# Have you designed a BMS?



## jorhyne (Aug 20, 2008)

Have you contacted GGoodrum (Gary) of Endless-Sphere? As I'm sure you know they have been working on revising what is already a very successful and popular BMS system.


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## cycleguy (Oct 7, 2009)

I recommend getting in touch with Dimitri, he's a member here and has developed a very nice, reasonably priced BMS system. He is certainly capable of more elaborate systems as well.

His current BMS
http://www.cleanpowerauto.com/MiniBMS.html


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## Gavin (Oct 7, 2008)

Check out these guys: Their CellLog 2-8S is $29. They will do a 24 cell logger if you order 1000. THe RC folks love them.

Yes, it is possible to make 24s CellLog if you order 1000 units in one time.
If you think it is no problem, then we can have a detail discussion.

Regards,
Cindy

*Shenzhen Junsi Electronic Co.,Ltd*

Room 578 & 588, Building 9A 
Anhua Industrial Zone
8th Tairan Rd, Che Kung Temple 
Futian, Shenzhen, China, 518040

Tel: 086-0755-88845648 
Fax : 086-0755-88845648-12 
Email: szjun[email protected], [email protected]

website: www.jun-si.com! 
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## Amberwolf (May 29, 2009)

You might also check with Methods over on Endless Sphere (and here on DIYEC a little); he was working on a BMS but most details were not yet available last I read up on it, so I don't know it's specs.
________
mariaK


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## CroDriver (Jan 8, 2009)

jorhyne said:


> Have you contacted GGoodrum (Gary) of Endless-Sphere? As I'm sure you know they have been working on revising what is already a very successful and popular BMS system.


IMO, this isn't a BMS for a full size EV. Their BMS is a analog device with no logic nor "brains". 

We are designing a very sophisticated BMS but it's more for our own projects than for the market.


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## Gavin (Oct 7, 2008)

After reviewing Jack Rickard's videos a sophisticated BMS seems counter productive (as well as a waste of money) unless it can bottom balance. EV Components should sell the Pak Trakr or the CellLog 48. Perhaps a sophisticated SOC that automatically resets at full charge and counts AH. Tough problem but it certainly seems shunting and top balancing is not the way to go.


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## CroDriver (Jan 8, 2009)

For serious projects you have to have a serious BMS. We EV guys can drive a car without a BMS but someone who has no clue about EVs would kill the batteries within days.

What do you think how many Teslas would still be alive if they haven't had a BMS?


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## Gavin (Oct 7, 2008)

I am sure you are correct about that. I bet they still kill them.


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## Gavin (Oct 7, 2008)

*Re: Have you designed a BMS? see recall*

http://www.gpev.us/
IMPORTANT SAFETY BULLETIN: BattEQ

SmartSpark Energy Systems, Inc. ("SmartSpark"), in cooperation with the
U.S. Consumer Product Safety Commission ("CPSC"), is implementing a
voluntary recall of BattEQ(tm) battery equalizers. BattEQ(tm) battery
equalizers may overheat and pose a risk of fire to consumers.


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## Overlander23 (Jun 15, 2009)

It seems that, realistically for mass market usage the safest way to utilize a battery pack is to only use a small portion of it somewhere in the middle. 

The most successful real-world implementation of this can be seen in a hybrid such as the Prius. It only uses a small percentage of its pack and has a very long life-span because the end-user isn't allowed to get anywhere near the sensitive ends of the pack, be it high or low.

A BMS can't hurt by monitoring this type of usage, but most of what we in the DIY market are doing is seeing how far we can push the cells.

The Tesla is supposedly rated at 32-33 khw / 100 miles regardless of city or highway driving, and that seems conservative to me. The real question is, how much are they really pushing their 50kwh+ pack?

The interesting thing will be seeing how something like the Nissan Leaf does in the real world since its performance claims vs. tech specs seem less conservative than most.

At the end of the day, I imagine staying away from the top 5% and bottom 20% of a LiFePO4 pack can't hurt reliability. Cells are going to go bad, you just need to monitor them. And using a balancing method is just trying to extend the life of a bad apple (cell).

If the Prius is using only 15% of its total pack capacity, that leaves a lot of room on the ends for aging cells to slip to over time.

The major manufacturers can't be bothered to engineer complex solutions to manage that actively (though I admit ignorance regarding the battery management of the Prius). There would be too many unique situations... the simplest way to reliability is through "de-rating".

Having said all that, as a technically-minded end-user I'm very interested in a robust monitoring solution. But that's just me.


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## MN Driver (Sep 29, 2009)

Overlander23, The Prius, Insight, Fusion, etc.. hybrid vehicles use Nickel-metal hydride batteries instead of LiFePO4 so things are a little bit different. What is even more different about it is their usage. These hybrid vehicles will store energy when stopping every time and when accelerating will use that stored energy. They are small Ah capacity cells (6.5Ah, more or less depending on the hybrid) that are setup for power output and storage at large quantities. For example the Insight will charge them at over 7C and discharge at around 15C (50 and 100 amps), they can't accept a charge of 50 amps if they are nearly full and when towards empty that 'knee of the curve' as we are familiar with calling it sure comes up mighty quick at 15C. The 1st gen Insight is setup to use 4Ah of capacity, so you get to use 60% in the middle when the pack is fresh and happy. NiMh is different and has self-discharge and like any battery the internal resistance changes over time which affects charge acceptance and causes voltage sag. Aiming for the middle helps to cover that issue up a bit. With the Insight, every two subpacks(each subpack/module is a stick of 6 cells) the car monitors for any rapid voltage drop that would indicate that the pack has reached a discharged state. Then its battery condition monitor sets that as its new empty point and then it will prevent the pack from getting that low again while it charges the pack up with a background charge and while regenerative braking monitoring the Ah in and out until it eventually hits its full point and then it does the math to derate the pack a little if its needed and continues on.

NiMh drifts in SOC from cell to cell when trying to monitor Ah in and out, it eventually needs to be balanced, usually it happens after a long pack life and needs to be pulled apart, each 7.4 volt subpack cycled to get lazy cells active again and to get them to the same SOC and capacity checked and any modules with lower capacity or high internal resistence swapped out with ones of similar capacity to the rest of the pack, everything goes back together and the car is back on the road. This goes for Prius packs, Insight packs, any hybrid using NiMh when it 'wears out' usually isn't worn out but most of the time the pack gets a bit lazy due to the bad apple affects of a few subpacks out of the pack being worse than the rest. Hybrid packs continue to operate without pushing a failure condition or in most cases even being obvious as having a problem until the usable capacity is below 1Ah.

Do I think LiFePO4 is as bad with losing their balance as NiMh? Since they don't have widely varying self-discharge issues as they age(at least it doesn't seem like it), probably not, but a cell that isn't fully charged will falsely look empty when discharged which is a balance issue that needs to be addressed and you won't know it if you don't ever empty your pack, and it isn't going to be something you want to find out cruising down the road either. I think that internal resistence issues will become an issue as they age though as that's usually what happens with Lithium packs including the TS LiCo after they are used a number of years based on someone who used them in the UK.


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## AndyH (Jun 15, 2008)

CroDriver said:


> IMO, this isn't a BMS for a full size EV. Their BMS is a analog device with no logic nor "brains".


I would disagree, CroDriver. Thie Goodrum/Fechter BMS is being used in DIY cars now and is good up to 40S. The new V4 BMS is being designed for up to 400V packs.

The BMS is designed to do the two things that need to be done to protect a pack -- protect any single cell from over discharge and manage charging (via a combination of both shunts and charger throttling) so that cells are not over charged. I've been using versions of this BMS on my 60Ah 21S pack for more than year and have built and sold up to 31S versions for cars.

Here's a video for a 40S version:
http://www.youtube.com/watch?v=-yMgWl2xF2Y




 
'Simple analog' is a perfect match for a noisy environment. There's no data corruption, no false positives or negatives from the LVC detection, and the charger throttling means that folks can string together a couple $40 power supplies instead of spending $$$$s on an overpriced 'EV' charger. In this device, "BMS" means Battery Management System - not Battery Monitoring System. There are other devices available from commercial manufacturers that provide digital data, count cycles, store cell alert events - and are inexpensive. Unfortunately they work better on the bench than on the road.

Andy


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## arddea (Jan 23, 2010)

Gavin said:


> I am sure you are correct about that. I bet they still kill them.


No bet, Copart just had two up for auction in CA with blown ESS and they still expected someone to pay 50K (according to an inspector I talked with). I won the first auction at 15,500 but AAA didn't approve the sale, then re-listed the car twice sense then and the highest bid has gone down each time re-listing.


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## Guest (Mar 27, 2010)

> charger throttling


So explain Charger Throttling? Explain so we all can understand, not just the EE's here. 

Pete


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## AndyH (Jun 15, 2008)

gottdi said:


> So explain Charger Throttling? Explain so we all can understand, not just the EE's here.
> 
> Pete


Throttle in the automotive sense? LiFePO4 needs the constant voltage phase of charging to saturate and fully charge the cells.

A management solution that simply shuts the charger off when the first cell hits a set voltage point means that the high cell isn't fully charged and all the rest are lower still.

If a management solution has simple shunts, the shunts can easily be overridden. A 2.1A charger can override a 2.0A shunt and overcharge cells.

The Fechter/Goodrum BMS directly controls the charge current so that it's reduced to a point the shunts can handle. The charger is allowed to run all-out until the first cell reaches the high voltage point and that shunt activates. Then charger current is reduced to a point the shunts can handle until charging is complete (and is allowed to increase if shunts are released).

Cell voltage is kept at or below the limit, all cells are allowed to complete both the constant current and the constant voltage phase, and charging finishes with a full pack every time.

Andy


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## CroDriver (Jan 8, 2009)

arddea said:


> No bet, Copart just had two up for auction in CA with blown ESS and they still expected someone to pay 50K (according to an inspector I talked with). I won the first auction at 15,500 but AAA didn't approve the sale, then re-listed the car twice sense then and the highest bid has gone down each time re-listing.


Shouldn't TM replace the batteries in warranty since the cars are newer than two years?


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## dimitri (May 16, 2008)

AndyH said:


> A management solution that simply shuts the charger off when the first cell hits a set voltage point means that the high cell isn't fully charged and all the rest are lower still.


With all due respect Andy, this statement is too simplistic and seems like a cheap shot towards competition 

In reality, most EVs have CC/CV chargers and when charger is properly configured for the pack size it will peform full charge with both CC and CV phases. In this case BMS acts as insurance policy in case a weak cell or otherwise "non-uniform" cell gets HVC too soon. In this scenario charger throttling would not do any good anyway since that cell would always be the limiting factor no matter how gentle you are at pushing the current.

Charger throttling has a lot of merit when using dumb cheap chargers, I give you that. But majority of modern chargers sold in EV market don't need throttling, and in fact many of them will produce errors if they sense PWM control on the output ( which of course can be addressed if need be ).


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## Elithion (Oct 6, 2009)

AndyH said:


> There are other devices available from commercial manufacturers that provide digital data, count cycles, store cell alert events - and are inexpensive.
> 
> Unfortunately they work better on the bench than on the road.


Hummm, Andy. Aren't we generalizing a wee bit here? 

There are 100s of 1000s of digital, MiHH BMSs on the road today, one in each HEV, and they have none of the problems you describe. I grant you that a few of the new commercially available LiIon BMs struggle with that issue, but most of them do not suffer from noise issues (http://liionbms.com/php/bms_options.php#Digit._balancers).
________
Honda sh125


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## GGoodrum (Dec 11, 2009)

gottdi said:


> So explain Charger Throttling? Explain so we all can understand, not just the EE's here.
> 
> Pete


I decided it was time I came over for a visit, to this side of the playground. 

The "throttling" we use in our charge controller card is simply a PWM-controlled current limiter that keeps any cell from going over the HVC voltage set point. Instead of setting a much higher HVC set point, and then shutting the charger off completely, when a cell first hits the HVC set point, we instead use the HVC signal to keep that cell right at an "optimum" HVC point and let the current taper off so that at least this cell will get full. It is like having individual cell CV modes. Actually, that's all a CV mode on a "real" charger does, it uses a PWM-controlled circuit to limit the current so that the voltage doesn't go over a set limit. 

Another new feature we've just added, is an adjustable current limiter that can take the place of a "constant current" (CC) mode on a "real" charger. This allows any number of inexpensive power supplies to be used, instead of an expensive, dedicated CC/CV chargers. Many of us have been using Meanwell power supplies, available from a number of ebay sellers, but the problem with these is that many don't really have a real CC limiter for overload protection. Some do have a limit circuit, but they are typically set at around 130% of the rated current limit. The reason is that these types of supplies are typically used in applications like audio amplifiers, that may have higher instantaneous peaks but the average power used is under the rated limit. For use as a battery charger, the current really is constant, so the limit needs to be set to 100%, so that the current rating isn't exceeded. Some have come up with hacks, to try and adjust the limit down, but it turns out there are many different versions of the PCBs inside these, so there was no universal fix, that would work with all of them. On some models, there's no CC limit at all, instead just a crude "hiccup" mode on the AC side, for overload protection. Anyway, putting the CC mode logic on our charge controller card was pretty easy, because we already had the PWM-controlled FET logic that is used for the "individual cell" CV mode/throttling feature. 

The rest of the functionality of the charge controller card is there mainly to support auto turn-on and auto turn-off features, so that the card can be permanently connected to the pack without drawing any current. The auto turn-on works by using the sudden difference in voltage between the charger and pack voltages to charge a cap that then fires an SCR to turn on the +12V regulator that powers the rest of the card. The auto turn-off function shuts off the +12V two ways. One is when the charge current drops down below about 300mA. This will keep the charge controller logic from continuing to run after the charger/supply is disconnected. The other way for auto shut-off to occur is at the end of programmed time delay. This timer is used to let the shunts, if present, have time to balance the cells. It can be set from off to about 4 hours, but a single resistor change can double, or quadruple that time limit, if need be.

Now I'm not going to get into big philosophical discussion on the merits of balancing, as I don't want to encourage Jack to come back over to our side of the park, take a big dump in our sandbox and then leave again eek:). I will say, however, that periodic balancing does make sure that first cell hitting the HVC point truly is the low capacity cell and not one that may in fact be the highest capacity one in the pack, but for whatever reason, just happens to be at a lower state-of-charge. Some sort of balancing, whether at the top, in the middle, or wherever, will ensure that you are getting the most amount of usable capacity.

Our shunt circuits work basically the same way as with other designs, including Dimitri's, but we have found we need to include some filtering to keep cell-to-cell interactions in check, as the shunt current gets up to, and over 1A. We also use a shared opto connection for the LVC and HVC signals, but we use the HVC signal a bit differently. We have the logic set to trip the HVC signal right at the point the shunt is fully operating, but not overloaded, or swamped. It is quite easy for this swamping to occur, at higher shunt currents, if it is not kept in check.

Oh, there is one more section of the control board I didn't mention, which is there to separate and isolate the LVC signal from any interaction with the charge control logic. The isolated LVC output is basically disabled during charging. If nothing else, this keeps an audible LVC alarm from going off, once the HVC signal starts interacting with the throttling logic.

The net result of all this is that with the shunt circuits, the first cell that hits the HVC point will control the current, which will taper off allowing this cell to become full, but instead of tapering off all the way down under 300mA, the shunts will keep the current at 1A, so that the rest of the cells can also get full. The timer is then used to control how long they have to get balanced.

We actually have additional versions of the BMS design, where the functions are broken out into separate pieces. Many of us are now using RC-type LiPo cells as the building blocks in our EV packs. These are available in pre-made 5, 6 or now 8-cell "sub-packs" with either 5.0 or 5.8Ah capacities. These packs have balance taps brought out into separate JST-type connectors. Anyway, these LiPo-based packs have extremely high C ratings, are well-matched in capacity, IR and thermal characteristics, and as a result they stay amazingly well-balanced. Eventually, like all cells, they will drift apart a bit, but not anywhere near as much as I've seen with most LiFePO4-based setups, including a123s. In any case, they don't need to be balanced with every charge. I have seen them get out-of-balance, however, if the pack is discharged down to the point the individual cell LVC circuits are tripping. I think this is because that although the LVC circuits will keep the cell from "jumping off the cliff", so to speak, at the end of capacity, just getting near the ledge will cause it to get farther out-of-balance, in relation to the rest. 

Anyway, what I've done is split the shunts off from the LVC/HVC logic, into separate units which can then be used as external "balancers", for occasional balancing. This works well with many LiPo setups, which tend to want to be as small and light as possible. The LVC/HVC boards are "buried" with the packs, with a cable coming out that the balancers plug into. The full BMS design can also work in a way that has the shunts essentially disabled, if balancing is not required. 

Hope this helps to clarify what we are doing. 

-- Gary


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## karlos (Jun 30, 2008)

GGoodrum said:


> I decided it was time I came over for a visit, to this side of the playground.
> 
> The "throttling" we use in our charge controller card is simply a PWM-controlled current limiter that keeps any cell from going over the HVC voltage set point. Instead of setting a much higher HVC set point, and then shutting the charger off completely, when a cell first hits the HVC set point, we instead use the HVC signal to keep that cell right at an "optimum" HVC point and let the current taper off so that at least this cell will get full. It is like having individual cell CV modes. Actually, that's all a CV mode on a "real" charger does, it uses a PWM-controlled circuit to limit the current so that the voltage doesn't go over a set limit.
> 
> ...


Sorry Gary. I did not get which BMS system you represent?


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## GGoodrum (Dec 11, 2009)

karlos said:


> Sorry Gary. I did not get which BMS system you represent?



The one I've been working on with Richard Fechter, on Endless-Sphere. 

-- Gary


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## CroDriver (Jan 8, 2009)

I posted a thread about dying Tesla Roadster batteries based on this post:



arddea said:


> No bet, Copart just had two up for auction in CA with blown ESS and they still expected someone to pay 50K (according to an inspector I talked with). I won the first auction at 15,500 but AAA didn't approve the sale, then re-listed the car twice sense then and the highest bid has gone down each time re-listing.


Here is what one of the guys at the Tesla forum said: 



vfx said:


> Both those salvage Roadsters were front end collision write offs. Now imagine the car being towed to an auto body shop. Or a scrap yard. *No one is going to charge it*. So now you have what was probably perfectly good battery going dead from neglect.
> 
> One of the cars was Dr Taras'. After the accident he drove it onto the flatbed so it worked fine. Then it was almost 6 months before the car came up for sale. Can you say, "doonail"?
> 
> CroDriver, can you kill this roomer?


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## arddea (Jan 23, 2010)

CroDriver said:


> Shouldn't TM replace the batteries in warranty since the cars are newer than two years?



In the manual there is an disclaimer that if the ESS is destroyed due to physical damage (accident) or neglect (leaving it unplugged for 6+ months or not keeping the coolant to the right level) the warranty does not apply. With the 2 AAA cars both exclusions apply.


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## arddea (Jan 23, 2010)

VFX said:


> Both those salvage Roadsters were front end collision write offs. Now imagine the car being towed to an auto body shop. Or a scrap yard. *No one is going to charge it*. So now you have what was probably perfectly good battery going dead from neglect.


Bingo. What happens when you over discharge a LiCo cell? The damage to the ESS is not from the accident but from the criminal neglect of the AAA. The manual states the car should not be stored for more then 4 week unplugged otherwise damage to the _ESS will occur_. Also when storing it that the you need to set the storage option on the touch screen. 



VFX said:


> One of the cars was Dr Taras'. After the accident he drove it onto the flatbed so it worked fine. Then it was almost 6 months before the car came up for sale. Can you say, "doonail"?
> 
> CroDriver, can you kill this roomer


What is a doonail? 

Cro As a DIY EVer you should understand the difference in technology of the cells used in the Tesla vs Cells used by other manufactures. LiCo has some very special properties, some of them good others suicidally bad.

Now with the orange / yellow one it may just be dead. On the black one I had an inspector take a look at it and plug her in. The ESS failed all diagnostics, but the parts I was interested in passed (motor/controller) . As such I would not consider it a rumor. I had made the bid just for the drive train and the fact bidding has not exceed mine in the last 2 re-listings imply others feel the same way. 

Also regarding your warranty question, in the US if a item gets a salvage title most, if not all automakers will consider the warranty null and void. This is independent of what triggered the Salvage title. I have a coworker who bought a Lexus that was a theft recovery (no damage) from an insurance auction. A year later at 2 years old with 27K miles they refused to do recall work (for free) on the car as it was salvage. I also heard GM, Chrysler, Ford, and Toyota has similar polices regarding salvaged vehicles, as such I would assume Tesla Motors would follow their lead, (I could be wrong).


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## AndyH (Jun 15, 2008)

I can assure you, Dimitri, that I"m not into cheap shots. If I had something that I wanted to say about any specific system it wouldn't be veiled. I have absolutely no poker face. 

There are a lot of different situations - many types of chargers, many types of cells, and many management goals beyond the walls of this group.

I looked at your BMS development thread and your instructions and like what you've done. The only difference of opinion is one we've already talked about.

One of the legacy vehicles on the street has a CC charger designed for NiMH. It needs a bit of help on the CV side of things when one converts it to LiFePO4. Just one example.

Best,
Andy



dimitri said:


> With all due respect Andy, this statement is too simplistic and seems like a cheap shot towards competition
> 
> In reality, most EVs have CC/CV chargers and when charger is properly configured for the pack size it will peform full charge with both CC and CV phases. In this case BMS acts as insurance policy in case a weak cell or otherwise "non-uniform" cell gets HVC too soon. In this scenario charger throttling would not do any good anyway since that cell would always be the limiting factor no matter how gentle you are at pushing the current.
> 
> Charger throttling has a lot of merit when using dumb cheap chargers, I give you that. But majority of modern chargers sold in EV market don't need throttling, and in fact many of them will produce errors if they sense PWM control on the output ( which of course can be addressed if need be ).


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## AndyH (Jun 15, 2008)

You're absolutely right - there are many NiMH management systems on the road today in hybrid vehicles. Not many specific types, necessarily, but they certainly have numbers.

I'm not interested in working with NiMH or with hybrids, and have no desire to try to adapt a management system from that 'world' to a LiFePO4 EV.

For the record, none of my comments were directed towards your systems as I have no first-hand experience with them.

I do have a couple of digital commercial systems in my 'junk box' that work beautifully on the bench and in stationary equipment (UPS, genset starter packs, etc.) but absolutely cannot handle the EMI/RFI from a road vehicle. ( I also use a PakTrakr. Dimitri will giggle about that as well, I'm sure. ) Then there's the Thunder Sky monitoring system...

Best,
Andy




Elithion said:


> Hummm, Andy. Aren't we generalizing a wee bit here?
> 
> There are 100s of 1000s of digital, MiHH BMSs on the road today, one in each HEV, and they have none of the problems you describe. I grant you that a few of the new commercially available LiIon BMs struggle with that issue, but most of them do not suffer from noise issues (http://liionbms.com/php/bms_options.php#Digit._balancers).


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## arddea (Jan 23, 2010)

AndyH said:


> I do have a couple of digital commercial systems in my 'junk box' ~ Then there's the Thunder Sky monitoring system...
> 
> Andy


Andy the TS is in your Junk Box? What was wong with it? From the documentaion it looked to be designed to actively balance the pack as well as monitor, and seemed to be very cool. 

Curious


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## AndyH (Jun 15, 2008)

arddea said:


> Andy the TS is in your Junk Box? What was wong with it? From the documentaion it looked to be designed to actively balance the pack as well as monitor, and seemed to be very cool.
> 
> Curious


The docs I've read from Thundersky and from the BMS manufacturer suggest it's a monitoring system that can also kill a charger on a high-cell event. Brian Blocher posted the only 'real-world' info I've read:
http://s2kev.blogspot.com/2009/05/elite-power-solutions-not-so-elite.html

Andy


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## AndyH (Jun 15, 2008)

dimitri said:


> With all due respect Andy, this statement is too simplistic and seems like a cheap shot towards competition
> 
> In reality, most EVs have CC/CV chargers and when charger is properly configured for the pack size it will peform full charge with both CC and CV phases. In this case BMS acts as insurance policy in case a weak cell or otherwise "non-uniform" cell gets HVC too soon. In this scenario charger throttling would not do any good anyway since that cell would always be the limiting factor no matter how gentle you are at pushing the current.
> 
> Charger throttling has a lot of merit when using dumb cheap chargers, I give you that. But majority of modern chargers sold in EV market don't need throttling, and in fact many of them will produce errors if they sense PWM control on the output ( which of course can be addressed if need be ).


Sorry, no.

Your point about protecting the weakest cell is valid, but there's a LOT more going on in a pack than just a difference in cell capacity.

A single cell on a single-cell charger or power supply will behave as you've outlined. A series string of cells and a bank-charger does not behave as a single cell. As much as it might be easier to imagine that all the cells are in lock-step as they evenly reach the CC/CV transition point, saturate, and the charger shuts down, that isn't what I find when I actually log pack behavior.

Here's an example. Take a series string of cells. Attach a shunt set to 3.7v. Connect a bank-charger set to 3.6V per cell. What should happen?

Does anyone think that the pack will completely charge, the charger will move thru CC then CV and shut down and no shunts will activate? Does anyone think that all the cells will be fairly similar in state of charge?

Here's real-world info. This is from my motorcycle after a 20 mile ride - less than 1/2 of total range. The pack was completely balanced before the ride by using a 5A bench power supply and a BMS. After balancing, I swapped a shunt and LVC BMS, rode 20 miles, connected the data logger and charger and let it work.

The first image - First_105min - shows the entire CC phase of charging for a 21S pack of TS cells. The top of the graph is 3.7V. All cells are below that point and all of the .64A shunts are off.

Now we move to the CV phase in TSL_lite. Please note a few things. At the arrow - where the high cell hit 4.05V - it and another 10 cells are above the shunt. That voltage climb is the result of 1.2A of charge input minus .64A of shunt = .56A of net current. Please also note that seven cells are still below 3.5V with current flowing into them - and quickly drop back into the 3.3V range when the charger shuts down. Clearly these cells are not yet charged.

Some might say the fix is easy - the shunts must be too small! Ok - should we have 15A shunts for a 15A charger? That's the only way to ensure a shunt-only solution won't be over-run during charge.

Maybe the answer is to cut power when the first cell reaches 3.7V. It is better than leaving the charger on. But it still leaves (in my real-world example) 1/3 of the pack under charged. Maybe that' s ok, maybe not. In my case it cuts top speed by more than 10 mph and cuts my range.

A LiFePO4 cell only needs a current-limited power supply. A bench power supply does the CC/CV work on it's own. In other words, all the pack needs is a dumb charger. Why in the world do we need to add more complexity and expense to get around the limitations of a too-smart charger?

My Thunder Sky charger was designed for use without a BMS. It's designed to undercharge the pack. It must have a clear connection to the pack so it can pause and sense pack voltage during charge. And with all these smarts, it can not protect the pack from overcharge, cannot ensure the low cells are charged, cannot be brought in-line with shunts, and cannot work thru a BMS throttle. That's why I've dumped it into the spares bin and bought a proper charger that doesn't make my life harder.

Andy


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## dimitri (May 16, 2008)

Andy,

do you have a similar analysis of the same pack during discharge at your typical discharge patterns ( assuming you get up to 2C at acceleration or perhaps even more )?

The reason I ask is that it seems to me you have some issues with your cells. I have never seen such large imbalance on my pack or any other properly sized and healthy packs I have seen. My own pack is somewhat beat up by now and still I don't have such large difference between high and low cells. I can only conclude from this picture is that you need to fix your pack and complex BMS is only helping to prolong their shortening life.

In my own experience and multiple MiniBMS customer's feedback on a healthy and properly sized pack, cells don't get that far off and BMS acts as long term insurance policy, while CC/CV charger is doing its job quite well without any interference. Even small (less than 1 Amp) amount of shunting seems enough to keep the cells from drifting apart long term.

Its interesting that our experiences don't match, I really can't explain it.


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## MN Driver (Sep 29, 2009)

AndyH said:


> A LiFePO4 cell only needs a current-limited power supply. A bench power supply does the CC/CV work on it's own. In other words, all the pack needs is a dumb charger. Why in the world do we need to add more complexity and expense to get around the limitations of a too-smart charger?


Most power supplies are just CV and will either overheat, hiccup off(like the Meanwell RS-25-48's would without a CC supply in series like the setup that I have for a different battery chemistry), or blow their fuse as they aren't current-limited supplies. I need to use a different supply but what most people are using for their dumb charger is just a current-limited power supply by definition anyway. Even the Manzanita is just a current-limited supply with a few extra features added, right? It's not isolated and blows up if you lose a fuse or a connection isn't there.


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## AndyH (Jun 15, 2008)

MN Driver said:


> Most power supplies are just CV and will either overheat, hiccup off(like the Meanwell RS-25-48's would without a CC supply in series like the setup that I have for a different battery chemistry), or blow their fuse as they aren't current-limited supplies. I need to use a different supply but what most people are using for their dumb charger is just a current-limited power supply by definition anyway. Even the Manzanita is just a current-limited supply with a few extra features added, right? It's not isolated and blows up if you lose a fuse or a connection isn't there.


No disagreement here. I did say current-limited, though.  I have a couple of HP and Mastech bench supplies and they do a perfect CC/CV charge. Some of the Meanwell supplies are limited and some aren't as you already know. Just because one particular charger doesn't handle rejection well doesn't mean it shouldn't, or that others don't. 

Andy


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## AndyH (Jun 15, 2008)

dimitri said:


> Andy,
> 
> do you have a similar analysis of the same pack during discharge at your typical discharge patterns ( assuming you get up to 2C at acceleration or perhaps even more )?
> 
> ...


The focus is on what a pack actually does, not what people hope it does. I have about 13 months of logged data from charge and discharge. My max draw from the pack is 1.5C and I have only discharged down thru the shoulder a few times - most of the discharges only go to 50-60% SoC.

For valid customer feedback I would expect you'd need folks that are logging data. Most people talking about their packs say things like "I measured all the voltages after returning from a drive and all the cells were at 3.33 so everything's balanced". In other words, better or worse, they really don't understand what's going on. And just as with computer programming or data analysis - garbage in, garbage out.

This pack has certainly changed over the past 14 months. Deeper sag when cold, lower top speed, more time to balance. But hey - we don't buy these cells because they're the best - we buy them because they're relatively inexpensive, right? 



dimitri said:


> Even small (less than 1 Amp) amount of shunting seems enough to keep the cells from drifting apart long term.


I can see that if one looked at voltages after a charge. I see the same once all the shunts have done their work and everything's shut off. But what's happening when the shunts are on? How many cells have over-run the shunts?

The attached image immediatly follows the previous two. The Thunder Sky charger finished and left the pack in a bit of a mess. I connected a bench supply to the pack and let it finish the pack with a proper CC mode. You're looking at a two-hour period of time. The pink line is input charge current. Most of the balancing took place with a 400mA input. As expected, the initial 3A input pushed the full cells over the shunts. (I ran this to collect the data - I normally turn the current down to slightly less than the shunts. When I do that there's no over-run.)

If someone measures cell voltages during the CV stage, they're likely to get a different view of the pack than if they check voltages 15 minutes after everything shuts down.

Andy


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## tomofreno (Mar 3, 2009)

> If someone measures cell voltages during the CV stage, they're likely to get a different view of the pack than if they check voltages 15 minutes after everything shuts down.


 No, they all track fairly well during charging. I've checked with a cell log 8 and by just repeatedly measuring all cells with a dvm. I have one lower capacity cell which hits HVC a bit before the others. The rest are typically within less than 0.008V of each other while charging at 30ADC.


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## AndyH (Jun 15, 2008)

tomofreno said:


> No, they all track fairly well during charging. I've checked with a cell log 8 and by just repeatedly measuring all cells with a dvm. I have one lower capacity cell which hits HVC a bit before the others. The rest are typically within less than 0.008V of each other while charging at 30ADC.


What cells, what BMS, what shunt set point, what charge voltage, what pack age?

My cells track well while charging as well - right up to the point where the first ones 'turn the corner' and leave the rest. I've also seen it with lead-acid and NiMH so I think it's more about bank charging than chemistry.

And yet Gary made it clear that his LiPo packs don't need balancing at all unless they're discharged more deeply so maybe my understanding of 'why' is missing something. 

Two things I do know - this pack behaves differently now compared with 14 months ago when new, and the data I posted shows how the pack behaves now.

Andy


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## tomofreno (Mar 3, 2009)

> What cells, what BMS, what shunt set point, what charge voltage, what pack age?


 36 180Ah Sky Energy, minibms, no shunts. Charge voltage limit is set at about 120V, but the Manzanita continues to climb in voltage a few volts above the limit as it slowly throttles back current - semi CV/CC. It is set so the charger shuts off when the lowest capacity cell hits about 3.5V. Most of the time anyway, sometimes goes over and the minibms shuts it off when this cell hits 3.6V. Pack age is about 5 months, about 38 charge/discharge cycles.


> ...this pack behaves differently now than 14 months ago when new


 It wouldn't surprise me if performance degrades with age. I expect this is a strong function of what discharge rates the cells regularly see though. Mine see about 1 to 1.5 C most of the time when accelerating, about 0.8C cruising on the highway at 60 mph, and about 0.4 C +/- 40% for most cruising. I don't discharge the lowest cap cell more than 65% DoD.

When the lowest capacity cell gets above about 3.45V it starts climbing in voltage significantly faster than the other cells. Thats where the exponential rise in voltage with charge time starts for my cells. So yeah I agree if you have several cells above this threshold, and others not, you will see a wider spread in cell voltages. My cells are bottom balanced. I just charge until the lowest capacity one gets to about 3.5V and stop. That is about all the charge I can discharge from the pack, so no reason I can see to charge the others more. On my pack there is only about 3 Ah additional charge storage if I charge the lowest capacity cell to 3.6V versus 3.45V. Less than 2 miles range for my car.


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## tomofreno (Mar 3, 2009)

People are regularly stating prismatic cell specs such as continuous discharge at 3C. But no one seems to question what that means. There is nothing in the spec that says anything about the affect of this discharge rate on cell cycle life, or performance over time. What does that 3C spec mean? That you can do it 100 times, 1000? Who knows? And what effect does it have on performance of the cells, and cell matching over time? The life cycles stated in the spec are at much lower discharge rate. I have no data, but I expect prismatic cell performance will degrade much more, and cycle life will be much more limited if they are regularly discharged above 2C. I've written quite a few specs, and what is not said in a spec is just as important as what is said.


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## raymond.nl (Mar 17, 2010)

tomofreno said:


> What does that 3C spec mean? That you can do it 100 times, 1000? Who knows?


Based on the chemical reactions within a cell knowledgeable people may be able to tell what the impact of short (10s) bursts of 3C might be. Would there be any logic in 3C bursts being less harmful than prolonged 3C use? Are 1000 10-sec bursts just as harmful as 1000 seconds of continuous 3C use?


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## AndyH (Jun 15, 2008)

Dimitri and Tomofreno,

I appreciate your experience and observations very much. I hope my info has been or will be useful to you at some point. I'll certainly add your observations to my 'knowledge base' and see how it all shakes out.

I found a reference that I think has at least part of the answer. The following is from "Electric Vehicle Technology Explained". It's available from a number of on-line vendors, and Google will likely lead to a number of on-line sources of the PDF version. It has a 2003 publication date. If either of you can recommend a more robust reference, I'm all ears. 

Here's a simplistic view of two cells. From the book:

"An important point that applies to all battery types relates to the process of charge equalisation that must be done in all batteries at regular intervals if serious damage is not to result.

A problem with all batteries is that when current is drawn not all the individual cells in the battery lose the same amount of charge. Since a battery is a collection of cells connected in series, this may at first seem wrong; after all, exactly the same current flows thru them all. However, it does not occur because of different currents (the electric current is indeed the same) it occurs because the self-discharge effects we have noted...take place at different rates in different cells. This is because of manufacturing variations, and also because of changes in temperature; the cells in a battery will not all be at exactly the same temperature.

The result is that if nominally 50% of the charge is taken from a battery, then some cells will have lost only a little more than this, say 52%, while some may have lost considerably more, say 60%. If the battery is recharged with enough for the good cell, then the cells more prone to self-discharge will not be fully re-charged. The effect of doing this repetedly is shown in [SOC_1.jpg].

Cell A cycles between about 20% and 80% charged, which is perfectly satisfactory. However, Cell B sinks lower and lower, and eventually fails after a fairly small number of cycles. If one cell in a battery goes completely flat like this, the battery voltage will fall sharply, because the cell is just a resistance lowering the voltage. If current is still drawn from the battery, that cell is almost certain to be severely damaged, as the effect of driving current thru it when flat is to try and charge it the 'wrong way'. Because a battery is a series circuit, one damaged cell ruins the whole battery. _This effect is probably the major cause of premature battery failure_.

The way to prevent this is to fully charge the battery till each and every cell is fully charged (a process known as charge equalisation) at regular intervals. This will inevitably meant that some of the cells will run for perhaps several hours being overcharged. Once the majority of the cells have been charged up, current must continue to be put into the battery so that those cells that are more prone to self-discharge get fully charged up."

The authors go on to say:

"This issue of some cells slowly becoming more deeply discharged than others is very important in battery care. There are two particular cases where it is especially important.

Opportunistic charging: some users are able to put a small amount of charge back into a battery, for example when parked in a location by a charger for a short time. This is helpful, but the user MUST make certain that fairly frequently a full long charge is given to the battery to bring all cells up to 100% charged.

Hybrid electric vehicles: in these it is desirable to have the battery NOT fully charged normally, so that the battery can always absorb energy from regenerative braking. However, this must be done with caution, and the battery management system must periodically run the battery to fully charged to equalise all the cells to 100% charged."

We know that we don't want to over-charge lithium to balance it, so some type of shunt or charge transfer and charge limiting is necessary to provide a similar balancing effect.

This info helps me understand two things. First, we know our cells are not identical from the factory and are not in climate-controlled bubbles, so I think we must expect that variation and imbalance will be the rule rather than the exception. It's not a case of 'if' but of 'when'. We can also see that multiple less-than-complete charge cycles will make the charge imbalance worse.

The authors do state that lithium can be balanced at any state of charge, but that it requires more sophisticated BMS devices to do this (think 24/7 inductive or capacitive charge transfer).

Please note that the info published is for cells only - it doesn't include any additional loads - such as those from a BMS or pack monitoring equipment. These loads add to the imbalance! It also doesn't factor in cell aging or negative effects of high-charge or discharge rates.

My data posted earlier shows that it takes nearly two hours to top balance my pack. My data also shows that terminating charge when the first cell is full results in leaving the pack in it's out of balance state.

The info and charts from the book shows what happens with a pack of only two cells after a couple of cycles if the cells are not properly balanced. It also shows the problem with simply returning to the garage with 30% of the energy still in the pack.

Based on this, I would strongly recommend that any BMS system (whether manual or automated) include periodic full top charging and balancing.

I would also strongly recommend that anyone that chooses 'bottom balancing' as a viable option better budget for a BMS that does charge transfer and has cell-level low voltage protection.

Please - if you can shoot holes in my current understanding, please do! I'm still learning, I don't play a 'battery expert' on TV, and didn't sleep in a Holiday Inn Express last night. 

Andy


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## tomofreno (Mar 3, 2009)

> An important point that applies to all battery types relates to the process of charge equalisation that must be done in all batteries at regular intervals if serious damage is not to result.


 I go by data Andy. It could be a year from now my cells start drifting apart and require frequent balancing. Up to now this has not been the case. Nor has it been the case for Jack's cells for over one year. To quote Richard Feynman: "It doesn't matter how famous the guesser is, or how beautiful the theory is. If the theory doesn't fit the data, its wrong." That sums up my general attitude (not just on balancing cells) very well. 


> it occurs because the self-discharge effects we have noted


 The self-discharge rate of LiFePO4 cells is very small, resulting in negligible charge loss from cells that are charged every day or every few days.



> The authors do state that lithium can be balanced at any state of charge, but that it requires more sophisticated BMS devices to do this


 I have the most sophisticated bms there is - a human being.


> My data posted earlier shows that it takes nearly two hours to top balance my pack.


 My pack is balanced more toward the bottom. The cells have varying capacities so if charged for a given length of time they will not all charge to the same SOC. When the lowest capacity one hits the high voltage the charger stops. The rest are not fully charged I agree, but I don't see why this matters. I can only discharge the pack until the lowest capacity cell is at 20% SOC (actually I only go to 35 - 40 % typically) so I couldn't use the extra charge I put in the others by continuing to charge them past that point. Once some cells get to the point of exponential voltage rise with charge time, cell voltage range under charge will obviously increase due to differences in internal resistance at that point. But I don't think that has much bearing on how well balanced the cells are in SOC, since there is only about 3Ah or so (1.6%) difference between charging one of my cells to 3.45 versus 3.6V. I do not see any accumulating effects leading to cell voltages drifting apart over time. They always have about the same voltage difference from the lowest capacity cell both during charge and at rest (the difference is different in the two cases of course). So I don't see a problem. Maybe I will at some point, but not yet. No animosity at all. I just don't see a problem, and I go by data.


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## AndyH (Jun 15, 2008)

I appreciate that you go by data! As far as I can tell you're one of the few. 

I probably don't have to remind you that we cannot judge state of charge from voltage, so unless we're talking about what happens from one 'shoulder' to full, or the other shoulder and empty, there's not a lot of meaning to voltage.

Yes - self discharge rate is very small. But along with 'self discharge' the authors include affects of temperature on internal resistance, capacity variations, internal shorts, and other production variations.

In the same way that the charger and the controller's minimum voltage cut works at pack level, any current sensor/Wh meter works at the pack level as well. I'm interested in cell level. The real critical point from the charts is that pack SOC and cell SOC are not necessarily the same. That suggests to me that anyone that thinks they are protecting their pack by bottom balancing once and returning to the barn after using 70% of pack energy might not have all the bases covered.

What I wanted to bring to the discussion is a big-picture view of what one might look for when crafting their overall management solution. While I have spent a bit over 2 years bench testing cells and the past 13 months logging data from my road pack, and all the single-cell charging, BMS building, rewiring, etc. etc. that goes along with it, today I want a toaster.  I want to be able to plug in and walk away knowing for sure that the pack is charged when I get back and that all cells have stayed below 3.7V in all stages of the charge process. On the road I want to be certain that no cell will drop below the low voltage point in any situation.

In order to understand how the cell and pack will respond, I spent time with engineers at a LiFePO4 cell company, had conversations with engineers at a commercial BMS producer, talked with engineers that have many years experience with LiFePO4 cells and packs, and had multiple 'retraining sessions' with my friend the PhD EE (who sometimes has to use a 2x4 to get things thru my skull). I promise that I'm not trying to use an excerpt from a single book to 'wag the dog'. 



tomofreno said:


> I have the most sophisticated bms there is - a human being.


 Not good enough, I'm afraid, and I've got the trashed cells to prove that they didn't heed my false assumptions. I hope you do better than I. 

You say your cells are balanced toward the bottom. How do you know?

When I take the time to completely top-balance my pack I know the cells are full. The rest of the time I have no idea - until I start bouncing cells of the LVC. And most of the time this is fine - I seldom do max-range drives. But it doesn't take much time for those PakTrakr remotes to disrupt pack balance, and not all of my BMS ideas worked well enough to pull things back together.

Maybe none of this applies to you - you may know more than I about pack behavior - and for that reason I look forward to what you'll be able to teach me!

Andy

[edit] uh-oh. I see from the strapping thread that you've already replaced cells from both overcharge and over discharge. [/edit]


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## AndyH (Jun 15, 2008)

Just a giggle's worth of data. 

I just removed the four Duracell AA primary cells from my Nordic Track monitor. They've been in there a bit over 2 years and there was just enough energy to make a beep and light a few LCD segments but no more. I have a battery tester that puts a load on the cells then spits out voltage. In order:
1: 1.05V
2: 1.02V
3: 0.11V
4: 1.02V

I have an old Sangean AM/FM/General coverage receiver that I fill with six NiMH D-size cells. They are charged singly and come off the charger between 1.46 and 1.49V. Here's end of use for the last three discharge cycles:

1: 0.81V
2: 0.13V
3: 0.98V
4: 1.08V
5: 1.03V
6: 0.02V

1: 0.75V
2: 0.04V
3: 0.98V
4: 1.02V
5: 0.96V
6: 0.02V

1: 0.63V
2: 0.58V
3: 0.94V
4: 0.99V
5: 0.90V
6: 0.05V

Yeah - I *do* figure that anyone that thinks any type of series battery discharges (and charges!) evenly has their head in...the sand.  

Andy


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## tomofreno (Mar 3, 2009)

> You say your cells are balanced toward the bottom. How do you know?


We aren't making much progress here are we? I based that statement on measurement of cell rest voltages at around 35% SOC. What in your judgement defines a "balanced" pack? Do you compare cell voltages at rest, under charge (if so, at what current), or under discharge (at what current)? What, in your mind does "balanced" mean? That all cell rest voltages are equal at some SOC, or that all cell voltages are equal during some current flow, either charge or discharge? The latter two include the effect of differences in internal resistance (ir). In that case two cells could concievably have the same voltage, with one having lower ir and higher SOC than the other. When you top balance, you ensure all cells are charged to the same voltage under similar current magnitude. If that magnitude is the same as the manufacturer's spec, and they are charged to the voltage in the spec, then they are considered fully charged, 100% SOC. In this case, they will have different rest voltages at low states of charge, such as below around 30% SOC, assuming they do not have identical capacities. At SOC in between they will not differ much in rest voltage even if though they are at somewhat different states of charge (assuming they do not all have identical capacity), due to the very small slope of the voltage versus Ah curve. So if you observed the differences in cell voltages in this pack at say 25% SOC, and did not know it had been top balanced, would you say it is unbalanced? Similarly, if the cell rest voltages are all the same at some low SOC, such as 30%, and they are then charged until the lowest capacity cell is at 100% SOC as defined by the charging current and voltage of the manufacturers spec, they will be at different SOC and have different rest voltages (though hardly different at all due to the very small slope of the curve there). If you observe this difference in voltages would you say the pack is unbalanced? Or would you observe cell voltages during charging, and declare the pack unbalanced because the low capacity cell is at significantly higher voltage than the others due to its being on the exponentially rising part of the curve? I'm trying to understand how you define balanced and unbalanced. If someone runs a pack from 40% SOC to 90% SOC of the lowest capacity cell, and the other cells remain at SOC in between these, would you say this is damaging the pack and will decrease its lifetime? If so, what is the physical cause?


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## aeroscott (Jan 5, 2008)

AndyH said:


> Dimitri and Tomofreno,
> 
> I appreciate your experience and observations very much. I hope my info has been or will be useful to you at some point. I'll certainly add your observations to my 'knowledge base' and see how it all shakes out.
> 
> ...


 I'm looking for more info on inductive and cap-charge transfer . I believe in the 24/7 bms route . i saw programmable controller 4 months prier , just looked it up yesterday 8,000 inputs 8,000 outputs , older stuff 1990's , big box . I was thinking of it for off grid system . Fanuc series six . It's gone to china now .


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## AndyH (Jun 15, 2008)

tomofreno said:


> We aren't making much progress here are we?


 Sure we are! Before we can communicate we need to understand each other's definitions and viewpoints. It's all good!



tomofreno said:


> I based that statement on measurement of cell rest voltages at around 35% SOC.


 How are you estimating 35%? Do you find that it's consistent across all your cells?



tomofreno said:


> What in your judgement defines a "balanced" pack? Do you compare cell voltages at rest, under charge (if so, at what current), or under discharge (at what current)? What, in your mind does "balanced" mean? That all cell rest voltages are equal at some SOC, or that all cell voltages are equal during some current flow, either charge or discharge?


That's a beautiful question! Cells can be capacity balanced at any point on the curve, they can be voltage balanced, one can match internal resistance (Ri). But it's a huge moving target - capacity changes with discharge rate and temperature. Voltages and Ri change with SoC, temperature...etc...



tomofreno said:


> The latter two include the effect of differences in internal resistance (ir). In that case two cells could concievably have the same voltage, with one having lower ir and higher SOC than the other. When you top balance, you ensure all cells are charged to the same voltage under similar current magnitude. If that magnitude is the same as the manufacturer's spec, and they are charged to the voltage in the spec, then they are considered fully charged, 100% SOC. In this case, they will have different rest voltages at low states of charge, such as below around 30% SOC, assuming they do not have identical capacities.


Exactly. From the earlier reference comes a basic cell model: V=E-IR The voltage inside the cell is E. It is reduced or increased at the terminals (V) by current in (charging) or out. If the cell is at rest with no load and no charge current, the 'open circuit' voltage at the terminals equals the voltage 'inside the box'. And R (Ri) varies with cell temperature.

I think we agree that it's all a moving target? And this makes it very difficult to really know the state of charge of any cell at any point. And this takes us back to my original point - that what's happening with a pack on the road might not be what one thinks is happening. 



tomofreno said:


> At SOC in between they will not differ much in rest voltage even if though they are at somewhat different states of charge (assuming they do not all have identical capacity), due to the very small slope of the voltage versus Ah curve. So if you observed the differences in cell voltages in this pack at say 25% SOC, and did not know it had been top balanced, would you say it is unbalanced? Similarly, if the cell rest voltages are all the same at some low SOC, such as 30%, and they are then charged until the lowest capacity cell is at 100% SOC as defined by the charging current and voltage of the manufacturers spec, they will be at different SOC and have different rest voltages (though hardly different at all due to the very small slope of the curve there). If you observe this difference in voltages would you say the pack is unbalanced? Or would you observe cell voltages during charging, and declare the pack unbalanced because the low capacity cell is at significantly higher voltage than the others due to its being on the exponentially rising part of the curve? I'm trying to understand how you define balanced and unbalanced. If someone runs a pack from 40% SOC to 90% SOC of the lowest capacity cell, and the other cells remain at SOC in between these, would you say this is damaging the pack and will decrease its lifetime? If so, what is the physical cause?


I'm not suggesting that one will damage a pack if they limit all cells to a range defined by the lowest capacity cell. What I am confirming is that it's very difficult to actually do that. I have already proven to myself that the cell does not feel it necessary to be bound by my beliefs.  (While I feel good about the data I've collected, I didn't expect you to - that's why I offered a view from a pool of 17 battery and electronics experts in the form of a quote from a book.)

Yes - voltage is only a 'symptom' of what's really happening. But the cell manufacturer gives me a process to ensure a cell is charged to near 100% by using a combination of temperature, charge current, and voltage. Sure - it's not necessarily exact - it's an approximation based on 2nd order inputs. But, as I understand it today, in order to know for sure the SoC of any one cell, I would have to track voltage, current, Coulombs/Ah in and out, and heat energy in and out of the cell. If I could reliably do that, then it seems I could choose to absolutely capacity-balance my pack at 30% SoC or 90% or anywere else.

"So far we have taken the process of charge equalisation to be equalising all the cells to full. However, in theory it is possible to equalise the charge in all cells of the battery at any point in the process... This is practical in the case of the 'super-capacitors' ... but is not usually practical with batteries. The main reason is the difficulty of sensing the state of charge of a cell. However, in the case of lithium-based batteries charge equalisation by adding circuits to the battery system is more practical and is used. Chou et al. (2001) give a good description of such a battery management system." [Chou, Peng, Huang, Pun, Lau, Yang, and Shuy A battery management system of electric scooter using Li-ion battery pack. _Proceedings fo the 18th International Electric Vehicle Symposium_]

But I don't have this capability, so I use what I have. And that means that when it's important to get the best range from my pack I top balance.

Take care,
Andy


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## Dolphyn (Nov 17, 2009)

Gavin said:


> Check out these guys: Their CellLog 2-8S is $29. They will do a 24 cell logger if you order 1000. THe RC folks love them.
> 
> Yes, it is possible to make 24s CellLog if you order 1000 units in one time.
> If you think it is no problem, then we can have a detail discussion.
> ...


I have two of the CellLogs, and they're great.

The company also makes some nice-looking chargers that actively balance and monitor the cells as you charge, for example this one which has some great features, including configurable parameters such as maximum current and maximum voltage per cell. But, these chargers only go up to a maximum of 10 cells and an they require external DC power supply. I suppose that's great for the RC folks who want to be able to plug the charger into a 12V car battery, but maybe not so great for us.

I love the idea of an _integrated system_ for charging and monitoring batteries, capable of handling a variable number of cells. I think this company could easily produce a good and affordable system designed for the EV community, if someone can convince them to do it.


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## methods (Jan 29, 2010)

Going back to the topic that was started by the original poster: 

I have designed a BMS based on the LTC6802. Here are some details

USB interface that updates all of the following ever 40mS:
6 battery temperature probes
2 motor temperature probes
Individual cell voltages (to 1.5mV resolution)
Bi-directional shunt measurement to 1% on a 100uOhm shunt
1.2A balance current (can be upgraded)
Expandable to any number of cells (i.e. 1000V or more)
Currently in a 36 cell grouping
Fan cooled in an extruded aluminum case

** Any feature could be modified, expanded, eliminated, enhanced, etc. Easy to change digital design.

So that answers the original question. I don't even want to comment on a lot of the arguing I heard above - it sounds like non-sense to me.

There are a few things that should be pointed out though:

1) as EV's become more popular there will be a lot more used cells on the market. Many people (including myself) will have packs made up of very imbalanced cells - different capacities, different internal resistance, different aging, etc. You simply must have some form of balancing if you want to get the maximum energy density from your system. The assumption that cells will be "healthy" and "balanced" is not sound logic moving forward. (see picture of my salvaged 960 cell 20S 48P pack)


2) This "bottom balancing" is ridiculous - you always want to top balance for the simple sake of energy density - V*Ah - the higher the voltage is on your cells the higher the energy density. You would always want to charge all of your cells to the fullest and discharge until the first one hits LVC. To make this more clear - imagine you had a cell that was 10V full and 1V empty. If you paired two of these - one with half the capacity - then you would have two possible ranges:

* assume 10ah and 5ah
* assume linear discharge curve

Top balanced:
10V HVC 10Ah + 10V HVC 5Ah = 20V 5Ah
5V LVC 5Ah + 1V LVC 0Ah = 6V 0Ah

Bottom balanced:
5V HVC 10Ah + 10V HVC 5Ah = 15V 5Ah
1V LVC 0Ah + 1V LVC 0Ah = 2V 0Ah

So everyone raise their hand who wants to have a 15V 5Ah pack.
Now everyone else who wants to have a 20V 5Ah pack 

So in both cases you burn up 5 amp hours but by top balancing you get more energy density. Getting close to LVC - the top balanced pack has 6V * X and the bottom pack has 2V * X. I dont see how this could ever be desirable.

Yea.. yea... I know there is more to it but that illustrates the point of power density. Maybe with a LiFep04 it does not make that much difference but it definitely does with a Lipo or an Emoli

but... I am not going to come back and argue about it - so no need for a rebuttal 













































-methods


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## Tahoe Tim (Feb 20, 2010)

Are you selling this BMS? Looking for another vehicle to test it in? PM me to discuss.


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## Elithion (Oct 6, 2009)

methods said:


> I have designed a BMS based on the LTC6802. Here are some details...


I added it to the list of all Li-Ion BMSs.
http://liionbms.com/php/bms_options.php#Digit._balancers
Let me know if you would like me to make any corrections.
Davide
________
YAMAHA YZ125


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## methods (Jan 29, 2010)

Tahoe Tim said:


> Are you selling this BMS? Looking for another vehicle to test it in? PM me to discuss.


You will see this BMS soon as part of a larger system. I will post back here when it is released.




Elithion said:


> I added it to the list of all Li-Ion BMSs.
> http://liionbms.com/php/bms_options.php#Digit._balancers
> Let me know if you would like me to make any corrections.
> Davide


Thanks - that is fine for now. This particular version is really just a pre-production for a motorcycle application - hence not a distributed design. The next version will be in 12S modules that I hope will be suitable both for the ebike market (thinking 12S lipo) and the EV market (thinking distributed groupings of cells from 4S to 12S)

As I said above - once the "rest of the system" is released I will post back here so that you can get all the details on the display and additional features. 

-methods


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## Tahoe Tim (Feb 20, 2010)

Great, I can't wait. I am a dealer for a bicycle retro kit and need a BMS for those packs as well. 

I recognize the battery pack you are using.  I need to try harder to get a few of the duds...


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## methods (Jan 29, 2010)

-methods


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## Elithion (Oct 6, 2009)

Patrick,
Regarding your high power balancing, if asked about why so much current, you may refer them to the "gross balancing" argument presented in this white paper:
http://liionbms.com/php/wp_balance_current.php








(I refer people to the same paper, pointing them to the "maintenance balancing" section instead.)
Davide
________
DODGE D SERIES HISTORY


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## methods (Jan 29, 2010)

Interesting.

I actively balance during charging. My algorithm just brings all the higher cells down to the lowest cell within 0.005V. I never passively balance after a charge.

If I had it my way I would have 5A active balance currents 

One of the most common things that can happen to a pack is a "wrench across one cell". This is the case where you blow off 1Ah in about 2 seconds by doing something stupid  I want my balancer to be able to correct that situation in a very short period of time - perhaps an hour - so I can be back on the road.

I also want to be able to hook up a new set of unballanced cells to my charger and have it balance them overnight at the longest.

If someone tried to tell me that 200mA balancing was enough for a 140Ah pack I probably would not even bother arguing with them. I am a guy who has spend thousands of hours sitting at a desk watching cells balance.....

This is one case where more is better. I hate watching paint dry.

-methods


EDIT: Wow - you are arguing for 100mA balance current? We must come from different planets.


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## methods (Jan 29, 2010)

Ok - I read the rest of your argument.

You make a good case. I agree that for an OEM application your methods make sense.

I guess I am an experimentalist... Always hooking up a new this or a new that. For me - I would rather trade cost to buy time.

Thanks for sharing that - it was informative.

-methods


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## dimitri (May 16, 2008)

In my experience, burning off more than 2-3 Watts per cell is a waste of energy and a heat hazard. That is why I limited MiniBMS shunting at 0.75Amp. I find it plenty to keep my 160AH pack balanced long term. "Long term" is the key here, why bother with perfect balance at every charge/discharge cycle? It doesn't need to be perfect every time, as long as there is counter-imbalancing mechanism in place it will keep the pack balanced long term.

As for big stuff like dropping the wrench or marrying new cells into existing pack, this deserves manual balancing since its a one time thing. Why add all this every day cost and complexity to BMS to manage things that don't need to be managed every day. I go by KISS principle and it seems to work well.

Another point regarding data collection and fancy screens. Its good for nerds and data junkies ( OK, I know I am one of those  and I know many others are), but majority of EV drivers don't care how hot cell 37 is or what the voltage on cell 19 is while driving the car. All EV driver needs to know is that pack is OK, available range and/or SOC, and discharge current ( indicating real time power usage ). All I need my dash instrumentation to do is alert me when pack is not OK and when I am getting near empty. IMHO, fancy screen on the dash is a distraction and a driving hazard. Once I have been alerted that something is not OK, then I can get off the road and use my tools to find the culprit. All I need is a cell level LEDs to quickly identify the cell which is not OK.

Its great that fancy digital BMSs are available for those who are willing to pay for them, but their cost premium is hard to justify for a regular EV driver. For me a simple analog BMS is good enough and small SOC gauge and ammeter is all I want on my dashboard.

_DISCLAIMER: Since I sell MiniBMS my opinion may seem as anti-competition remark, but I assure you that I welcome competition and applaud everyone who brings variety to the market , rather than sitting on their butt critisizing everyone else._


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## methods (Jan 29, 2010)

Sounds like both of you guys are coming from the perspective of marketing to "normal people" with OEM type EV's. I totally agree with your logic. I definitely dont want to argue 

I should probably state that I am an idealist - interested more in the advancement of the Electric Revolution than any sort of sound business plan  When I design something it is pretty much to the specification that I want -> with the idea that I need to sell only enough to offset my costs - so I can build more and play more. 

Personally I am only interested in the market of people who are pushing the limits - Race teams, experimentalists, geeks, etc. I am picturing the motorcycle race team who is building a pack the night before the race. They dont have time for manual balancing -> they want to build a battery, hook up a box, and know that it will be perfectly balanced and ready to go the next day with every last ounce of WH available.

It is pretty clear that we have different goals for our BMS systems. I am glad I saw both of your posts because it never even occurred to me that anyone would want slower balance times.... But it makes sense from a simplicity, cost, and reliability perspective. I like that.

As far as that business plan?

I am of the opinion that the OEM market will be swamped very shortly with high end BMS's coming out of china that utilize chips like the LTC6802. Digital - Analog - does not really matter when you are cranking out 10,000 per day on a machine. Just look at the PMDC controllers that are popping up every 2 months from XIE (commonly incorrectly refereed to as Infineon). They will catch on real soon....

I have no desire to try and compete with companies like XIE from China... so I will stick to the niche market of freaks, geeks, and experimentalists.

Thanks for sharing guys.

-methods


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## JRP3 (Mar 7, 2008)

methods said:


> You would always want to charge all of your cells to the fullest and discharge until the first one hits LVC. To make this more clear - imagine you had a cell that was 10V full and 1V empty. If you paired two of these - one with half the capacity....


Sorry, I have to rebutt since you've setup an impossible situation to "prove" your point. In reality with the 100ah and larger cells most of us are using and a voltage range of 3.4 to 2.8 or so bottom balancing leaves a minuscule amount of capacity on the table. When my smallest capacity cell hits 3.50 and my largest cells are at 3.43, there is a tiny amount of actual difference in capacity and final voltage. If I want more capacity I can purchase an extra cell or two for a lot more range for a lot less money than a complex BMS.


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## EVfun (Mar 14, 2010)

methods said:


> One of the most common things that can happen to a pack is a "wrench across one cell". This is the case where you blow off 1Ah in about 2 seconds by doing something stupid  I want my balancer to be able to correct that situation in a very short period of time - perhaps an hour - so I can be back on the road.
> 
> I also want to be able to hook up a new set of unballanced cells to my charger and have it balance them overnight at the longest.
> 
> If someone tried to tell me that 200mA balancing was enough for a 140Ah pack I probably would not even bother arguing with them. I am a guy who has spend thousands of hours sitting at a desk watching cells balance.....


Why should the regular balancing system be able to handle pack initiation or maintenance mistakes? If you drop that wrench across a cell you didn't miss it (I hope.) This stuff seems more like one time setup than in service balancing. When you are setting up the pack you can turn the current down to under and amp and surf with Fluke  

What does in service balancing actually require?


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## Elithion (Oct 6, 2009)

EVfun said:


> What does in service balancing actually require?


Well, as I said:
http://liionbms.com/php/wp_balance_current.php









________
Ecstasy Rehab Advice


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## methods (Jan 29, 2010)

JRP3 said:


> Sorry, I have to rebutt since you've setup an impossible situation to "prove" your point. In reality with the 100ah and larger cells most of us are using and a voltage range of 3.4 to 2.8 or so bottom balancing leaves a minuscule amount of capacity on the table. When my smallest capacity cell hits 3.50 and my largest cells are at 3.43, there is a tiny amount of actual difference in capacity and final voltage. If I want more capacity I can purchase an extra cell or two for a lot more range for a lot less money than a complex BMS.


Impossible to prove?

I clearly framed my argument by explaining that a lot of people are starting to use "salvaged cells" - cells like Emoli - which are not like your 100Ah TS cells at all. 

My example was sound - just because it does not apply to you and "most of us" does not mean it is false. I happen to run 960 individual Emoli cells and just like Lipo they hold a great deal of their charge "up top". There is a HUGE difference between bottom and top balancing for a chemistry like that.

The motor cycle that this BMS is going into uses Lipo - it too would suffer greatly if "bottom balanced".

If you think that bottom balancing a chemistry like Lipo will result in performance similar to top balancing they you and I have nothing further to discuss. I understand if you dont think my example applies to you but that in no way makes it false or "impossible to prove"

I cant believe I am actually arguing about this with someone 

-methods


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## JRP3 (Mar 7, 2008)

I think we are both slightly misunderstanding each other. I didn't say, or mean, "impossible to prove", though I can sort of see how you read it that way. I was saying that to make your point, or "prove" it, you set up an impossible situation, i.e. a cell that operates from 10-1 volt, and one with half the capacity of another, both highly unlikely events. I guess I didn't realize that you were focused on smaller capacity cells and smaller ah packs.
I would only add that it probably makes more sense to spend money on more closely matched new cells than spending a lot of money on a complex BMS trying to manage sub par out of balance cells.


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## EVfun (Mar 14, 2010)

That page you link to is an interesting read. However, does anyone have actual delta cell leakage numbers for various ThunderSky and SkyEnergy cells?


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## MN Driver (Sep 29, 2009)

EVfun said:


> That page you link to is an interesting read. However, does anyone have actual delta cell leakage numbers for various ThunderSky and SkyEnergy cells?


As the cells wear the difference of self discharge would likely become pronounced over time but since nobody has had their cells that long, nobody will have that information and I doubt Sky Energy or Thunder Sky will do the 'accelerated aging' tests, or at least publish them if they did(if they could even be trusted), to tell us what the difference is.

It doesn't matter much if they self-discharge if they are do it evenly. I think the internal resistance degradation will likely have a bigger impact as it allows the cells with less internal resistance to discharge faster and charge faster, while the ones with more internal resistance have more voltage sag and resist charging causing them to become unbalanced. There are some examples of that happening to a few people on ES but I don't think anyone has had the Thunder Sky or Sky Energy cells through enough cycles to notice or definitively see it yet. I haven't exactly run into anyone who has been using them for say 50k miles yet or we might have a guess, but even then that's only 1000 cycles at 50 miles per cycle.


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## Elithion (Oct 6, 2009)

MN Driver said:


> I think the internal resistance degradation will likely have a bigger impact as it allows the cells with less internal resistance to discharge faster and charge faster, while the ones with more internal resistance have more voltage sag and resist charging causing them to become unbalanced.


Just to clarify, the effect you describe does occur, but only in cells connected directly in parallel. 

That effect does not occur in batteries in which cells are connected in a single string in series: in those, the resistance has no direct effect on balance. The exact same current from the charger goes into each and every cell equally, so each cell receives exactly the same charge, and no unbalance is added to the cells' SOC. Similarly, the exact same current from each and every cell equally goes into the load, so each cell gives exactly the same charge, and, again, no unbalance is added to the cells' SOC. The variation in resistance results in variations in cell voltages, but no variation in charge transferred.

(A poorly designed BMS can have an indirect effect, but only during charging: if the BMS only looks at the cell terminal voltage, and only while charging, if may mistakenly assume that high resistance cell is fully charged, and start taking charge from it.)

Davide
________
Yamaha Qy10


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## methods (Jan 29, 2010)

Elithion said:


> (A poorly designed BMS can have an indirect effect, but only during charging: if the BMS only looks at the cell terminal voltage, and only while charging, if may mistakenly assume that high resistance cell is fully charged, and start taking charge from it.)
> 
> Davide


Depends on how poorly designed it is.

A digital BMS like mine does not measure the cells while under shunt load or under charging load - it turns off both - waits - and reads the resting voltage 


Here is the type of vehicle that I like to cruse around in.

50mph
Blistering acceleration
24S 15Ah Lipo 25C rated (375A continuous)
Custom 100V 100A controller
300A peak current, 120A continuous limit
Modified 9x7 wound 9C in a 20" wheel
Disk brakes that stop so well it will catapult you out of the seat 

Has all the amenities like reverse, cruise control, and chick magnet.



















-methods


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## Elithion (Oct 6, 2009)

methods said:


> A digital BMS like mine does not measure the cells while under shunt load or under charging load - it turns off both - waits - and reads the resting voltage


Exactly! Perfect.
________
Jaguar mark x specifications


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## GGoodrum (Dec 11, 2009)

methods said:


> Here is the type of vehicle that I like to cruse around in.
> 
> 50mph
> Blistering acceleration
> ...


What, no iPad?? That laptop "dashboard" is *so* 2009.


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## aeroscott (Jan 5, 2008)

I want one , that's so hot . 30 kw peak 10 kw continuous ? am I dreaming !


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## aeroscott (Jan 5, 2008)

Methods, I learned to fly in Livermore and worked at the NIF labs last fall . I should be starting back at the lab next month . I would love to see your machine sometime .


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## EVfun (Mar 14, 2010)

Elithion said:


> (A poorly designed BMS can have an indirect effect, but only during charging: if the BMS only looks at the cell terminal voltage, and only while charging, if may mistakenly assume that high resistance cell is fully charged, and start taking charge from it.)


That is a valid point. If you are going to use voltage while charging you only want to do that at a low current. After all, if you need 200 amps from a pack and 2 amps is causing a noticeable increase in terminal voltage due to internal resistance, "He's dead Jim." 

I also suspect you need to bring the pack up slowly until all the regs are blinking on a regular basis. If you don't it would seem to me that one or more cells could slowly slip lower and lower and the only warning you would get is reduced range before setting off low voltage alarms.


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## JRP3 (Mar 7, 2008)

methods said:


> Has all the amenities like reverse, cruise control, and chick magnet.
> 
> 
> -methods


And yet no room for said chick


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## methods (Jan 29, 2010)

aeroscott said:


> I want one , that's so hot . 30 kw peak 10 kw continuous ? am I dreaming !


Not really... I see 300A off the line, 120A for about 5 seconds, then the back EMF kicks in and it is stable. I can only launch like that a couple times a minute though or else the motor starts smoking. I hit 200C on the windings (on video) a few weeks back and it survived.



aeroscott said:


> Methods, I learned to fly in Livermore and worked at the NIF labs last fall . I should be starting back at the lab next month . I would love to see your machine sometime .


Sure - I live less than 1 mile from the lab. I fly RC (but I assume you mean full scale). Anyone is welcome to come by and see my toys any time. You can ride it - but bring your own gear. Full face + gloves minimum.



JRP3 said:


> And yet no room for said chick


On my lap 

We are way OT...

-methods


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## Guest (Apr 21, 2010)

methods said:


> G
> 2) This "bottom balancing" is ridiculous - you always want to top balance for the simple sake of energy density - V*Ah - the higher the voltage is on your cells the higher the energy density. You would always want to charge all of your cells to the fullest and discharge until the first one hits LVC. To make this more clear - imagine you had a cell that was 10V full and 1V empty. If you paired two of these - one with half the capacity - then you would have two possible ranges:
> 
> 
> -methods


This is what is nonsense. 

You're charging at 15 amps and discharging at 500 amps. When your one cell goes over the curve, you have about 3 seconds to stop it or lose it to cell reversal. We have demonstrated this three times empirically.

Balancing them at the top exaggerates the differences in capacity at the bottom - where the power is going.

If you want to top balance, never overdischarge your cells, and spend $2000 on a fire hazard, it will all work. 

But if you want to avoid cell reversal and cell death in the odd event you drive too far, they had better be balanced at the bottom, not the top. And I DO have the pile of zero volt cells to prove it.

Jack RIckard


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## methods (Jan 29, 2010)

$2000? 

You mean 2000 pesos? Because it sure looks like Gary sells them for about a dollar a channel. 

http://www.tppacks.com/proddetail.asp?prod=EBKE-LiPo-LVC-HVC

You must have a 2000 cell pack if you want to spend $2000 USD - so 6,000V 

You must not be aware of how easy it is to do cell level protection. Allow me to explain.

You take a TC54 chip - which costs only a few cents.
http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en010716

This chip draws only 1uA quiescent current and will output an active low signal if its input drops below the threshold (say 3.0V). You take that active low output and drive an optocoupler (with a current limiting resistor). You hook the opto-coupler to the Pot THROTTLE of your car.

Now - we have used 4 parts totaling under 1 dollar that are extremely reliable. The instant 1 cell drops below LVC your throttle is cut stopping you from destroying your cells.

A lack of knowledge about available technology does not equate to a logical argument. Driving around in a car without LVC protection is what is truly illogical.

Sir - what you have said is nonsense. 


-methods


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## methods (Jan 29, 2010)

BTW: The pictures in my original BMS posting were hot-linked from Endless-Sphere and they appear to not be working. I am going to upload them to the DIYEV server which will show up as an edit to my post.

-methods


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## Elithion (Oct 6, 2009)

jrickard said:


> This is what is nonsense.
> 
> You're charging at 15 amps and discharging at 500 amps. When your one cell goes over the curve, you have about 3 seconds to stop it or lose it to cell reversal. We have demonstrated this three times empirically.
> 
> ...


To the people who think that Jack Rickard is a troll at best, and a pompous fool at worst (and a dangerous one because of how effectively he spreads his unorthodox opinions), let me stand out alone in his defense and state unequivocally that what he says is indeed correct (though only when viewed within the narrow context of his own specific situation of purposely operating without a BMS) and can withstand any argument to the contrary (brought about by his opting not to accept offers he has received of an education on the mechanics of cell balancing and low voltage cutoff).

Here is why Jack is absolutely correct:
If (and only if) a Li-Ion pack does not have a BMS to protect its cells from under-discharge, then it is indeed possible to bottom balance the pack, and monitor the pack voltage to detect when the pack is discharged. Jack is correct about this point, and no one can deny him this! So stop rolling your eyes whenever he makes such statement! He is no fool. You must believe him because he says that he has a bunch of dead cells to prove that top balancing kills cells (the fact that no BMS was in use if purely incidental).

(Though, I must also point out that a bottom balanced pack, when charged without a BMS, by the time its voltage reaches the CCCV charger's constant voltage, some of the cells will be badly overcharged; I am not sure what's best: to keep cells from dying due to undercharge, or to keep the car from burning down when overcharged cells catch fire? I am not quite sure. Installing a BMS on Jack's pack (which would prevent both overcharge and over-discharge) is not an acceptable option to Jack, so that leaves top balancing resulting in dead cells vs. bottom balancing resulting in a burned car...Hmmmm. I need to think about this one for a bit.)

Davide
________
BUY IOLITE VAPORIZER


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## Amberwolf (May 29, 2009)

methods said:


> BTW: The pictures in my original BMS posting were hot-linked from Endless-Sphere and they appear to not be working.


ES appears to still be down, since about midday AZ time till right now so far (at least 3 hours). (all the domains on that IP address are unavailable and it doesn't respond to a ping, either).
________


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## JRP3 (Mar 7, 2008)

Elithion said:


> (Though, I must also point out that a bottom balanced pack, when charged without a BMS, by the time its voltage reaches the CCCV charger's constant voltage, some of the cells will be badly overcharged; I am not sure what's best: to keep cells from dying due to undercharge, or to keep the car from burning down when overcharged cells catch fire? I am not quite sure. Installing a BMS on Jack's pack (which would prevent both overcharge and over-discharge) is not an acceptable option to Jack, so that leaves top balancing resulting in dead cells vs. bottom balancing resulting in a burned car...Hmmmm. I need to think about this one for a bit.)
> 
> Davide


I guess I need to think about it as well, since I bottom balanced my pack, and I set my charger so that it goes into CV when my first cell hits 3.4 volts and then shuts off 15 minutes later. No cells have overcharged or caught fire. Sure I'm leaving a few ah's on the table, but nothing worth worrying about that I can see. It might be worth adding a cell level HVC but I see no benefit to top balancing. Once my smallest cell is full I can't get any more range by filling the rest.


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## Elithion (Oct 6, 2009)

JRP3 said:


> I bottom balanced my pack, and I set my charger so that it goes into CV when my first cell hits 3.4 volts...


Good! That means that you have a high voltage cutout (Jack doesn't). Your pack is safe (Jack's isn't).

Davide
________
HAWAII MARIJUANA DISPENSARIES


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## methods (Jan 29, 2010)

JRP3 said:


> Once my smallest cell is full I can't get any more range by filling the rest.


I really dont want to argue - I want to lay this to rest - but that actually is not technically a true statement 

You can pack more WH (notice I said WH, not AH) into top balanced cells than bottom balanced cells. I realize that with your chemistry it makes almost no difference - but... Some day you might run a chemistry that has a larger swing to the discharge - and if that day ever comes - you will remember my nagging 

I really am not trying to start an argument - just want to keep the record straight 

-methods


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## methods (Jan 29, 2010)

Wow Davide - I always have to read your posts a few times to figure out if you are being flippant or serious  You are a pretty funny guy...

I have never heard of this Jack (or his reputation) before today but I suppose you are correct - any argument could be true if you bound it tight enough.

"The sky is black!"
(but I am blind... )


-methods


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## JRP3 (Mar 7, 2008)

Elithion said:


> Good! That means that you have a high voltage cutout (Jack doesn't). Your pack is safe (Jack's isn't).
> 
> Davide


Well not exactly, I don't have cell level signalling. What I mean is I set my pack voltage at the charger such that the charger goes into CV mode when my smallest cell gets around 3.4 volts, but the charger is actually reacting to total pack voltage. So potentially it could be a little higher or a little lower than 3.4 volts before going into CV.


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## JRP3 (Mar 7, 2008)

methods said:


> I really dont want to argue - I want to lay this to rest - but that actually is not technically a true statement
> 
> You can pack more WH (notice I said WH, not AH) into top balanced cells than bottom balanced cells. I realize that with your chemistry it makes almost no difference - but... Some day you might run a chemistry that has a larger swing to the discharge - and if that day ever comes - you will remember my nagging
> 
> ...


 There is nothing wrong with constructive argument and your points are well taken. I hope never to use small cells with large voltage swings


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## MN Driver (Sep 29, 2009)

JRP3 said:


> There is nothing wrong with constructive argument and your points are well taken. I hope never to use small cells with large voltage swings


It's not just small cells. LiFePO4 has a tremendous advantage of having an open circuit terminal voltage that is roughly .3 volts from top to bottom if you exclude the top 5% or so and the bottom 20 or 30% of the discharge.

What he was referring to are other chemistries. Lithium Cobalt charged to somewhere between 4.0-4.2 volts will stay around that point without dropping down and it doesn't settle at a specific voltage and then drop at the end quite the same way. Safe fully discharged point is at 3 volts or so. It's a fairly flat curve but the voltage difference between 90% SOC and 40% SOC. This is significant due to wattage being volts and amps. So, without the advantage of LiFePO4 where things remain roughly the same until they are nearly finished with their discharge curve, most other chemistries don't remain anywhere near as flat. As a comparison, NiMh is similar but with NiMh you want to charge all the way(in cyclic use, it's difference for hybrid vehicles where it's beneficial to avoid the top and bottom for cycle life) and at least once and awhile cycle them down and all the way back up. NiMh with very high power capacity will operate in a range of 1.4volts from open circuit terminal voltage until they drop to 1.2 volts and start dropping like a rock once they've passed that point and then crash at 0.9 volts, although NiMh and NiCd can tolerate being reversed a few times and same with overcharging to a point.

This is a very nice advantage to LiFePO4, he's just saying that if you go to another chemistry that you'll notice a difference and want to them all to be at the top. I prefer the top too especially when it comes to high amp draws towards the end of discharge, it stresses the cells less when they have the most current available to provide, the difference is small, however, and one might not know see the difference or be able to acknowledge it a few thousand cycles down the road when they expect diminished performance anyway.


----------



## Guest (Apr 23, 2010)

Elithion said:


> (Though, I must also point out that a bottom balanced pack, when charged without a BMS, by the time its voltage reaches the CCCV charger's constant voltage, some of the cells will be badly overcharged; I am not sure what's best: to keep cells from dying due to undercharge, or to keep the car from burning down when overcharged cells catch fire? I am not quite sure. Installing a BMS on Jack's pack (which would prevent both overcharge and over-discharge) is not an acceptable option to Jack, so that leaves top balancing resulting in dead cells vs. bottom balancing resulting in a burned car...Hmmmm. I need to think about this one for a bit.)
> 
> Davide


First, no dead cells in the car. I've killed plenty in the lab, and on the GEM test bed. The car is fine at 17 months and 9500 km. I manually checked all cells today and it was astounding how close in voltage they were fully charged 3.37-3.38 across the board.

Second, we do not routinely bottom balance. If you have to balance, that's demonstrably where to do it, but in practice, they only time we would do this is if adding new cells to an existing pack or replacing cells. 

The cells in no way ever become overcharged. We charge to an average pack cell voltage of 3.65 and I never have anything over 4.00 at all - these are Thundersky's. It just simply isn't true. The variation after 17 months is like 2-3% in capacity and the range is 3.55 to 3.85 most of the time.

You can warn. You scream. You can cry. And you can offer. As I said privately, if you have any DATA or direct information that can be reproduced, I' m all ears. If you want to offer your "years of experience" and countless "thousands of hours" of watching batteries, I've been down this trail before. There are no years. There are no hours. There is furious typing. And anecdotal evidence of what someone THINKS happened. A lot of stuff that just obviously makes sense, whether it works that way or not, and so on and on and on.

And a bit of selling....

I don't have a religion here guys. I'm from Missouri. I show what I find. ANd you kind of have to "show me" rather than assure me you are most excellently the most brilliant young engineers on the planet and if I'll just spend a couple of grand with you it will all be better. 

I've traced fires to these BMS, dead cars, confused people, and a whole lot of people that are embarrassed to report their experiences at the hands of snake oil salesmen. 

Had one today. Vendor sending out e-mails noting a customer car BURNED TO THE GROUND BECAUSE OF LACK OF BMS - better get yours today before you too join this unfortunate soul. Three phone calls and the whole tale came unraveled. 

I try not to become cynical, because there are a lot of people out there working hard to bring the dream to ground. But like all frontier industries, it does indeed attract it's share of fast traders and hangers on quacks and charlatans - ever ready to make a quick buck.

So if you want to publicly proclaim that I'm little, I'm ugly, and my mother dresses me funny, I'm more or less ok with it. I've been all three for a very long time. And yes David, if you actually have any information I can verify experimentally, I have nothing but time. If you want to impress me with your vast knowledge kind of off the top of your head with snowballs, it just isn't going to work. You'll have to peddle as best you can and hope I go away.

Living BMS free - one day at a time.

Jack Rickard


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## GGoodrum (Dec 11, 2009)

Jack, you are a funny guy.  No, seriously, I love reading your well-articulated posts. I don't always completely agree with what you say, but I love reading them, nonetheless.

I do have a few comments, though. First of all, I don't want to sell you anything, period. Secondly, although I'm not "brilliant" and certainly not "young", I have been an aerospace engineer for 30+ years. Almost none of my aerospace experience is of much good here, though, unless we want to start arming our EVs.  Anyway, I'm not going to disagree with most of your comments. What you are doing obviously works. I'm actually doing very similar things with my own setups, which are based on using RC-type "LiPo" packs, but for slightly different reasons. 

I don't use a "full" BMS with these packs, and I rarely balance them at all. I do, however, have small boards with the low-voltage cutoff circuits for each block of paralleled cells. Although I don't balance these packs, I also don't want to worry about letting cells get over-discharged. Most of the time, I never run the packs down far enough for this to be an issue, but more than once, these circuits have saved cells from killing themselves. These RC packs we're using typically are only 5Ah, so we have to parallel a bunch together to get decent capacities. I've had cases with bad connections, and just plain "senior moments", where I've forgotten to connect some, where I ended up with less capacity than I thought I had. Without the LVC circuits, I would've been walking, for sure.  Anyway, I am a believer in cell-level low voltage protection, in any form. 

What really got me off balancing, though, is that much to my pleasant surprise, it is amazingly difficult to get these inexpensive, but high-quality RC LiPo packs to go out-of-balance, period. I've known for years that they do a good job of initially matching cells, in capacities and in IR, but I just didn't expect that they would stay that way over any significant number of cycles. Now I don't have packs with thousands of cycles yet, but I do have some with hundreds. Anyway, with these packs, there's no significant difference in capacities, so there's really no "bottom" balancing, or "top" balancing, just balancing, period. 

I find no fault in the way you charge, either. I don't think there is anything wrong with not letting all the cells go until they are absolutely completely full. If you do have capacity differences, this will knock them askew, when it comes to being balanced at the bottom, which clearly is a valid form of low-voltage protection. So-called bottom balancing allows a pack-level low voltage check to work. Personally, I'd be nervous as a cat, doing this, but I do see how it could work. All low-voltage protection is trying to do is catch any cells from jumping off the voltage "cliff". Cell level LVC tries to catch any and all "cliff jumpers". With bottom balancing, all the cliff jumpers lock arms, and try to commit mass suicide, at the same time. 

There is one more part of the typical BMS functionality that I find useful for use with our LiPo packs, and that is the use of a HVC signal to control the end-of-charge function. With Lithium Cobalt-based LiPo packs, it is a little more important to make sure cells don't get over-charged. In the early days of using LiPo packs, this was critical. If a cell got too much above about 4.3V, it would simply explode in a brief, but spectacular fireball, and then cook at 2000F until there was nothing left to burn. Now, however, the latest cells we've been using seem to be much more tolerant. I still don't want to tempt fate any more than I have to, though, so I now do individual cell HV protection as well. It only took a couple extra parts, to add this to my LVC circuits. Anyway, what I do with this HVC signal is a bit different from what I've seen others do in BMS designs. Some set the HVC voltage fairly high, like 3.8-4.0V, for LiFePO4 cells, and simply shut off the charger the first time a cell hits this point. I guess this works okay, but it doesn't let this first cell go through the full CV phase, where the current tapers off. I think having no HVC check, and just using the charger's pack level CV mode might be more effective, because the low capacity cell is going to control the current reduction anyway, because its voltage will rise quicker, causing the charger's CV mode to kick in. The only issue is if the low cell is pretty far out of whack, in relation to the others, its voltage can rise pretty high before the charger's CV mode kicks in.

Again, I don't want to worry about what might happen, so I make use of the HVC signal, but a bit differently. I use it to in essence individually control the CV mode, so that no one cell can ever go over the HVC trip point, which I set fairly low (3.62V for LiFePO4 and 4.16V for LiPo...). This just starts the CV mode a bit earlier. It does, however, let the low capacity, "1st arrival" cell get fully charged, as it will go through the complete CV phase. 

Anyway, by making sure the low capacity cell is allowed to get completely full, and by making sure the low capacity cell doesn't try and take up cliff diving, I can get the maximum capacity out of the pack, with no worries. 

-- Gary


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## Guest (Apr 23, 2010)

GGoodrum said:


> Jack, you are a funny guy.  No, seriously, I love reading your well-articulated posts. I don't always completely agree with what you say, but I love reading them, nonetheless.
> 
> I do have a few comments, though. First of all, I don't want to sell you anything, period. Secondly, although I'm not "brilliant" and certainly not "young", I have been an aerospace engineer for 30+ years. Almost none of my aerospace experience is of much good here, though, unless we want to start arming our EVs.  Anyway, I'm not going to disagree with most of your comments. What you are doing obviously works. I'm actually doing very similar things with my own setups, which are based on using RC-type "LiPo" packs, but for slightly different reasons.
> 
> ...



Actually, I'm onboard with almost all of that. I don't do HVC and LVC - here's why.

I charge to an average voltage of 3.65vdc. I have manually checked the cells numerous times, and they do not go over about 4.0v. The spec is 4.25 on these large LiFePo4 cells. We do Sky Energy's at a little more aggressive 3.5 v on their 3.6 v spec, but their curve is much flatter and more stable. They also seem more closely allied in capacity.

I think the CV is VERY important. But I can't talk to it because I have no data. But I think having a period of diminishing current and constant voltage does something to these cells toward a mild balance. It is not really measurable, and maybe my imagination. But charging to a voltage and then shutting off the charger, as some use a BMS to do, rather obviates the CV phase where the string is held at a specific voltage for a period of time with the current gradually diminishing. I can't prove it, but I think it's important.

On the LVC. Ok. I'm onboard. Have been from the beginning. But it's a lot of wiring and little circuits, and I've had bad experiences with that. What am I monitoring for, and what am I going to do with the information.

The reason I phrase it that way, is in the Speedster, but also the Mini, 3C excursions are normal. There is some sag. Worse, the sag varies with two things primarily, temperature and the part of the discharge curve they are on. Fully charged, very little voltage drop under current. End of curve, BIG drop in voltage under current load. Lower temperatures, bigger drop. Higher temperatures, smaller drop.

I've got to many things going on here. What would I set it for? I've seen 2.75 volts. Ok, but I get that voltage driving normally, and certainly toward the end of charge. In fact, I can get 2.5v. On the speedster that would be about 90 volts if ALL of them were 2.5v. I've done that. No damage. Accelerating it dips to 90, release and I'm back up at 106 or 107 volts. This is way at the end of the curve, and it's true I'm past 80% discharge. But everybody is happy.

Fully charged, in warm weather, I could have a drop to 2.6 volts and it be because of a cell dying in front of me. If I was set to 2.5, I wouldn't get the alarm. Now it's cold and I'm at 90% discharge, and ALL of them read 2.5 volts, but nothing is wrong.

So if I did run hundreds of wires all over the car, and had 72 little circuits on the cells, all ready to burst into flames of their own accord with NOTHING wrong with the battery pack, what am I to make of this LVC monitoring?

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.

What's wrong? I don't care. I'm driving a car. Let's go back to the garage and put a meter on it. THERE I can see which cell, find out it's really a loose and very hot terminal, etc. etc. I can't troubleshoot while I'm driving down the road anyways.

So I have NO use for HVC monitoring. I'm not going to hook it up to my charger. I'm just going to blindly undercharge the cells - quite intentionally. There is nothing good for me climbing that curve wall. A half mile more range? I don't need it. Buy more batteries.

ANd I have no use for LVC monitoring. What I might save I can easily loose by having two sense wires short and burn the insulation off of them. Ask me how I know.

$400? No. IF you start to take this apart, it starts to look ugly. Since I don't want just the WIRING of a BMS, never mind the BMS, causing a problem, I really need a fuse on each terminal. But if I have a cheapo fuse, then the FUSE connection connection can screw up my readings. What I really need here is a pretty good quality inline fuse holder. I'm at six bucks a cell and I haven't measured anything. Of course I need a heat shrink terminal ring, and that's a few cents. As you start to add up all the backup and current limiting and safety to the individual cell module, the costs start to go up. It really doesn't stop until you get to over $100 per cell. So I have $7200 in BMS, to cover $8600 in cells. Why not just buy more cells? I'm not having any problems now.

Digital. If you've been in Aerospace you know about EMI. This got me again this week. This TIMS600 has to be the noisiest controller on the planet. It absolutely wipes the EVISION out. So I made a little Arduino AH counter with a couple of LEM HASS hall effect current sensors. Actually, it was pretty cool as I have a little GPS module and I can integrate not only AH, but also distance travelled, which gives me MILES TO EMPTY. That's what we really want to know.

It worked truly excellently for 22 miles. Now all I have to do is replace the main Arduino board and fix my shield. Arduinos don't have much in the way of spike suppression on the inputs. And I didn't put much either. Who knew?

Well actually I did. I even talked about it at length on a video six months ago. An EV is a radio station. What works in the garage won't work on the road. I laid it all out. But I thought it would be neat if it worked this week, since the EVision was squirrelled out. Since I already KNEW I was having EMI, I don't know why I thought it wouldn't effect the Arduino, but it obviously did. It was cool for 22 miles though. Ah, current, SOC%, mph, distance travelled, and Miles Remaining, all in 2x16LED.

So I'm flying blind in the Mini until I can get things quieted down. I've got some huge ferrites on order that should be here soon. If those don't do it, I don't really know how to filter this out. Huge spikes on the main battery cables, both sides, at 7500 hz and all resonant multiples of course. 


So, your saying I'm not little and ugly and my mother dresses me funny. I'm actually funny, my mother's ugly, and you agree - a little. With me? Or my mother?

Jack Rickard


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## tomofreno (Mar 3, 2009)

> What really got me off balancing, though, is that much to my pleasant surprise, it is amazingly difficult to get these inexpensive, but high-quality RC LiPo packs to go out-of-balance, period.


 That is what I have observed on my series 36 SE (CALB) 180Ah cells over the past 5 months and close to 2000 miles. Only balancing I've done is on over-discharged cells (caused by defective bms boards), and the new cells that replaced them.


> Anyway, by making sure the low capacity cell is allowed to get completely full, and by making sure the low capacity cell doesn't try and take up cliff diving, I can get the maximum capacity out of the pack, with no worries.


 I operate similarly, but I stopped letting the low capacity cell get completely full. I now set the Manzanita charger to time out when the lowest capacity cell hits about 3.45 - 3.5V (3.6 is full charge). I never drive to less than 30% soc (I use an Ah counter, TBS), and use Dimitri's minibms without shunts as insurance, but it never triggers for HVC during charge anymore since I tweeked the Manzanita voltage limit back a bit. When I checked few weeks ago, all cells were within 1 mV of each other the morning after charge. They were within +/-2mV of each other during charge at 30ADC.

I see Jack's point with LVC, but I wanted something to keep me from doing something stupid, like driving cells too low because I phased out and didn't watch soc. I agree the difference voltage would be more robust against false alarms. 'Course, I don't get any since I don't go below 30% soc and never pull more than 2C (Edit: I also should mention the battery boxes are insulated and I keep the cells heated to 60F while the car is parked in the garage in winter, so they haven't gone below about 45F -this was after sitting outside for 6 hours). I also view lots of wires as increased opportunity for failure Jack. That was one reason I liked the minibms - one wire hookup.

If Jack is correct that the CV phase is important, my charging to only 3.45V may be a problem since the charger doesn't drop back in current as much before timing out. I can see where some balancing might occur when cells are permitted to do the exponential climb in voltage toward end of charge, since those cells then have higher internal resistance than others that are still on the flatter part of the curve, so more of the energy going into them is being dissipated rather than stored. They still accumulate the same charge (current continuity) but some of this is likely so called "surface charge" that diffuses back to the counter electrode after charge completion and turn off of the externally applied electric field. Anyway, I'll be watching to see if you get any data to show not doing the entire CV phase is detrimental Jack. Thanks Gary and Jack for two very good posts.


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## GGoodrum (Dec 11, 2009)

I love your half-pack checker idea. I still consider this a form of cell-level low-voltage protection. I said I'm a believer in cell-level low-voltage protection, in *any* form. I'll have to think about this some more, but it sounds like you would definitely get *some* sort of indication if you have a sad cell taking diving lessons. 

I also agree that running a bunch of wires all over the place to a centralized board with LVC and/or HVC detector circuits is asking for trouble. This isn't the case with our LiPo setups, because each of the 5A packs we use have handy little balancer plugs, pre-wired. These have keyed JST-XH connectors on them and I include a parallel adapter right on the LVC/HVC boards so that a bunch of these 5Ah packs can be plugged straight in. I just need to remember to actually plug the little buggers in.  Anyway, it is all very modular and each board works with paralleled groups of 5Ah packs, each with 6 or 8 cells in a pack. The output of these boards is a ganged opto output that is shared between the LVC and HVC functions.

For these large format cells, I think a better approach for cell-level LVC protection is the cell top-type boards Dimitri has done. The temp problem you described is easily handled by using temp sensors to shift the LVD detection point south, when it is cold out. These are not active devices, but basically just temp-sensitive resistors. If I'm not mistaken, I think Dimitri's design has this feature. If you exclude the shunt balancing, for the moment, I think there's a lot to like about his design. He reverses the opto logic, and makes them all "normally closed", which at the expense of a bit more standby current draw, allows a single wire to be used to connect all the modules together. The only real issue I have with his design is how he uses the HVC signal in his "control head". I, of course, like what I do better, or I wouldn't have done it, but that's just my opinion. As for the "balancing" shunts, I'll just leave it that I currently have no opinion. I've done it both ways myself, but I'm a firm believer now in "external" balancing. I have a single 6s HobbyCity Battery Medic balancer that I've added a "booster" to that bumps the balancing current up from about 200mA to about 1.3A. this makes quick work of any balancing I need on any of my LiPo or a123-based packs, even if it is only 6 channels at a time.

I hear you about EMI, and that has been the bane of my professional existence since Nixon was in office.  I actually started out life as a software engineer, programming fire control and anti-submarine warfare helicopters, back in the early '70s. EMI was always a *huge* issue. That is why I've gone back and re-learned analog based circuits, with the help of many "real" EEs. Doing a digital-based system would be more up my alley, but it just dredges up old suppressed memories of being on frozen tarmacs, chasing down EMI problems with the rotors turning. Bad ju-ju.  Back then, the aircraft systems were still mostly analog, but it was the digital stuff we were trying to add that kept f'ing up. Anyway, I love simple and reliable now. 

Finally, to set the record straight, I think your mother is beautiful, but has funny dresses, and you are just a little bit ugly. 

-- Gary


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## GGoodrum (Dec 11, 2009)

tomofreno said:


> That is what I have observed on my series 36 SE (CALB) 180Ah cells over the past 5 months and close to 2000 miles. Only balancing I've done is on over-discharged cells (caused by defective bms boards), and the new cells that replaced them.
> I operate similarly, but I stopped letting the low capacity cell get completely full. I now set the Manzanita charger to time out when the lowest capacity cell hits about 3.45 - 3.5V (3.6 is full charge). I never drive to less than 30% soc (I use an Ah counter, TBS), and use Dimitri's minibms without shunts as insurance, but it never triggers for HVC during charge anymore since I tweeked the Manzanita voltage limit back a bit. When I checked few weeks ago, all cells were within 1 mV of each other the morning after charge. They were within +/-2mV of each other during charge at 30ADC.
> 
> I see Jack's point with LVC, but I wanted something to keep me from doing something stupid, like driving cells too low because I phased out and didn't watch soc. I agree the difference voltage would be more robust against false alarms. 'Course, I don't get any since I don't go below 30% soc and never pull more than 2C. I also view lots of wires as increased opportunity for failure Jack. That was one reason I liked the minibms - one wire hookup.
> ...


If you set the CV set point to the equivalent of 3.45V per cell, and charge until the current drops to under about 1/4-1/2A, or so, the low capacity cell *will* have gone through the full CV phase. If your cells are that closely balanced, then all of them will have gone through the full CV phase. You might get a slight bit more capacity by picking 3.65V per cell as the set point, but not much, and I would guess you are helping the longevity significantly by using a lower CV set point.

When I charge with my HVC/charge controller combo, I see the supply's CV mode kick in way before the individual HVC set points are being hit, even for moderate imbalances. For example, I have forced the cells in a 15Ah LiPo pack to have an imbalance of about 60-70mV between the lowest and highest cells. That's not a huge difference, but typical of what I've seen using a123-based packs. I charged this pack at 13.5A. The CV mode of the supply was set at 75V and it kicked in at around the "normal" point The current then started to drop, at a steady rate, roughly at the same rate the voltage rose during the CC phase. The current had to drop to around 2-2.5A before the "high" cell started bumping up against the HVC set point. The current still dropped at the same rate. My widget is setup to shutoff the charge current when the current drops below 180mA. When I do the same thing when theres only 5-10mV of difference, the HVC doesn't start tripping until the current is down around 1A.

Anyway, the point is that you could simply let your charger go until the current drops to a low level, and I'm guessing your "high" cell will still be well under 3.6V, probably under 3.5V, and if you checked the balance at some point other than right off the charger, I'm guessing it would still be pretty much the same.

-- Gary


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## dimitri (May 16, 2008)

> The only real issue I have with his design is how he uses the HVC signal in his "control head".


Gary,

thanks for your kind words, however I'd like to clarify this point which is often taken out of context by some people. MiniBMS was designed to be simple, safe, flexible and affordable. Head end board simply provides NO/NC signals for cell level LVC and HVC. What user does with those signals depends on many factors and its a mistake to label it one way or another. As clearly documented in the user guide, properly configured CC/CV charger will do its job from start to finish and HVC is merely an insurance policy in case some cell(s) misbehave or the pack is severely imbalanced. MiniBMS was not meant to balance severely imbalanced pack or marry new cells in one charge cycle, although it would do it given enough cycles, little by little. However, there is no need to blame BMS for cutting off the charger at last 5 minutes of CV phase when current is 1-2 Amps, its just silly to point out that we would be cutting off 0.1-0.2AH from the pack.

However, if user chooses not to buy proper CC/CV charger, but just take dumb CC charger and use MiniBMS to stop the charge, that is fine too, considering that user understands that it will likely produce incomplete charge. How much incomplete depends on many factors and its very much possible that such solution can work well if managed properly. It would not be perfect, but it would work.

I have a 100 Amp dumb charger that I use occasionally and MiniBMS cuts it off on HVC. It serves its purpose when I need a quick boost and don't care about full charge. Still, if I top it off with CC/CV charger afterwards, I only get a few additional AH, so I am not sold that CV phase is all that important, as long as full charge is done at least occasionally. This whole CC/CV business has important variables which people often miss or choose to ignore to make their point, but without taking all variables into consideration the whole conversation is a moot point and a big waste of time.


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## tomofreno (Mar 3, 2009)

> If I'm not mistaken, I think Dimitri's design has this feature.


 That is correct.


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## EVfun (Mar 14, 2010)

GGoodrum said:


> I love your half-pack checker idea. I still consider this a form of cell-level low-voltage protection. I said I'm a believer in cell-level low-voltage protection, in *any* form. I'll have to think about this some more, but it sounds like you would definitely get *some* sort of indication if you have a sad cell taking diving lessons.


This is easy to do. Lee Hart posted a simple circuit for exactly this purpose many years ago on the other EV list:

2 red LEDs connected in series with a single green LED connected in parallel to them. This gives you 3 connections points. One point is connected to the positive end of a red and the green LED. One point is connected to the negative end of a red and the green LED. One point is where the two red LEDs are connected to each other. The positive connection goes through a current limiting resistor to the positive end of the pack. The negative connection goes through a current limiting resistor to the negative end of the pack (these 2 resistors have the same value.) The point between the two red LEDs is connected to the center of the battery pack. 

Normally, only the green LED is lit. If the voltage difference between the two halves of the pack is 1 volt or greater one of the red LEDs will light. With some component changes the red LEDs could be replaced by the infrared LEDs inside of optical isolators.

This is a remarkably easy way to detect a single cell going either high on charge or low on discharge. The catch is it will miss the event if 2 cells go crazy and one is in each half of the pack.


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## Guest (May 2, 2010)

Elithion said:


> Good! That means that you have a high voltage cutout (Jack doesn't). Your pack is safe (Jack's isn't).
> 
> Davide


You seem to be famously familiar with what Jack has and hasn't. What JRP describes is exactly what I "have" and I have to point out, 9000 km now and 16 months on the road with the same pack and no failures. Better, I can manually measure my voltages of these cells whenever the mood strikes, and can categoricallly deny that everything you warn of doesn't happen at all as apractical matter.

As JRP points out, when you've run out your smallest cell in capacity, it doesn't matter what the others have left. You're done.

We basically advocate undercharging your cells a bit, and monitoring to avoid discharge beyond 80%. 

I have personally discharged to what SHOULD be 100% on several occasions with no ill effects on any cells. I have also demonstrated precisely the steps necessary to perform your top balance and utterly destroy cells int he process irrecoverably. I duplicated this on three consecutive occassions on the same equipment within one week.

Jack Rickard


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## methods (Jan 29, 2010)

jrickard said:


> I have also demonstrated precisely the steps necessary to perform your top balance and utterly destroy cells int he process irrecoverably. I duplicated this on three consecutive occassions on the same equipment within one week.
> 
> Jack Rickard



I think this is my favorite quote - though there are so many that deserve a spot on my wall of logical fallacies....

I love how Jack can bulldoze his way through a thread full of electrical engineers who have *actually designed* BMS circuits and manage to bring a fruitful discussion to a complete halt using nothing but his hot breath and a relentless onslaught of anecdotal evidence, logical fallacies, hasty generalizations, and in general - BS.

Jack may be an asset in other aspects of EV (I will let you be the judge of that) but in the area of Battery Management anyone trying to gain an education would be wise to tune his blathering out. 

I dedicate V3.0 of my BMS to Jack. Thank you sir for your kind words and support.

























































 

-methods
​


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## Justalabrat (Jul 28, 2008)

*Jack Rickard is now gone!*

*This is from Jack's blog at EVTV.ME I had to split it in to two parts to fit in this space. The full text is here:*
http://jackrickard.blogspot.com/2010/05/online-forums-signing-off.html#comments


*Friday, May 28, 2010*

*Online Forums - signing off *



My experience with online forums goes back to the early 1980s, and indeed I wrote one of the very few 8080 assembly language software programs to manage large numbers of Usenet Newsgroups - PIMP.

But the experience has always been mixed. The written word in the forums or newsgroups leaves many more able than others, depending on their ability to express themselves using the written word. And the instant nature of the technology leads to some rather interesting interactions.

One of the things we're trying to do with EVTV is of course promote the evolution of electric vehicles as a personal indiidual effort that many can take to demonstrate or lead us to an energy policy and practice that reduces our dependence on foreign oil and the existing oil based unholy alliance between government, extremely large oil corporations, and equally large automotive manufacturers.

And we've been somewhat successful. Despite lower gasoline prices, there has been renewed and indeed increased interest in electric cars and doing conversions, and the chatter from the large manufacturers has changed subtly from "maybe someday" and "hybrid, hybrid, hybrid" to "me too, we've got plans" and "battery, battery, battery."

The latest of course is Toyota CEO's joy ride in a Tesla Roadster and subsequent announcement that he had "felt the winds of the future."

For individuals converting cars to electric drive, information is at a premium. The obvious attempt to get it involves Google, and that subsequently leads to forums such as Electric Vehicle Discussion List (EVDL) and Do It Yourself Electric (DIYElectric).

Like all forums, these lists attract a set of "regulars" who simply post more than anyone else. And any information, repeated often enough,, becomes "the word" simply because everyone has read it, passed it on, and read it again.

Unfortunately, there is no check on technical accuracy. 

Combine this with a certain level of anonymity, most of the "regulars" have pseudonyms and do NOT post their real names. And you have pretty much a formula for misinformation. 

I call this "online engineers typing themselves smart." 

In most cases, despite screens full of text proclaiming their expertise, these are self taught diletanttes, whose education and engineering practice again comes primarily via Google, Wikipedia, DigiKey, and most of all, by typing in the forumes themselves furiously.

As an engineer and technical writer for 30 years, this all smells like opportunity. I don't mind wading into technical confusion at all, it's probably what I do best. Misinformation in bulk is a little harder to deal with. DISinformation is just beyond the pale.

With the rise in interest and the search for ever better components, there has been some economic opportunity. We were deeply disappointed when one of our suppliers, James Morrison of EVComponents, came under some internal strife and economic issues and made a startling move to simply disavow responsibility for some $400,000 in prepaid orders from potentially 75 customers who had paid in advance for batteries and components. Apparently Morrison has deecided to stiff these people of their products, and sell the already sold stock AGAIN at bargain basement prices to raise further money and so deal with his economic difficulties.

Like all new frontier industries, this one has attracted its own bevy of snake oil and patent medicine sales force. 

The EASIEST target is Battery Management Systems or BMS. After spending $10,000-$15,000 on the most necessary component, batteries, most innovators are struggling to get maximum life from these cells. The problem is the manufaturers provide very little information, and some of that not terribly accurate. 

continued on next post.


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## Justalabrat (Jul 28, 2008)

*Jack Rickard is now gone!*

continued from previous post


Enter our hero, BMS designer. They throw together some ill thought through designs using inexpensive components, rush it off to Sundstone to make PCBoards, and immediately start selling them to any hapless yuck that they can find. NO testing of any kind in most cases and in the thoroughly tested cadre we are talking about thoroughly tested by running it on the designers car for two weeks. These are available at ALL prices, ranging from $12 per cell to several thousand dollars. The tout is essentially always the same:

If you don't have a BMS, YOU'LL BE SORRY WHEN YOUR $15,000 BATTERY PACK BLOWS UP HORRIBLY. DON'T SAY WE DIDN'T WARN YOU.

I have spent some time and effort on a particular forum DIYelectric over the past year trying to sort all this out and counter the disinformation provided. The result has been a very understandable attack from those who more or less huant these forums, using them as barely concealed fronts for sales operations. If I come along and mention that their design won't do what they claim, they go berserk. And if I offer real data information from real cell tests that indicate that the BASIC premises they are using in BMS design are fatally flawed from the beginning, they go into rage.

They are quite accustomed to simply shutting up this talk by gathering the herd, jumping on the heretic, and giving him a good thrashing. Of course, as I said, I was in a VERY rough and tumble world of online forums before many of these people were born. And as a technical writer, I sometimes feel like a child molester picking apart their wholly unsupportable technical nonsense in writing. So the gang up and abuse stunt neither awes or dissuades me. Rather, I find it entertaining and indeed can stoop as low as they want to go in the ad hominum attacks. It's just not a problem.

We've been effective. The sales of useless blue elephant gun BMS systems has plunged. The top balance shunt systems are virtually dead. And generally we have shifted the goal toward Battery MONITORING Systems and informational instrumentation. 

But many of the regulars have at least side-business type income from these activities and some are trying to make a living at it. It's hurt. Since the usual bullying and attempts to simply "vote" me off the island haven't had their usual result -- most people don't want the abuse and simply quit the forums, the new tactic is to appeal to the forum operator to have me removed or edited.

This came up on EVDL some months back. Administrator David Rhoden contacted me with some very paternalistic advice on how not to stiur up controversy or anger any of his participants. I pointed out to him that I WANTED to stir up controversy and did not MIND angering his participants if it helped anyone sort through the dreck of disinformation and bullshit. But if he intended to delete messages I posted or "edit" them to a tone he felt more comfortable with, I would simply leave the list. And I did so.

Over the past year I've posted a lot on DIYElectric and indeed paid for advertising on thise widely used service. This week, I was attacked wholesale by a 14 year old who only identifies himself as METHODS and posts photos of his BMS systems, which are particularly inept. We actually weren't even in a discussion. He just launched a bomb of ad hominen attacks likening me to "cake and dogshit in a blender."

My response was quite muted, as the entire thing reallyhad no context. I simply asked if this anonymous person might be another 14 year old boy blunder forum engineer who just might have a BMS product on the table.

Incredibly, I heard from Robert Green, forum administrator, cautioning that several people had complained about my posts. I pointed out that if he cared to check he would find ALL of them were in some way involved in BMS design and sales. I quoted the message I had responded to and he seemed at the time to agree it was a very provoked attack and a measured response.

I got on the service later, and found the attack slightly reworded (edited) and my response deleted entirely.

I pointed out to him that he had apparently decided to edit the stream and essentially disable my ability to respond in a public forum. If we're going to manage the debate by falsifying the text, what the hell are you doing? He simply explained he was trying to reduce the anger.

I asked him to delete me from the group and remove the ad and incredibly, he initially REFUSED to do so. I then asked him what he thought he was doing. DId he intend to have me "appear to be" active on the forums and condoning the site despite my leaving? Who was going to fake my posts? Was he aware of the legal implications of this?

He finally agreed to delete the account and the ad. 

This attempt at editorial "control" which essentially borders on onlien identity theft and fraud. What if someone, with the access of an administrator, starts editing your posts to change their meaning? Or worse, starts posting under your login things you were not even aware you had posted? Where would this end? Online identity theft out of control....

In any event, we are going to continue publishing a video series online with the best information we can determine at the time. Its likely imperfect. But it isn't dishonest. And having learned now twice how insidious these little relationships are between the forums and the "engineers" that are trying to sell product (most of the ads on Mr. Greens service are BMS ads with the exception of the EVCOMPONENTS ad and ours). 

Basically the information on these sites is no longer to be trusted at all. They are willing participants in a scam to milk ducats from people who are interested in electric cars. It is done quite cynically, and quite by design. That is not to say everyone on these forums are part of the conspiracy. Most are simply unaware of the level or purpose of the manipulation. That it would extend to actually editing posts by subscribers, to subtly alter their meaning, by the administrators, is beyond the pale. 

We're probably going to avoid the forums in the future entirely. It takes a lot of time and effort, and I cannot correct every technical idiot theory on perpetual motion in any event. I'll try to post here to the blog more regularly, and let the forums do what forums do, lead to a lot more heat than light.

I would urge you all to view what you read online with a skeptical eye and exercise critical thinking. The level of misinformation/noise is always horrendous. But at this point there are actually unholy alliances between the forum administrators and their friends, the BMS designers, that are quite deliberate DISinformation.

Jack Rickard 

Posted by Jack Rickard at 10:44 AM   

I for one am sad to see him go.


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## EVfun (Mar 14, 2010)

*Re: Jack Rickard is now gone!*

You are sad to see him go with your first and second posts ever to this forum?


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## zwmaster (Nov 23, 2009)

there goes freedom of speach... what's next?


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## EVfun (Mar 14, 2010)

zwmaster said:


> there goes freedom of speach... what's next?


Yea, private property sucks


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## JRP3 (Mar 7, 2008)

Not happy about how this turned out but it's not my forum. I don't agree with everything Jack said and I'm not sure how much of it is accurate but editing posts after the fact seems pointless. The damage is done and changing history serves no purpose other than to confuse.


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## Guest (May 29, 2010)

There was no damage. He called out those that were promoting BS. The result is always the same. They cry and have a temper tantrum and get their way. They did and he's gone. I am actually glad he left. I will be following suit. I got moderated in a like manner and I decided to stay because there was still some good information around here that helped me with my build. Now however it is more like a bunch school children on the playground yacking and chattering with nothing much to say that will help anyone build an electric vehicle. 

It is my hope that all those with real information on building an electric car will follow suit and build a true community that will thrive and grow. 

This place has gotten cold and dark. 

Later


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## JRP3 (Mar 7, 2008)

gottdi said:


> There was no damage. He called out those that were promoting BS.


No, sometimes he attacked people needlessly, some who even agreed with him. He used a shotgun approach when a sniper rifle would have been more effective. Dimitri's situation is a good example, Jack verbally beat him about the head with a two by four over his BMS, basically calling him a criminal. Then when Dimitri developed a SOC gauge that Jack thought was interesting, Jack was surprised when Dimitri was less than enthusiastic about Jacks support. I've been a big supporter of Jack's efforts for the DIY community but I can also see his delivery needs some work, though I doubt he'll change.


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## Guest (May 29, 2010)

> No, sometimes he attacked people needlessly, some who even agreed with him.


Too bad so sad. He's had more to offer here than most could even consider. You all shit out one of the best we had. I see another exodus like happened at EVDL coming. Let the likes of Tom Sines rule here. It's about the extent of the education being taught anymore on this forum.


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## MN Driver (Sep 29, 2009)

Jack's attitude left something to be desired. It didn't really bother me because I can ignore the verbal abuse when it comes my way, but it bothered many others here. It's not uncommon for any forum to have it's administrators and moderators step in when someone treats another like s###. I would have expected it with any other forum. In the reply that was deleted, which I saw before it was removed, I didn't see any substance to it as far as an argument goes, seemed to be a personal attack. It sucks that Jack got emotional over it and decided to leave because of it. I'm against censorship as well but I've come to terms with the way of life in these forums, after so much abuse, good threads get locked, like the excellent Soliton review thread after it turned rough.

Jack didn't know Dmitri's BMS and Jack said that it was Dmitri's BMS that he tested and the shunt that he used was Dmitri's that drained his cell to 0 volts, it wasn't Dmitri's, in fact Dmitri took that specific BMS, which is no longer produced, and improved upon it, adding very nice features to it. Jack stomped into a different forum that primarily uses Lithium Cobalt and told them that using a BMS was stupid in his very special way. Anyone who has ever used Lithium Cobalt knows what not to do with Lithium Cobalt, what Jack suggested would have caused many Lithium Polymer battery fires as those cells are not tolerant to overcharge or overdischarge at all, it doesn't take much of stretching the limits to burn down your garage. It's happened to a few people and not because of using a BMS but due to not using one and causing problems.

As far as LiFePO4 goes, Jack ignored two of the three very important details about LiFePO4. Don't overcharge or overdischarge. Every person I know who uses a BMS with LiCo or LiPo knows to prevent your cells from dropping low on voltage. LiPo loses balance faster than LiFePO4, especially with the higher discharge rates and due to them sitting around a bit too as some people don't use their equipment daily like we do in cars. Jack ignored some details about BMS's and that you need to prevent the cells from overdischarging and then says this here


> I have also demonstrated precisely the steps necessary to perform your top balance and utterly destroy cells int he process irrecoverably. I duplicated this on three consecutive occassions on the same equipment within one week.
> 
> Jack Rickard


...yeah, top balance and ignore the rest of the details the forum tells you. Of course there was a problem.

Jack is good at ignoring details and forgetting to read past the first paragraph to the second and see the big picture. ...granted you don't necessarily need a BMS with LiFePO4 because it won't burn up your car if you overcharge or overdischarge but having something to prevent that from happening can save your cells but you do need to be sure that you don't just throw your cells directly from the manufacturer into the car without making sure they are at the same state of charge and just drive, they need to have balance and need to be implemented in a way that will not destroy them.
It was a ton of drama over not too much IMO.

For what it's worth, for everything else not regarding battery rants, I think he has a cool head without too much to argue about. With that I have respect for him for trying to show us what he is doing and why he does it. I wouldn't mind sitting down and opening a bottle of wine and discussing electric cars with him and his garage buddies.

Jack, keep making the videos, I enjoy them and I know I'm not the only one that does.


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## DaveAK (Jun 28, 2009)

So Jack's a petulant little child who can't stand criticism? That's no way for grown ups to behave, so I won't be upset to see him go.

To quit in such a fashion is pathetic.


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## Guest (May 29, 2010)

DaveAK said:


> So Jack's a petulant little child who can't stand criticism? That's no way for grown ups to behave, so I won't be upset to see him go.
> 
> To quit in such a fashion is pathetic.


Actually it was the petulant little children who went crying to momma that got Jack ousted.


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## DaveAK (Jun 28, 2009)

gottdi said:


> Actually it was the petulant little children who went crying to momma that got Jack ousted.


Really? I'll take your word for it, but it seems to me that he left of his own free will. So maybe he wasn't the only petulant child in this affair, but he still gets no sympathy from me for his part in it, or his storming out the door in a huff 'cause of all the mean kids.


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## JRP3 (Mar 7, 2008)

It's hard to have that opinion if he was in fact kicked out, which I believe is exactly what happened.


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## MN Driver (Sep 29, 2009)

In the first 15 mins or so of his new video, he discusses why he left. He keeps calling this site "DIY electric" and blames his woes on people selling things and some more talk of the 'conspiracy of people teaming up to sell BMS systems'. It's only 30% done downloading for me and I don't have the fastest internet so it might be awhile before I see the rest, but talks about hall effect throttles and slap shut-off's it seems.

Worth watching if you want to see him talk about it.


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## dimitri (May 16, 2008)

gottdi said:


> Actually it was the petulant little children who went crying to momma that got Jack ousted.


Some people have their head so far up Jack's ass they lose touch with reality.

Since you are such a big MAN, why not show petulant little children what a real MAN does, and start by keeping MAN's word.



> I am actually glad he left. I will be following suit.


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## karlos (Jun 30, 2008)

dimitri said:


> Since you are such a big MAN, why not show petulant little children what a real MAN does, and start by keeping MAN's word.


Yes this did not pass my notice nor that of many I'm sure. Enjoy your other Forums gottdi and let the light dawn on this thread again. I was enjoying it and being very informed before Jack told everyone he was right they were all wrong. I would have enjoyed his contribution as well until he killed the dialogue with his shotgun approach.
A Forum is " A medium for open discussion or voicing of ideas" and not a place for 'inflicting' one's view and certainly not with personal attacks where logic has failed.

Something I certainly have gotten from this thread though, whether using a BMS or not, there is a lot at stake and I personally, before I purchase one, will be looking at the options with a very critical eye.


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## Guest (May 30, 2010)

dimitri said:


> Some people have their head so far up Jack's ass they lose touch with reality.
> 
> Since you are such a big MAN, why not show petulant little children what a real MAN does, and start by keeping MAN's word.



Your true colors are clear. Jack has put his money where his mouth is and has earned his place. Sure he can be edgy but it is clear you are too. So what gives. Jack has shown his work and proven what he says. 

Pete


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## karlos (Jun 30, 2008)

gottdi said:


> Your true colors are clear. Jack has put his money where his mouth is and has earned his place. Sure he can be edgy but it is clear you are too. So what gives. Jack has shown his work and proven what he says.
> 
> Pete


Gottdi, nice to see your smiles and I guess you must have reconsidered that this forum is not so bad after all. Why don't you let people defend themselves and let this thread get back on topic? What's your experience with BMS systems?


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## Guest (May 30, 2010)

It was not meant to pass notice. It was very much meant to be seen. Jack has invested and tested and proven what he says and since it is a free forum personal attacks are going to happen when one disproves another that has a stake in the business. I have seen it for years and those that attack those the have proven are the petulant little children. A few got real pissed and kept hounding Jack and insisting he is telling lies. Since you have not really seen entire picture you I guess follow the others with no proof. Have you spent well over $100,000 in batteries and building and testing and teaching to truly say Jack it wrong? He even shows his stuff to all for free because he likes to teach. Others only want money. Move over Jack I'm on the way over. I'd prefer to teach too. I side with Jack. Did you read my stance on BMS systems? If not you best go see before you make judgments. 

Absolutely you have a lot of invested but if a poorly built BMS shorts out you may loose that investment. The other issue is balancing and monitoring. Balancing is not required if you follow the teachings of others who have built electric cars. Like Toyota, GM. Batteries are not fully charged and not fully discharged and the balance issue is moot. Why spend another $2000 to $15000 for something you don't need. Who's is the best? What do they all actually do for you? What do you do with the information now that you have it? Is it something that can be checked once per year? Most likely. Batteries can be monitored but managed? What the hell are you managing for your money? 

Jack it showing you don't need it. Others insist you do. The war is on. The ones that went crying got him ousted. He's not the first. Nor will he be the last. Enjoy your forum. It is dead and dry. 

How many more will I piss off again. This is not my first time rocking the boat. I'll rock hard enough to knock some off. 

Have a wonderful day.


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## karlos (Jun 30, 2008)

gottdi said:


> Balancing is not required if you follow the teachings of others who have built electric cars. Like Toyota, GM. Batteries are not fully charged and not fully discharged and the balance issue is moot.


I didn't know Toyota and GM have experience with Li batteries??? If you have made this point without knowing your facts.... you are about as credible as Jack. If I'm going to be influenced by someone's experience in not using a BMS I will be from someone like JRP3.
Toyota & GM have experience with hybrids, very different from pure EV's. I think you are on the wrong forum gottdi.


gottdi said:


> It is dead and dry.
> How many more will I piss off again. This is not my first time rocking the boat. I'll rock hard enough to knock some off.


Honestly, if you were on my boat I would have knocked you off long ago. Now keep to your intentions and go play in Jack's sandpit. You'll probably have fun until he kicks sand in your face.


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## Guest (May 31, 2010)

karlos said:


> I didn't know Toyota and GM have experience with Li batteries??? If you have made this point without knowing your facts.... you are about as credible as Jack. If I'm going to be influenced by someone's experience in not using a BMS I will be from someone like JRP3.
> Toyota & GM have experience with hybrids, very different from pure EV's. I think you are on the wrong forum gottdi.
> 
> Honestly, if you were on my boat I would have knocked you off long ago. Now keep to your intentions and go play in Jack's sandpit. You'll probably have fun until he kicks sand in your face.


Go right ahead and use JRP3's expert opinion. No problem. Hope he proves you need one. 

No I am not on the wrong forum. If you think they have no experience with lithium then you are pretty ignorant of the scope these guys have. I am sure they have years more experience than all the collective here on this forum and the other combined. Hybrid or not the value of the experience is paramount. A hybrid is an all electric if you ditch the gas. So yes they have lots of experience with electric drive systems. They just happened to couple an engine to theirs. 

I doubt you have what it takes to rock the boat hard enough. If I were to vote a few off this list it would never have been Jack. He also owns his mistakes and when he is wrong. Many here would never do that. 

Jack kicks those who kick him. You'd do the same. So do I. Jack is not in a sand pit. DIY is the sand pit. I have watched it from day one till now. It had a fast climb and a hard fall. Yes it is pretty much washed up at this point. Not many are posting much that would help anyone build an EV. It used to be real good. There are only a few posts that are of any value right now. Has not been much. Too bad. 

Whats sad is that you all ditch and piss off such good information because someone pissed you off. That is so sad. So childish. Jack has more information for this forum than many others. Most are just talking garbage and most just old stuff. Not many new conversions. New folks are seeing a lack of involvement and help that they are going elsewhere. 

EVDL is looking good again. 

Pete


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## Guest (May 31, 2010)

There is one truth. All selling will still take my money.


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## karlos (Jun 30, 2008)

gottdi said:


> No I am not on the wrong forum. If you think they have no experience with lithium then you are pretty ignorant of the scope these guys have. I am sure they have years more experience than all the collective here on this forum and the other combined. Hybrid or not the value of the experience is paramount. A hybrid is an all electric if you ditch the gas. So yes they have lots of experience with electric drive systems. They just happened to couple an engine to theirs.


I think the point has been made, a hybrid does not need to use the depth of battery use an EV uses so therefore the scenarios are different. I understand Jack, to be safe does not even get the full 80% sensible usage most of those with/or wanting to build and EV want to. Of course Toyota and GM have been messing with Li lately, but I am not aware that they will not be using a BMS system in any pure EV they might make. Want to tell me how you know they are? EV makers like Tesla have and DO use a form of BMS. Oh yes, the Leaf uses a BMS too but in Jack's book they are wrong too right? you and Jack seem old school and to be talking hybrid battery technology and in Toyota's case, not even Li at that.
Sorry, I have no use for a battery pack I might only be able to use say, 50% of.
You don't seem to get the very different way batteries in an EV and a hybrid are used.


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## Guest (May 31, 2010)

Monitor system not management system. Doing the 80% is just flat out smart. Always pushing your pack to the limits every charge and discharge is just asking for trouble. Jacks position is simple and smart and it works. That is why the Hybrids do it. It is not about any thing else but to keep the batteries lasting longer. Hell they are expensive. I want mine to last as long or longer than required. So if I need to use x amount of batteries and run at the bare limits every charge and discharge then I will opt to go with a few extra to pad that max so I don't stress the pack. Many BMS systems do cost more than what a few extra batteries in your pack would cost and you can always run your pack at the flat level of the discharge curve and get the most from your pack. How simple and smart. Why would anyone get pissed about that kind of thinking and proving it works. Actually Toyota and others proved it long ago. Jack just put it in our face. Some got pissed. I am sure Toyota has a controller that limits the discharge and the charger that limits the charge and a computer that monitors the voltage. It does not manage anything. Just watches.


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## Roy Von Rogers (Mar 21, 2009)

gottdi said:


> Monitor system not management system. Doing the 80% is just flat out smart. Always pushing your pack to the limits every charge and discharge is just asking for trouble. Jacks position is simple and smart and it works. That is why the Hybrids do it. It is not about any thing else but to keep the batteries lasting longer. Hell they are expensive. I want mine to last as long or longer than required. So if I need to use x amount of batteries and run at the bare limits every charge and discharge then I will opt to go with a few extra to pad that max so I don't stress the pack. Many BMS systems do cost more than what a few extra batteries in your pack would cost and you can always run your pack at the flat level of the discharge curve and get the most from your pack. How simple and smart. Why would anyone get pissed about that kind of thinking and proving it works. Actually Toyota and others proved it long ago. Jack just put it in our face. Some got pissed. I am sure Toyota has a controller that limits the discharge and the charger that limits the charge and a computer that monitors the voltage. It does not manage anything. Just watches.


Those who would like to sell you Blue Elephant Guns...


Roy


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## JRP3 (Mar 7, 2008)

gottdi said:


> Go right ahead and use JRP3's expert opinion. No problem. Hope he proves you need one.


You do realize that I do not use a BMS?



> EVDL is looking good again.


Didn't Jack get kicked off of there as well? Not that it's hard to do, if you think this place is too heavily moderated it's nothing compared to the EVDL.


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## Guest (May 31, 2010)

JRP3 said:


> You do realize that I do not use a BMS?


I know but don't think the other poster knows. 




JRP3 said:


> Didn't Jack get kicked off of there as well? Not that it's hard to do, if you think this place is too heavily moderated it's nothing compared to the EVDL.


I don't think so. Many left EVDL because it has stagnated. Some of the big names left and many did the exodus to here. I for one moved because nothing was happening. Not because someone got moderated. There was some problems but not much. I can understand ousting someone that is being a problem if no good is coming from the person but Jack did far less than I and got banned where I remained. That is selective moderation. I have been moderated here too. Still here. Some gone. 

I still belong to EVDL and get all the email and don't recall Jack being a problem ever over there. Not to get ousted anyway.


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## karlos (Jun 30, 2008)

gottdi said:


> Monitor system not management system. Doing the 80% is just flat out smart. Always pushing your pack to the limits every charge and discharge is just asking for trouble. Jacks position is simple and smart and it works. That is why the Hybrids do it. It is not about any thing else but to keep the batteries lasting longer. Hell they are expensive. I want mine to last as long or longer than required. So if I need to use x amount of batteries and run at the bare limits every charge and discharge then I will opt to go with a few extra to pad that max so I don't stress the pack. Many BMS systems do cost more than what a few extra batteries in your pack would cost and you can always run your pack at the flat level of the discharge curve and get the most from your pack. How simple and smart. Why would anyone get pissed about that kind of thinking and proving it works. Actually Toyota and others proved it long ago. Jack just put it in our face. Some got pissed. I am sure Toyota has a controller that limits the discharge and the charger that limits the charge and a computer that monitors the voltage. It does not manage anything. Just watches.


True, using 80% DOD is not the way to go day in day out but when you really need it you need it and not having to get the volt meter out first is certainly a great advantage!
Jacks systems works not because it is proven hybrid non Li technology, it works for HIM because he is an EV enthusiast who knows how to safely use a voltmeter and drives and EV for fun and not a commute.
So tell me, if you are so clever, what % less battery use do you get from using the 'flat curve' as against 80% discharge? Honestly, if we are to take EV's to the world, it won't be because we so conservatively use the batteries we have to carry around a big extra % of batteries for the sake of not having an on board BMS system.
What I don't understand about you is how you constantly compare what a Prius does to what a Tesla does, if a Tesla used your spawn of Jack method, it would not be a sports car, it would be a battery sled!
What's the point in using Li over lead if your can't safely use an 80% discharge now and then!
Oh, I know exactly what JRP3 uses BECAUSE I read his interesting posts. You soon learn what to skip which is what I did for most of Jack's long rants. 
Now spawn of Jack, weren't you going off to play with Jack or does this Forum interest you after all?


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## JRP3 (Mar 7, 2008)

By bottom balancing my cells I can use as much as I want of my smallest cell's capacity, which will always limit your range with or without a BMS. Longest cell life will be had by limiting the charge and discharge of your cells. I try to slightly undercharge my smallest cell and never fully discharge it. I can easily use 80% or more of my capacity without danger and without a BMS.


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## JRP3 (Mar 7, 2008)

gottdi said:


> I don't think so. Many left EVDL because it has stagnated.


John Wayland and some others left because they were tired of the moderation.


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## Guest (May 31, 2010)

Why on earth would you subject your very expensive battery pack to greater than 80% DOD on a daily basis. The last 20% or so is the down slope of the Li curve and that is the area of greatest danger to your pack. Build your pack larger than needed and you get to use the FULL benefit of your pack . You get to use the full power. I could use that last tiny bit on the down curve of the discharge but since that is where every thing goes south real fast you have the greatest potential of disaster. Kill your pack. I could care less. A few extra pounds and a few extra dollars will allow me to keep mine going. Your going to limit your charge curve too because you don't want to waste electricity while charging. You also don't want to over charge your battery. That is just foolish waste. You don't want to drive if you have less than 20% left in your pack either because you may be limping home due to some poor calculations of your true range or unforeseen traffic situation. 

Do you have first hand knowledge of how Tesla charges and discharges their pack? You really think that they will allow that super expensive pack to be abused by some stupid dolt that has no clue but has the money to buy the car? To make it in the market the the vehicle needs to perform in many different environments and that means they must be conservative. All automobiles are built that way. The manufacturer has no clue about the environment that person is going to be using the vehicle in. 

Jacks approach is conservative but not the vehicle, it still has performance. In fact it uses the best part of the curve on a daily basis. 

The spawn of Jack would prefer to be a bit more conservative than to risk loosing a huge investment. Sorry you don't see that. 

As for the Prius, it is an electric car. Not like mine or yours (if you have one) or Jacks or anyone else here but it is electric. It must perform like any other electric. It just happens to have a small battery pack vs a large one. They could set every thing to run at its maximum and push that pack to its limits but at a great risk. It is no different if you push a lead battery pack or a NiMH pack or Li pack. Push your limits and you will have trouble. I have seen it here already. It is simple logic. It works. Push and kill or conserve and live. 

As for interest in the forum. I have been here since its beginning. Of course it has interest to me since I am learning about converting to electric. I always want to learn and when something smart comes along I will latch on to it. I don't go blindly into the fire. 

The thing with Jack is only about how he pissed someone off anyway. His methods are excellent and they work. It means you don't need to spend thousands on a BMS. The other problem comes up that he has said and I said too is WHAT FRIGGIN BMS ARE YOU GOING TO CHOOSE. That alone is cause for alarm. Do we know who builds the best and safest one out there? I sure don't and I frankly was pounding my head trying to decide which one to use. Some were required to buy this one or that because the battery supplier would not honor an warranty with out the one they said you needed to buy. That too is utter nonsense. So when Jack was able to show and continues to show you don't need one that makes things easier. But there are those who still think it is required thanks to those who influenced the suppliers that is in required with no real knowledge that it is true. EXCEPT if you decide to put the minimum sized pack for your system and PUSH your pack to the UTTER LIMITS then you DO need some sort of Management system because the limits your pushing are beyond what you can manage yourself. So in that situation I would agree that you need a BMS of sorts. But the problem arises again. What friggin one will do what I require? This maker says his is best while another says his is best and at this time there are a ton of so called BMS systems floating around. 

I hope you find your perfect BMS and I hope it allows you to push your pack to its limits every day and live a nice long life. 

Who's BMS are you going to choose? Choose Wisely. 
I know what JRP3 uses. 

Pete


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## Guest (May 31, 2010)

JRP3 said:


> By bottom balancing my cells I can use as much as I want of my smallest cell's capacity, which will always limit your range with or without a BMS. Longest cell life will be had by limiting the charge and discharge of your cells. I try to slightly undercharge my smallest cell and never fully discharge it. I can easily use 80% or more of my capacity without danger and without a BMS.


Yes, Since you conserve by undercharging and limit your discharge you use the flat curve of the pack and you can use the full amount of that. In effect your using only around 80% of the available capacity of the pack. It works for any battery. Full power is available within that range and you keep your pack alive. Long live the pack. No danger and no BMS.


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## Guest (May 31, 2010)

JRP3 said:


> John Wayland and some others left because they were tired of the moderation.


I think it was watching others get moderated. I don't think they got moderated but I could be wrong. It was also because there was no more teaching going on and it became very dry. Every once and a great while there is some good stuff still coming from EVDL but not much. 

Wayland ditched both forums. Too many pissy know it all's.


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## JRP3 (Mar 7, 2008)

John Wayland's own words:


> I left the EVDL in protest over that list administrator's heavy-handed
> antics, and am still quite upset over being censored after 14 years of
> what I think were largely positive and helpful contributions.


http://sports.groups.yahoo.com/group/NEDRA/message/1129


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## Guest (May 31, 2010)

JRP3 said:


> John Wayland's own words:
> 
> http://sports.groups.yahoo.com/group/NEDRA/message/1129



Thanks. Clear as a bell. So he got hit too. Lots of us did. Don't blame him.


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## michaelplogue (Jan 18, 2010)

BMS's are like condoms - you never need one if you always pay attention and pull out in time. 

However, all you need is that one that slip-up and you'll end up paying dearly for your mistake.


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## JRP3 (Mar 7, 2008)

Not exactly, running without a BMS is a lot easier  Besides, if you do "slip up" without a BMS you might have to replace a cell or two, which is still a lot cheaper than a whole BMS system.


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## Lordwacky (Jan 28, 2009)

JRP3 said:


> Not exactly, running without a BMS is a lot easier  Besides, if you do "slip up" without a BMS you might have to replace a cell or two, which is still a lot cheaper than a whole BMS system.


 
I'm going to have to disagree with that statement. If you bottom balance your pack like Jack advocates, and you have no LVC circuit you could kill your entire pack, not just 1 or 2 cells.

just for the record I'm on the fence about this whole BMS thing, espeacialy for LiFePo batteries which seem to be proving more and more tolerate in application then we were lead to believe when they were first introduced.

My opinion is similar to the one above. a proper BMS provides a certain level of saftey simply in the fact that if it is properly integrated into the system you have access to realtime data from each individual cell in your pack. As for shunt "top" Balancing I'm going to join Jack's side of the fence and say it isn't really all that useful for the reasons he has mentioned, at great length and with great effort. 

I am not willing to say the top balancing is unsafe however, If you have a properly configured and reliable BMS shunt balanceing should be no more or less safe then bottom balancing. Either way you are relying on some kind of Voltage cut off to keep you out of trouble.

but there in lies the rub. I have heard many stories and have first hand seen what a less then reliable BMS can do. If installed or assembled improperly a certain BMS (that shall not be named) can and will discharge your battery completely, thus killing that cell. Likewise if you are Shunt balancing and the BMS fails to engage HVC you have a dead cell.

In principle I love the idea of a bms, but inpractical application I'm a bit nervous about the reliability/durability of these systems. As well the general complexity of the install poses multiple opertunities for error which can lead to dead cells.

Personaly if I were go this path again I would probably bag the BMS and free ball it Rickard style. 

I'm going to Jack on this forum, I apprechiate his Kalashnikov approach to engineering, the fewer the cogs the less there are to break and there is a lot to be said for that, espeacialy in the DIY environment.

So Jack, I'll keep typing myself smart here, and you can keep talking yourself smart on your videos, keep up the good work. You'll be missed, if for nothing else then the entertainment of it all.


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## JRP3 (Mar 7, 2008)

Lordwacky said:


> I'm going to have to disagree with that statement. If you bottom balance your pack like Jack advocates, and you have no LVC circuit you could kill your entire pack, not just 1 or 2 cells.


Unlikely unless you were practically trying to do so. Here's why. I had an extreme discharge situation a few weeks back. A number of reasons led me to undercharge my pack and over estimate my range. I found myself 3-4 miles from home with dropping voltage and the controller cutting back current. I decided to push it and limp home, and saw 1.77V per cell under load by the time I got there and the vehicle was barely moving, maybe 10 miles an hour as the controller kept cutting back. As soon as I stopped I checked the cells and they were already back to 2.4V and climbing. I wish I had waited and see what they recovered to on their own but I started charging them instead. In any case, because I bottom balanced no single cell was driven to zero volts and damaged, all I did was cycle my pack to one low discharge. If your controller has any sort of low voltage cut back and it's set properly I doubt you can kill an entire pack of bottom balanced cells. If this same pack had been top balanced I certainly would have had some cells driven to zero and killed.


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## karlos (Jun 30, 2008)

JRP3 said:


> If your controller has any sort of low voltage cut back and it's set properly I doubt you can kill an entire pack of bottom balanced cells. If this same pack had been top balanced I certainly would have had some cells driven to zero and killed.


Thanks guys, lots of informative comments and the reason I subscribed to this thread.
JRP3, how do you practically 'bottom balance' your pack, how often do you need to do it and how do you monitor the 'weakest' cell? 
Good to hear the 'flat part of the curve' gives you 80% DOD which I would not want to go beyond and never talked of doing so gottdi. Like most people, mot of the time I would not need to go near 80%.
Crikey gottdi you exaggerate a lot, who really has been saying their BMS "is the best" as I have not seen one example of this although I have seen explanations of the advantages of certain approaches. Lets not be too emotional and get factual please.


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## JRP3 (Mar 7, 2008)

I bottom balanced by driving until average cell voltage was around 3.10 volts but I probably could have taken it lower. I then took a 12 volt halogen headlight and hooked it to 4 cells at a time until the lowest of the 4 was nearing 3.00 volts. I then used a bottom balancing circuit with a resistor that pulled each cell down to 3.00 volts individually and shut off. You could do the same with a 3 volt flashlight bulb and monitor it with a voltmeter. I've only done this once, not sure how often I'll really need to do it but next time I do a deep discharge I'll take the pack down to an average of 3.00 volts per cell and see how close they are sitting.
To find my "weakest" or smallest capacity cell when I charge I monitor which cell gets full first. It will show up by starting to quickly gain voltage faster than the others when it hits around 3.45 volts. This does require some close attention when first charging as you near 3.45 volts as it can shoot up depending on how many amps you are charging at. I have 4 cells that get full faster than others and within those 4 there is one that is more pronounced. That's the one I use to set my charger shutoff point. When it hits 3.45V the charger goes into CV mode and cuts back on amps until it times out. I'm using a PFC30 charger.


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## karlos (Jun 30, 2008)

JRP3 said:


> I bottom balanced by driving until average cell voltage was around 3.10 volts but I probably could have taken it lower. I then took a 12 volt halogen headlight and hooked it to 4 cells at a time until the lowest of the 4 was nearing 3.00 volts. I then used a bottom balancing circuit with a resistor that pulled each cell down to 3.00 volts individually and shut off. You could do the same with a 3 volt flashlight bulb and monitor it with a voltmeter. I've only done this once, not sure how often I'll really need to do it but next time I do a deep discharge I'll take the pack down to an average of 3.00 volts per cell and see how close they are sitting.
> To find my "weakest" or smallest capacity cell when I charge I monitor which cell gets full first. It will show up by starting to quickly gain voltage faster than the others when it hits around 3.45 volts. This does require some close attention when first charging as you near 3.45 volts as it can shoot up depending on how many amps you are charging at. I have 4 cells that get full faster than others and within those 4 there is one that is more pronounced. That's the one I use to set my charger shutoff point. When it hits 3.45V the charger goes into CV mode and cuts back on amps until it times out. I'm using a PFC30 charger.


Thanks, good explanation! I will be really curious to know how 'stable' the pack is and what you find out the next time you check the bottom voltages. I could see a system like that working for me as long as I did not have to check more often than maybe 6mths to a year. What I see the guys who are making the BMS systems doing is making something that works for someone with NO electrical knowledge or interest and for whom it would be downright dangerous to go anywhere near the batteries. In some ways, that is why I don't see where the argument comes from, we are talking about two different needs that work for very different people. I could get by with your method or that of Jack but someone like Blade in Aus NEEDS to sell EVs with a BMS system (that is proven and works of course). Isn't that the end of the debate apart from which BMS (IF one needs to use one) is the safest, is the most reliable, is best value for money and suits the requirements?
What I can see is that if you use a BMS, like with an ICE, it would be very wise to regularly have the system checked over by a specialist if you did not have the skills yourself.
Let us know the results of your next bottom balance test and what you would estimate to be the best time period between tests please!


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## Tesseract (Sep 27, 2008)

I keep thinking how useful it would be to have a constant current load for bottom balancing cells that would shut off when a precise voltage was reached, so you could attach it and forget it. Something that will pull a good 10-20A so it doesn't take 40 f'in forevers to get the job done. 

I'm not particularly motivated to make something like this just for our internal use, but if there is sufficient interest from the peanut gallery here I could be persuaded to go ahead and design it. I'll make it open source, too. For those that don't want to bother building the stupid thing I will rent them out for a nominal fee + a deposit. Don't return it within, say, 30 days and it's yours 

Any interest?


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## JRP3 (Mar 7, 2008)

Are you talking about something that bottom balances each cell individually all at once? Basically the reverse of a top balancing resistor BMS? I used a single cell version of that concept that Dimitri made. It did take a while finishing off each cell individually.


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## JRP3 (Mar 7, 2008)

You'd have to be able to set it lower than 3 volts since under 10-20amps of load the cells will sag a bit and then spring back up when the load is removed. Might want to aim for 2.7-2.8V.


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## Tesseract (Sep 27, 2008)

JRP3 said:


> Are you talking about something that bottom balances each cell individually all at once? Basically the reverse of a top balancing resistor BMS? I used a single cell version of that concept that Dimitri made. It did take a while finishing off each cell individually.


Something that balances each cell individually, and similar, but different, from a simple resistor-based top balancing circuit.




JRP3 said:


> You'd have to be able to set it lower than 3 volts since under 10-20amps of load the cells will sag a bit and then spring back up when the load is removed. Might want to aim for 2.7-2.8V.


Pulling 0.1C or less from these cells barely budges the voltage, in my experience, except as it relates to state of charge. 2.90V would probably be what I set it to shut off at, though.


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## karlos (Jun 30, 2008)

An efficient way to bottom balance of course would be very good.
After listening to all the ideas I can't help thinking that if each cell had it's own charger (cheap mass produced) as as far as I understand a cell phone has, it would work very well and then all that would need to be done is monitor the system so the weakest cells are not over discharged. I know it may not seem like and ideal solution but has it ever been considered? I know EVers with 12 volt cells sometimes do this and it seemed smart to me.


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## JRP3 (Mar 7, 2008)

Tesseract said:


> Pulling 0.1C or less from these cells barely budges the voltage, in my experience, except as it relates to state of charge. 2.90V would probably be what I set it to shut off at, though.


I don't know exactly what amps I was pulling with the 12 volt headlight on 4 cells but when I took it off I remember the cells would go from 3.00V under load to 3.04V or so without the load. There was even a slight spring back of 0.01V with Dimitri's 3 amp circuit. You want to get into the steep part of the discharge curve where voltage gives an indication of SOC. Smaller cells will of course sag more. You could do a test and see what a 100Ah cell does after going to 2.90V under load.


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## JRP3 (Mar 7, 2008)

karlos said:


> After listening to all the ideas I can't help thinking that if each cell had it's own charger (cheap mass produced) as as far as I understand a cell phone has, it would work very well and then all that would need to be done is monitor the system so the weakest cells are not over discharged. I know it may not seem like and ideal solution but has it ever been considered? I know EVers with 12 volt cells sometimes do this and it seemed smart to me.


You'd need a large number of individual chargers that could each do 20 or more amps, and then you'd end up with a top balanced pack, which is really not what you want. Slightly overcharging a cell or two at 20 amps or less is a lot better than discharging a cell while driving at 200+ amps.


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## karlos (Jun 30, 2008)

JRP3 said:


> I don't know exactly what amps I was pulling with the 12 volt headlight on 4 cells but when I took it off I remember the cells would go from 3.00V under load to 3.04V or so without the load. There was even a slight spring back of 0.01V with Dimitri's 3 amp circuit. You want to get into the steep part of the discharge curve where voltage gives an indication of SOC. Smaller cells will of course sag more. You could do a test and see what a 100Ah cell does after going to 2.90V under load.


Wouldn't the sagged voltage be a better measuring stick if all the batteries were balanced to the sagged voltage cut off? Wouldn't that give you a better indication of the real situation with the battery and when the damage will start and also indicate what is happening during use?
If you used the 'recovered' voltage, could that not mean under use one of your cells could still drop far quicker than the rest, despite being balanced at rest?


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## karlos (Jun 30, 2008)

JRP3 said:


> You'd need a large number of individual chargers that could each do 20 or more amps, and then you'd end up with a top balanced pack, which is really not what you want. Slightly overcharging a cell or two at 20 amps or less is a lot better than discharging a cell while driving at 200+ amps.


I hear what you are saying.


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## Dalardan (Jul 4, 2008)

I'd be interested. I'm starting to play with batteries right now, and I'm looking for a tool like that.

Let's see who's interested.

Dalardan


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## JRP3 (Mar 7, 2008)

karlos said:


> Wouldn't the sagged voltage be a better measuring stick if all the batteries were balanced to the sagged voltage cut off? Wouldn't that give you a better indication of the real situation with the battery and when the damage will start and also indicate what is happening during use?
> If you used the 'recovered' voltage, could that not mean under use one of your cells could still drop far quicker than the rest, despite being balanced at rest?


As long as you have actually gotten to a low enough SOC so that the voltage actually tells you where you are. It's possible you could sag to 2.9V or so under load but spring back above 3.0V where you would not yet be in the steep part of the curve. The deeper you are in the curve the more resting voltage tells you about SOC.


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## dimitri (May 16, 2008)

JRP3 said:


> I bottom balanced by driving until average cell voltage was around 3.10 volts but I probably could have taken it lower. I then took a 12 volt halogen headlight and hooked it to 4 cells at a time until the lowest of the 4 was nearing 3.00 volts. I then used a bottom balancing circuit with a resistor that pulled each cell down to 3.00 volts individually and shut off. You could do the same with a 3 volt flashlight bulb and monitor it with a voltmeter. I've only done this once, not sure how often I'll really need to do it but next time I do a deep discharge I'll take the pack down to an average of 3.00 volts per cell and see how close they are sitting.
> To find my "weakest" or smallest capacity cell when I charge I monitor which cell gets full first. It will show up by starting to quickly gain voltage faster than the others when it hits around 3.45 volts. This does require some close attention when first charging as you near 3.45 volts as it can shoot up depending on how many amps you are charging at. I have 4 cells that get full faster than others and within those 4 there is one that is more pronounced. That's the one I use to set my charger shutoff point. When it hits 3.45V the charger goes into CV mode and cuts back on amps until it times out. I'm using a PFC30 charger.


I just thought I'd point out that such approach requires you to have adjustable charger, with ability to fine tune CV voltage to a fraction of one volt. I know of 2 of such chargers, Manzanita at $2000 and Brusa at $3500. Most affordable chargers like Elcon or Zivan are not easily adjustable. So, make sure you plan for a proper charger in advance if you want to follow this method.

Do I even need to mention that you'd spend extra $1000-1500 on charger to avoid spending $500-$700 on simple BMS  ?

I also don't know how well these chargers stick to fine tuned CV voltage, I hope the trimpot can hold adjustment level despite being installed in a moving car with variety of ambient temperatures. I hope you won't go to bed thinking you have it at 120V when its in fact at 125V.

I know, I know, this is where Jack would bring the Blue Elephant argument , so feel free to throw some stones my way


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## karlos (Jun 30, 2008)

dimitri said:


> I just thought I'd point out that such approach requires you to have adjustable charger, with ability to fine tune CV voltage to a fraction of one volt. I know of 2 of such chargers, Manzanita at $2000 and Brusa at $3500. Most affordable chargers like Elcon or Zivan are not easily adjustable. So, make sure you plan for a proper charger in advance if you want to follow this method.
> 
> Do I even need to mention that you'd spend extra $1000-1500 on charger to avoid spending $500-$700 on simple BMS  ?
> 
> ...


Some good points! Once again, your approach is something more suitable for commercially produced EV's and I'm not talking about hydrids where the battery use is different. I still see a big difference between the requirements of an EV enthusiast and a someone who just wants to commute to the office. Therefore, keep up the good work Dimitri! The point I take from Jack is the need for any BMS to be well tested and regularly checked for loose connections etc.
When I joined the forum, what i used to hear all the tiem was that EV's because of the motor have the advantage of many less moving parts, BUT there are many many critical electrical connections and through faulty installation, vibration or whatever, this is a weakness that needs regular checking for.... I wonder what the Tesla requirements are in this respect?


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## dimitri (May 16, 2008)

Yes, loose connections have always been my concern as well, that is why I focused on designing a BMS that will alert when ANY connection is lost, including signaling and power connections. Even now, every month or so I check how tight terminal bolts are on all my cells, just being a little paranoid after I found a couple bolts weren't as tight as I thought, although its possible they were like that from last time I bolted them down. When working on 80-100 power connections you have to be VERY detailed and triple check everything, then come back next day and check again. Any mistake can be costly.


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## karlos (Jun 30, 2008)

dimitri said:


> Yes, loose connections have always been my concern as well, that is why I focused on designing a BMS that will alert when ANY connection is lost, including signaling and power connections.


Well if you have designed this into the system, that seems quite impressive and the way it should be


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## Guest (Jun 1, 2010)

dimitri said:


> Yes, loose connections have always been my concern as well, that is why I focused on designing a BMS that will alert when ANY connection is lost, including signaling and power connections. Even now, every month or so I check how tight terminal bolts are on all my cells, just being a little paranoid after I found a couple bolts weren't as tight as I thought, although its possible they were like that from last time I bolted them down. When working on 80-100 power connections you have to be VERY detailed and triple check everything, then come back next day and check again. Any mistake can be costly.


Agreed. Can you catch a bad connection when the resistence is high but before you actually loose a connection? I'd think that you'd want to catch early because if you loose a connection it could be too late.


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## JRP3 (Mar 7, 2008)

dimitri said:


> I just thought I'd point out that such approach requires you to have adjustable charger, with ability to fine tune CV voltage to a fraction of one volt. I know of 2 of such chargers, Manzanita at $2000 and Brusa at $3500. Most affordable chargers like Elcon or Zivan are not easily adjustable. So, make sure you plan for a proper charger in advance if you want to follow this method.
> 
> Do I even need to mention that you'd spend extra $1000-1500 on charger to avoid spending $500-$700 on simple BMS  ?


Certainly skipping a BMS is not the reason to get a Manzanita. I got it so that I could charge on available line voltage from 110-250V and be able to adjust my amperage draw from 0-30. Dual voltage charging made for a much more useful vehicle for me.


> I also don't know how well these chargers stick to fine tuned CV voltage, I hope the trimpot can hold adjustment level despite being installed in a moving car with variety of ambient temperatures. I hope you won't go to bed thinking you have it at 120V when its in fact at 125V.


This is a good point, and though I haven't seen that happen there is another issue that I'm dealing with. Setting the voltage trim when charging from 120VAC gives you a higher cutoff voltage than when charging from 230VAC, by about 2-3 volts. This means you either end up undercharging from 230VAC or overcharging from 120VAC. Other than going to a full cell level BMS a simple single pack voltage shutoff would probably provide a good solution. Feel like whipping something up Dimitri?  Or I suppose I could take a single Mini-BMS unit on the cell that reaches full first and use that to shut down the charger. Does that count as using a BMS?


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## karlos (Jun 30, 2008)

JRP3 said:


> Or I suppose I could take a single Mini-BMS unit on the cell that reaches full first and use that to shut down the charger. Does that count as using a BMS?


I like your ingenuity but once again this would work only for an enthusiast right, but then again you could sell each pack with an 'intentionally' slightly weak cell so you always knew which cell to monitor? Ha ha.


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## dimitri (May 16, 2008)

gottdi said:


> Agreed. Can you catch a bad connection when the resistence is high but before you actually loose a connection? I'd think that you'd want to catch early because if you loose a connection it could be too late.


When I said "power connections" I meant connection from the battery to the BMS module, not from the battery to the busbar, i.e. loose BMS module will signal alert, etc.

Its not simple to imagine what happens to loose power connection because it depends on how loose and how quickly it gets loose, right? With my BMS modules, if cell terminal disconnects from busbar it will likely blow a fuse on the BMS module since the module will complete high voltage circuit. Blown fuse will generate BMS alert, but it might be too late if loose connection is passing large current, it might melt by then. There are just too many variables to say exactly what would happen, but one thing for sure is that having BMS in this scenario is not any worse than not having it. Afterall, it was not designed to manage loose connections, it was designed to manage batteries 

Loose power connection in EV is a bad thing all around, not sure if it's possible to manage it with more electronics, rather than just being extra careful when making those connections in a first place.


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## EVfun (Mar 14, 2010)

JRP3 said:


> Or I suppose I could take a single Mini-BMS unit on the cell that reaches full first and use that to shut down the charger. Does that count as using a BMS?


Except that the slight load from the cell module will slowly pull the cell down and the other cells can't dissipate the extra charge required. 

Differential loads on the traction pack are a bad idea AFAIC.


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## JRP3 (Mar 7, 2008)

Yeah didn't think about the drain on the cell, though I'd imagine it would be pretty small? I could have it switched so it's only connected during charging.


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## JRP3 (Mar 7, 2008)

dimitri said:


> Loose power connection in EV is a bad thing all around, not sure if it's possible to manage it with more electronics, rather than just being extra careful when making those connections in a first place.


 Temperature sensor on every connection?


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## EVfun (Mar 14, 2010)

JRP3 said:


> Yeah didn't think about the drain on the cell, though I'd imagine it would be pretty small? I could have it switched so it's only connected during charging.


Well... just 7 milliamps adds up to about 5 amp hours per month. If you are plugged in only 5 hours a day (less than overnight) that would drop to 1 amp hour per month.

Even tiny loads add up to real amp hours over time.


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## dimitri (May 16, 2008)

JRP3 said:


> Certainly skipping a BMS is not the reason to get a Manzanita. I got it so that I could charge on available line voltage from 110-250V and be able to adjust my amperage draw from 0-30. Dual voltage charging made for a much more useful vehicle for me.


I didn't mean to point my post at you specifically, I just quoted your battery management technique and clarified that adjustable charger is required for it to work as described, it might not have been clear to those who stumble across this thread and want to follow this method.

BTW, Elcon is dual voltage too, at 30% the cost of Manzanita.


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## dimitri (May 16, 2008)

JRP3 said:


> Temperature sensor on every connection?


I have PTC fuses on my modules, so it would trigger BMS alert if fuse gets hot enough, but I am not sure it will happen fast enough to save the terminals. It all depends on how hot the terminal half an inch away from PTC fuse must get to raise the temperature of the fuse to 170F, which is tripping point of the fuses I use. And the opposite terminal is even further away, so even less effective.

You could get sensitive PTC fuses and epoxy them on each terminal and connect all in series to signal head end relay, but I am not sure how practical this would be when all you needed was to make good quality connection and not make a mistake like forget a lock washer.


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## JRP3 (Mar 7, 2008)

dimitri said:


> BTW, Elcon is dual voltage too, at 30% the cost of Manzanita.


Is it user adjustable from 12-450 Volts, 0-40 Amps output, 0-30 Amps input, adjustable time in CV phase, and a regbus interface?


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## drivin98 (May 9, 2008)

Not to bring up the name of a certain someone who recently departed the forum, but the latest installment of EVTV (June 25) touches on the BMS issue again. All I can say is "Holy SmoothTalk TM custom EV Battery Management Systems meltdown Batman!"

I wish I could discuss the loss of thousands of dollars worth of batteries and "BMS Management" equipment so calmly. Wowsers!


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## karlos (Jun 30, 2008)

drivin98 said:


> Not to bring up the name of a certain someone who recently departed the forum, but the latest installment of EVTV (June 25) touches on the BMS issue again. All I can say is "Holy SmoothTalk TM custom EV Battery Management Systems meltdown Batman!"
> 
> I wish I could discuss the loss of thousands of dollars worth of batteries and "BMS Management" equipment so calmly. Wowsers!


Yes quite an enlightening show for anyone wanting to use Kokam batteries. I was very surprised to see the current between the terminal/s (?) and casing, something seems really strange with that and obviously if there was current between both terminals and the casing the battery would be dead in no time. I hope if it is normal that there is a possible current between at least one terminal and the casing that Kokam clearly warns any users of this. Seems more to this than meets the eye


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## JRP3 (Mar 7, 2008)

Some people have a lot of money. To be honest I don't think the BMS ever came into play and I think he made a bit of a leap when talking about the "BMS" problem. Now the BMS may not have been any good, I have no idea, but it seemed to me that all the problems came from poor design and physical construction of the case and cell assembly. Everything was so loose it bounced around in shipping, and the live edges of the pouch cells were not insulated so they shorted and fried everything. Looked to me the same thing would have happened BMS or not.


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## karlos (Jun 30, 2008)

JRP3 said:


> Some people have a lot of money. To be honest I don't think the BMS ever came into play and I think he made a bit of a leap when talking about the "BMS" problem. Now the BMS may not have been any good, I have no idea, but it seemed to me that all the problems came from poor design and physical construction of the case and cell assembly. Everything was so loose it bounced around in shipping, and the live edges of the pouch cells were not insulated so they shorted and fried everything. Looked to me the same thing would have happened BMS or not.


I think that's pretty fair comment regarding both BMS and casing. I think it would be good if Victor responded here or somewhere, maybe he has? Obviously he is going to be pretty gutted by having this broadcast on the show, what's his side of the story?


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## dimitri (May 16, 2008)

I just love this one. As usual he comes to idiotic conclusions. All the talk about BMS, which hadn't even had a chance to work, while completely dismissing the fact that CELL CASING IS LOADED WITH VOLTAGE !!!!!!!

Who in their right mind makes a cell where the casing is conductive and loaded????? They are backing Kokam's position and this guy is apologizing to Kokam's rep?????? If these cells conduct thru their casing they are complete garbage and should never be sold to anyone.

"we just taped the edges and now they are good to go..." this is from the guy who just spoke about R&D and mechanical testing, these two should keep doing shows together, they certainly add to each other's incompetence.


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## JRP3 (Mar 7, 2008)

Actually I seem to remember reading about similar behavior with A123 pouch cells.


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## karlos (Jun 30, 2008)

Post by Victor from another website on 10 Dec 2009....
http://www.mentby.com/metric-mind/kokam-cells.html


> Watch out for one "feature" that ruined many of cells: the fused seams along
> sides are *conductive* and there is voltage potential between edges of
> the cell and its terminals. I found it hard way when put aluminum around
> thinking that plastic pouch the cell is in is insulator. Cells got
> ...


If there's not a warning on the website, well, seems not right to me; purchasers should be able to know all the dangers as well as benefits.


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## dimitri (May 16, 2008)

It should be written in big bold red letters all over the pouch, "*DO NOT USE IN CONDUCTIVE CASING*" or something to that effect.

Its strange that Victor knew about this and still placed cells in the aluminum box without apparent insulation. The whole thing smells fishy, I would not trust this story until I hear Victor's point of view.

I certainly would put more trust in EE with years of experience than magazine publisher and a medical doctor, playing EV experts on TV


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## karlos (Jun 30, 2008)

Yes, there is something 'fishy' about the timing although I don't know when the Doctor's experience was dated or missed it, kind of puts me to sleep listening to J.
I agree with your comments about the unproven BMS system, it appeared to me a cheap shot of Mr J.


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## karlos (Jun 30, 2008)

Seems others have become aware and am dealing with the problems but unless Kokam publishes the potential problem, others are going to get caught.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=15408&start=75


> *Re: Terminating the 15Ah and 20Ah Cell-Man cells*
> 
> by *liveforphysics* » Sun Jan 31, 2010 7:15 am
> olaf-lampe wrote:If I got LFPs comment correctly, he said that _sooner or later_ every cell get's a bit conductive between tab and pouch.
> ...


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## JRP3 (Mar 7, 2008)

I was correct, it's not just Kokam:


> I'm starting to assemble my cell and wonder if insulating sheets between the cells in the stack is a good idea?
> With any pouch cell it's a good idea, even something simple like a layer of wide double side tape is enough.
> 
> 
> ...



http://endless-sphere.com/forums/viewtopic.php?f=14&t=15408&start=240


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## Guest (Jun 29, 2010)

> Contact Us to discuss how we can help you meet your challenges.


Seems like someone thought they knew what they were doing and they did not. The Doc with the money expected that level of professionalism but got scammed. For $40K you'd expect that level too. Most here are not even close to that level. That is quite evident by the responses. Have you been to the Kokam web site? 

metric mind is at fault. Not the Doc who expected a high level of professionalism for what he paid and it is not Kokam's fault because metric mind did not discuss what might need to be done to properly make a working pack. 

And what's with the BMS being Half the cost? That is total garbage and that is what they were talking about but the BMS system did short out and burn too. 

Sorry but I am with Jack. He has far more to give than this place any longer. Just look around at the types of discussions there are here. A few others over at EVDL and a few here but not much any more. 

Metric Mind is one to watch out for if your going to buy batteries or to have them do the work for you. 

Pete


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## JRP3 (Mar 7, 2008)

The BMS probably burned because of the cells shorting out to the case. I'm still not sure the BMS ever had a chance to do anything. I think the cost included the case and assembly, not just the BMS boards. Still too expensive, especially since the case design seems to have been poor. I do think a battery manufacturer should have a warning if the outside of their cells is conductive, but it's also up to the pack builder to be aware of the cell characteristics.


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## karlos (Jun 30, 2008)

gottdi said:


> Have you been to the Kokam web site?


No, don't have the time to visit the Kokam site but please tell us, do they warn that the pouch seams can be 'livend' with a terminal and if so which one or both
I understood the other half than the batteries included the rather pricey looking casing, not just the custom developed and untried BMS; seriously what do you think is going to happen to a BMS with all that shorting out going on? Same thing a spanner would do if you dropped it across any battery terminals I imagine. 
Beat me too it JRP3!


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## Guest (Jun 29, 2010)

Did they contact Kokam to discuss what was required. I saw that and know that I would contact them for further information. Kokam is not a DIY site. They require you to contact them and if you don't then you are on your own. Kokam sells both bare cells and complete packages for your application. Regardless you must contact them. If your not smart enough to do that then you should not be building custom parts. Kokam does not need to nor are they required to put that on the site. You who are going to build must be the one to ask and contact them on your intentions. Zapi controller is the same way. You must contact them for application information. If you don't your on your own and have no warranty. Metric mind is at fault. No one else. 

I don't disagree that the BMS was destroyed because of the battery bongle but the cost is insane. The Doc would not know and was told that he needed a BMS if the pack was to have a warranty. It is not up to the Doc to eat the cost of the bongle but Metric mind as they were the ones to build for the Doc. He was willing to pay because he had the money and did not have the knowledge. That is what people do. People also screw people too and Metric mind now has the doc's money and won't return it. No different than another company screw up we all know so well. 

Pete


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## karlos (Jun 30, 2008)

gottdi said:


> Did they contact Kokam to discuss what was required. I saw that and know that I would contact them for further information.


No could not find any recommendation on Kokam site to contact them regarding what material to use for a battery case but they ask you to contact them re BMS selection.
It's slightly amusing that Jack hammered the Swiss motor company for not enough instal information and appears to think it's OK in this case a battery company does not proactively warn to insulate the battery casings... to me some mixed standards of expectation here, imagine if Jack had made the casing and they shorted...


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## Guest (Jun 29, 2010)

> Contact Us to discuss how we can help you meet your challenges.


Once again you must contact them for the information. As for Jack and the Swiss company it is nothing like what happened with Metricmind. Jack DID contact them and WORKED with them and they balked and balked and never gave the information. Just like all those companies who only want to work with big companies and not the DIY back yard JOE. Kokam has taken a risk and that risk is real as can be seen. Jack did work through the issues with the motor and has a working system and has done what was needed to make it work. He EARNED the right to BITCH. The DOC paid for the right to BITCH. 

Pete


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## Guest (Jun 29, 2010)

To bad the Doc can BOAST about Metric Mind but instead he has to BITCH. For $40 you'd be much louder. 

Go figure that Metric did not consult. If they had I am quite sure they would have come up with a working system. I have no doubt. 

Come at this from Kokam's view. Come at this from the Doctor's view? Come at this from the expectation that the money spent was for a proven accepted warranted and working system. You'd expect the same level. It's easy for all of us to sit here but remember that money IS REAL. The PROBLEM IS REAL. Lets point fingers some more. Pretty obvious Metric did not contact Kokam. With a warranty in hand the Doc has full legal control and metric will be in trouble from this. Not the Doctors fault. Not Kokam's fault. 

Pete


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## Roy Von Rogers (Mar 21, 2009)

karlos said:


> No could not find any recommendation on Kokam site to contact them regarding what material to use for a battery case but they ask you to contact them re BMS selection.
> It's slightly amusing that Jack hammered the Swiss motor company for not enough instal information and appears to think it's OK in this case a battery company does not proactively warn to insulate the battery casings... to me some mixed standards of expectation here, imagine if Jack had made the casing and they shorted...


 
I'm sorry but there is a big difference between a pouched cell which is NOT a complete package by itself, and comparing it to a motor that is a completed unit, without instructions to proper mounting procedures.

The weak front motor mounting plate was bad engineering, period. 

Roy


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## karlos (Jun 30, 2008)

gottdi said:


> Once again you must contact them for the information. As for Jack and the Swiss company it is nothing like what happened with Metricmind. Jack DID contact them and WORKED with them and they balked and balked and never gave the information. Just like all those companies who only want to work with big companies and not the DIY back yard JOE. Kokam has taken a risk and that risk is real as can be seen. Jack did work through the issues with the motor and has a working system and has done what was needed to make it work. He EARNED the right to BITCH. The DOC paid for the right to BITCH.
> 
> Pete


Ok Pete, we are going to continue to disagree, but Kokam DOES sell to DIYers and therefore the "risk they took " was not supplying ALL the relevant information. It is just not good enough to publish data on the strengths and weaknesses of theirs to other batteries and then not warn of a situation which is unusual in the battery world. OK maybe most pouch cells can it seems have this problem but no other type of batteries does that I have ever heard of. Just as with their BMS requirements, a is warning required in my book as like Jack I expect ALL relevant information to be published when supplied with batteries. Maybe you would not have been Pete but I can see I could have caught out with this one.


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## Guest (Jun 29, 2010)

I disagree. You are required to call. They have it right on their site. Beyond that you have no clue what information the provide. The motor mount was a poor design but for it's original purpose it worked just fine. It needed or was decided it needed beefing up. Jack decided it was weak and make it better. There was other stuff involved too. Until your talking to the horse it really is all BS. I talk to the Horse and I contact companies for information. Do you? No you expect to have a road sign up for all the little nuances to be posted.

Pete


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## karlos (Jun 30, 2008)

Roy Von Rogers said:


> I'm sorry but there is a big difference between a pouched cell which is NOT a complete package by itself, and comparing it to a motor that is a completed unit, without instructions to proper mounting procedures.
> 
> The weak front motor mounting plate was bad engineering, period.
> 
> Roy


I see it differently; a motor IS part of a bigger system and the 'weak' mounting plate works in other applications and has to interface with other products/materials just as the cell pouch has to, period. In an ideal world ALL information should be supplied or don't sell them to DIYers, it's now pretty obvious why isn't it?
Anyway, this is a BMS thread so lets get back on topic.


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## karlos (Jun 30, 2008)

gottdi said:


> little nuances
> 
> Pete


Had to laugh at that once, this is not a "little nuance" to me or those who lost out.


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## Guest (Jun 29, 2010)

The motor was designed and what was given will work. Not saying it was a good design but a usable design. All Jack did was improve it and they got pissed at him for doing so. Go figure. He did them a favor buy giving information that will be useful for future sales. But no they had to slam him for improving and making a decent product better. Did he have to improve it? NO. But when he got slammed he slammed back. What else would you expect. 

Pete


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## karlos (Jun 30, 2008)

To get backon topic, what interests me is, Kokam seems they will only approve certain BMS systems which does not seem uncommon in the high end battery producers world and did they approve Victor's BMS design? Did they get design drawings/details etc and how they would be attached to the casings for example. You might guess where I'm coming from


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## JRP3 (Mar 7, 2008)

The end plate on the MES motor was NOT intended as a motor mount, yet MES never had any warnings about it. Since face mounting is common practice with motors they should have made it clear that theirs was different and it was not for mounting. It's like selling an engine block that you can't mount a transmission to directly. I don't think they are changing their design at all, though they should, but maybe they will at least include a warning, stamped on the motor face. As for Kokam, if I'm selling a battery cell that has voltage potential on the OUTSIDE of the cell, a simple printed warning would be advised: "Cell Case Must Be Insulated", printed on every one, or at least mentioned in the literature. They have spec sheets available, with C rates, operating temps, and dimensions, why not mention a live cell case? Did anyone directly contact TS, SE, Hipower, or any LA battery supplier to see if the outer case had voltage potential? I doubt it, because you don't expect that to be an issue. I'm not saying Victor wasn't at fault, he clearly was, but a simple warning from the manufacturer might have avoided a lot of problems.


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## dexion (Aug 22, 2009)

I just don't see why the heck they would do that. By making it so the cells couldn't be laid on top of each other or side to side mounting and securing is very difficult. Is there any advabtage to the design I'm not seeing?


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## JRP3 (Mar 7, 2008)

Maybe the foil pouch is a cheap, easy way to package the cell and manage heat buildup?


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## revhead (Jul 2, 2010)

dimitri said:


> In my experience, burning off more than 2-3 Watts per cell is a waste of energy and a heat hazard. That is why I limited MiniBMS shunting at 0.75Amp. I find it plenty to keep my 160AH pack balanced long term. "Long term" is the key here, why bother with perfect balance at every charge/discharge cycle? It doesn't need to be perfect every time, as long as there is counter-imbalancing mechanism in place it will keep the pack balanced long term.
> 
> As for big stuff like dropping the wrench or marrying new cells into existing pack, this deserves manual balancing since its a one time thing. Why add all this every day cost and complexity to BMS to manage things that don't need to be managed every day. I go by KISS principle and it seems to work well.
> 
> ...


Dimitri your mini bms appears to be a copy of the EV Power BMS.
www.ev-power.com.au


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## Tesseract (Sep 27, 2008)

revhead said:


> Dimitri your mini bms appears to be a copy of the EV Power BMS.
> www.ev-power.com.au


It doesn't look at all similar to me. This is pretty brazen first post, btw.

(edit) Whoever designed the EV-Power BMS made a classic blunder - soldering stranded wire directly to a pc board. The solder wicks up the strands and causes fatigue cracking, especially in a high vibration environment like an EV. I read the entire manual just now and I am even more convinced that any similarity between the two BMS designs (like the ultra-obvious and much-discussed NC loop for reporting errors) is simply because a BMS has a relatively limited and defined functionality requirement.


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## dimitri (May 16, 2008)

revhead said:


> Dimitri your mini bms appears to be a copy of the EV Power BMS.
> www.ev-power.com.au


Rather than chasing me all over the internet with empty cheap shots, please take time to read MiniBMS design thread, so you can follow MiniBMS from its inception as an open source project, developed with help of forum members.

I'm assuming you are the same person who repeatedly posted similar comments to my YouTube videos. 

Define a "copy" please. Many BMSs have similar features, there are not too many ways to do a BMS. 

Maybe you are one of those people who like to patent "circular device designed to move loads from point A to point B"


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## revhead (Jul 2, 2010)

I read back through some your of the posts just now.
It must be just a coincidence then. Two ways of doing the same thing.

Its just strange that apart from the NC loop even the LEDs on the cell boards operate the same way.


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## ewdysar (Jun 15, 2010)

revhead said:


> Dimitri your mini bms appears to be a copy of the EV Power BMS.
> www.ev-power.com.au





revhead said:


> I read back through some your of the posts just now.
> It must be just a coincidence then. Two ways of doing the same thing.
> 
> Its just strange that apart from the NC loop even the LEDs on the cell boards operate the same way.


I just realized that my wife's Camry appears to be a copy of my Accord. Maybe it's just a coincidence, but all of the primary controls are the same and they even have the same size tires. However the gas fillers are on opposite sides, so it may not be a copy after all. 

Eric


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## revhead (Jul 2, 2010)

To Quote an early post from Dimitri:

"I especially liked the idea of simple BMS proposed by Johnny on Australian forum, so I have taken his schematic and applied few changes based on input from other BMS discussions. I also done some research on key components and their prices at Digikey, to make sure we keep total parts cost around $5 per cell."

Ahah, the trail leads back to Australia... Johnny!

I guess the idea of the wheel appeared pretty obvious to everyone after the guy first invented it. He (or she) was probably the first person broken on it too.


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## Tesseract (Sep 27, 2008)

revhead said:


> ...Ahah, the trail leads back to Australia... Johnny!


Good work, detective revhead!  

So this Johhny dude posted his schematic on to a forum much like this one? He shouldn't be surprised, then, that someone else was enterprising enough to adopt it for their own purposes. Indeed, I bet that was more or less the reason for Johnny making it _public domain_ in the first place!


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## dimitri (May 16, 2008)

revhead said:


> Ahah, the trail leads back to Australia... Johnny!


That's right, I never claimed original idea, I have been open about it, unlike other "inventors". What Johnny posted on AUEV forum was a functional schematic of "voltage window detector" using comparator IC. I loved this idea for its simplicity and minimum discreet components, so I took it from there. Later I found that "voltage window detector" of this type wasn't a new idea at all, its one of most basic circuits which has been around for decades, as long as LM339 IC existed, so I guess even Johnny can't claim it, although he never did.

I never seen EV Works modules up close, but yesterday, after you posted the link, I looked at their site again and in some close up pics I can barely make out components inside the potted unit. I can see 3 or 4 SOT-23 components, which are likely separate voltage reference ICs and I can't see 14 pin LM339 ICs anywhere, so I guess their system is a classic 3 stage voltage divider, using separate voltage ref for each stage, and I guess that proves that I didn't "copy" it. This type of BMS existed long before I knew what BMS is, and I seriously doubt that EV Works "invented" any more than I did, so lets drop the silly copycat subject, shall we?

Also, 20 page long BMS thread on AUEV forum is the best source of BMS related ideas I ever found. My hat goes to AUEV members for keeping calm, friendly and respectful discussions, resulting in great developments......until Jack came along and laid big pile of poop all over it, just like he does on all other forums.

So, yes, the trail leads to Aussies, like I said in the very first post about MiniBMS , I always try to give credit where its due 

Oh, and if you aren't the same person who posted idiotic comments on my YouTube videos, then I apologize, but you can see where my reaction came from to someone's first post on the forum being a cheap shot.


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## dimitri (May 16, 2008)

Also, for those who don't know the difference between "functional schematic" and actual production schematic, it takes countless hours of calculations, prototyping, blowing parts and ordering bunch of new ones, until you get it right. Then countless hours of PCB design, ordering prototypes, fixing mistakes, ordering again. Then having to spend $$$ to get 1000s of parts to get bulk pricing, so I can keep the price of complete module affordable, then working 14-16 hour days to get it all ready for customers, then spend countless hours on Web site, documentation, answering questions. Then seeing all your hard work being crapped all over by magazine publisher who likes to drink scotch in front of the camera, smacking lips while laying poop on everyone who doesn't have their head up his ass already.

So, yes, I have been busy "copying" EV Works BMS.... and I welcome anyone else to try and do the same and see how much easier it is to be armchair expert.


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