at Electric Conversions in Sacramento today about reprogramming my Zivan NG5. I had asked him to set my maxV to 170.7 or about 3.41V/cell. I told him that is only a little, <10Ah shy of fully charged. He disagreed and said he thinks that's a mistake for 50 cells as he's talked to numerous knowledgeable people and they all say the batteries will be nowhere near fully charged at that voltage, said most energy is added between 3.5-3.6V or 175-180V for my pack so I'll be leaving a lot out.


 Doesn't exactly instill confidence that someone dealing with EV conversions has no understanding at all how LiFePO4 cells work. He must have never charged a cell since it's so obvious how little time it takes to go from 3.45 to 3.5-3.6


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## ElectriCar (Jun 15, 2008)

Gizmo and JRP I told him I knew a couple of people, you two, who weren't charging like that and your data showed otherwise. The Cycle Analyst proves our data and disputes his. He's an electrical engineer JRP but it's obvious he knows nothing first hand about Lifepo4 cells. What he's claiming doesn't even make sense...


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## tomofreno (Mar 3, 2009)

In fairness, Greg did not say there was significant energy above 3.45V. He said above 3.41V:


> I spoke to Greg at Electric Conversions in Sacramento today about reprogramming my Zivan NG5. I had asked him to set my maxV to 170.7 or about 3.41V/cell.


I agree there is significant energy between 3.41V and where the exponential V rise with Ah starts, compared to above 3.45V which is at the start of the "knee" for CALB cells. By "significant" I mean something on the order of 0.05C, which would increase my range by about 5 miles or so. Could probably get a better idea of how much could be gained by looking at Jack R's charge curves.



> Also told him I was counting Ah and that what I'd removed was being added back with the charger shutting down at 171V.


 Did you use that charger to charge the pack in the first place? If so, that doesn't say you used full capacity of the cells which was his point, just that you replaced what charge you used.

I am not saying do not charge only to 3.41V. If charging to 3.41V gives you plenty range to meet your needs, then great! You can probably extend your cell life by only charging to that voltage. Just pointing out the guy wasn't as far off base as the comments seem to indicate.


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## ElectriCar (Jun 15, 2008)

tomofreno said:


> In fairness, Greg did not say there was significant energy above 3.45V. He said above 3.41V:
> I agree there is significant energy between 3.41V and where the exponential V rise with Ah starts, compared to above 3.45V which is at the start of the "knee" for CALB cells. By "significant" I mean something on the order of 0.05C, which would increase my range by about 5 miles or so. Could probably get a better idea of how much could be gained by looking at Jack R's charge curves.
> 
> Did you use that charger to charge the pack in the first place? If so, that doesn't say you used full capacity of the cells which was his point, just that you replaced what charge you used.
> ...


No Tom he specifically said that between 3.5 to 3.6V is where most of the energy is added. He may have misspoke but that's what he said. It's not most, not even much, it's very little. In my situation 10Ah is nothing. My cells are labeled 200ah. They tested at 216-218 IIRC, thus my ability to go over 100 miles averaging <300wh/mile.

Yes this charger did the initial charge, however as the voltage approached 171 it began to increase very quickly. I recorded the time between each tenth of a volt increase which I think was around 8 minutes each or so until close to 171. From 171.2-171.4 only took maybe 3 minutes total and the Ah added was only about 1, maybe less as the amperage had decreased to about half but I don't have the notes in front of me. 

However he did notify me that there is a voltage adjustment pot on it enabling me to change the final voltage significantly if I wanted to later and sent me instructions on how to do it, something he wouldn't do before I sent it in. He actually told me there was no way to adjust the voltage. I even told him I could change a resistor or such if I needed to since I have worked in electronics for years.


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## JRP3 (Mar 7, 2008)

Also remember that the voltage SOC indication is dependent on charge current. 3.41V at 20 amps will be at a lower SOC than 3.41V at 5 amps. If you stopped charging at 3.41V at 20 amps you will leave a good amount of charge on the table, at 5 amps not as much.


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## ElectriCar (Jun 15, 2008)

Yes that's right JRP3. The charger was however throttling back pretty quickly and the current was about half, maybe 8-10A with the voltage rising quickly. I think it's safe to say they were pretty well charged based on the length of time it took to charge from the factory 60% SOC up to that point, the long trip I made and the Ah removed on that trip. 

I plan to balance them again at a higher voltage once more then see how they behave. I've balanced them once to within 1/1000V but that was about 3.4V roughly. After driving it a bit and recharging, I had several cells going high again and drained them off closer to the others but not to such close tolerance as before. Obviously they weren't top balanced at a high enough voltage the first time. The first time I started at the point where several had started to spike.

Regardless though I don't see anything of value above 3.41 or 3.42V. I really think I'd be wasting time trying to go any higher but I'll see what happens anyway, just in case. If nothing else I'll have a bit more leeway in overcharging before something starts spiking.


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## yarross (Jan 7, 2009)

JRP3 said:


> Also remember that the voltage SOC indication is dependent on charge current. 3.41V at 20 amps will be at a lower SOC than 3.41V at 5 amps. If you stopped charging at 3.41V at 20 amps you will leave a good amount of charge on the table, at 5 amps not as much.


CC-CV charging algorithm should be immune to this effect, right?


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## Roy Von Rogers (Mar 21, 2009)

JRP3 said:


> Also remember that the voltage SOC indication is dependent on charge current. 3.41V at 20 amps will be at a lower SOC than 3.41V at 5 amps. If you stopped charging at 3.41V at 20 amps you will leave a good amount of charge on the table, at 5 amps not as much.


 
You know thats something not well understood about these cells. In theory you can charge these cells with the max amount of current without care about voltage, if you had an accurate ah/wh meter.

The real problem lies in the fact we dont have an exact way to know how much we removed from a pack, if we did, we could charge at max amps and stop the charging process at the point of what we removed, and the pack would be right back where it was before discharge.

The voltage has realy no meaning, exept the way we charge at this time (CC/CV) is the only way to charge, and not to go over the knee damage.

Roy


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## JRP3 (Mar 7, 2008)

yarross said:


> CC-CV charging algorithm should be immune to this effect, right?


If it's done accurately, yes.


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## JRP3 (Mar 7, 2008)

Roy Von Rogers said:


> You know thats something not well understood about these cells. In theory you can charge these cells with the max amount of current without care about voltage, if you had an accurate ah/wh meter.


I think that's true in theory but when getting near full at higher current you might end up generating excess heat as you dump in high current and the cells have fewer places to take that charge.


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## MN Driver (Sep 29, 2009)

Ditto, they generate a bunch more heat and have had cells near my personal safe temperature of 140 degrees F at an ambient of 70 degrees by trying Ah counting only. I don't think CC/CV is only there to not overcharge, they generate a bunch of heat and I don't think that can be a good thing for life.

I generally test for myself and don't have the instruments for fancy graphs but take a look at Rickard's graphs when he did the same, my results were close to the same, they were hot there too.


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## icec0o1 (Sep 3, 2009)

Roy Von Rogers said:


> You know thats something not well understood about these cells. In theory you can charge these cells with the max amount of current without care about voltage, if you had an accurate ah/wh meter.
> 
> The real problem lies in the fact we dont have an exact way to know how much we removed from a pack, if we did, we could charge at max amps and stop the charging process at the point of what we removed, and the pack would be right back where it was before discharge.
> 
> ...


 
Incorrect. Any time you go above a certain voltage (usually 4.2V) you begin to split the electrolyte in the lithium batteries through electrolysis. If you're doing max amps towards the end of charge, the voltage would be higher than the resting voltage and usually enough to reach that electrolysis threshold.


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## DIYguy (Sep 18, 2008)

icec0o1 said:


> Incorrect. Any time you go above a certain voltage (usually 4.2V) you begin to split the electrolyte in the lithium batteries through electrolysis. If you're doing max amps towards the end of charge, the voltage would be higher than the resting voltage and usually enough to reach that electrolysis threshold.


I believe Roy is correct. I think you are also. The difference is in charge vs resting voltage. During charge, u don't really know where the resting voltahe is. U cld b charging with 10 volts on a battery with little stored energy. This is not representative of the cell's voltage at rest. Voltage higher than what the cell has is a "force" required to push the current in. As long as you don't exceed thermal limits, I don't think it is too big of a deal.


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## icec0o1 (Sep 3, 2009)

DIYguy said:


> I believe Roy is correct. I think you are also. The difference is in charge vs resting voltage. During charge, u don't really know where the resting voltahe is. U cld b charging with 10 volts on a battery with little stored energy. This is not representative of the cell's voltage at rest. Voltage higher than what the cell has is a "force" required to push the current in. As long as you don't exceed thermal limits, I don't think it is too big of a deal.


Resting voltage isn't important. At any instant if the voltage of a battery is above the electrolysis level of the electrolyte, it'll begin to split and produce gasses. 

The SOC of a battery can be 10%, but if you charge it with a high enough current, the voltage will be high enough to split the electrolyte before the battery even comes close to 50% SOC. 

If you try to charge a LIFEPO4 battery at 30C, I guarantee you the voltage will be above 4.2V even at 5% SOC. At that point, the EC/DMC/LiPF6 electrolyte will undergo a chemical reaction and will split into gasses.


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## JRP3 (Mar 7, 2008)

Do you have any reference material for that information?


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## ElectriCar (Jun 15, 2008)

icec0o1 said:


> The SOC of a battery can be 10%, but if you charge it with a high enough current, the voltage will be high enough to split the electrolyte before the battery even comes close to 50% SOC.


Where did you learn this and how sure are you of it? That may be the "terminal" voltage applied but not necessarily the actual battery voltage as I understand it so I'm not sure you'll be destroying electrolyte. Then again I'm not fully versed on this aspect either.


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## DIYguy (Sep 18, 2008)

icec0o1 said:


> Resting voltage isn't important. At any instant if the voltage of a battery is above the electrolysis level of the electrolyte, it'll begin to split and produce gasses.


hmmm, well, I dunno if I would say it isn't important. It's not a good reference for state of charge,...but I think if most ppl had a cell that showed 4.2 volts at rest...they would be worried. How do you really know that the internal voltage of a cell is when you have charger connected to it? If the charger was at 5 volts, u think u wld b gassing the cell?...even though it was drinking current at good rate??


icec0o1 said:


> The SOC of a battery can be 10%, but if you charge it with a high enough current, the voltage will be high enough to split the electrolyte before the battery even comes close to 50% SOC.


 Ya, i dunno about this. Have you demonstrated this ? You are kind of mixing up current and voltage now. I understand that to get high C rates (which was not the point of discussion) you prolly would need higher voltage levels.. . but lets not just arbitrarily link them. Most low resistance batteries will take current at a good rate without significantly higher than terminal voltage. . . and likely able to handle about the same C rate as their discharge... even though its not normally done.


icec0o1 said:


> If you try to charge a LIFEPO4 battery at 30C, I guarantee you the voltage will be above 4.2V even at 5% SOC. At that point, the EC/DMC/LiPF6 electrolyte will undergo a chemical reaction and will split into gasses.


Well, lifepo4 is not a 30C rate chemistry...so, I dunno where this came from. The comments were regarding voltage levels, not current levels. (at least that what I remember,,, it has been all of a half hour and I'm getting older... lol) I better go look..lol OK, he said max amount of current without worry of voltage. I took this to mean generally accepted maximums for the chemistry.. . not 30 C.

Charge a 100 ah cell that is at 10% state of charge with C1 at 5 volts for until it hits say 80% state of charge. Remove the charge let it rest and you have a battery that is what???? damaged? I'm not a battery tester...but, I don't or at least didn't think this was the case. Thoughts.?


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## icec0o1 (Sep 3, 2009)

DIYguy said:


> hmmm, well, I dunno if I would say it isn't important. It's not a good reference for state of charge,...but I think if most ppl had a cell that showed 4.2 volts at rest...they would be worried. How do you really know that the internal voltage of a cell is when you have charger connected to it? If the charger was at 5 volts, u think u wld b gassing the cell?...even though it was drinking current at good rate??


Yes, if you measure the battery leads with a multimeter and it reads 5 Volts, that means the electrolyte in the battery is exeriencing 5 volts of electrical potential and would be gassing. For water, as an example, if you provide 1.2 volts of electrical potential, it'll begin to split into hydrogen and oxygen; the rate the reaction being dependent on the current. Battery electrolyte begins to undergo a chemical raction at about 4.2-4.3 volts. 



> Ya, i dunno about this. Have you demonstrated this ? You are kind of mixing up current and voltage now. I understand that to get high C rates (which was not the point of discussion) you prolly would need higher voltage levels.. . but lets not just arbitrarily link them. Most low resistance batteries will take current at a good rate without significantly higher than terminal voltage. . . and likely able to handle about the same C rate as their discharge... even though its not normally done.
> 
> Well, lifepo4 is not a 30C rate chemistry...so, I dunno where this came from. The comments were regarding voltage levels, not current levels. (at least that what I remember,,, it has been all of a half hour and I'm getting older... lol) I better go look..lol OK, he said max amount of current without worry of voltage. I took this to mean generally accepted maximums for the chemistry.. . not 30 C.


My point was that at "max current" for a battery, let's say 3C for LIFEPO, there'll be a %SOC where that current will raise the battery's voltage above 4.2v... it'll be close to 85-90% SOC or so. I used 30C as an example because it'll raise the battery's voltage above 4.2V even at 10% SOC. That all depends on internal resistance of the battery; some lipo batteries can do well at 30C. Although that's a 2 minute charge and I guarantee you the battery will be above 4.2V after a minute at 30C so the charger would have to then go into CV. 



> Charge a 100 ah cell that is at 10% state of charge with C1 at 5 volts for until it hits say 80% state of charge. Remove the charge let it rest and you have a battery that is what???? damaged? I'm not a battery tester...but, I don't or at least didn't think this was the case. Thoughts.?


You can't charge a 100ah cell at 1C at 5 volts. If you measure the battery leads, the voltage would be about 2.9-3.0V?


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## JRP3 (Mar 7, 2008)

What ice is saying is that if enough current is used to push battery voltage above 4.2 regardless of SOC the electrolyte starts to breakdown. It doesn't matter if the cell is at 50% SOC or 99% SOC, the mere fact of going above 4.2V causes the damage. I've never seen reference to that before that I can recall, and I've seen cells held at much higher voltage with no evidence of venting, but with unknown long term effects, so I'd like some verification of his claims. He may be correct, I just don't know.


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## JRP3 (Mar 7, 2008)

That seems like a plausible explanation.


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## icec0o1 (Sep 3, 2009)

There was a great hour and a half lecture by a college professor on lithium ion batteries like 6 months ago linked on here and by Jack's blog. Can't seem to find it though.


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## JRP3 (Mar 7, 2008)

Yes I watched it but didn't catch the voltage breakdown of the electrolyte. I was having some audio issues.


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## JRP3 (Mar 7, 2008)

Here's a link
http://www.ri.cmu.edu/video_view.html?video_id=60&menu_id=387


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## icec0o1 (Sep 3, 2009)

ElectriCar said:


> Where did you learn this and how sure are you of it? That may be the "terminal" voltage applied but not necessarily the actual battery voltage as I understand it so I'm not sure you'll be destroying electrolyte. Then again I'm not fully versed on this aspect either.


You have to think of voltage as just a potential. If you give a high potential to a battery, say 5V, the battery will be willing/forced to absorb a ridiculous amount of amps. If you have a controller to PWM the current to limit it, it'll drop the voltage as well. You have to remember that a lithium battery is a resistor, a capacitor, and an inductor. 

Just like a controller limits the amps it draws from the batteries and drops their voltage a bit. But on the motor side, the amps and voltage can be completely different.


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## icec0o1 (Sep 3, 2009)

JRP3 said:


> Here's a link
> http://www.ri.cmu.edu/video_view.html?video_id=60&menu_id=387


Added to bookmarks, thanks  It's in there... I don't have the time to look for it again as it is a long video.


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## JRP3 (Mar 7, 2008)

I'm downloading it with Download Helper and I can then scroll through it and play it at faster speed with VLC player. It's how I usually watch Jack Rickard's shows


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## tomofreno (Mar 3, 2009)

> Yes I watched it but didn't catch the voltage breakdown of the electrolyte. I was having some audio issues.


I watched it twice and took notes. Quote: "Above 4.3 - 4.4V you see the electrolyte solvent breakdown and evolve as a gas. You get a jet if it happens at a high rate. It is flammable, so you get a blowtorch."

At another point in the presentation: "Heat breaks down the electrolyte which then coats the electrode - happens at about 50 - 60C. Causes loss of capacity - less volume for Li+ ions in the films, harder to get in and out."


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## tomofreno (Mar 3, 2009)

> CC-CV charging algorithm should be immune to this effect, right?


 No. I see it all the time with my Manzanita using CC/CV, as I've posted here a number of times, so sorry to bring it up again. If I charge at the same cell temperature but two different current values, and use about 50 minute CV stage, the higher current charge will terminate at a lower SOC than the lower current one - because the charger reaches it's preset limit voltage at a lower SOC when charging at the higher current.


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## JRP3 (Mar 7, 2008)

Here's a headway cell being overcharged with 60 amps, driven to 19 volts with no visible venting. Then it gets shot with a crossbow for fun


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## JRP3 (Mar 7, 2008)

tomofreno said:


> No. I see it all the time with my Manzanita using CC/CV, as I've posted here a number of times, so sorry to bring it up again. If I charge at the same cell temperature but two different current values, and use about 50 minute CV stage, the higher current charge will terminate at a lower SOC than the lower current one - because the charger reaches it's preset limit voltage at a lower SOC when charging at the higher current.


That's more of a weakness in the Manzanita than the CC/CV method. To really do CC/CV the CV should not be a time out termination but shut off when current is zero or nearly so, and voltage should be more accurately clamped. The Manzanita's do neither.


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## icec0o1 (Sep 3, 2009)

JRP3 said:


> Here's a headway cell being overcharged with 60 amps, driven to 19 volts with no visible venting. Then it gets shot with a crossbow for fun


No visible venting? Look at all of that smoke as he punctured the outer shell. He should be glad that it didn't spark and turn into a flamethrower. 

Btw, it'at 50:30 into the video. And i'm certainly not saying that 30 seconds at 5 volts will kill a cell. It is still a very slow process. I was just trying to say that designing a CC charger which limits charge based on %SOC and amp hours is not a great idea long term. In fact, as the battery degrades, the end of charge voltage will get higher and higher where the battery will explode at some point in time.


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## tomofreno (Mar 3, 2009)

> That's more of a weakness in the Manzanita than the CC/CV method. To really do CC/CV the CV should not be a time out termination but shut off when current is zero or nearly so, and voltage should be more accurately clamped. The Manzanita's do neither.


 They do the do the former well when the pack is top balanced, not so well when the pack is bottom balanced.


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## GizmoEV (Nov 28, 2009)

tomofreno said:


> They do the do the former well when the pack is top balanced, not so well when the pack is bottom balanced.


I don't see how that should matter. The charger doesn't know what the individual cell voltages are. If it is set to stop at a max particular voltage, it should just stop at that voltage and not go any higher. This is regardless of the DOD of the last discharge, input voltage, or temperature. That doesn't seem to be the case from reports I've read.


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## DIYguy (Sep 18, 2008)

icec0o1 said:


> You have to think of voltage as just a potential. If you give a high potential to a battery, say 5V, the battery will be willing/forced to absorb a ridiculous amount of amps. If you have a controller to PWM the current to limit it, it'll drop the voltage as well. You have to remember that a lithium battery is a resistor, a capacitor, and an inductor.
> 
> Just like a controller limits the amps it draws from the batteries and drops their voltage a bit. But on the motor side, the amps and voltage can be completely different.


ok... it makes some sense in my little brain. Thanks. I do recall the prof talking about this, I guess I assumed it to be referring only to end of charge issue and not during the process of charging. I thought that if it was absorbing current, even if somewhat above say, 4.2, it wouldn't cause breakdown. But I can see what you are saying now. To get to 5 volts you have to be at a pretty high C rate. Thing is, we may not see evidence of this until a cell fails early... if it is not an extreme case, I suppose.


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## JRP3 (Mar 7, 2008)

icec0o1 said:


> No visible venting? Look at all of that smoke as he punctured the outer shell. He should be glad that it didn't spark and turn into a flamethrower.


I think any cell that is punctured, and therefore internally shorted, will start smoking. I was just saying that until it sustained external physical damage there was no visible venting even at more than double the electrolyte breakdown voltage.


> Btw, it'at 50:30 into the video. And i'm certainly not saying that 30 seconds at 5 volts will kill a cell. It is still a very slow process. I was just trying to say that designing a CC charger which limits charge based on %SOC and amp hours is not a great idea long term. In fact, as the battery degrades, the end of charge voltage will get higher and higher where the battery will explode at some point in time.


Yes I watched the video again and I agree. I believe Jack Rickard has the same misconception that I did as he's mentioned that voltage during charging doesn't matter.


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## JRP3 (Mar 7, 2008)

tomofreno said:


> They do the do the former well when the pack is top balanced, not so well when the pack is bottom balanced.


I'm not sure I follow. The voltage is not held precisely and drifts a bit over time and because of that the current will not necessarily taper to zero properly. Certainly the effect will be lessened with a top balanced pack. Of course my smaller cells have less leeway than your larger ones when nearing full so I'm more sensitive to the effects. Now that I'm skipping the CV phase to leave more capacity on the table it's not really an issue.


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## tomofreno (Mar 3, 2009)

> I'm not sure I follow. The voltage is not held precisely and drifts a bit over time and because of that the current will not necessarily taper to zero properly.


 The pack voltage continues to increase somewhat after the charger limit voltage is reached, but the current is cut back to less than 0.5A if the pack voltage rises to about 3V above the limit voltage. When the pack is top balanced, and the limit voltage is set so most cells are at the knee of the curve when the limit voltage is reached, the 3V increase is achieved with only a very small change in pack SOC, and current is cut back to near zero by the time the charger times out. That is because most cell voltages increase quickly with pack SOC, charge into the pack, since they are climbing the exponential part of the V versus Ah curve after the limit voltage is reached. 

When bottom balanced, with limit voltage set so the lowest capacity cell is at the knee of the curve when the limit voltage is reached, the pack SOC has to change quite a bit for pack voltage to increase by 3V because most of the cell voltages are not at the knee of the curve, so don't change much with pack SOC. As a result, the charger has to add considerably more charge, Ah, into the pack to achieve the 3V increase, so it usually times out before current is cut back much. How much depends on how different the cells are in capacity relative to the lowest capacity cell. The closer they are, the larger the number of cells in the pack that will be close to the knee when the limit voltage is reached, and the more the current will be cut back as they climb the exponential part of the V versus Ah curve, increasing the pack voltage appreciably.

It just boils down to the fact that the Manzanitas need to see around a 3V increase in pack V to cut back charge current to a value close to zero, and you get that voltage increase with small change in SOC, or Ah into the pack, when the pack is top balanced, and you don't when it is bottom balanced, unless most cells are very close in capacity to the lowest capacity cell. Now that my pack is top balanced the charge current is consistently less than 0.2A before the charger times out and shuts off, for the range of charge currents I have used - from about 7A to 28A. Usually 0.1A. That is when charging at the same cell temperature. At the higher currents the charger will time out before the pack is full, about 1 to 3Ah less depending on charge current level, but charge current is always cut back to less than 0.2A before the charger times out.

When the pack was bottom balanced that was not the case. Sometimes it would time out when charge current had been cut back only slightly, other times I, or the bms, would have to shut the charger off so it didn't overcharge the lowest capacity cell, depending on charge current setting. Hence my comment that the Manzanitas do cut back current to about zero if the pack is top balanced - and I should add, that the charger limit voltage is set correctly.

That is what I have observed running with a top balanced pack and a bottom balanced pack. If you have observed different, please elaborate.


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## JRP3 (Mar 7, 2008)

Since I've never tried a fully top balanced pack or an extended CV phase I'll defer to your experience.


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## GizmoEV (Nov 28, 2009)

tomofreno said:


> The pack voltage continues to increase somewhat after the charger limit voltage is reached, but the current is cut back to less than 0.5A if the pack voltage rises to about 3V above the limit voltage.


So the Manzanitas appear to need a 3V increase to taper current. What is the voltage at the output of the charger? That is one thing I want to measure on my Zivan when I get the time. My max charge current is a little under 15A and holds quite steady right up to the end but there is still a little voltage rise after it starts to taper back the current before reaching the max voltage. It is not a 3V rise, however. It is closer to a 1V rise and I'm only charging to 3.485vpc, so just into the knee.

I figured that the majority of the voltage rise was due to a voltage drop in the charging wires. As the current tapered back the voltage drop decreased but maybe the voltage at the charger stayed relatively constant. Is that possibly the case with the Manzanita? Does it hit the same target voltage whether you are charging from 120VAC or 240VAC?


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## icec0o1 (Sep 3, 2009)

JRP3 said:


> I think any cell that is punctured, and therefore internally shorted, will start smoking.


No, it won't. I've tried it  It smokes very little and leaks some electrolyte. 



> I was just saying that until it sustained external physical damage there was no visible venting even at more than double the electrolyte breakdown voltage.
> 
> Yes I watched the video again and I agree. I believe Jack Rickard has the same misconception that I did as he's mentioned that voltage during charging doesn't matter.


There's internal pressure forming in the battery as the electrolyte gassifies. The case probably got quite a bit bigger, although it's much harder to tell with a cylindrical cell (will be easier to see with a prismatic). The case is pretty sturdy though and it'll take quite a bit of pressure for it to rupture by itself.


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## JRP3 (Mar 7, 2008)

icec0o1 said:


> No, it won't. I've tried it  It smokes very little and leaks some electrolyte.


You realize you just contradicted yourself? You say no it won't smoke, then you say it smokes very little and leaks some electrolyte. So the answer is yes it will smoke.


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## JRP3 (Mar 7, 2008)

GizmoEV said:


> Does it hit the same target voltage whether you are charging from 120VAC or 240VAC?


No it does not.


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## icec0o1 (Sep 3, 2009)

JRP3 said:


> You realize you just contradicted yourself? You say no it won't smoke, then you say it smokes very little and leaks some electrolyte. So the answer is yes it will smoke.


Bah, it's like comparing cigarette smoke to a locomotive. Technically correct but you know what I meant...


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## Roy Von Rogers (Mar 21, 2009)

icec0o1 said:


> Incorrect. Any time you go above a certain voltage (usually 4.2V) you begin to split the electrolyte in the lithium batteries through electrolysis. If you're doing max amps towards the end of charge, the voltage would be higher than the resting voltage and usually enough to reach that electrolysis threshold.


 
Ok I'm going to say it again. If you have a fully charged battery, and you remove 50% of the battery, and then recharge the battery with lets say 100amps and backward count what you removed, the voltage will not be a concern, for the battery voltage will not go above maximum.

Now considering there maybe a slight inaccuracy in the count, you may want to stop at 90%, but I can asure you that you will be near full on the battery.

Now, could there be a concern about battery temperature, yes it could....but how many of you could charge a full battery pack at 100 amps from a house main supply, not too many, and if even you did, having a fan in the battery compartment would mitigate that problem, considering that those batteries are rated at a pretty high temps.

Here is a chart that shows a 1C (100A) charge rate, now look at the percentage on the bottom, and the voltage....

http://1.bp.blogspot.com/_i_c2BM_uB...AABXQ/bj_KhONGd8w/s1600/+0416chargecurve2.jpg


Roy


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## JRP3 (Mar 7, 2008)

Saying that you aren't likely to be able to put enough current into a cell to raise the voltage is different than saying voltage doesn't matter.


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## Roy Von Rogers (Mar 21, 2009)

JRP3 said:


> Saying that you aren't likely to be able to put enough current into a cell to raise the voltage is different than saying voltage doesn't matter.


 
If you re-read my op you will see it was about putting back in what was removed, I never said that voltage doesn matter as far as over charge is concerned, it was about having an accurate way of metering the removal and recharging to the same amount removed. If you recharged to the amount removed, voltage isnt a concern,

Roy


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## spdas (Nov 28, 2009)

Getting back to the points made a couple of pages ago. How much lead voltage do you need to charge to 3.45v? ie. for lead 12v batteries the charger voltage is around 15v. 

Or is your lithium charger set to charge at max Amps at 3.45v, or does it taper in amps and start at 3.9v or so? 
(if say 44 cells in series do you charge 44x3.45=151.8v or do you select a higher voltage like 165v to start?)

thanks
Francis


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## Coulomb (Apr 22, 2009)

Roy Von Rogers said:


> If you have a fully charged battery, and you remove 50% of the [ charge from the ] battery, and then recharge the battery with lets say 100amps and backward count what you removed, the voltage will not be a concern, for the battery voltage will not go above maximum.


That's true enough. So I guess what you're saying is that for the exercise outlined above, you don't need a BMS or even a volt meter.



> Now considering there maybe a slight inaccuracy in the count, you may want to stop at 90%, but I can assure you that you will be near full on the battery.


Right. So there are two points here. Firstly, without a BMS, how do you know that you started with a full cell? Ok, you could guesstimate it from the overall pack voltage, and hope that they're reasonably balanced. Now suppose you do recharge to 90% to be safe, now you have about 90% SOC. If you keep doing that, you'll end up with 81% then 73% and so on. But of course each time you'll charge till the overall pack voltage indicates a 90% or higher SOC. Each time hoping that none of the individual cells is getting too high in voltage.



> Now, could there be a concern about battery temperature, yes it could....but how many of you could charge a full battery pack at 100 amps from a house main supply, not too many, and if even you did, having a fan in the battery compartment would mitigate that problem, considering that those batteries are rated at a pretty high temps.


Temperature is one of the things that has to be managed during charging. I don't have a lithium iron pack charging yet, so I don't have a feel for how critical temperature management is. But it's another thing that a BMS can do for you.

I also disagree with "those batteries are rated at a pretty high temps". I've read from various sources that bad things start happening at 60C, possibly even with reduced effects as low as 50C. That doesn't leave a whole lot of room for outdoor opportunity charging (depending on your climate, of course). Fortunately, mild charging (perhaps up to about 0.3C, I really don't know the threshold) is endothermic, but the nature of opportunity charging is that you'd like to charge as quickly as possible.



> Here is a chart that shows a 1C (100A) charge rate, now look at the percentage on the bottom, and the voltage....
> 
> http://1.bp.blogspot.com/_i_c2BM_uB...AABXQ/bj_KhONGd8w/s1600/+0416chargecurve2.jpg


That chart suggests that charging a CALB cell to 3.60 V leaves it at about 21% DOD (depth of discharge). But I suggest that the vast majority of the amp-hours that go into the cell above that voltage go into heat and other damage to the cell. Whether Winston/Thunder Sky cells are different is an open question in my book; certainly the shape of the voltage verses energy (Ah) curves are different, so there may be some fundamental difference between the cells that makes 4.0 VPC safe for Winston and unsafe (or at least highly not recommended) for CALB.

So I don't agree with the implication of this graph, namely that amp hours into the cell correspond exactly with SOC, particularly at the upper extreme of the curve.


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## EVfun (Mar 14, 2010)

Coulomb said:


> That chart suggests that charging a CALB cell to 3.60 V leaves it at about 21% DOD (depth of discharge). But I suggest that the vast majority of the amp-hours that go into the cell above that voltage go into heat and other damage to the cell. Whether Winston/Thunder Sky cells are different is an open question in my book; certainly the shape of the voltage verses energy (Ah) curves are different, so there may be some fundamental difference between the cells that makes 4.0 VPC safe for Winston and unsafe (or at least highly not recommended) for CALB.


The chart suggest that charging at 160-200 amps (1C) until the cell reaches 3.6 volts leaves the it at a 79% SOC. That is entirely believable. Charging the cell to 3.6 volts at 16-20 amps (0.1C) leaves it considerably closer to 100% SOC.

I have my (TS) cells top balanced and charge to 3.60 vpc plus 50 minutes hold. The cells stay real close during the taper. The best part is I can turn the charger up by 2 volts and they still stay close, no one cell rises 0.2 volts because all rise some. 

The graph suggests a couple things to me. Something happens at 12% SOC when charging at 1C. Charging fast with a voltage regulated charger can leave you 20% short if you don't have a voltage hold time.


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## GizmoEV (Nov 28, 2009)

spdas said:


> Getting back to the points made a couple of pages ago. How much lead voltage do you need to charge to 3.45v? ie. for lead 12v batteries the charger voltage is around 15v.
> 
> Or is your lithium charger set to charge at max Amps at 3.45v, or does it taper in amps and start at 3.9v or so?
> (if say 44 cells in series do you charge 44x3.45=151.8v or do you select a higher voltage like 165v to start?)


Charging LiFePO4 cells is quite different than lead acid batteries. You can literally charge at max amps until you reach your cutoff voltage and then just hold that voltage and let the current taper down to a small value like 0.015C and terminate charging. As the current tapers down any voltage drop in the charging wire will diminish so that it won't matter any more. For safety it is a good idea to have a timer to terminate charging in case the charger doesn't stop when the current diminishes to near zero.

In the case of my Zivan it was designed for 4 stages: (1)bulk charge, (2)absorption phase, (3)equalize phase, and (4)float. For my LiFePO4 pack it is set to (1)Bulk charge at max current until 3.485vpc is reached, (2)continue to hold voltage at 3.485vpc while current fades, (3)hold voltage until it times out, (4) do nothing but light the green light. It is a way to use a lead acid algorithm for LiFePO4 cells. If it was designed for LiFePO4 from the beginning it would charge at max current until termination voltage is reached, charge until current dropped to something like 200mA and turn off. A timer would be running as a back up.


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## GizmoEV (Nov 28, 2009)

Coulomb said:


> That chart suggests that charging a CALB cell to 3.60 V leaves it at about 21% DOD (depth of discharge). But I suggest that the vast majority of the amp-hours that go into the cell above that voltage go into heat and other damage to the cell. Whether Winston/Thunder Sky cells are different is an open question in my book; certainly the shape of the voltage verses energy (Ah) curves are different, so there may be some fundamental difference between the cells that makes 4.0 VPC safe for Winston and unsafe (or at least highly not recommended) for CALB.


That is why you don't charge at 1C all the way to 100%SOC. As EVfun said, the ending current also has to be considered. If I were to charge my pack at 1C (200A) then according to that graph the charge current would start tapering back at about 55% DOD and be held there until the current dropped to 3A unless I was using some sort of shunting top balance mechanism then it should drop to below 0.5A during the balancing stage and stop. My cutoff voltage is 3.485vpc. Based on my tests my cells would be sitting at no lower than 1%DOD. Voltage AND current are both to be considered when charging these cells.



> So I don't agree with the implication of this graph, namely that amp hours into the cell correspond exactly with SOC, particularly at the upper extreme of the curve.


That is because you are not considering the fact that they are being charged with 1C. Ah into the cell do exactly correspond with SOC but you have to stop charging, let them rest and then measure the open circuit voltage at least to the thousandths of a volt. The problem is, the OCV vs. SOC curve isn't linear.

As for temperature rise during charge, my cells case temperature usually rises for a short while after a long drive and then starts to drop while charging. I have a 200Ah pack and can only charge at ~14A so it is relatively slow. The reason the case temperature rises and then falls is that the case temp will lag behind internal temp while warming. From my experience, warming under charge isn't an issue with low C rates.


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## icec0o1 (Sep 3, 2009)

Roy Von Rogers said:


> Ok I'm going to say it again. If you have a fully charged battery, and you remove 50% of the battery, and then recharge the battery with lets say 100amps and backward count what you removed, the voltage will not be a concern, for the battery voltage will not go above maximum.
> 
> Here is a chart that shows a 1C (100A) charge rate, now look at the percentage on the bottom, and the voltage....
> 
> ...


The chart clearly disproves your statement. If you're charging at 1C, i.e 160 amps for the 160ah TS-LFP, you'll go above the maximum voltage at about 85% SOC. At that point, the voltage will be above 4.2V and you'll begin degrading the electrolyte. In order to charge the battery that last 15%, you need to taper down the amps and hold the voltage below 4.2V. 

You're trying to charge that last 15% in 9 minutes and you just can't do that. Even if you know the absolutely exact amount of energy you need to put into that battery, you have to do it at a continuously slower rate at you approach full charge or you'll damage the battery over time.


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## Coulomb (Apr 22, 2009)

GizmoEV said:


> That is because you are not considering the fact that they are being charged with 1C.
> 
> 
> > Ah, point taken. I was considering 1C to be a moderate charge current, but really it's quite high.
> ...


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## Coulomb (Apr 22, 2009)

icec0o1 said:


> At that point, the voltage will be above 4.2V and you'll begin degrading the electrolyte. In order to charge the battery that last 15%, you need to taper down the amps and hold the voltage below 4.2V.


Right. Unless you believe Jack Rickard's statement that terminal voltage doesn't matter. It seems to me that the instantaneous voltage from one active plate to the other is what is important. There will be some ohmic resistance from the terminals to the active part of the cell, but that will be pretty much negligible, at least to _some part_ of the cell. So at least some damage will occur with terminal voltages above the various critical chemical potential levels, especially the one at 4.2 V where the electrolyte dissociates.


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## icec0o1 (Sep 3, 2009)

Coulomb said:


> Right. Unless you believe Jack Rickard's statement that terminal voltage doesn't matter. It seems to me that the instantaneous voltage from one active plate to the other is what is important. There will be some ohmic resistance from the terminals to the active part of the cell, but that will be pretty much negligible, at least to _some part_ of the cell. So at least some damage will occur with terminal voltages above the various critical chemical potential levels, especially the one at 4.2 V where the electrolyte dissociates.


Yes, I agree quite a bit with Jack but definately disagree with him on this point if he said terminal voltage doesn't matter. Haven't heard him saying it but I've missed a few shows I guess.

Just a theoretical question... why can't you charge at 60C? Lets say you only do it for two minutes or till the battery hits 60 degrees C. I think you can stay within the thermal envelope, but I guarantee you'd be instantly splitting the electrolyte into gasses as the voltage would rise quite a bit.


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## GizmoEV (Nov 28, 2009)

Coulomb said:


> GizmoEV said:
> 
> 
> > Ah into the cell do exactly correspond with SOC ...
> ...


At some point all the Li ions have moved from one plate to the other. The theoretical "full bottle." Any more energy in will do something else like heat the cell, breakdown the electrolyte, etc. I suspect that you may be close on the efficiency starting to go down at about 3.5vpc. The CALB data sheet lists 3.4V as the "float voltage" which is really a misnomer since there is no charge shuttle reaction in a LiFePO4 cell. If 3.4V is an ok voltage to hold indefinitely then I think that 3.4v is either right at "full bottle" or just below it. Besides my bench testing, this is another bit of info to support not charging the cells to more than 3.5vpc.



Coulomb said:


> GizmoEV said:
> 
> 
> > but you have to stop charging, let them rest and then measure the open circuit voltage at least to the thousandths of a volt. The problem is, the OCV vs. SOC curve isn't linear.
> ...


And that is the beauty of the CC/CV charging profile. It is easy to determine 100%SOC because as the current drops the terminal voltage approaches open circuit voltage or maybe more accurately the OCV approaches the terminal voltage.


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## spdas (Nov 28, 2009)

GizmoEV said:


> In the case of my Zivan it was designed for 4 stages: (1)bulk charge, (2)absorption phase, (3)equalize phase, and (4)float. For my LiFePO4 pack it is set to (1)Bulk charge at max current until 3.485vpc is reached, (2)continue to hold voltage at 3.485vpc while current fades, (3)hold voltage until it times out, (4) do nothing but light the green light. It is a way to use a lead acid algorithm for LiFePO4 cells. If it was designed for LiFePO4 from the beginning it would charge at max current until termination voltage is reached, charge until current dropped to something like 200mA and turn off. A timer would be running as a back up.


Let me give you charging scenario. I will be charging from my solar panels and I have dedicated one charge controller to charge the car. The charge controller is a sophisticated MMPT controller that has several input and output configurations and charges Lead batteries great. 

I have it set up to output 80V. (That is the absolute max it will output at the finish. The controller may drop to 75v and increase the amperage if the batteries are low) and according to the clouds, it will be varying the amps. I can adjust the amps to max or to taper to 80V. So if I put 23 cells in series I come up with 3.478 volts each.

Question is shud I put only 22 in series and have the voltage pushing 3.63v each cell and taper the current to drop at 3.47v and use a timer to shut off or???

thanks
Francis


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## GizmoEV (Nov 28, 2009)

spdas said:


> Let me give you charging scenario. I will be charging from my solar panels and I have dedicated one charge controller to charge the car. The charge controller is a sophisticated MMPT controller that has several input and output configurations and charges Lead batteries great.
> 
> I have it set up to output 80V. (That is the absolute max it will output at the finish. The controller may drop to 75v and increase the amperage if the batteries are low) and according to the clouds, it will be varying the amps. I can adjust the amps to max or to taper to 80V. So if I put 23 cells in series I come up with 3.478 volts each.
> 
> Question is shud I put only 22 in series and have the voltage pushing 3.63v each cell and taper the current to drop at 3.47v and use a timer to shut off or???


Since LiFePO4 is nearly 100% efficient I doubt that your charge controller can reach 80V if the pack is discharged very much. The cells will accept the charge quite easily. If your controller can be set to 80V output and let the current do what it will you can have it shut off after the current drops to a small value and also have a timer to shut it off if the current is below say 0.5A for an hour that it quits charging the pack.

The reason your controller "drops" the voltage with a low pack is because it is incapable of pumping the current high enough to keep the output at 80V. You just want to set the controller to max current until the voltage reaches 80V and then hold that voltage. The current will naturally taper as the cells fill up.

I would go with the 23 cells. There is very little energy above 3.45V so you wouldn't gain much but shortening the life of your cells. The CALB data sheet lists 3.4V as a "float voltage" even though that is a misnomer. You may actually want to lower your termination voltage to 78.2V (3.4vpc) to prolong the life of your cells. Just remember that the cells are "full" when both voltage and low current parameters are met, not just when the terminal voltage reaches a set point.


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## bmentink (Apr 22, 2011)

DIYguy said:


> Charge a 100 ah cell that is at 10% state of charge with C1 at 5 volts for until it hits say 80% state of charge. Remove the charge let it rest and you have a battery that is what???? damaged? I'm not a battery tester...but, I don't or at least didn't think this was the case. Thoughts.?


So you are trying to charge at 1C "and" 5V? You can't do that!, if you are constant-current charging at 1C your terminal voltage will be what the cell decides, not 5V. That is why you constant-current charge the 1st part of the charge cycle.

You can't have constant current *and* constant voltage.


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## spdas (Nov 28, 2009)

I understand that I want to charge to 3.45 or so, but like LA, you need to charge at 14.8 to end up at 12.65, so is it not necessary to charge the Lithium battery as well at say 3.7 to end up at 3.45? 

francis


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## DIYguy (Sep 18, 2008)

bmentink said:


> So you are trying to charge at 1C "and" 5V? You can't do that!, if you are constant-current charging at 1C your terminal voltage will be what the cell decides, not 5V. That is why you constant-current charge the 1st part of the charge cycle.
> 
> You can't have constant current *and* constant voltage.


Ya, thanks. I figured that out..  It was kind of a hypothetical...but without much thought... lol


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## GizmoEV (Nov 28, 2009)

spdas said:


> I understand that I want to charge to 3.45 or so, but like LA, you need to charge at 14.8 to end up at 12.65, so is it not necessary to charge the Lithium battery as well at say 3.7 to end up at 3.45?
> 
> francis


That is correct. Like bmentink said above, you can NOT have constant current and constant voltage when charging a battery. In fact, if you look at the chart referred to earlier it wasn't until the cells were at about 50% SOC that the voltage finally reached 3.5V. This is charging at a current of 1C or 180A, 200A, and 160A for the CALB, TS 200Ah, and TS 160Ah batteries, respectively. These cells do not have the same internal resistance that lead acid does. They also do not have the chemical reactions that lead acid does. In fact, very little of your understanding of how to charge lead acid batteries transfers over to LiFePO4 cells.

If you set your charge controller to just charge at max current but not go above 78.2V for 23 cells (3.4vpc) you will be good to go and your cells will sit at 98-99% SOC and have a long life. They will last longer if you don't fully charge them. I'm seriously considering having a device for my car which will turn off the charger when my pack reaches 90% SOC and only when I know I'll need the extra range will I tell it to charge till the charger terminates.


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## tomofreno (Mar 3, 2009)

> Ya, thanks. I figured that out..  It was kind of a hypothetical...but without much thought... lol


 Based on the CMU prof's comments I posted earlier (or more accurately my notes on his comments) I would guess (and that is all it is) that if you charge a cell at a current level at or below the manufacturer's spec, you cannot get 4.3 to 4.4V developed across any cell in a series connected, well-matched set of cells until the cells are full, and voltage rises exponentially with Ah in. 

If so, I would expect if you charge at very high charge current in very warm ambient you may overheat cells causing deposition on the electrode surfaces, then if charging is continued until at least one cell is full, you may cause decomposition of the electrolyte and possibly venting. But if you start at some SOC below full, remove x amount of charge, then charge to add that same x amount back in at a current at or below the spec, it shouldn't be a problem - which is what I think Roy is saying.

That is what I would expect from the prof's comments, but I also recall Jack charging a cell with high current to a voltage level much higher than 4.4V and claiming no apparent damage. Maybe that is because at such high current, the voltage rose very rapidly near end of charge, so the cell was not above 4.4V for long enough for much decomposition to occur before he shut off the charger, but if held at that voltage for longer it would. Don't know - don't remember how long he had it at that voltage. The devil is in the details - and knowing if you or someone else did the experiment you think you or they did.


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## icec0o1 (Sep 3, 2009)

There isn't any deposition at high voltage, just damage to the electrolyte. High temperature would damage a Li-MnO2 three dimentinal structure (laptop batteries) but FePO4 structure would hold up just fine. Deposition occurs at <0.5V and it's a far faster chemical reaction.


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## JRP3 (Mar 7, 2008)

Pretty sure he said around 60C or so you'd get deposition from excess heat with LiFePO4 cells.


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## tomofreno (Mar 3, 2009)

> There isn't any deposition at high voltage, just damage to the electrolyte. High temperature would damage a Li-MnO2 three dimentinal structure (laptop batteries) but FePO4 structure would hold up just fine.


 Are you referring to my comments? I was referring to the prof's comments that deposition occurs at temperatures above 50 to 60 C, and decomposition of the solvent/electrolyte occurs at voltages above 4.3 to 4.4V. So you are saying the first comment does not apply to LiFePO4, that deposition on the electrodes will not occur at 50 to 60 C and above?


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## Roy Von Rogers (Mar 21, 2009)

I look at this battery charging a little bit different. IMO I want to taylor my battery pack in such a way where I need the least amount of items to make it all work without taking any chances of damaging the cells, and make them last. Just to show you in what direction I'm thinking at, let me give a little mind exercise and see whats what.

I have 50 200ah TS cells....I take 120v ac and bridge rectify it and connect it directly to the pack.....

What would happen ???

and please dont say "blow a braker"....lol

Roy


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## bmentink (Apr 22, 2011)

Roy Von Rogers said:


> I look at this battery charging a little bit different. IMO I want to taylor my battery pack in such a way where I need the least amount of items to make it all work without taking any chances of damaging the cells, and make them last. Just to show you in what direction I'm thinking at, let me give a little mind exercise and see whats what.
> 
> I have 50 200ah TS cells....I take 120v ac and bridge rectify it and connect it directly to the pack.....
> 
> ...


Well 120v AC = ~170v DC = 3.4v per cell, so voltage most likely will not be an issue if your supply is quite stable ... but if the 120v climbs upto 130v for example, you are looking at 3.67v per cell, which will shorten the cell life.

Current on the other hand is a different issue. If the cell is severely discharged, then you could be thumping in huge un-limited charge currents which will sky-rocket the cell temperature eventually destroying the cells (especially as they are TS cells, if you had Headway cells which can handle 5C charge .. well they might last a bit longer). It all really depends on how many amps your 120v supply can handle before you "blow the breaker" as you say ... also if your bridge rectifier is not rated accordingly, you will blow that as well ..


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## Roy Von Rogers (Mar 21, 2009)

bmentink said:


> Well 120v AC = ~170v DC = 3.4v per cell, so voltage most likely will not be an issue if your supply is quite stable ... but if the 120v climbs upto 130v for example, you are looking at 3.67v per cell, which will shorten the cell life.
> 
> Current on the other hand is a different issue. If the cell is severely discharged, then you could be thumping in huge un-limited charge currents which will sky-rocket the cell temperature eventually destroying the cells (especially as they are TS cells, if you had Headway cells which can handle 5C charge .. well they might last a bit longer). It all really depends on how many amps your 120v supply can handle before you "blow the breaker" as you say ... also if your bridge rectifier is not rated accordingly, you will blow that as well ..


The cells can handle 3c, at that voltage it wont come near the max.

And high amp diodes are no problem to get.

Roy


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## icec0o1 (Sep 3, 2009)

Roy Von Rogers said:


> The cells can handle 3c, at that voltage it wont come near the max.
> 
> And high amp diodes are no problem to get.
> 
> Roy


If the cells were discharged to 10% SOC, they would need more than 10C amount of current to get them to 3.4V i.e. the cells would try to draw 10+ * 200amps = 2000 amps from the grid. You don't want me to say it but you'll instantly blow the fuse if the cells are less then 80-90% SoC.


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## bmentink (Apr 22, 2011)

Roy Von Rogers said:


> The cells can handle 3c, at that voltage it wont come near the max.
> 
> And high amp diodes are no problem to get.
> 
> Roy


3C is not a voltage, it is an amp/hr rating! It just means you can DISCHARGE at 3 times the amp/hr rating .... in your case 200a/h x 3 = 600 amps. However, you will find that the CHARGE rating of the cells is only 0.5C .. that means you can only safely charge at 100 Amps.

Like icec0o1 states, at anything less than 80% DOD (depth of discharge) you will be trying to stuff huge currents into the cells (well over 100 amps) stuffing them good and proper before the BREAKER (there I said it ) BLOWS to tiny little breakers ..

Do you get it! Don't try this at home!!!!


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## EVfun (Mar 14, 2010)

Roy Von Rogers said:


> I have 50 200ah TS cells....I take 120v ac and bridge rectify it and connect it directly to the pack.....
> 
> What would happen ???
> 
> and please dont say "blow a braker"....lol


Blow a breaker -- if the cells are at a low state of charge. It will also fail to fully charge the cells as the average voltage at the end will be only about 3.36 volts per cell if your line is really at 120 volts. 

If you want to try this you should add a 0.1 ohm 100 watt resistor resistor to the mix (easy to make with 4, 25 watt 0.1 ohm resistors) and start with cells at about 50% SOC (about 3.30 volts resting.) You should check your line voltage because some places can be as high as 130 vac or as low as 110 vac (those extremes are rare, but 4 volt differences are common.) You should have your cells at the same state of charge or close before doing any charging. 

I don't predict any doom and gloom. I've charged lead packs as low as 120 volts with a bad-boy charger (nothing but a bridge rectifier and some long extension cords to limit current.) I recommend you have a good multi meter on hand to watch the current and watch the cell voltages. You can use the resistors as a shunt to measure current (0.1 volts per amp.) If the current is over 30 amps (3 volts measured on the resistors) you will need to terminate charging after a minute because the resistors will be getting to hot. 

Remember that charging this way is unsafe. The entire pack is live with line voltage. You can be seriously shocked touching any terminal or exposed wire while charging. Wise words from my instructor, "remember, electricity doesn't care what YOU think is the shortest path to ground.)


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## Roy Von Rogers (Mar 21, 2009)

bmentink said:


> 3C is not a voltage, it is an amp/hr rating! It just means you can DISCHARGE at 3 times the amp/hr rating .... in your case 200a/h x 3 = 600 amps. However, you will find that the CHARGE rating of the cells is only 0.5C .. that means you can only safely charge at 100 Amps.
> 
> Like icec0o1 states, at anything less than 80% DOD (depth of discharge) you will be trying to stuff huge currents into the cells (well over 100 amps) stuffing them good and proper before the BREAKER (there I said it ) BLOWS to tiny little breakers ..
> 
> Do you get it! Don't try this at home!!!!


I'm not sure how to reply to this nonsense, exept you need to read a TS spec sheet, fyi the cell can be discharged and charged at 3C.

Also in order to get amperage in to a battery pack you need a voltage higher then the pack voltage.

So the question is, if you have a 50 cell pack at 150v and you put 169v across the pack, how many amps would you be charging at??

Do you know??

Roy


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## bmentink (Apr 22, 2011)

EVfun said:


> Blow a breaker -- if the cells are at a low state of charge. It will also fail to fully charge the cells as the average voltage at the end will be only about 3.36 volts per cell if your line is really at 120 volts.


Already stated that, please read the last few posts ...



EVfun said:


> If you want to try this you should add a 0.1 ohm 100 watt resistor resistor to the mix (easy to make with 4, 25 watt 0.1 ohm resistors) and start with cells at about 50% SOC (about 3.30 volts resting.)


No, you must add 4, 25 watt 0.4 ohm resistors in parallel to get 0.1 ohm.



EVfun said:


> You should check your line voltage because some places can be as high as 130 vac or as low as 110 vac (those extremes are rare, but 4 volt differences are common.)


Again, already stated in my post, please keep up ..



EVfun said:


> I don't predict any doom and gloom.
> " "
> Remember that charging this way is unsafe. The entire pack is live with line voltage. You can be seriously shocked touching any terminal or exposed wire while charging. Wise words from my instructor, "remember, electricity doesn't care what YOU think is the shortest path to ground.)


Well your above two statements contradict themselves.
What he is doing is fool hardy and will only end in tears, or worst case death ..

Buy a proper charger ... what value do you place on your life ??
Obviously if you are contemplating this ... <$2000 .....


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## Roy Von Rogers (Mar 21, 2009)

EVfun said:


> Blow a breaker -- if the cells are at a low state of charge. It will also fail to fully charge the cells as the average voltage at the end will be only about 3.36 volts per cell if your line is really at 120 volts.
> 
> If you want to try this you should add a 0.1 ohm 100 watt resistor resistor to the mix (easy to make with 4, 25 watt 0.1 ohm resistors) and start with cells at about 50% SOC (about 3.30 volts resting.) You should check your line voltage because some places can be as high as 130 vac or as low as 110 vac (those extremes are rare, but 4 volt differences are common.) You should have your cells at the same state of charge or close before doing any charging.
> 
> ...


If you would have quoted my whole post it would have shown that this was a mind exercise, and not a real world attempt.

Just for information I'm 67 and have been a technician for 50 of those years, I work with high voltages on a daily basis in my business and dont need a safety lesson, especially when it has nothing to do with the question in my post.

The only correct answer you gave was 3.36v per cell, so at leat you know how to multiply by 1.414.

I'll ask you the same question I asked in the other reply.

If I had a 50 cell pack that was at 150v, and I charge it at 169v from the scenerio I put forward, how much amperage would show on my amp meter ??


Roy


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## bmentink (Apr 22, 2011)

Roy Von Rogers said:


> I'm not sure how to reply to this nonsense, exept you need to read a TS spec sheet, fyi the cell can be discharged and charged at 3C.


I think you are the one who is talking nonsense, I have attached the data sheet it CLEARLY states 0.5C charge for a TS 200a/hr cell, and this is straight from the Chinese manufacturer ..




Roy Von Rogers said:


> So the question is, if you have a 50 cell pack at 150v and you put 169v across the pack, how many amps would you be charging at??
> 
> Do you know??
> 
> Roy


Do you?? How long is a bit of string? No one can possible answer such a ridiculous question, it all depends on the state of charge, temperature, internal resistance of the cells, bridge losses, and a number of other factors to numerous to mention...

You might want to give up at this point ....


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## bmentink (Apr 22, 2011)

Roy Von Rogers said:


> Just for information I'm 67 and have been a technician for 50 of those years, I work with high voltages on a daily basis in my business and dont need a safety lesson, especially when it has nothing to do with the question in my post.
> 
> 
> Roy


The gentleman was entirely relevant and was correct in giving you a safety lesson if only to protect you from yourself.

And stop with the one oneupmanship, quoting your work history doesn't make your case, it only makes us wonder how you have survived all these years ..

... and I am an Electronics Engineer for the last 40 years specializing in power electronics ... but so what .. my or your profession has nothing to do with the fact that what you are trying to do is foolhardy and unsafe.

I am tired of this game ... good night.


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## pm_dawn (Sep 14, 2009)

Yes that Pdf clearly states a max charge rate of less then 3C.

But to your case.
With a 19v voltage differense and a total pack resistance of less then 50mOhm, you would be looking at a current leves higher than 350A. 
19/0,05 = 380

So please do not try that right.....

Best Regards
/Per


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## Roy Von Rogers (Mar 21, 2009)

bmentink said:


> I think you are the one who is talking nonsense, I have attached the data sheet it CLEARLY states 0.5C charge for a TS 200a/hr cell, and this is straight from the Chinese manufacturer ..
> 
> 
> 
> ...


What do you think this is...a pissing contest, your making a fool out of yourself, and thats not my intention of why I post here, do yourself a favor and at least READ the PDF you posted, where it obviously states "Max Charge <3CA.

The 0.5C rate has to do with how to arive at a full pack. In another words, if you charged at 0.5C and stoped at the max voltage posted on the spec sheet, the cell would be considered full.

It was a exercise in theory, nothing more and nothing else. Since I dont have a 50 TS pack to try this, my guess would be somewhere in the 50 amp range, depending on line losses. 

Btw this has already bin done by someone in here, I'll see if I can find the post.

Here it is...http://www.diyelectriccar.com/forums/showthread.php?t=36368

Roy


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## EVfun (Mar 14, 2010)

bmentink said:


> Already stated that, please read the last few posts ...
> 
> No, you must add 4, 25 watt 0.4 ohm resistors in parallel to get 0.1 ohm.
> 
> ...


1. I have no obligation to "keep up." I can reinforce a point if I choose. I can answer a question being asked without deferring to anything you have written.

2. 4, 0.1 ohm resistors hooked in a series/parallel arrangement will make a fine 0.1 ohm resistor.

3. Dangerous activities may be safely undertaken with proper precautions. If he understands the safety precautions needed, and remains present to monitor the charging, this can be done.


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## Roy Von Rogers (Mar 21, 2009)

bmentink said:


> The gentleman was entirely relevant and was correct in giving you a safety lesson if only to protect you from yourself.
> 
> And stop with the one oneupmanship, quoting your work history doesn't make your case, it only makes us wonder how you have survived all these years ..
> 
> ...


Show me anywhere were I stated that I was attempting to do that, it was a math exercise. 

There was no upmanship attempted, it does matter who we are, especially if we are professionals. I dont know about you, I came here to learn things about EV's, and what others have discovered, so I can further my knowledge about this subject.

And since your an EE, why didnt you just give me the answer I was looking for. But never mind I asked the question, it was answered with a pm by someone who as actual knowledge about it, since he tried it.

Have a nice day.

Roy


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## icec0o1 (Sep 3, 2009)

pm_dawn said:


> Yes that Pdf clearly states a max charge rate of less then 3C.
> 
> But to your case.
> With a 19v voltage differense and a total pack resistance of less then 50mOhm, you would be looking at a current leves higher than 350A.
> ...


This math is not completely correct. You divide 19 volts by (50 cells times 0.006 mOhm = 0.3 total mOhm) = 63 amps


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## taken by aliens (May 26, 2011)

bmentink said:


> Well 120v AC = ~170v DC = 3.4v per cell, so voltage most likely will not be an issue if your supply is quite stable ... but if the 120v climbs upto 130v for example, you are looking at 3.67v per cell, which will shorten the cell life.
> 
> Current on the other hand is a different issue. If the cell is severely discharged, then you could be thumping in huge un-limited charge currents which will sky-rocket the cell temperature eventually destroying the cells (especially as they are TS cells, if you had Headway cells which can handle 5C charge .. well they might last a bit longer). It all really depends on how many amps your 120v supply can handle before you "blow the breaker" as you say ... also if your bridge rectifier is not rated accordingly, you will blow that as well ..


HAHAHA 120v AC is not 170v DC.... and if you are an EE you must be one of those Indian EEs that know nothing... I do have a B.S. in Electrical Engineering, and you are a retard to think 120v AC is 170v DC.

First of all you have to rectify your AC voltage so that the negative part of the sine wave becomes positive. And then you've decreased the voltage below 120v. Then you would have to regulate your rectified AC voltage signal to DC by runing it into a cap or some uC voltage regulator... but in no way is 120v AC the same as 170v DC.

Go back to school man



As for a simple BMS you can make on your own...
using a zener diode that reverse biases just under your full charged cell voltage level, and send that signal to a uC that shunts the current away, or add a 0.5A (whatever amount of current you want to shunt away) light to the reverse biases loop to be able to do it without a uC.


..............................__ 
(-)____|\|_________/...\____________
.......|. |/|..............\__/ #PR2 lamp |
.......| 3.0v zener.......__..................|
.......|_____________/.. \_____|\|____|__ (+)
...............#PR2 lamp\__/....... |/|
.....................................3.0v zener

each lamp shunts 0.5A so this would shunt 1A as soon as the cell voltage is brought upto 3.0v


And as for No BMS or BMS... you can have a car with air bags our without... and it is simply up to you and how much protection you want. Doing a risk vs. reward analysis is probably best. Battery packs can run 10k and up for longer range LFP. BMS runs less then 1k. So to spend less then 10 percent of the cost of the Battery pack to insure its safty and max cycles seems like a really good investment.


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## Roy Von Rogers (Mar 21, 2009)

Ok I'll bite...

Whats the peak voltage of a 120ac sine wave??

Lets see if those aliens were good teachers, unless of course they are the south of the border types, then you have to adjust for weed induced trauma....lol


And since you only have three posts, I'm not even going to discuss your BMS issue, but if it makes you feel better, stick anything you want on your batteries, after all its your money.

Roy


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## icec0o1 (Sep 3, 2009)

Haha, don't bother Roy.


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## frodus (Apr 12, 2008)

Apparently the aliens took your brain, Alien boy...... sit down and pay attention..... I've got a BSEE too, and have some experience in actually building these things.

120VAC is RMS, 170V is it's peak voltage (120 x 1.414), we notate that as 170Vpp.

If you don't smooth it (100% ripple), you get ~120VDC, which is the average of the "humps". So no, an unsmoothed rectified 120VAC input has a ~120VDC output.

But it's rare that people DON'T put a smoothing cap on the output, So if you put it through a full wave bridge rectifier with a smoothing capacitor, you get just a little less than 170VDC (170 - voltage drop of the diodes).


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## taken by aliens (May 26, 2011)

120 AC sine wave is 240 V pk to pk. Your graph shows an amplified 120 V AC sine wave that has been amplified to 170 V AC and then rectified through diodes to become all positive. 120V AC is not 170 V DC. And if you have a 4 diode rectifier that is adding an extra 20 V to the high pk i suggest you patent that really quick. Diodes dont make the peak bigger on an AC sine wave thats 120V. They just flip the negative part of the sine way so it is positive. Your graph shows amplification prior to rectifiying an AC sine wave of 120V to 170V. You should understand the graphs you post before you comment on them.


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## frodus (Apr 12, 2008)

Go back to school, or return that BSEE degree

120VAC is RMS (Vrms = Vp / sqrt(2) = 0.707*Vp), it is not 240V peak. You're probably mixing that up with normal residential wiring. it's 120V between hot and neutral on 2 hot's, and it's 240V between those 2 hot's. They call it single phase 3-wire, or split phase.

that "graph" is not an amplified 120VAC sine wave, it's a normal sine wave. Look it up. 120VAC is RMS and it's 170Vp. Period. End of sentance. 

Look it up chief. I work with this stuff daily, I'd love to argue with you. 

I don't have to patent it. It's common knowledge for everyone in power electronics, except for you....


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## taken by aliens (May 26, 2011)

so i stated 120V AC is not 170V DC and it is 240 V pk to pk... I never said it was 240Vpp... you just confirmed I am right... your graph even shows what I stated but you claim im wrong and need to go back to school?

Please if you think you are still right... go to your function generator and set it up to generate a 120V AC sine wave. Build your 4 diode rectifier and send that 120V AC sine wave through it. Put an O-scope prob at the end... and watch your 120V AC sine wave rectified signal be 120V max... I just did it... I know I am right... 120V AC did not get rectified to 170V... O-scopes dont lie. So really maybe you should go back to school... cause i just proved im right.


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## frodus (Apr 12, 2008)

(note, DC on that graph is a filtered, non rectified output using caps and an inductor).

The voltage we're talking about is the rectified output with Cap, in yellow.


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## frodus (Apr 12, 2008)

> so I stated 120V AC is not 170V DC... you just confirmed I am right... your graph even shows what I stated but you claim im wrong and need to go back to school?


AC does not equal DC, you're right. Not without a rectifier and some smoothing caps.

The point where you're wrong is that 120VAC is an RMS voltage, and you still can't seem to get that through your thick little skull.



> Please if you think you are still right... go to your function generator and set it up to generate a 120V AC sine wave. Build your 4 diode rectifier and send that 120V AC sine wave through it. Put an O-scope prob at the end... and watch your 120V AC sine wave rectified signal be 120V max... I just did it... I know I am right... 120V AC did not get rectified to 170V... O-scopes dont lie. So really maybe you should go back to school... cause i just proved im right.


That doesn't prove your point, actually proves mine! Lets say you set your function generator to 120V magnitude. That'd be 120V peak, 240V peak to peak. But the problem is, if you measured the 120 V magnitude sinewave with an RMS meter, you'd get 120V / sqrt(2) = 84V. You just don't understand RMS, it's ok, we all make mistakes.

If you want to see, go measure the 120V from a wall, on an oscilloscope and tell me what the peak voltage is! Guess what, smarty pants, it's 170V.

If you're so right, find ONE example of a 120VAC signal being a peak voltage. I want a graph.


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## taken by aliens (May 26, 2011)

I understand I was wrong about the RMS voltage and that was never what I was trying to address... The only point I tried to make is that 120V AC is not 170V DC... 

The graphs you just put out have a 170 V AC sine wave as your function generation and not 120V AC. I know RMS is just root mean square or simply a theoretical mathmatical conversion formula, that transforms variable AC wave forms into something more mathmatically easy to work with.

Look at your own graphs... the RMS voltage is not the same as the DC.... so even what you have been trying to convince me of is wrong.

Why dont you put up the graphs of a 120V AC sine wave rectified?


Too afraid of what your DC voltage will read out? considering your 170 V AC wave put out a DC of 120V... I guess putting up those would just make you look bad.


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## Coulomb (Apr 22, 2009)

taken by aliens said:


> 120 AC sine wave is 240 V pk to pk.


Sorry, mate, it is you that is wrong. 120 VAC is about 340 V p-p. 170 V p-p after rectification.



> Your graph shows an amplified 120 V AC sine wave


Amplified? That's just scale. If you "amplify" a sine wave, you still get a sine wave. Its peak to RMS ratio is always the square root of two (after rectification).

Please be sure of your facts before using such aggressive language.

[ Edit: oops, I see that this has been well and truly dealt with; I must have not refreshed my browser. Sorry for the bandwidth. ]


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## frodus (Apr 12, 2008)

> I understand I was wrong about the RMS voltage and that was never what I was trying to address... The only point I tried to make is that 120V AC is not 170V DC...


Yes, you're wrong. Completely. You took his words out of context and started insulting someone when you're the idiot who's actually wrong. No if's and's or but's. You're wrong to argue with a bunch of other engineers, especially me, who really enjoys arguing about verifiable fact, which I've done, several times.



> The graphs you just put out have a 170 V AC sine wave as your function generation and not 120V AC. I know RMS is just root mean square or simply a theoretical mathmatical conversion formula, that transforms variable AC wave forms into something more mathmatically easy to work with.


That's because 170V peak is what you get out of the wall. Go measure it. Do I need to go over that again? Go find me ONE GRAPH of 120V being the actual peak coming out of a normal residential 120VAC line. 




> Why dont you put up the graphs of a 120V AC sine wave rectified?


Why don't you? I mean, you're the ONLY person arguing that 120V is what you get out of a rectified 120VAC signal. I can't seem to find a 120V peak sinwave. You know why? Because that isn't what comes out of the wall.

Again, go measure it. I'm right, You're wrong, deal with it.

I've been working in power for over 10 years now, mostly with single and 3-phase power products like AC drives, DC drives, Lighting and automation controls. I see this every day. I'm actually trying to find an O-scope to plug into the damn wall so I can snap a photo and show you.... but even if I did, you'd say I was making it up.

Maybe go look in some of those expensive books from college you bought. I'll see if I can dig up my Power Electronics book, or maybe my signals systems and transforms book.... hell, I think it might be in my freshman year physics book.....

[edit to include alien-boy's snide comment]


> Too afraid of what your DC voltage will read out? considering your 170 V AC wave put out a DC of 120V... I guess putting up those would just make you look bad.


Actually not afraid at all. 120VAC, rectified and filtered with a cap, is slightly less than 170V (diode drop). In fact, I already put those up, chump.




Find me a 120VAC waveform, that shows 120V as the peak voltage?

I've got plenty of proof, I'm still waiting on yours. I've got my fact to back it, where's yours...... I mean, if you're SO smart and that's REALLY how things are, how come you have yet to prove it with verifiable fact?


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## frodus (Apr 12, 2008)

more proof:
http://www.compwest.com/Library/hudhipotpaper.pdf

some more:
http://www.tvss.net/train/vrms.htm

more:
http://www.spgs-ground.com/information/equipment-voltage-surge-thresholds

still want some more?

I could do this all day.


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## EVfun (Mar 14, 2010)

taken by aliens said:


> Please if you think you are still right... go to your function generator and set it up to generate a 120V AC sine wave. Build your 4 diode rectifier and send that 120V AC sine wave through it. Put an O-scope prob at the end... and watch your 120V AC sine wave rectified signal be 120V max... I just did it... I know I am right... 120V AC did not get rectified to 170V... O-scopes dont lie.


I just proved you wrong. I grabbed a 120 vac outlet with old cut off power cord, a grabbed a little bridge rectifier, and a nice 400 volt cap pulled from an old power supply. My outlet measured 118.7 vac so I expected the peak to be 167.8 volts. I expect about a 2 volt drop from the bridge rectifier. I hooked the input of the bridge to the line and the output to the cap to charge it (a quick way to find the peak.) I ended up with 161.7 volts, a quick confirmation of something I already knew. That was below the theoretical peak by less then 2.5%. Not quite hitting the peak is expected as most 400 volt diode bridges have more than a 1 volt drop per diode and lots of household electronics have a bad power factor that tends to clip the peaks. Your O-scope seems to be broke.


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## frodus (Apr 12, 2008)

EVfun said:


> I just proved you wrong. I grabbed a 120 vac outlet with old cut off power cord, a grabbed a little bridge rectifier, and a nice 400 volt cap pulled from an old power supply. My outlet measured 118.7 vac so I expected the peak to be 167.8 volts. I expect about a 2 volt drop from the bridge rectifier. I hooked the input of the bridge to the line and the output to the cap to charge it (a quick way to find the peak.) I ended up with 161.7 volts, a quick confirmation of something I already knew. That was below the theoretical peak by less then 2.5%. Not quite hitting the peak is expected as most 400 volt diode bridges have more than a 1 volt drop per diode and lots of household electronics have a bad power factor that tends to clip the peaks. Your O-scope seems to be broke.


Thanks EVFun....

Anyone else got a scope?


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## steven4601 (Nov 11, 2010)

Whow.

That was a whole lot of effort in trying to convince someone the obvious. 

Trying to cheer this thread up a little with a off-topic fun intended (but correct) answer:

In order to measure 120V peak/dc from 120Vac @50Hz line you need an "Oh-Scope"  with a bandwidth of 53Hz

At 60Hz line & 120Vac your "Oh-scope"  needs to have a bandwidth of 63.7Hz.



In the real world, oscilloscopes  & probes usually have a bandwidth starting at few kilohertz for pocket scopes to 100Mhz and up for bench scopes.


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## Duncan (Dec 8, 2008)

*Super Cheap Charger*
There has been some discussion on the BMS tread about simply using rectified mains to charge your pack.
Being a Scotsman I found the financial aspects interesting

So – we have 230vAC (+/-6% max – usually +/-3%) (RMS voltage)
Stick that through a Bridge Rectifier and a smoothing capacitor we get 230vDC 
(You guys with anaemic 110v systems can use a “doubling rectifier” to get something similar)

Just putting this across the pack would simply blow your breakers, but what about using a resister in series?

The discharged pack has a voltage – by subtracting that voltage from the rectified mains voltage I came up with a differential voltage – dividing that differential voltage by the sum of the packs internal resistance and the series resister give the current that will flow

I looked up the TS manual and searched the web for data about Headway charge curves and I came up with some figures for Voltage v Charge 

What I found was
TS
With a 40 x 100Ah pack and a 8 Ohm resister I can charge a pack from 3v (7%) to 4v (86%) in 6.8 hours with a maximum current of 13.3 amps

Headway 
With a 3P x 44S x 16Ah pack and a 8 Ohm resister I can charge a pack from 3v (3%) to 3.37v (88%) in 3.9 hours with a maximum current of 12.1 amps

The resister “wastes” about 40% of the power to give 60% efficiency

A max voltage shut down circuit would be a good idea! (ESSENTIAL)

So I can make a cheap charger
Bridge Rectifier ~ $5
Smoothing Cap ~ $5
Voltage Switch Kit ~ $30 (to limit max voltage)
Fit two for belt and braces!
8 Ohm power resister ~ $60 – or make out of old electric fire elements 

It’s not sensitive to resistance – substituting a 9 Ohm leads to a max current of 10.7 amps and a charge time of 4.4 hours (Headway)


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## ElectriCar (Jun 15, 2008)

Never argue with a fool... BSEE my big ole ass! I don't even have a degree and know about peak voltage calculation, RMS etc. I bet he didn't even know what RMS meant until looking it up after reading this thread.


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## DIYguy (Sep 18, 2008)

Duncan said:


> *Super Cheap Charger*
> There has been some discussion on the BMS tread about simply using rectified mains to charge your pack.
> Being a Scotsman I found the financial aspects interesting


Hey frugal Duncan...lol Did you read the following thread? (I haven't followed it, but it appears to be down your line of interest). 

I guess one issue with this whole idea is the lack of secondary isolation...although many chargers are this way anyways.... 

http://www.diyelectriccar.com/forum...build-your-own-intelligent-charger-36627.html


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## Coulomb (Apr 22, 2009)

Duncan said:


> There has been some discussion on the BMS tread about simply using rectified mains to charge your pack.


This is the basic "bad boy" charger. It is really only of interest for emergency use. It's non-isolated, very poor "power factor" (actually very high harmonic distortion), and no regulation to speak of.



> So – we have 230vAC (+/-6% max – usually +/-3%) (RMS voltage)
> Stick that through a Bridge Rectifier and a smoothing capacitor we get 230vDC


Groan! Haven't we just said you get about 1.4x out? So 230 * 1.4 ~= 322 V. So you need a moderately high pack for this to work. You can see how it's more tempting for Americans with about 115 V mains, so this gives about 161 V. Much more suitable for DC conversions.



> Just putting this across the pack would simply blow your breakers, but what about using a resister in series?


Ok, but the resistor dissipates a lot of heat, wastes a lot of power, and you get even less charge current when then pack is nearing full. In your example with a 9 ohm resistor and 10.7 A, that's over 1000 W dissipated in the resistor. You'd likely need liquid cooling. Granted, the current will drop a lot, and the power dissipated will drop with the square of the current. But it will still have hours at very high power.


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## Roy Von Rogers (Mar 21, 2009)

Coulomb said:


> This is the basic "bad boy" charger. It is really only of interest for emergency use. It's non-isolated, very poor "power factor" (actually very high harmonic distortion), and no regulation to speak of.
> 
> Groan! Haven't we just said you get about 1.4x out? So 230 * 1.4 ~= 322 V. So you need a moderately high pack for this to work. You can see how it's more tempting for Americans with about 115 V mains, so this gives about 161 V. Much more suitable for DC conversions.
> 
> Ok, but the resistor dissipates a lot of heat, wastes a lot of power, and you get even less charge current when then pack is nearing full. In your example with a 9 ohm resistor and 10.7 A, that's over 1000 W dissipated in the resistor. You'd likely need liquid cooling. Granted, the current will drop a lot, and the power dissipated will drop with the square of the current. But it will still have hours at very high power.


The chart he put up said 162.6 rms, Thats how he arived at 230, I dont know where you get 162.6 ac from.

Roy


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## bmentink (Apr 22, 2011)

Roy Von Rogers said:


> The chart he put up said 162.6 rms, Thats how he arived at 230, I dont know where you get 162.6 ac from.
> 
> Roy


And if you look closer at the chart you will see he has identified 230v as "Mains voltage" which is RMS not DC, which when rectified is ~325v DC .... he is clearly wrong .. and you are defending him, rather than correcting him in your nice personable manner ....


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## Roy Von Rogers (Mar 21, 2009)

bmentink said:


> And if you look closer at the chart you will see he has identified 230v as "Mains voltage" which is RMS not DC, which when rectified is ~325v DC .... he is clearly wrong .. and you are defending him, rather than correcting him in your nice personable manner ....


I know its messed up..lol..I'm just telling that its said under rms 162.6..and if you times that 1.414 it comes to 230..lol

The chart is goofed up.

Roy


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## frodus (Apr 12, 2008)

bmentink said:


> And if you look closer at the chart you will see he has identified 230v as "Mains voltage" which is RMS not DC, which when rectified is ~325v DC .... he is clearly wrong .. and you are defending him, rather than correcting him in your nice personable manner ....


Look at the very top, he indicated mains voltage as 230VAC and the RMS as 162.6V.... wrong either way since 230VAC is mains voltage and it's an RMS value.

And you're right, it's ~325V IF AND ONLY IF rectified with a CAP. If it is only rectified, it's actually the RMS value, since there's no smoothing caps to keep the voltage up between sinusoidal "humps".

good discussion though about charging, glad I'm not building a charger.


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## Coulomb (Apr 22, 2009)

frodus said:


> And you're right, it's ~325V IF AND ONLY IF rectified with a CAP. If it is only rectified, it's actually the RMS value, since there's no smoothing caps to keep the voltage up between sinusoidal "humps".


Right. But in practice, when battery charging, you really want a smoothing capacitor. Otherwise, you are heavily charging the battery for a millisecond or so, then wait about 7 ms (assuming 60 Hz mains) with no charging at all. That might be an interesting way attempt to "desulfate" a lead acid cell, but it's not sensible for LiFe.


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## frodus (Apr 12, 2008)

Coulomb said:


> Right. But in practice, when battery charging, you really want a smoothing capacitor. Otherwise, you are heavily charging the battery for a millisecond or so, then wait about 7 ms (assuming 60 Hz mains) with no charging at all. That might be an interesting way attempt to "desulfate" a lead acid cell, but it's not sensible for LiFe.


I know, I'm explaining for the other people in this thread that don't understand how to rectify and install a smoothing capacitor correctly. Just don't want anyone hooking a rectifier up and wonder why they aren't getting the right voltage.

Just helps to clarify.


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## JRP3 (Mar 7, 2008)

Coulomb said:


> Right. But in practice, when battery charging, you really want a smoothing capacitor. Otherwise, you are heavily charging the battery for a millisecond or so, then wait about 7 ms (assuming 60 Hz mains) with no charging at all. That might be an interesting way attempt to "desulfate" a lead acid cell, but it's not sensible for LiFe.


Actually, didn't Jay Whiticare talk about pulse charging/discharging lithium in the video? I think it was mostly theoretical but something about a short break or even reversal being beneficial.


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## Duncan (Dec 8, 2008)

Hi Guys

I have just had a better look at Wikipedia 

http://en.wikipedia.org/wiki/Rectifier

Voltage (RMS) = Voltage (peak) / Sqrt2

Voltage (dc) = 2 x V(peak) / pie

230v (RMS) = Vpeak / 1.41 therefore Vpeak = 325v

Voltage DC = 325v x 2 / 3.14 = *207v* 

that makes my table work even better - less losses

Where are you guys getting the 325vDC?


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## Coulomb (Apr 22, 2009)

Duncan said:


> ... 230v (RMS) = Vpeak / 1.41 therefore Vpeak = 325
> 
> Voltage DC = 325v x 2 / 3.14 = *207v*


Huh? Voltage DC from a smoothed (with capacitor) rectifier = Vpeak. Pi doesn't come into it.



> Where are you guys getting the 325vDC?


You found it yourself. The peak voltage of the mains, less diode drops and some sag, is about what you get from rectifying AC.

[ Edit: oops, I didn't read your equation properly; I'm used to seeing it the other way around. Your equation is correct; my apologies. ]


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## Duncan (Dec 8, 2008)

Hi DIYGuy

I have been following the $200 charger thread but I am a mechanical engineer - the only way I would dare make something like that would be if they made a kit!


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## Duncan (Dec 8, 2008)

Hi Coulomb

Direct quote from Wikipedia -

_The average and root-mean-square output voltages of an ideal single phase full wave rectifier can be calculated as:

Vdc = Vav = 2 x Vpeak / pie

Vdc,Vav - the average or DC output voltage,_

I am just a mechanical engineer but I don't see how putting a fluctuating variable in and "averaging"it by any means could have the mean/average equal to the peak of the input variable


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## Coulomb (Apr 22, 2009)

Duncan said:


> I don't see how putting a fluctuating variable in and "averaging"it by any means could have the mean/average equal to the peak of the input variable


Easy: the capacitor charges to the peak of the mains, and you make it large enough to only sag say 5-10% from there.

As mentioned in another post, for battery charging, you always want the capacitor. As mentioned in someone else's post, without the capacitor the effective DC voltage is the same as the RMS AC voltage (by definition, and ignoring diode voltage drops). By effective voltage, I mean the steady voltage that will cause the same average power to be dissipated in a resistive load. But note that a battery is very different from a resistive load.

The average value of the rectified waveform, while it intuitively seems useful, has no real meaning. Note that the average of an unrectified AC waveform is zero.


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## Coulomb (Apr 22, 2009)

Duncan said:


> Direct quote from Wikipedia -
> 
> _The average and root-mean-square output voltages of an ideal single phase full wave rectifier can be calculated as:
> 
> ...


Bummer. You've been misled by a slightly misleading Wikipedia page. It implies that the Vav has a real meaning, and calls it Vdc. I would say that calling the average Vdc is wrong; others might say merely misleading.

For reference: http://en.wikipedia.org/wiki/Rectifier#Full-wave_rectification
(as of 2011/May/28). Someone may care to update it.


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## Duncan (Dec 8, 2008)

Hi Coulomb

Thanks for the clarification

So if I use my beefy 230v - 110v transformer - then a Bridge rectifier and capacitor 
I should get ~ 167v DC
(and its isolated!)
With a 3 ohm resistor and a 3p x 46S 16Ah Headway set I get a charge time of 9 hours,
a maximum current of 9.3 amps - a maximum resister power of 270 watts and resistive losses of 8%

Even better the max voltage is less than the max allowable (3.65v x 46S)(167.9v) 
I think I will still need a max voltage cutoff due to mains variability and as I would intend to stop charging at ~ 155v


You mention that I would get 5-10% less depending on the capacitor - I may have to reduce my pack from 46S to 44S 

Sounds like a cheap plan!


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## ElectriCar (Jun 15, 2008)

Coulomb said:


> Easy: the capacitor charges to the peak of the mains, and you make it large enough to only sag say 5-10% from there.
> 
> As mentioned in another post, for battery charging, you always want the capacitor. As mentioned in someone else's post, without the capacitor the effective DC voltage is the same as the RMS AC voltage (by definition, and ignoring diode voltage drops). By effective voltage, I mean the steady voltage that will cause the same average power to be dissipated in a resistive load. But note that a battery is very different from a resistive load.
> 
> The average value of the rectified waveform, while it intuitively seems useful, has no real meaning. Note that the average of an unrectified AC waveform is zero.


FWIW, I have a bridge rectifier on a 120V circuit WITH NO CAPACITOR connected and get over 160VDC as measured with my Fluke DMM. I built it for an emergency charger on my 144V lead pack in case I needed it in an emergency as my charger is 240V only.


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## Coulomb (Apr 22, 2009)

ElectriCar said:


> FWIW, I have a bridge rectifier on a 120V circuit WITH NO CAPACITOR connected and get over 160VDC as measured with my Fluke DMM.


I assume that this is using a DC range on the DMM. I'd say the meter must be peak reading. With a pulsating output being read on an ordinary DC range, I'd expect to get erratic results, as the meter samples at different parts of the pulsating waveform. To get a stable reading, you'd have to hit a button that causes the DMM to read the peak value, which will effectively put a capacitor in the circuit (a small one, internal to the DMM). The peak value will be as stable as the AC the bridge is being fed from. Or maybe peak reading was switched on and you didn't realise it.

As discussed, a little over 160 V peak is expected from rectifying a 120 VAC waveform.


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## Coulomb (Apr 22, 2009)

ElectriCar said:


> FWIW, I have a bridge rectifier on a 120V circuit WITH NO CAPACITOR connected and get over 160VDC as measured with my Fluke DMM.


Oh, if this is measured across the pack with the bad boy charger connected, then this is expected. In effect, the pack acts somewhat like a large capacitor. At the peaks of the mains, power will flow to the battery, and it will eventually get to over 160 VDC. However, you will get much smoother charging if you use a capacitor. During at least 90% of the time, without a capacitor, there will be no current into the pack (at least when it's charged), as the pack voltage will be higher than the instantaneous mains voltage, and the diodes will be reverse biased (not conducting).

If the pack is low, say 120 VDC, then some current may end up going into the pack for as much as (wild guess) 30% of the time.

Granted, for an emergency charger, it could well be convenient to omit the capacitor, as it adds cost, bulk, and an electrical shock hazard after it is disconnected from both the pack and the mains. At least some of the resistance could be from the resistance of the power cord, leads, and internal resistance of the battery, further simplifying the emergency charger.

If I had to use one, I'd want to monitor the pack voltage and charge current very closely.


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## Coulomb (Apr 22, 2009)

Duncan said:


> So if I use my beefy 230v - 110v transformer


Yes. Unfortunately, those are bulky and heavy, so they are usually not convenient for on-board charging. Fine for garage charging, however.



> - then a Bridge rectifier and capacitor
> I should get ~ 167v DC


Yes! This is getting more practical now.



> (and its isolated!)


A good thing. Some commercial chargers aren't even isolated.



> With a 3 ohm resistor and a 3p x 46S 16Ah Headway set I get a charge time of 9 hours,


It's very difficult to estimate the charge time. To charge in 9 hours from 80% DOD and 16*3 = 48 Ah, you'd need an average current of 48*.8/9 = 4.3 A. Suppose that the pack voltage changes linearly from 3.0 to 3.45 V. Let's say you do get a steady 167 VDC from the charger, before the resistor, and we neglect all other resistances (of the mains wiring, power cord, leads, pack voltage, diodes). We ignore the voltage sag. So the pack voltage will rise from 3.0 to 3.45 V, averaging 3.225, for an average pack voltage of 46*3.225 = 149 V, or 18 V across the 3 ohm resistor. That would make an average of 6 A into the pack. Considering the other variables, most of which will reduce the charge current, your numbers seem reasonable. (The only variable that I can think of that would increase charge current is higher than nominal mains voltage). 

I would point out that 46 cell triples of 48 Ah each (2208 Ah, about 7kWh) is a fairly light pack. We have about 4x as much in our MX-5, for example.



> a maximum current of 9.3 amps


Assuming a minimum of about 3.0 VPC average, and nominal mains.



> - a maximum resister power of 270 watts and resistive losses of 8%


These numbers seem reasonable. Some commercial chargers might not be much more efficient than that. But 270 W is a lot of power to dissipate. You might think you could get away with say 6 50 W resistors, but 50 W resistors only dissipate 50 W with a very substantial heatsink. You would likely require a significant block of finned aluminum and a decent fan. This will add to the size and cost of the charger.



> Even better the max voltage is less than the max allowable (3.65v x 46S)(167.9v)


Yes, the average will be safe as long as the mains is within specification. However, without a BMS (oh, that's what this thread is supposed to be about), any one cell could end up significantly higher than that. Of course, that applies to any charger (assuming one charger and a series string of cells).



> I think I will still need a max voltage cutoff due to mains variability and as I would intend to stop charging at ~ 155v


Right. High mains could cause the current at the start of charge to be too high, and low mains could mean that you will take a very long time to charge. 155/46 = 3.37 V, which is way too low to terminate the charge at (assuming LiFe chemistry).


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## Roy Von Rogers (Mar 21, 2009)

You would be much better off to use a heating element as a resistor, and tap it off for proper drop.

You can get a restring kit for electric heaters or clothes dryers.

Roy


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## Duncan (Dec 8, 2008)

Hi Coulomb

I take your points about the small size of my pack - I don't think this would be suitable for everybody (or even anybody else) 

The data I have has Headway at a lower voltage than TS 
155v for 46S is a between 75% and 88% full for Headway 

I culled the numbers from some charts - in the document below if anybody is interested

I do have one question - What size capacitor?
I want to lose less than 5% of the voltage and I will be drawing 15 amps max

Roy
I intend to try and make my own resister using a couple of old electric fires,
only if that fails will I open my wallet


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## Coulomb (Apr 22, 2009)

Duncan said:


> What size capacitor?
> I want to lose less than 5% of the voltage and I will be drawing 15 amps max


That's straigtforward maths. For a capacitor, I = C. dV/dt . That is, the current is the product of the capacitance and the derivative of the voltage with respect to time (rate of change of voltage, in volts per second).

If you want to stick to 5% sag, that's 5% of 167 V = 8.35 V. I see you're from New Zealand, so your mains is 50 Hz, and rectified output will pulse at 100 Hz (there will be 100 half-full-sine waves per second). So after our capacitor charges almost instantaneously, we want it to discharge at 8.35 V in 1/100th of a second, or 835 V/s.

So C = I / dV/dt = 15 / 835 = 0.018 F = 18,000 uF (eighteen thousand microfarads). Wow, that's pretty big; you're probably going to have to parallel a fair few electrolytic capacitors to get that. If you were prepared to tolerate about 9% sag, you could get away with 10,000 uF.

You'd need 10-18 of these: 

*UNITED CHEMI-CON - ESMQ201VSN102MQ35S - CAPACITOR ALUM ELECT 1000UF 200V (element14)* (I believe that those prices are in New Zealand dollars, 1 NZ$ = about US$ 0.82 as I write.)

Actually, it might be safer to get 250 V capacitors. Just use the supplier's wonderful search mechanisms.

Or pay a bit more for 1 or two of these:

EVOX RIFA - PEH200SV5100MU2 - CAPACITOR, 10000UF, 250V, 75X145 (element14)

That's 145 mm high; larger than a soup tin in size. You can probably get an equivalent cheaper elsewhere.

The big one seems to have a ripple current rating of 18 A @ 85C; it might get mighty hot and may require cooling. There's a decent fraction of a coulomb of charge running in and out of that capacitor at 100 Hz (think 6000 RPM). Two in parallel to share the ripple current load (and reduce the sag) might work better. 

That's one reason that proper chargers have active power factor corrected front ends; they don't need huge capacitors to smooth the rectified mains. Note also that 15 A DC is going to cause massive current spikes from your transformer; a figure of ten to a hundred times the average is often used (so that's 150 to 1500 amp spikes). Considering the ~ 0.6 power factor of a rectifier with capacitor, you will need around a 169 *15 / 0.6 / 230 ~= 18 A circuit breaker for 15 A DC output (the /2 is due to the 2:1 ratio of the 230:115 V transformer). So a 16 A circuit breaker would likely trip after a short time; a 20 A circuit breaker should just hold (at 15 A output; for lower output there should be no problem).

Perhaps you're starting to see why these things are not common. Note also that your transformer would need to be rated at some 169 * 15 ~= 2500 W. Most "beefy" step down transformers are in the 200-500 W range. Most people have larger packs, so losing some 40% of the available power from a power point (even if most of that "lost" power is not wasted as heat) means it would take a bad boy a long time to charge a typical EV pack.


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## Duncan (Dec 8, 2008)

Thanks Coulomb

I have a 1600VA (continuous) transformer - so I will have to drop a bit in current
The fact that the voltage drop is proportional to the current means that the drop is less as the pack charges and the current drops 
I will run the numbers and see if I can use this cheap solution, 
(I am splitting the recharge curve into four parts and using linear solutions for each part) 
It's not going to be useful to most people but it may be OK for me

-Back onto the track -BMS or not
My plan is to use a split voltage pack as an indicator (zero balance) and lots of manual monitoring until it either becomes clear it's stable or that I must lever my wallet open and buy a BMS


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## dtbaker (Jan 5, 2008)

....just a quick report after my first 1000 miles with pack of 38x100ah Thunderskies. 

Average cycle is less than 50% DOD. I parallel top-balanced the pack prior to install to 3.9v until amps dropped to zero with a power supply, then did multiple small discharge and re-balancing in series after install to get all cells within .02v after charger 'finished' (at nominal 3.65 average per cell x 38). I do NOT have any kind of BMS or cell level monitors installed.

I found it easiest to measure after waiting for float CV to drop to 3.55 (135v pack) while still plugged in so I am not measuring a moving target.

The net is that after 1000 miles, the entire pack is still within .02v at 'end of charge', and levels out even closer than that after surface charge dissipates if I unplug or go for a short drive.


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## taken by aliens (May 26, 2011)

Saw a clip on the TI website about BMS

Here is the pdf
http://focus.ti.com/lit/an/slua524a/slua524a.pdf?DCMP=hpa_growth_hev&HQS=Other+OT+powerpump

i guess TI uses zener diodes just like my DIY drawing... so really discredit my cheap BMS and then look at TI's schematic and give me back my credit please

and here's TI's solutions to EVs
http://focus.ti.com/lit/ml/szza058a/szza058a.pdf


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## ElectriCar (Jun 15, 2008)

dtbaker said:


> ....just a quick report after my first 1000 miles with pack of 38x100ah Thunderskies.
> 
> Average cycle is less than 50% DOD. I parallel top-balanced the pack prior to install to 3.9v until amps dropped to zero with a power supply, then did multiple small discharge and re-balancing in series after install to get all cells within .02v after charger 'finished' (at nominal 3.65 average per cell x 38). I do NOT have any kind of BMS or cell level monitors installed.
> 
> ...


That's great news! Thanks for posting it Dan.


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## dtbaker (Jan 5, 2008)

gottdi said:


> Dan,
> 
> Excellent news. What is your ending or cut back voltage. I too find that after I charge my cells settle at the same voltage. My ending voltage is now at 2.8 for cut back.


I doubt you mean 2.8v... you mean 3.8v?

I had my charger set to switch from CA to CV at 139v, I have 38 Thundersky cells, which is 3.65v per cell average...I notice that there is an audible 'click' inside the charger when it shifts gears, and the CV phase only lasts about 10-15 minutes until the amps drop to about 1...and then drop to basically nothing and the pack voltage slowly settles to about 133v (3.5 per cell) if I leave it plugged in, or 130v (3.4v per cell) if I unplug.


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## GizmoEV (Nov 28, 2009)

dtbaker said:


> I had my charger set to switch from CA to CV at 139v, I have 38 Thundersky cells, which is 3.65v per cell average...I notice that there is an audible 'click' inside the charger when it shifts gears, and the CV phase only lasts about 10-15 minutes until the amps drop to about 1...and then drop to basically nothing and the pack voltage slowly settles to about 133v (3.5 per cell) if I leave it plugged in, or 130v (3.4v per cell) if I unplug.


So the pack voltage drops after the switch to CV? What Ah pack do you have? Also, if you can, I recommend you adjust the CC to CV switch voltage to 133V. If the charger truly holds that voltage it will only take slightly longer to drop to below 1A and your cells will still settle to 3.4vpc. The benefit to you is that it will not stress your cells as much but they still will be very close to full since the current drops to basically nothing.


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## dtbaker (Jan 5, 2008)

GizmoEV said:


> So the pack voltage drops after the switch to CV?


no... not until after the amps drop to about 1amp, then the unit pretty much switches off and the pack voltage settles a little.



GizmoEV said:


> What Ah pack do you have?


I have 38 Thundersky 100ah cells.




GizmoEV said:


> Also, if you can, I recommend you adjust the CC to CV switch voltage to 133V. If the charger truly holds that voltage it will only take slightly longer to drop to below 1A and your cells will still settle to 3.4vpc. The benefit to you is that it will not stress your cells as much but they still will be very close to full since the current drops to basically nothing.


The Elcon1500 is not really user adjustable other than to select different internal curves based on the nominal voltage set at the distributor. I think a pack voltage trigger of 133v would be too low as it is just barely off the flat for Thundersky. I think the 139 (3.65 average) is fine... my highest cell finishes at 3.67, and they are only there for around 10 minutes, then drop to settle after charger turns itself off...


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## GizmoEV (Nov 28, 2009)

dtbaker said:


> The Elcon1500 is not really user adjustable other than to select different internal curves based on the nominal voltage set at the distributor. I think a pack voltage trigger of 133v would be too low as it is just barely off the flat for Thundersky. I think the 139 (3.65 average) is fine... my highest cell finishes at 3.67, and they are only there for around 10 minutes, then drop to settle after charger turns itself off...


Ok so the charger basically shuts off at 1A or 0.01CA which is slightly lower than the charge profile specified by TS. My Zivan starts cutting back at 69V (3.45vpc) and tapers the current down to under 200mA. It takes less than 20 min to do this taper while the pack voltage peaks at 69.7V (3.485vpc). Only about 1Ah is added after the current starts to taper. This is into a 200Ah pack (40 buddy paired 100Ah cells).

If your charger actually shuts off current at 1A you are probably fine. If it tapers it down into the 200mA region then I wouldn't be the least bit surprised if you aren't slightly overcharging your cells. Why push it when it doesn't gain much, if any, range?


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## dtbaker (Jan 5, 2008)

GizmoEV said:


> Why push it when it doesn't gain much, if any, range?


I just think its better to set the CA-CV voltage to the recommended spec of 3.65.... not really trying to 'push it'. Seems like it would be a little easier and more predictable for the charger to catch it off the flat of the voltage curve if there were some differences due to temperature, etc. With CALB I would go a little lower, but I don't think 3.65 +/- .02 is pushing the TS according to their specs.

Numerous chargers and systems charge TS to 3.8 or even 3.85v... which seems to be pushing it.


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## GizmoEV (Nov 28, 2009)

dtbaker said:


> I just think its better to set the CA-CV voltage to the recommended spec of 3.65.... not really trying to 'push it'. Seems like it would be a little easier and more predictable for the charger to catch it off the flat of the voltage curve if there were some differences due to temperature, etc. With CALB I would go a little lower, but I don't think 3.65 +/- .02 is pushing the TS according to their specs.


The Zivan nails it every time at the lower setting. Also, the recommended spec is to get maximum capacity not maximum life of the cell. Undercharging a Li cell does extend its life. Also, finishing charging just before use rather than charging and let sit extends the life of the cells.

There is some interesting info in this NASA document: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090023862_2009023573.pdf

Included is a statement about the degradation of the cells when charged at low temperatures. Maybe we should be heating our packs to 20°C in the winter time.


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## GizmoEV (Nov 28, 2009)

dtbaker said:


> Numerous chargers and systems charge TS to 3.8 or even 3.85v... which seems to be pushing it.


That is for sure. It will be interesting over time to see how packs survive and compare their use/abuse. Maybe in time we can narrow down the best way to treat the packs for longest life.


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## dtbaker (Jan 5, 2008)

GizmoEV said:


> ...the recommended spec is to get maximum capacity not maximum life of the cell. Undercharging a Li cell does extend its life.


This IS a good point. 

In retrospect I could be sold on setting a slightly lower trigger next time, but at this stage, the reprogramming of the charger would entail sending it away, paying a fee, etc... The downside of an inexpensive charger is that the parameters are pretty fixed.

I could add a cell or two without getting my total pack voltage above where all the other components are rated, but then have matching/balance issues of a used cell into a pack I would rather avoid.

I guess I will just be content with becoming a data point in how many cycles I get charging to 3.65vpc, typical 50%DOD use, moderate temps, etc. I am lucky enough to have a garage that stays around 50-60 deg F in the winter, and my typical use does not leave the vehicle out in sub-zero weather so that is another point in the favor of this particular pack.

I sort of have accepted that what I have in this car now is INTENDED to be a 'lifetime' study, and I don't want to mess with it and change things mid-stream unless I HAVE to.


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## JRP3 (Mar 7, 2008)

I think your 50% DOD will do far more to extend the pack life than a few lower percentage points of charge. In other words, don't sweat it


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## dtbaker (Jan 5, 2008)

JRP3 said:


> I think your 50% DOD will do far more to extend the pack life than a few lower percentage points of charge. In other words, don't sweat it


I do wish we knew more about the actual mechanism of internal breakdown... is it just heat? whether from overcharge, or over-amp discharge, both would raise internal heat.... but then, why does deep discharge seem to make a difference? Perhaps that a deep discharge and recharge generates more heat, even at relatively low C-rate of charge?

anyway, off topic for THIS thread. On topic is simply that I have nt seen any balance change in the first 1000 miles at an average discharge cycle LESS than 50% as I often get recharged mid-day.


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## GizmoEV (Nov 28, 2009)

dtbaker said:


> I do wish we knew more about the actual mechanism of internal breakdown... is it just heat? whether from overcharge, or over-amp discharge, both would raise internal heat.... but then, why does deep discharge seem to make a difference? Perhaps that a deep discharge and recharge generates more heat, even at relatively low C-rate of charge?


The document I referred to talks a little about this. I haven't pulled up the referenced studies, however.



> anyway, off topic for THIS thread. On topic is simply that I have nt seen any balance change in the first 1000 miles at an average discharge cycle LESS than 50% as I often get recharged mid-day.


Except that charging to the max voltage and discharging as far as possible probably is what pushes the need for cell level monitoring/BMS whereas staying away from the extreme ends is looking like a cheaper and safer alternative.



dtbaker said:


> I sort of have accepted that what I have in this car now is INTENDED to be a 'lifetime' study, and I don't want to mess with it and change things mid-stream unless I HAVE to.


I'm in the same position. I really want to know how closely my cells are matched but don't want to do a bottom balance to find out because it will then mess up my tracking of cell balance at end of charge since I started with a top balanced pack.

I agree with JRP3 about staying above 50%DOD will likely do more than lowering ending voltage from 3.65vpc to 3.5vpc. With my 3.485vpc cutoff I can afford to have my cells go much farther out of balance than you can, however.


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## tomofreno (Mar 3, 2009)

> Included is a statement about the degradation of the cells when charged at low temperatures. Maybe we should be heating our packs to 20°C in the winter time.


 I find that 18 C (65 F) works fine. I see little difference in capacity or performance summer/winter using that temperature. Winter of 2009 I used about 15 C and seemed to notice a bit more difference compared to the following summer, but I think that was probably due to the cells increasing in capacity over the first several months (they were put into use in fall of 2009).


> Also, the recommended spec is to get maximum capacity not maximum life of the cell.


 True, but the cycle life part of the spec is for charging to the spec'ed voltage, so he should get at least that much if the spec is correct. I think as long as they are just going up a little of the exponential part of the curve during CC they should be fine. But of course that is just a guess.


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## spdas (Nov 28, 2009)

A consideration for BMS is warranty on the cells. I have trouble with 5 calb 180ah cells out of my pack that went to 0.3v when the rest of the pack was still at 3.15v or so. I originally carefully balanced by paralleling them and charging at the top. 

Calbs (China) position is "no BMS-no warranty". The jury is still out as that is not quite their "final answer", but is looking that way. We will see.

francis


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## Roy Von Rogers (Mar 21, 2009)

You should have a monitoring system that would tell when a cell is out of balance from the rest of the pack. Its easy enough to do, and has been discussed in here ad nauseum.

There should be no reason that if any cell goes down that far, without you knowing about it.

That doesnt mean you have to have an active balancing system.

Thats the whole problem with this BMS abreviation, it doesnt state what the M stands for.


Roy


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## dtbaker (Jan 5, 2008)

spdas said:


> A consideration for BMS is warranty on the cells. I have trouble with 5 calb 180ah cells out of my pack that went to 0.3v when the rest of the pack was still at 3.15v or so. I originally carefully balanced by paralleling them and charging at the top.
> 
> Calbs (China) position is "no BMS-no warranty". The jury is still out as that is not quite their "final answer", but is looking that way. We will see.
> 
> francis


how would they know whether you have a BMS, or not, or that it was installed and functioned correctly.... or for that matter if you consistently pull 10C for extended periods, or drove the pack to 99% DOD multiple times?

I will be checking balance on my pack again soon... first 1000 miles showed little to no 'un-balancing' (without any BMS), so I am curious what the second 1000 will show.


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## bmentink (Apr 22, 2011)

gottdi said:


> The cells were top balanced, not bottom balanced. Ouch. Ripe for loosing cells. No problems so far with my bottom balanced cells and no BMS.


Can you specify your procedure for bottom balancing ...

Thanks,
B


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## dtbaker (Jan 5, 2008)

gottdi said:


> The cells were top balanced, not bottom balanced. Ouch. Ripe for loosing cells. No problems so far with my bottom balanced cells and no BMS.


we've all been through this before, but I feel obligated to state that the risk of OVER-charging some cells in a bottom balanced pack without a BMS to stop the charge when the first cell hits the limit, is no less than the risk of over-discharging a top-balanced pack... 

I personally feel that I am highly unlikely to over-discharge, so choose to trust my charger to operate correctly and stop charging automatically on a top-balanced pack.

no regrets or issues thus far.


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## steven4601 (Nov 11, 2010)

dtbaker said:


> we've all been through this before, but I feel obligated to state that the risk of OVER-charging some cells in a bottom balanced pack without a BMS to stop the charge when the first cell hits the limit, is no less than the risk of over-discharging a top-balanced pack...
> 
> I personally feel that I am highly unlikely to over-discharge, so choose to trust my charger to operate correctly and stop charging automatically on a top-balanced pack.
> 
> no regrets or issues thus far.


Hi,

There is no right or wrong in choosing top or bottom balancing. Each solution provides its own set of problems. To BMS or not. A bms can fail, costs more to replace than individual (reversed or vented) cells, and is a fire hazard during charging. without a bms, you have no information what is going on, if they are balanced or not. etc etc. 


Here's my assumption why top-balancing is safer:
1. 
Reason behind this is not to keep the cells from reversing, but from prevent cells from venting during charging.. *1 Charging is often done unattended, or even when the owner is asleep. A rapid venting event can go unnoticed until the fire department arrives.

2. Cell reversal (over discharging the pack) will ruin the cell, might short, go high-impedance, might rupture the vent and cause smoke or a small fire. This will happen when the occupants are awake and have enough time to escape or take preventive actions to prevent more damage. (hopefully)



*1, assuming that a top balanced pack is in balance enough no cell voltages over 4.0 or 4.2Volts are present in the pack. This equalizing may have to be done annually or every 1.2. or 3 seasons. Pick your interval .


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## dtbaker (Jan 5, 2008)

steven4601 said:


> Hi,
> 
> There is no right or wrong in choosing top or bottom balancing. Each solution provides its own set of problems. ...
> *1, assuming that a top balanced pack is in balance enough no cell voltages over 4.0 or 4.2Volts are present in the pack. This equalizing may have to be done annually or every 1.2. or 3 seasons. Pick your interval .


agreed.... although I would tighten up on the definition of 'balance'; I am looking for no cell above 3.8 at end-of-charge (where the 'average' should be 3.65 for Thunderskies). After 1000 miles, my cells were still less than .02v difference at end of charge, so I did not do anything. I have run alonst another 1000 miles, and will check again to try and pick a good interval.

I figure I am probably going to check every 6 months at a minimum when I unbutton and add or remove top insulation for the winter.


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## JRP3 (Mar 7, 2008)

spdas said:


> A consideration for BMS is warranty on the cells. I have trouble with 5 calb 180ah cells out of my pack that went to 0.3v when the rest of the pack was still at 3.15v or so. I originally carefully balanced by paralleling them and charging at the top.


Could you give some more details? How long have you been using the cells, when was the last time you checked those cells, how closely matched were the cells in capacity, and was there anything that could have drained those specific cells?


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## tomofreno (Mar 3, 2009)

About 1 1/2 years ago I had some bms boards with defective voltage supervisor chips which resulted in a significant leakage path directly between cell terminals on several cells and drained them down. Is it possible something like this occurred? Did you record all cell voltages after parallel charging them? If so, and they were all close, something like the above must have occurred, or the cells were defective with an internal leakage path. Did you record cell voltages when they arrived? If they were all fairly close that would eliminate the second possibility - other than the internal leakage starting right after you received them, which would be unlikely.

Of course bottom or top balance would make no difference in this case.


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## spdas (Nov 28, 2009)

JRP3 said:


> Could you give some more details? How long have you been using the cells, when was the last time you checked those cells, how closely matched were the cells in capacity, and was there anything that could have drained those specific cells?


Cells were brand new. First time use. All were top balanced, with putting in parallel for 24 hours. They all settled to a resting voltage about 3.40 or so. There was nothing hooked up to drain the cells. The 5 cells depleted to 0.5v or so and the rest were at 3.19v or so. I charged the remaining cells up and counted the KWH and by specs they were 35% SOC, not dead like the 5. I have now bottom balanced all the cells and the 5 cells volted up to 3.9v and the rest were still at 3.37 (about 85% charged). All cells came in at 195 to 196v and close resistance when I got them. 
I would believe the scenerio if you were to tell me the 5 were 130ah and the rest were 180ah, as that is what it seems like to me. 

Francis


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## dtbaker (Jan 5, 2008)

spdas said:


> Cells were brand new. First time use. All were top balanced, with putting in parallel for 24 hours. They all settled to a resting voltage about 3.40 or so.



if all you did was parallel them, then that is not really top balancing... balancing voltage in the middle is ineffective because the middle is so flat you really cannot tell where you are.

top balancing would involve wiring in parallel, and using a power supply set to your intended top voltage, or slightly above, until amps going in drops to zero; which can take days or even weeks depending on how stout a power supply you have.

so, if the cells were not really balanced, it is entirely possible that you got 5 from a different 'batch', or were sitting on the shelf long enough to self-discharge a couple ahr and they got hammered when you got close to the bottom.


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## spdas (Nov 28, 2009)

They were charged with constant V in series of 3.55v each cell until amperage became 0. (And each cell was 3.5 or so, although not necessarily balanced) They then were paralleled and a desk Power supply was set at 3.5 until the amperage became 0.

As I remember the serial numbers were sequential. 

And yes it seems obvious to me that the 5 did/do not have the same capacity of the rest of the pack and when I have some time I will do a capacity test with my CBA111. 

francis


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## JRP3 (Mar 7, 2008)

Not to mention that if they were at resting voltage of 3.4 they certainly were fairly well top balanced and fully charged, especially if they were that closely matched in actual capacity. You don't get a resting voltage of 3.4 in the middle of SOC.


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## spdas (Nov 28, 2009)

Yes, I do not take 3.36 to 3.39v as "ok these are charged up". I count KWH above that vs. the quickness that the amps drop when I reach this target voltage. Voltage is only an indicator to me, not the measurement. Range to me is 3.10v="almost dead" and "will do a fast death spiral soon" and 3.40v "pretty charged" and "needs to closely watch as it can start to run away"

francis


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## bmentink (Apr 22, 2011)

Hi Guys, quick question:

I seem to have come up with the conclusion that bare minimum BMS (simple auto shunting at x volts ..) to protect top end charging over-volts and using the controller to cut off the discharge at too low volts should be effective at protecting a pack.

I.E If I charge at a max voltage of 3.5V and also have cell shunt regulators set to 3.5V ( to protect a low capacity cell going above 3.5V ..) and if I shutoff the discharge if the total cell voltage < (2.5V x no-of-cells), then I should be ok, right?

My simple shunt regulator would be a 5V P-FET that would gradually turn on harder and harder from 3.5V(self current limiting).

Anyone see any problems with this approach?


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## Coulomb (Apr 22, 2009)

bmentink said:


> I.E If I charge at a max voltage of 3.5V and also have cell shunt regulators set to 3.5V ( to protect a low capacity cell going above 3.5V ..)


Sounds good so far.



> and if I shutoff the discharge if the total cell voltage < (2.5V x no-of-cells), then I should be ok, right?


It's slightly better than nothing, but it doesn't protect against a single cell going under 2.5 V. If you're top balancing, the you will have "ragged bottom", so the weakest (lowest capacity) cell will hit 2.5 V before the others. By using the total pack voltage, you are checking for an _average_ of 2.5 VPC; some may be around 2.0 V while about the same number are around 3.0 V. If you are top balancing, you have to be bottom monitoring.

I suppose you could attempt to bottom balance, and just have your 3.5 VPC bypass circuitry just to be safe. Then hopefully all your cells will approach 2.5 VPC at the same time, and it's safer to use the pack average.



> My simple shunt regulator would be a 5V P-FET that would gradually turn on harder and harder from 3.5V(self current limiting).


I don't like the idea of semiconductors across cells. If a semiconductor fails, and these will get hot, accelerating a possible failure, they often fail shorted, which will vaporize tracks and/or ruin a cell.

Also, the threshold voltage of a FET is rather variable. For balancing, you really want voltage references to set the bypass threshold, so that they bypass within one percent of the same voltage, or a bit better.

As far as I can tell, there is no cheap and easy solution; that's why people are tempted to do without a BMS altogether.


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## dtbaker (Jan 5, 2008)

bmentink said:


> Hi Guys, quick question:
> 
> I seem to have come up with the conclusion that bare minimum BMS (simple auto shunting at x volts ..) to protect top end charging over-volts and using the controller to cut off the discharge at too low volts should be effective at protecting a pack.
> 
> ...



you will have a hard time finding a shunting BMS that can handle the full load a charger can put out in CA mode. This means that you typically have to set BMS not to start shunting until a little higher up the charge curve when the charger is supposed to be slowing down...

This is part of why the initial top-balance is important prior to using a shunting BMS.... you need to be *pretty sure* that the cells are well enugh balanced in the beginning that no single cell is way ut in front of the rest toward the end, so the charger has started clamping down on amps to the point the shunts can handle it.


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## Coulomb (Apr 22, 2009)

dtbaker said:


> This is part of why the initial top-balance is important prior to using a shunting BMS.... you need to be *pretty sure* that the cells are well enough balanced in the beginning that no single cell is way ut in front of the rest toward the end, so the charger has started clamping down on amps to the point the shunts can handle it.


Yes. Or have the charger throttle down when the monitoring BMS detects a single cell at or a little above bypass voltage.

But then you have added complexity.


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## dtbaker (Jan 5, 2008)

Coulomb said:


> Yes. Or have the charger throttle down when the monitoring BMS detects a single cell at or a little above bypass voltage.
> 
> But then you have added complexity.




and the logical extension to the argument is that if you feel good abut having a good initial top balance, you might consider doing away with a lot of complexity and expense and forget the BMS completely.


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## EVfun (Mar 14, 2010)

Coulomb said:


> It's slightly better than nothing, but it doesn't protect against a single cell going under 2.5 V. If you're top balancing, the you will have "ragged bottom", so the weakest (lowest capacity) cell will hit 2.5 V before the others. By using the total pack voltage, you are checking for an average of 2.5 VPC; some may be around 2.0 V while about the same number are around 3.0 V. If you are top balancing, you have to be bottom monitoring.
> 
> I suppose you could attempt to bottom balance, and just have your 3.5 VPC bypass circuitry just to be safe. Then hopefully all your cells will approach 2.5 VPC at the same time, and it's safer to use the pack average.


I've run with a BMS, with just shunt regulators (the same BMS without anything connected to the optical isolator loop) and without a BMS. I have a few thoughts, starting with, there is no one correct answer.

If your cells are closely matched and your controller can cut back at 2.5 times the number of cells it does work with a top balanced pack. My pack ends up all resting above 3.00 volts after a range test. At the end the car is quickly loosing drivability because it takes perhaps 2C or 3C to knock a cell down to 2.5 volts when the resting voltage of 3.1 volts. If you cells are not closely matched you will toast the smallest cells if you discharge to far. 

I would recommend using amp hour counting with a top balanced pack. You set this up with careful range testing punctuated with checks every mile or so at the end. It should be the full amp hour capacity of the pack, perhaps minus a few for an extra margin of safety. You can go as far as to cut out the throttle or just annoy the driver with lights and/or noise when empty. Once set you should be able to drive knowing you can't reverse a cell. 

If you bottom balance I don't think it would be idea to have anything on each cell. Even a fraction of 1 milliamp in current draw between different cell boards adds up to real power of the course of a year (8760 hours per year.) That would create an imbalance from the bottom balanced state. I think it was the Black Sheep regs that where so close in standby power consumption between units that they may work. If you insist on cell level boards I would suggest using an over-voltage charger shutdown instead of shunting because the first time a cell is shunted you have undone the bottom balance. I think a Lee Hart battery bridge would be a better choice to detect a cell getting out of line.

I have considered using a basic and very low power shunt reg made up of just an LM431, 2 resistors to set the voltage, 2 100 ohm resistors for the load along with a 100 ohm resistor and red LED as a load and indicator. That would be less than 100 milliamps load for up to 1 hour at the end of each charge. Most likely a bump of less than 1/20th amp hour per cycle, but I haven't seen even a fraction that amount of drift with my top balanced pack. I do wonder if the cell charge efficiency will remain so consistently near 100% as they age. The standby current would be somewhere around 1/2 milliamp.


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## GizmoEV (Nov 28, 2009)

EVfun said:


> If you bottom balance I don't think it would be idea to have anything on each cell. Even a fraction of 1 milliamp in current draw between different cell boards adds up to real power of the course of a year (8760 hours per year.) That would create an imbalance from the bottom balanced state. I think it was the Black Sheep regs that where so close in standby power consumption between units that they may work.


That is correct. Of the 20 boards I have, 2 manufactured several months after the first 18, the high current board was at 1.021mA and the low one was at 1.010mA, measured at 3.400V. The two newer boards are in the middle of the range at 1.018mA and 1.013mA, so very low current draw and very consistent. The difference of 0.011mA comes out to less than 0.1Ah/yr.


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## bmentink (Apr 22, 2011)

dtbaker said:


> and the logical extension to the argument is that if you feel good abut having a good initial top balance, you might consider doing away with a lot of complexity and expense and forget the BMS completely.


all good points .. thanks.

So if I don't have a BMS, how do you perform a top balance? I am not familiar with how to do this manually .... can you give a quick howto? (I am assuming the cells are not balanced from the manufacturer ... or need a periodic top balance)

Actually re-reading this forum of the posts by the non-BMS group shows that bottom balancing together with only charging to the V/I knee seems to be the way to go ... and coulomb counting for SOC.
So ..... what is the best/easiest method to bottom balance? Anyone? 

Thanks,


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## JRP3 (Mar 7, 2008)

There are a number of ways of course, assuming the cells are closely matched and at similar SOC from the factory, I tend to drive and check till the pack is close to 3.10 VPC, then pull down groups of 4 with a 12V halogen headlight, checking their voltages closely. A cell log 8 makes it easier. I'll then bring low ones up individually with a charger to my target voltage. 2.8-2.9 seems to be low enough but lower voltage means closer balancing.


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## DIYguy (Sep 18, 2008)

bmentink said:


> So ..... what is the best/easiest method to bottom balance? Anyone?
> 
> Thanks,


This depends if the cells are in the car or not. JRP described one way if they are. 
If they are still in boxes or on your basement floor, you may want to consider paralleling them and perhaps loading them until they all balance somewhere beyond the lower knee. . like maybe 2.7 or 2.8vpc or so.


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## dtbaker (Jan 5, 2008)

bmentink said:


> all good points .. thanks.
> 
> So if I don't have a BMS, how do you perform a top balance?



initial top-balance is easiest to do before installation by wiring the whole pack in parallel, and using a power supply (like an inexpensive Mastech) to bring them up just a tad over where you plan to have your charger switch from CA->CV. When the amps drop to less than about 1, turn off power supply, but leave them in parallel for a while....they'll be well top-balanced and should finish a normal charge very close to the same time, not really even needing BMS shunting most likely.

....but then you MUST use an amp-hr counter to be sure to stay away from the 'ragged bottom'! use a conservative value, and if you try to go no deeper than 70% DOD, you're supposed to get significantly better life out of these cells.


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## dtbaker (Jan 5, 2008)

bmentink said:


> Actually re-reading this forum of the posts by the non-BMS group shows that bottom balancing together with only charging to the V/I knee seems to be the way to go ...



I am a non-BMS person, and absolutely think top balance is easier to 'do', and easier to maintain with a normal cheap charger using simple CA->CV charge curve to a conservative 'normal' vpc finish voltage part-way up the knee... as long as you watch your ah consumed and stay away from the bottom.


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## JRP3 (Mar 7, 2008)

If your cells are close enough in capacity bottom balance is just as easy, I do nothing to my cells other than charge them after the initial bottom balance, probably the same as you after the initial top balance.


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## dtbaker (Jan 5, 2008)

JRP3 said:


> If your cells are close enough in capacity bottom balance is just as easy, I do nothing to my cells other than charge them after the initial bottom balance, probably the same as you after the initial top balance.


... but one issue is that with an inexpensive charger like Elcon PFC with regular CA->CV factory set charge curve, there is no graceful way to end the charge. The chargers are designed to expect a top-balance pack, sense the voltage rise when it climbs into the knee, and 'finish'.

As far as I can tell, if you are bottom-balanced, you have to end the charge either manually, with an external timer/relay, or have a fairly sophisticated (non-shunting) BMS at the cell level that can signal a charger capable of taking a signal, to shut down... and NOT use the charger's normal built-in voltage sense to turn itself off. I say non-shunting, because if the BMS starts shunting at the top, then you mess up the bottom balance.

Definitely a personal choice, but in MY case it made more sense to go with cheap pre-set charger, no BMS, top-balance, let the charger do its thing to end charge at the top 'set and forget' to factory specs, and avoid the bottom like the plague. Easy in my case since daily use almost never over 30 miles, and 100%DOD would be around 50 miles.


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## bmentink (Apr 22, 2011)

dtbaker said:


> I am a non-BMS person, and absolutely think top balance is easier to 'do', and easier to maintain with a normal cheap charger using simple CA->CV charge curve to a conservative 'normal' vpc finish voltage part-way up the knee... as long as you watch your ah consumed and stay away from the bottom.


Ok, so can you describe how you would top balance in the car .. 

If I have 224 "cells" and you have to charge each separately, then that is going to take forever ..

PS: (my cells consist of two headways in parallel)


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## JRP3 (Mar 7, 2008)

dtbaker said:


> ... but one issue is that with an inexpensive charger like Elcon PFC with regular CA->CV factory set charge curve, there is no graceful way to end the charge.


True, I forget about that point since my Manzanita allows full adjustment.


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## dtbaker (Jan 5, 2008)

bmentink said:


> Ok, so can you describe how you would top balance in the car ..
> 
> If I have 224 "cells" and you have to charge each separately, then that is going to take forever ..
> 
> PS: (my cells consist of two headways in parallel)



you don't have to charge individually, but SHOULD have them in PARALLEL for initial balancing.... sadly, problematic if you already have them in series in the car.


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## GizmoEV (Nov 28, 2009)

dtbaker said:


> you don't have to charge individually, but SHOULD have them in PARALLEL for initial balancing.... sadly, problematic if you already have them in series in the car.


I would just charge the pack and watch it closely. As soon as one cell hits the knee then stop the charging and bring the rest up one at a time or put a resistor across the high one to knock it down and resume charging, slowly. It won't be as easy as paralleling them but it can work.


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## EVfun (Mar 14, 2010)

I did the balance of my cells in series with a resistor. I used a 5 ohm 10 watt resistor but it was slow. I recommend a 2 ohm resistor rated for at least a 15 watts. If you use over 1/2 of the power rating of the resistor it will get so hot you can't handle it. You just turn down the charger amp rate and bleed the cells that pop up during a slow finish charge. After a couple cycles you have them in a pretty tight line. You really don't have to worry about 0.1 volt variations at the end of charge so long as none of them go over about 3.75 volts (+/- a bit based on target finish voltage.)


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## dtbaker (Jan 5, 2008)

GizmoEV said:


> I would just charge the pack and watch it closely. As soon as one cell hits the knee then stop the charging and bring the rest up one at a time or put a resistor across the high one to knock it down and resume charging, slowly. It won't be as easy as paralleling them but it can work.



in his case, its pretty damn tough to watch 200+ headways during charge and catch the first one(s), I don't care HOW fast you are with a multimeter! This is possible maybe with 30 or 40 large format prismatics, but I cant imagine buzzing thru 200+headways trying to catch the first high cell.


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## Coulomb (Apr 22, 2009)

dtbaker said:


> in his case, its pretty damn tough to watch 200+ headways during charge and catch the first one(s), I don't care HOW fast you are with a multimeter! This is possible maybe with 30 or 40 large format prismatics, but I cant imagine buzzing thru 200+headways trying to catch the first high cell.


This is indeed a problem for high voltage packs, say over 144 V (45 cells).

But if your 200+ headways is actually 225 cells arranged 45S5P, then it's actually no more cells to check than a 45S1P pack. All the cells in parallel will have the same voltage, so you only need to check one of the paralleled cells. In effect, by measuring one, you are measuring all 5 (assuming 5P) at once.

It might still take longer than a 1P string, since it might take a while to figure out where to put the multimeter probe next, and you will need to be checking with one probe at the front and one at the back.

Maybe it makes more sense to measure pairs of cells, then as a second pass measure one of the cells in each pair. If any cell is particularly low, check the other one it is in series with. Now that I type this, it sounds like it might actually be harder that way. But perhaps running along the pairs will let you find any that are suspicious; if a little high, check the two cells in that pair, otherwise keep going.

I might point out that a Battery Monitoring System can watch all the cells at once for you. But I guess you're talking about only manually top or indeed bottom balancing now and then, so the cost of the monitoring system is not worth the occasional convenience.

In the conversion I'm involved with, there are 228 cells, and half of them are completely inaccessible without major works, so we have no alternative but to have a monitoring system that allows us to read the voltage of an individual cell. We've chosen to have cell-top balancers as well, with a "fail-safe" circuit (I know that nothing is completely fail-safe).

It will be interesting to see how much work it turns out for those who choose the occasional manual balance method, and how closely balanced the cells end up after some time.


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## dtbaker (Jan 5, 2008)

Coulomb said:


> It will be interesting to see how much work it turns out for those who choose the occasional manual balance method, and how closely balanced the cells end up after some time.



I saw basically NO measurble drift after the first 3000 miles of use... need to check again pretty soon, but swamped in other stuff...


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## bmentink (Apr 22, 2011)

Coulomb said:


> This is indeed a problem for high voltage packs, say over 144 V (45 cells).
> 
> But if your 200+ headways is actually 225 cells arranged 45S5P, then it's actually no more cells to check than a 45S1P pack. All the cells in parallel will have the same voltage, so you only need to check one of the paralleled cells. In effect, by measuring one, you are measuring all 5 (assuming 5P) at once.
> 
> ...


Actually I have 448 Headway 16A/H cells arranged in 224 x 2p but split up into 14 packs consisting of 16 pairs of headways. I aim to have each of the 14 packs easily removable so maybe the best approach is to use a 16x3.5V = 56V power supply, current and voltage limited to do the top balancing, will be much easier to manage .... what do you guys think of that approach?


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## GizmoEV (Nov 28, 2009)

dtbaker said:


> in his case, its pretty damn tough to watch 200+ headways during charge and catch the first one(s), I don't care HOW fast you are with a multimeter! This is possible maybe with 30 or 40 large format prismatics, but I cant imagine buzzing thru 200+headways trying to catch the first high cell.


What? Where is your faith in human nature? 



Coulomb said:


> It will be interesting to see how much work it turns out for those who choose the occasional manual balance method, and how closely balanced the cells end up after some time.


That is one reason I removed my BMS and have gone with just a 1/2 pack voltage monitor. I only have 20 cell pairs which are all relatively easily accessible. I can watch them over time and provide some data. The batteries are all in one box and I have them numbered and note where they physically are in the pack to see if there are any trends. Of course it will be quite some time to collect data on an aging pack, at lease I hope so. 



dtbaker said:


> I saw basically NO measurble drift after the first 3000 miles of use... need to check again pretty soon, but swamped in other stuff...


That is what I've found in 5k miles but then again, relative pack size, or more accurately, Ah delivered and average current draw might have a larger effect. I have a 200Ah pack and never draw more than 500A and usually well under 250A.

bmentink, I think working on each sub-pack one at a time would be best and simplest. I just use a bench top PS with current and voltage limit knobs. This would give you infinite variability with both voltage and current. For a resistor you could make one out of a length of SS welding rod mounted in a loop or in a coil with heavy wire leads coming off of them to hook to the individual cells. A friend of mine did this to bottom balance his CALB pack only he just hooked the SS rod directly to the cell terminals. I think they drew about 9A at 3.3V.


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## AmpedSpeed (Mar 25, 2012)

I just finished reading this entire thread over the course of a few days. Lots of good info here, though I am somewhat surprised by all the hot headed remarks throughout.

I do like the simplicity of the Lee Hart battery bridge, but I don't think it's precise enough. 

What if you have one cell on each side going bad? 

What if on one side of your pack you have one cell losing voltage by as much as another gains it? The two sides would look equal.

Still undecided yet, but so far I'm thinking maybe something based on the LTC6802-1 to monitor the voltage of each cell, with a 40mA fuse on each cell terminal. Monitoring each cell will tell me when a balance is needed, and then I can just easily replace the fuses with shunts while I balance, and then put the fuses back when I'm done.

I think this method would offer safety of not ruining your cells with a faulty BMS, the ability to automatically balance (with a quick fuse swap), and the peace of mind of knowing each of your cell's voltages.

I've been using LiCo and LiMn cells for years in the high power flashlights that I build. Not much experience with LiFePO4, but if it's anything like the former(and it probably is), bottom balancing is probably best for the life of the cells. Either end of the charge spectrum is destructive, but the high point of the charge is more destructive to the life of the cells than the low point.


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## JRP3 (Mar 7, 2008)

Nothing stirs things up like a good BMS debate  While I run a bottom balanced pack without BMS I don't think top balancing needs to mean charging to a higher SOC all the time. You can still undercharge your pack with a top balance, just pick a lower cutoff voltage, same as you would with a bottom balanced pack. Frankly with the closely matched sets of cells people seem to be getting from CALB I'm not sure it matters much if you choose top or bottom balance.


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## AmpedSpeed (Mar 25, 2012)

True indeed. Not everyone goes with Calb though. 

I'm still in the research phase, and will be for quite a while longer, but at the moment, the grey market A123 20AH pouches look best so far. I like the much higher discharge rate they can achieve, as well as the lower $/Ah. Of course there is the complexity of building the pack, but that's ok with me.

I prefer the idea of bottom balancing, simply because charging your pack can be completely controlled with redundant and/or per cell cut-offs if you so choose, and be charged quite safely until the smallest cell is full.

Driving is not controlled at all, and therefore it makes sense to me to have the discharged end of the pack less prone to failure if something goes wrong, which bottom balancing provides.


Edit: To elaborate further; you can charge with a known current, switch to a known voltage, and cut-off at a known current. When you're charging you can know your exact SOC once you near the top. 

When you're nearing the bottom as you drive, current drawn from the pack is fluctuating constantly, and getting a voltage reading from a low pack under these conditions to actually know when the smallest cell is depleted, before it's too late, is much more difficult than attaining state of charge information while charging.

From objectively viewing all options available it seems the most foolproof way to go is to bottom balance for natural safety of the pack when it's discharged under varying conditions (the backup plan), and charge to the uneven top under controlled conditions.

Watch the Ah as you drive, but if something goes wrong, at least you're bottom balanced.


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## Ziggythewiz (May 16, 2010)

AmpedSpeed said:


> Driving is not controlled at all, and therefore it makes sense to me to have the discharged end of the pack less prone to failure if something goes wrong, which bottom balancing provides.


You should really stick something behind the wheel to address that issue.


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## AmpedSpeed (Mar 25, 2012)

Ziggythewiz said:


> You should really stick something behind the wheel to address that issue.


Haha. Nice to have some light hearted humour in this thread, it needs some.

That kind of out-of-context quoting is a politician's nightmare! 

Obviously meaning the electrical conditions the cells are experiencing


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## bmentink (Apr 22, 2011)

AmpedSpeed said:


> Still undecided yet, but so far I'm thinking maybe something based on the LTC6802-1 to monitor the voltage of each cell, with a 40mA fuse on each cell terminal. Monitoring each cell will tell me when a balance is needed, and then I can just easily replace the fuses with shunts while I balance, and then put the fuses back when I'm done.


Hmm, not sure what you mean here .. shunts are by definition used "across" a cell, fuses are in series ... what is your circuit layout to replace a fuse with a shunt ... don't get it .. please post a drawing


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## AmpedSpeed (Mar 25, 2012)

bmentink said:


> Hmm, not sure what you mean here .. shunts are by definition used "across" a cell, fuses are in series ... what is your circuit layout to replace a fuse with a shunt ... don't get it .. please post a drawing


Took me a second to understand what you were meaning, then I realized you were using the EV world's definition of a shunt, not the general definition.

At each terminal on each cell there would be a 40mA or so slow blow fuse, in case of any malfunction of the BMS, or a short in the "spaghetti wiring" as some call it. (If if looks like spaghetti after you do it, then pay someone else to do it properly.) 

You wouldn't be able to balance with the fuses in place because they would obviously blow, from the data we already have, it's conclusive that you don't need to balance every charge. My plan is to monitor the cells with fuses in place so I can't start a fire with cell monitoring equipment if something goes wrong.

If I notice things going out of balance, I'll replace the fuses with shunts (I should have just said 0ohm resistor to avoid confusion) so I can draw some current from specific cells and balance the pack.

Then I'll put the fuses back in and drive for another few thousand, or however many it works out to miles, and watch for when I need to do it again.


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## bmentink (Apr 22, 2011)

Got it, thanks.

So are you using the built-in balancing circuit in the LTC6802 or an external fet .. and I take it you are doing the balancing via commands over SPI? or are you manually "shunting" ( as in with a resistor .. ;-) each un-balanced cell ..

Cheers,
Bernie


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## bmentink (Apr 22, 2011)

AmpedSpeed said:


> Took me a second to understand what you were meaning, then I realized you were using the EV world's definition of a shunt, not the general definition.
> 
> At each terminal on each cell there would be a 40mA or so slow blow fuse, in case of any malfunction of the BMS, or a short in the "spaghetti wiring" as some call it. (If if looks like spaghetti after you do it, then pay someone else to do it properly.)
> 
> ...


So why not make the fuse a 1A(fast blow), that won't cause a fire ... that way you can do the balancing "programatically" over SPI .. here is the procedure:

1. Controller indicates cells are out of balance .. "enough to cause a problem"

2. At your choice, you push the "balance" button, the controller shunts the offending cell(s) with say 200ma until the cells are all in balance ... (I am assuming the SPI is going to a controller that you can program here ... I was thinking of doing that with my controller )


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## GizmoEV (Nov 28, 2009)

AmpedSpeed said:


> I do like the simplicity of the Lee Hart battery bridge, but I don't think it's precise enough.


My setup reads pack difference to the hundredth of a volt. The most difference I have seen is 0.14V, IIRC. 



> What if you have one cell on each side going bad?
> 
> What if on one side of your pack you have one cell losing voltage by as much as another gains it? The two sides would look equal.


They won't do that. It is against the rules.

After playing with and monitoring my pack for a year with BMS boards on them I took them off and went with just the BattBridge setup. Between not seeing any drift to speak of before I'm confident that the probability of the same voltage issues happening on each half being exactly the same is actually quite low, at least with my 20 cell pack.




> Still undecided yet, but so far I'm thinking maybe something based on the LTC6802-1 to monitor the voltage of each cell, with a 40mA fuse on each cell terminal. Monitoring each cell will tell me when a balance is needed, and then I can just easily replace the fuses with shunts while I balance, and then put the fuses back when I'm done.
> 
> I think this method would offer safety of not ruining your cells with a faulty BMS, the ability to automatically balance (with a quick fuse swap), and the peace of mind of knowing each of your cell's voltages.


You might just install a set of jumper pins in parallel with the fuse and install a jumper when you want to balance and remove it when done. You should need less than 500mA balancing current any way.



> I've been using LiCo and LiMn cells for years in the high power flashlights that I build. Not much experience with LiFePO4, but if it's anything like the former(and it probably is), bottom balancing is probably best for the life of the cells. Either end of the charge spectrum is destructive, but the high point of the charge is more destructive to the life of the cells than the low point.


The charge/discharge curve is a bit different and the LiFePO4 are more difficult to get to burn. Other than that they are very similar. As for balancing method/end, pick one and collect data to share with the community so we can make more informed decisions.

Finally, get some LiFePO4 cells and play with them to get a better idea of how they behave.


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## AmpedSpeed (Mar 25, 2012)

bmentink said:


> Got it, thanks.
> 
> So are you using the built-in balancing circuit in the LTC6802 or an external fet .. and I take it you are doing the balancing via commands over SPI? or are you manually "shunting" ( as in with a resistor .. ;-) each un-balanced cell ..
> 
> ...


Not using anything yet, just thinking about it for now. I would use an external FET though, with commands over SPI. Would be nice to use an external FET and large enough load for balancing that you could automatically bottom balance your cells under load with software.



bmentink said:


> So why not make the fuse a 1A(fast blow), that won't cause a fire ... that way you can do the balancing "programatically" over SPI


With a 1A fuse a 900mA short could destroy a cell in the pack within a few days depending on the SOC it was left in.



GizmoEV said:


> My setup reads pack difference to the hundredth of a volt. The most difference I have seen is 0.14V, IIRC.


Precision was a bad choice of word. Of course it can be precise, but how accurate is it at determining a bad cell? Not very... You just know that there's a problem "somewhere" in one of the halves. If the right conditions are met, you won't even know that there's a problem. It's better than nothing, but far from ideal.


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## Ziggythewiz (May 16, 2010)

The question is what are the odds of cells drifting in the exact amount to offset?

And what are the odds that one will begin to die and turn down the knee while the other side is somehow heading up the knee?

Simple monitoring can let you know there is an issue before it is a real issue, and then you have to do a bit of work yourself to find the cause. Binary sorting isn't that tough.


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## GizmoEV (Nov 28, 2009)

Ziggythewiz said:


> The question is what are the odds of cells drifting in the exact amount to offset?
> 
> And what are the odds that one will begin to die and turn down the knee while the other side is somehow heading up the knee?
> 
> Simple monitoring can let you know there is an issue before it is a real issue, and then you have to do a bit of work yourself to find the cause. Binary sorting isn't that tough.


This is exactly it. After a year of checking voltages monthly for balance at the top of charge I got bored of consistency. Even with water and dirt landing on top of the cells it took that long for a 0.1V difference to show up. I cleaned up the sealing of my battery box, rebalanced the pack, pulled off the BMS boards and installed the BattBridge setup. Nine months into the new setup and the max difference between cells was 0.035V and a couple of months later it is down to 0.026V. This is why I don't think the probability of both halves going bad in just the right way to cancel out being detected by half-pack voltage comparisons is very high.


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## bmentink (Apr 22, 2011)

So in regards to the 1/2 pack balancing scheme I came across this awesome looking dual opto-isolator that has upto 8000% current transfer ratio. 

It would be ideal to use in a balanced bridge, with that sort of current ratio, you won't need any other components apart from a few resistors to give you an isolated voltage reading back to your controller or a dash meter or LED.

I thought I would feed the voltage back to my controller which would flash an LED on the dash if the voltage got out of balance by a programmed amount ..

You can get the datasheet from here: 
="http://search.digikey.com/us/en/products/CPC1302G/CLA295-ND/1649214

PS: You only need 0.5ma of LED current on the high voltage side too ..

Cheers,
B.


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## nucleus (May 18, 2012)

Wow, I just read this entire thread, all 92 pages. Do I get a T-shirt or something?


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## Ziggythewiz (May 16, 2010)

Yes! but you have to DIY or you get one that says BMS and might burn up on you.


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## steven4601 (Nov 11, 2010)

Ziggythewiz said:


> Yes! but you have to DIY or you get one that says BMS and might burn up on you.


Where in this tread is it proven that going without a BMS is safer? You make me sad!


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## Roy Von Rogers (Mar 21, 2009)

steven4601 said:


> Where in this tread is it proven that going without a BMS is safer? You make me sad!


 
Thats easy to proof, the fact that you need to ask this question, shows you havent understood these cells.


Roy


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## Ziggythewiz (May 16, 2010)

Has a BMS ever destroyed a battery? Yes. Has a battery ever been destroyed by decent monitoring and care during charge and discharge? By definition, no.


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## EVfun (Mar 14, 2010)

Have cells in a pack without a BMS ever been destroyed? Yes. Either way, I think it comes down to safe wiring practices and "decent monitoring and care during charge and discharge."


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## cpct (May 31, 2012)

Ziggythewiz said:


> Has a BMS ever destroyed a battery? Yes. Has a battery ever been destroyed by decent monitoring and care during charge and discharge? By definition, no.


This again 
Imagine you have a set of cells with a voltmeter on top of each cell, so you can always see the voltage of each cell. That's good right? You can always check what's happening when charging or driving and all is good in the world. After all, decent monitoring and care are what your pack needs.

But, some day you get tired of this. Inventive as you are, you hire a guy to watch those multimeters for you. He gets a sheet with a list of values that every cell voltage has to be inbetween. If they are not, he disconnects the charger or controller for you. You feel really safe now.

Some further down the line, labor costs have risen exponentionally. Unfortunately you do not want to "export" this job to another country. But then you hear something about microcontrollers. What if you could replace that guy with a small computer program? After all, what can possibly go wrong?

And the rest is history


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## Qer (May 7, 2008)

cpct said:


> And the rest is history


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## steven4601 (Nov 11, 2010)

Im agreeing with the Swede's choice of song title


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## Roy Von Rogers (Mar 21, 2009)

You would think by now most all who frequent in here would have gotten it...yes its sad.


Roy


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## dtbaker (Jan 5, 2008)

nucleus said:


> Wow, I just read this entire thread, all 92 pages. Do I get a T-shirt or something?


give it a day or two to sink in, and I'll be curious to see what you decide to do regarding top versus bottom balancing and active vs monitor-only vs none on BMS. The cherry on top is how that affects your choice in chargers and target charge curve/control of end-of-charge.


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## dtbaker (Jan 5, 2008)

cpct said:


> After all, what can possibly go wrong?


are you serious, or was this a sarcastic post....? 

just to be blunt; more connections that could fail, individual processors that could fail and shunt cells to death, shunts that could come 'on' when cell is still drawing too many amps and overheat or drain cells, unbalanced parasitic loads.... all things that introduce consequences that don't exist with a simple top-balanced pack with a simple charger.


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## JRP3 (Mar 7, 2008)

Or a simple bottom balanced pack and a simple charger


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## EVfun (Mar 14, 2010)

What Dtbaker or JRP3 said, so long as all of your cells are from 1 batch and have the same use history. I am seeing something like drift with the 6 cells I added to my pack.


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## cpct (May 31, 2012)

dtbaker said:


> are you serious, or was this a sarcastic post....?
> 
> just to be blunt; more connections that could fail, individual processors that could fail and shunt cells to death, shunts that could come 'on' when cell is still drawing too many amps and overheat or drain cells, unbalanced parasitic loads.... all things that introduce consequences that don't exist with a simple top-balanced pack with a simple charger.


Yeah I was being sarcastic 
You're right of course. But also compare it to modern-day safety features on cars. Lots of extra electronics and sensors that can go wrong (not in the least airbags, pre-brake systems etc) but in the end, every day people are saved by them...


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## Ziggythewiz (May 16, 2010)

Yes, lets compare to modern safety features on cars that have billions of dollars and millions of tests behind them...


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## cpct (May 31, 2012)

Ziggythewiz said:


> Yes, lets compare to modern safety features on cars that have billions of dollars and millions of tests behind them...


Sure! But it's not hard to see *how* these systems (e.g. abs and tc) help, and that is what matters.


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## mons2b (Nov 17, 2015)

spdas said:


> Aloha, I am trying to plan my Lithium purchase. Probably 50 Calb cells @200ah. But I am hearing conflicting heated, (even namecalling) arguments about weather to use a bms or not. So will the person with the most Lithium-use-hours experience stand up and give me the "skinny"? thanks
> Francis


I have coped rudeness about my plans to manually check my cells.


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## mons2b (Nov 17, 2015)

brainzel said:


> I don't use a "BMS" in my car.
> Why? I haven't found one that monitores my LiFePo-pack the way I want to a price that I could afford and with the safety issues I need.
> 
> Do I monitor the whole pack? Yes, that's neccessary I think.
> ...


Hello. I have the same charger. Two groups of Chevy volt cells configured for 144v. Running in parallel. I've had a suggestion to run charger at 151 volt. Do you concur?


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## Duncan (Dec 8, 2008)

mons2b said:


> Hello. I have the same charger. Two groups of Chevy volt cells configured for 144v. Running in parallel. I've had a suggestion to run charger at 151 volt. Do you concur?


How about a bit more detail on the modules - I assume 1kWh and 2 kWh modules - how many on each group?


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## cricketo (Oct 4, 2018)

mons2b said:


> I have coped rudeness about my plans to manually check my cells.


Try not to cry, and remember that CALB cells are LFP. You're on the other hand playing with NMC cells, which sometimes look like this :


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## Duncan (Dec 8, 2008)

cricketo said:


> Try not to cry, and remember that CALB cells are LFP. You're on the other hand playing with NMC cells, which sometimes look like this :


The data shows that CALB cells fail at well over 100 times the rate of OEM cells 
Everybody with aftermarket cells like CALB has a 2 - 5% failure rater
OEM cells however have a failure rate in the parts per million


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## cricketo (Oct 4, 2018)

Duncan said:


> The data shows that CALB cells fail at well over 100 times the rate of OEM cells
> Everybody with aftermarket cells like CALB has a 2 - 5% failure rater
> OEM cells however have a failure rate in the parts per million


Cell reliability is not the question, the question is what happens when the cell does fail - very much depends on the chemistry.

Here is a decent visual comparison of different chemistries in terms of response to overcharging :


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## Duncan (Dec 8, 2008)

cricketo said:


> Cell reliability is not the question, the question is what happens when the cell does fail - very much depends on the chemistry.
> 
> Here is a decent visual comparison of different chemistries in terms of response to overcharging :


In the real world its about BOTH and the thousands of times better quality with OEM cells completely overcomes the minor difference in base chemistry


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## cricketo (Oct 4, 2018)

Duncan said:


> In the real world its about BOTH and the thousands of times better quality with OEM cells completely overcomes the minor difference in base chemistry


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## Duncan (Dec 8, 2008)

cricketo said:


>


You may laugh but its completely true -
there are maybe 1/10,000th as many cars using CALB as using your "more dangerous chemistry" 
and there have been about a 100 times as many cars using CALB and the like going on fire as cars using the "more dangerous chemistry"


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## cricketo (Oct 4, 2018)

Duncan said:


> You may laugh but its completely true -
> there are maybe 1/10,000th as many cars using CALB as using your "more dangerous chemistry"
> and there have been about a 100 times as many cars using CALB and the like going on fire as cars using the "more dangerous chemistry"


I am laughing because you jumped into a conversation without any context and are continuing to push your line. I don't even need to debate with you on the specifics of the topic. Have a nice day.


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## Duncan (Dec 8, 2008)

cricketo said:


> I am laughing because you jumped into a conversation without any context and are continuing to push your line. I don't even need to debate with you on the specifics of the topic. Have a nice day.


You are the one without any knowledge of the context - I "jumped in" in order to help a fellow enthusiast asking about Chevy Volt voltages

Then you started adding your ignorance to the discussion


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## remy_martian (Feb 4, 2019)

mons2b said:


> Hello. I have the same charger. Two groups of Chevy volt cells configured for 144v. Running in parallel. I've had a suggestion to run charger at 151 volt. Do you concur?


WTF are you doing spamming the forum? 

You started a topic on your "problem", and now you brought it into a 9 year old thread? 

This forum is a resource for everybody, not you alone - do you expect somebody four or five years from now to chase you all over the site asking the same BS? Stay within a topic - the answers and discussions are not about just you.


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## remy_martian (Feb 4, 2019)

mons2b said:


> Hello. I have the same charger. Two groups of Chevy volt cells configured for 144v. Running in parallel. I've had a suggestion to run charger at 151 volt. Do you concur?


No.

You don't charge a lithium battery with voltage unless you plan to toast marshmallows.


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## Duncan (Dec 8, 2008)

remy_martian said:


> No.
> 
> You don't charge a lithium battery with voltage unless you plan to toast marshmallows.


Funny that I have been doing just that for the last eight years - no toast so far


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## remy_martian (Feb 4, 2019)

You also didn't set your charger to 151V to charge a 144V pack...


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## brian_ (Feb 7, 2017)

mons2b said:


> Hello. I have the same charger. Two groups of Chevy volt cells configured for 144v. Running in parallel. I've had a suggestion to run charger at 151 volt. Do you concur?


Since no combination of Volt modules has a nominal voltage of 144 V, no. My guess is that the plan is to run two 36S banks in parallel, which would have a nominal voltage of about 135 V; that's not the fully charged voltage.

I suggest that you look at the actual specifications of the modules that you are using and the cells that they contain, then determine appropriate charging parameters for them, including both current and voltage limits.

But this thread was about whether or not to use a BMS, and the above post doesn't even mention whether a BMS will be used or not, which does matter to charging voltage.


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## mons2b (Nov 17, 2015)

brian_ said:


> Since no combination of Volt modules has a nominal voltage of 144 V, no. My guess is that the plan is to run two 36S banks in parallel, which would have a nominal voltage of about 135 V; that's not the fully charged voltage.
> 
> I suggest that you look at the actual specifications of the modules that you are using and the cells that they contain, then determine appropriate charging parameters for them, including both current and voltage limits.
> 
> But this thread was about whether or not to use a BMS, and the above post doesn't even mention whether a BMS will be used or not, which does matter to charging voltage.


Hi Brian. Happy New year. I dont plan to initially use a BMS. But will manually check the cells. I do want to add one later and im looking at all options to do so. The cost to what we call "comply" the car in New Zealand is very expensive so the car is likely to be a garage queen for some time. I would very much like to get it to the point it can move under its own power up and down the drive way. Sans BMS any charging will be done outside at maximum safe cable length.


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