# top balancing Li before installation... ok?



## newbcake (Aug 5, 2010)

Not only is it ok, that's recommended. Under no circumstances would I take the manufacturer at its word and install cells as is without balancing them first. However, individually balancing cells is quite tedious, you should look into purchasing balance boards if you have several hundred or more cells.


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## dexion (Aug 22, 2009)

You have to get them all in line (somewhere in the charge) with the easiest being top or bottom top being much easier. Just snag one *(or more) of those $20 single cell lifepo4 chargers you see on ebay and let them work on each cell until you are done. Or if your cheap and lazy (like me) hook them all up in parrallel on the kitchen floor with some 10G wire and then stick a 10 amp power supply on the end at 3.6v and wait 3 days stepping over them to get to the poptarts.


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## A-Class-Driver (Aug 24, 2010)

Hi Dan,
I'd like to recommend watching these two "Friday Shows" from Jack Rickard:
http://media.ev-tv.me/news111309-1280.mov and
http://media.ev-tv.me/news121809-1280.mov

It takes a little time, but saves money...

After that, I think you'll never ever think about "top balancing" again

Michael


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## Guest (Aug 25, 2010)

Bottom balance them. Then charge them up. That way you won't be over charging any of them. Take them all down to lets say 3 volts then charge them up. Set your charger to charge to like 90% instead of 100%. Watch the videos mentioned. Build your pack a bit larger than expected. Buy a few extra batteries just in case you need to replace one, it's cheap insurance as is bottom balancing and not discharging all the way and not charging all the way. Works with any battery. 

Pete


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## dtbaker (Jan 5, 2008)

I will watch.... but am struggling with accepting bottom balancing as the answer. Since chargers all bring pack voltage UP to some voltage, which is hopefully just above the knee as voltage begins to rise, the only way to be sure no single cells are 'ahead' of the others is to top balance. 

Cells probably have slightly different capacity, and if you bottom balance, I think you are destined to have some cells 'finish' before others and start over voltage until the others catch up.... unless you have a shunting BMS. 

I plan on NOT using a shunting BMS, and so want to try to make sure the cells all are finishing at the same time and not going past the knee.....


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## A-Class-Driver (Aug 24, 2010)

dtbaker said:


> I will watch....


Please do so and you do will realize why bottom balancing is the right thing to do 

Michael


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## dtbaker (Jan 5, 2008)

I am having trouble downloading this GIANT .mov ... fills my old computer memory cache...
d


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## mcrickman (Sep 10, 2007)

I'm currently in the same boat as you are Dan. Except I'm out the money on a BMS that after installing and testing I decided I didn't want to pay good money to burn my house down. So I am also not going to be using a BMS and monitoring the batteries myself. The company I purchased my batteries had balanced them to 3.3 volts I believe. 

This is my plan:
I have a Zivan charger that's programed to charge to 3.6 and top off to 3.8 volts for my pack of 48 batteries. So I went ahead an charged the pack and I plan on discharging it until I get the first cell(s) down to 3.0 volts.

Then any other cells that are above that 3.0 I will discharge down to match the 3.0 volts. Then that should balance the pack at the bottom. 

I have learned a lot from watching Jacks Show. So now I need to just get my controller re installed and start discharging my first charge and logging it. 

Charlie


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## mcrickman (Sep 10, 2007)

dtbaker said:


> I am having trouble downloading this GIANT .mov ... fills my old computer memory cache...
> d


There is one of the earlier videos on battery management on you tube.
http://www.youtube.com/watch?v=tRISZS1l76k 

Charlie


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## Guest (Aug 25, 2010)

More reason to bottom balance. Run them down to equal balance then charge to a bit under full. If your batteries are so far off from each other then you need to replace them with batteries that match. Balanced from the top you run a greater risk of a battery draining too soon and kill the battery post haste. 

But if you must, you can listen to your own logic and go with that. It is after all your pack and your money.


Pete


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## dtbaker (Jan 5, 2008)

gottdi said:


> More reason to bottom balance. Run them down to equal balance then charge to a bit under full. If your batteries are so far off from each other then you need to replace them with batteries that match. Balanced from the top you run a greater risk of a battery draining too soon and kill the battery post haste.
> Pete


I am much more concerned with OVER charging an unbalanced cell that is 'full' before the total pack voltage reaches final voltage set by the charger. My charger does not monitor individual cells, just the pack total, so if one cell is full and climbing and the others are far enough behind not to trigger the charger, then I'd have problems.... I do not anticipate using more than 50% DOD most days, so am far less concerned with draining a short cell....


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## Overlander23 (Jun 15, 2009)

Bottom balancing would help if you intend on dipping into your pack's range enough to drop a weak cell too low while not having a per cell LVC monitor, because all the cells are lined up at their "weakest". The flipside is can't charge the pack to its individual cell max... ypu have stop when the first cell hits HVC, or just charge to 90 or 95% (or whatever voltage insures you can't overcharge a cell)

Top balancing means you shouldn't need to worry as much about charging to 100% without a per cell HVC monitor. But you have to stay well away from the bottom of the pack.

If you are reasonable with your pack usage and just decide to work between 25% and 90% SOC then I'd imagine that either method would work fine.

Some people say that bottom balancing is "safer" on the pack because chances are you're pulling more amps at that end.

Others like top balancing because it makes charge management easier (not that programming a charger to stop at something 3.65v vs 3.8+ is difficult)... or that you can carry slightly more capacity per cell if you're drawing from the very top... if the cells are really all over the place regarding potential capacity.

Does anyone have simple analog circuit that will "bottom shunt"? IE. a way of automatically discharging a cell to a set voltage rather than having to manually monitor the process?


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## Guest (Aug 25, 2010)

You need to be very very careful of over discharging your pack. The lithium will hit that point and just drop out under you in a heart beat and your pack is toast. Bottom balance is the best. I am sorry you are going the route of top balancing. I wish you the best and the least amount of trouble keeping them together. I will be bottom balancing my pack when I get mine. 

Pete 

Easy to keep from over charging and easy to keep from over discharging. Bottom balance and you will be good to go. Top balance and you will need to be sure your not over discharging one or more during your drives. All so far who bottom balance and keep just shy of 100% and 0% have had nothing but good things to say. They say they are keeping balanced with no further intervention. That is a good thing.


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## dtbaker (Jan 5, 2008)

gottdi said:


> You need to be very very careful of over discharging your pack.


yup, I think a decent aH counter and my normal driving habits will keep me up around 50% DOD at worst.




gottdi said:


> All so far who bottom balance and keep just shy of 100% and 0% have had nothing but good things to say.


If you can keep inside the limits I have no doubt everything is good. 
I have not etched my decision in stone, but the thing about bottom balancing that I just don't get is....
- lets say you do a great job bottom balancing all the cells, BUT you happen to have one cell with a capacity of 99aH, while all the rest are a nice fat 105ah (100ah nominal cells).
- lets say you have 38 cells for a 120v nominal system set your charger to take the cells up to a conservative 138.7v (3.65*38), or 140.0 v (3.68v/cell)

.... now, what happens during charging when that first low capacity cell is full and its voltage hits the knee and starts climbing, and the total pack voltage hasn't risen hardly at all because all the other cells are happily sucking up more juice. My logic is that without a shunting BMS in place, that one low capacity cell will get overcharged before the total pack voltage rises enough to shut down the charger if the cells are bottom balanced.

my current belief that top balancing is right for me is based on the thoughts that if they are top balanced, the cells remain in balance during use and all end up about the same ah depleted.... then will all fill the same during normal charge, and start registering a voltage climb at the same time, and raise the pack voltage enough to shut down charger with cells still being in balance..... maintained by periodic top balancing after a charge just to make sure they are all finishing at the same time. Since I am planning to avoid full discharge, I am not worried about the one short cell at the bottom end of capacity during discharge....


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## Elithion (Oct 6, 2009)

First, connect all the cells in parallel. Then:

If you do not plan to use a BMS, that's it. After a few days, the current between cells will be down to nothing. At that point, all the cells will be at the same OCV (Open Circuit Voltage), which inherently means that they are at the same SOC (meaning the pack is balanced). The pack won't be balanced at any other SOC, because of difference in cell capacitance, but, all and all, it will remain close to balanced as you fill it all the way, and empty it all the way.

If you will be using a decent BMS, which will do top balancing, you want to bring all the cells to their top voltage (3.4 V for LiFePO4, 4.0 for ThunderSky, 4.2 V for Lipo). Get a power supply or a charger, set it so that it will top off at that top voltage, and connect it to the cells in parallel. After a few days, the current between cells will be down to nothing. At that point, all the cells will be at the same OCV (Open Circuit Voltage), which inherently means that they are at the same 100 % SOC (meaning the pack is balanced). Again, the pack won't be balanced at lower SOC levels, because of difference in cell capacitance.

DO NOT DO BOTTOM BALANCING without a BMS: yes, it will keep you form killing a cell from undercharging, but you will risk overcharging a cell, which is a potential fire danger. JUST DON"T DO IT.

Here is an interactive tool to help you visualize the process:
http://liionbms.com/balance/index.html

This book goes into a lot of detail on why you should balance before building a pack, on how balancing maximizes pack capacity, and the 7 reasons why top balancing is good and bottom balancing is hare brained.
http://book.liionbms.com/
http://www.amazon.com/Battery-Management-Systems-Large-Lithium/dp/1608071049/ref=sr_1_1?

Davide
________
Rhode Island Marijuana Dispensary


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## Elithion (Oct 6, 2009)

gottdi said:


> Bottom balance is the best. I am sorry you are going the route of top balancing.


Top-balancing without a BMS: risk losing a cell due to undercharge
Bottom-balancing without a BMS: risk losing a vehicle due to overcharge

Will you take responsibility for giving such advice to the poor fellow who decides to follow it and then his EV catches fire when a cell is overcharged?
________
Variable Cylinder Management


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## Guest (Aug 25, 2010)

The bottom balance is just to bring the cells within a close range then connect and let sit like was said. Bottom balancing is not something you do daily or with a BMS. If you have one cell that is 99 AH and all others are sitting at 105 AH then you need to replace that one battery with one that matches closer to the 105 AH. Watch the shows. It will help you understand.


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## Overlander23 (Jun 15, 2009)

I'm not advocating top or bottom balancing, but this is a bit overstated if the correct practices are put in place.

Top balancing without BMS, risk losing a cell due to undercharge if you get near the bottom of SOC. At 50% SOC there's no risk of this (short of an already shot cell dying). At 25% SOC there's probably no risk of this, although if you do kill a cell, it probably needs changing anyway.

Bottom balancing without BMS, risk losing vehicle due to overcharge. Again, not necessarily a large risk if the charge management rolls off at a relatively low voltage (ie. max the pack out at 85-90% SOC). And/or roll the current off earlier so that you "top off" (still at 85%-90%) at a very low current.

Stay in the middle, so to speak, and treat the pack conservatively, and I can't come up with any negatives short of some potential range loss.



Elithion said:


> Top-balancing without a BMS: risk losing a cell due to undercharge
> Bottom-balancing without a BMS: risk losing a vehicle due to overcharge
> 
> Will you take responsibility for giving such advice to the poor fellow who decides to follow it and then his EV catches fire when a cell is overcharged?


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## dtbaker (Jan 5, 2008)

Elithion said:


> First, connect all the cells in parallel.


Thanks for the excellent, and very expert, confirmation that I am on the right track protecting from overcharge (without a shunting system) by top balancing. I also very much appreciate the simple idea to connect all in parallel and either balance at SOC as delivered, or throw in a power supply and top balance to a precise finish voltage initially before install. I was dreading the individual pre-charge with power supply, and hadn't thought of connecting all in parallel to balance before install and series connections.


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## Guest (Aug 25, 2010)

We give suggestions from real world information but in the end the end user is the one who decides what to do and what information to follow. No one is at risk except the end user. If he decides to go with x way of doing things or xy way it is his decision and he fronts the full risk. 

Pete


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## dtbaker (Jan 5, 2008)

gottdi said:


> If you have one cell that is 99 AH and all others are sitting at 105 AH then you need to replace that one battery with one that matches closer to the 105 AH.


this is part of my point.... if I top balance, and then 'never' go more than 90%DOD, I don't have to care whether one cell is 99 and others 105 because I will never use more than 90.


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## Guest (Aug 25, 2010)

There is a great chance you will at some point go well below the limits you have set. Unless you have that limit set in your controller then you run the risk of dropping a battery or more. Have a nice pack that is limited to not go below x and one that is close but not quite to the top and well within safe ranges if your batteries are real close then you won't have to worry. Saying you will only use 50% dod is like saying I won't use more than half throttle in my Porsche.


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## A-Class-Driver (Aug 24, 2010)

...ahead of all: i'm taking about LiFePo4 



dtbaker said:


> this is part of my point.... if I top balance, and then 'never' go more than 90%DOD, I don't have to care whether one cell is 99 and others 105 because I will never use more than 90.


That's -in my opinion and, Jack Rickards as well- the most dangerous thing:
If you indeed *once* discharge the pack to more than this 90% (that was your "personal" limit), you *just will not realize* that you are already killing the weakest cell in the battery system. Because the system runs very well furtheron, and the controller drains current from battery. Reason is, that the total voltage of battery in use drops only about less than 2V to 3V, which is "very normal" under load conditions.
Meanwhile this cell with e.g. 95 Ah leads exactly that current that your controlller needs, and 99% of other cells have still capacitiy and deliver it.
BUT the voltage at this cell drops to zero. That's the end of it. Maybe, if your battery contains more than one cells with about 5% less capacity, you'll have to replace even more than one cell  and spend lot of money.

J.Rickards told this story, because he had "murdered" 3 or 4 cells by not taking care of bottom balancing.

Everything won't happen, if indeed you use only 50% or 60% DOD continously.
I'm not yet driving an EV, but I'm sure that 90% DOD will happen -not often- but at any time in reality...

reg. over charging:
I believe, it's not as critical as some other here tell (LiFePo4).
In order to obtain a long lifetime/charging cycles of the battery, Jack recommends to switch from CC charging to CV charging even at 3.5V. Then current going to zero by itself.
What the hell does anyone need the last 3% or 4% of the nominal battery capacity?? No one can/could explain that 

Finally: everyone decides by himself, what's the best way to take care of his battery 

Good night, Michael


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## JRP3 (Mar 7, 2008)

I've been running a bottom balanced pack for around 4 months. Bottom balancing probably saved a number of my cells once when I underestimated my charge and my power use. I pulled my pack to 1.77 volts per cell under load. Consider which scenario is worse, draining a cell while pulling 100 amps or more, or over charging a cell at 10 amps or less. I stop charging when my smallest capacity cell hits around 3.45V or so, (SE cells), which gives me some leeway if conditions cause it to go higher. It does take some close watch during the first few cycles to adjust the charger properly, if it's adjustable, but the cells won't suddenly burst into flames if you slightly over charge them a bit. I've taken a few to 4 volts briefly, no swelling, not change in performance.
That said, middle balancing would likely work fairly well, hedging your bets on both ends. Your cells would top off closer together than a bottom balanced pack and they'd bottom out closer together than a top balanced pack. This is essentially what Jack did on his original Speedster with good success.


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## EVfun (Mar 14, 2010)

dtbaker said:


> my current belief that top balancing is right for me is based on the thoughts that if they are top balanced, the cells remain in balance during use and all end up about the same ah depleted.... then will all fill the same during normal charge, and start registering a voltage climb at the same time, and raise the pack voltage enough to shut down charger with cells still being in balance..... maintained by periodic top balancing after a charge just to make sure they are all finishing at the same time. Since I am planning to avoid full discharge, I am not worried about the one short cell at the bottom end of capacity during discharge....


I've started putting a little use on my TS pack. I have cell level battery monitors/regulators (only 1/2 amp bypass over 3.65 volts per cell) that watch for the voltage rising above 4.0 or below 2.5 volts. Any cell over 4.0 will shut off the charger and lock it off until I acknowledge the fault. A cell below 2.5 will cause buzzer under the dash to start squealing while I'm driving. I have a 40 cell pack with the Zilla set to a minimum pack voltage of 105 volts and maximum current of 5C (300 amps.) The charger is a Manzanita Micro PFC-20 set for 144 volts at <1 amp and a one hour timer after hitting the voltage limit. 

The pack is top balanced. The pack seems to be staying in line quite well with the time from the first cell hitting 3.5 to all the cells being over 3.5 is just a matter of minutes. I'm pretty sure that any regulation function of the BMS is not even needed because my initial few charges where done without the BMS and showed the same end of charge pattern. At this time I have no other working instrumentation in this EV, it's a work in progress. I firmly believe that the cell level monitors should be attached to the cells (like EVworks BMS or CleanPowerAuto BMS) -- spaghetti HV wiring should be avoided like the plague.


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## gdirwin (Apr 7, 2009)

My 2 cents: Top or bottom balancing - does not matter.

What matters is that you do balancing at some point, and that you have a method of shutting off the charger (if any cell gets too high) and shutting down the controller (if any cell gets too low).

Ie you need a BMS that monitors each cell and communicates with the charger and controller. You do not necessarily need active balancing/shunting (this is a nicety though) - manual/occasional balancing with monitoring will also work.

Without a cell level BMS monitor, there will always be cases where a cell gets too high or too low (for whatever reason, perhaps this cell has higher or lower internal resistance etc...). You can reduce the risk of a damaged cell (by using conservative upper and lower pack voltage limits, and by ensuring you do not charge or discharge at very high rates beyond the battery capability) but the risk is always there.

Yes, the BMS introduces more wires (and more points of failure) - it should have a diagnostic that gives you an MIL or error if it detects something missing (broken wire etc...).


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## tomofreno (Mar 3, 2009)

> Is there any reason NOT to work my way thru the cells individually, charging each up to 3.65v until amps drop to 'nothing'?


 Yes. If you are going to leave them sit unused for months it is said to be better for the cells if they are at 50% charge. I assume that is why they are not shipped fully charged. The self-discharge rate is extremely low, so no need to worry about them discharging. As far as balancing, just check the cells with a dvm with 3 decimal place display (mV). If they all are within a few mV of each other there is no need to balance them before install. Mine were all within 2 mV of each other when I received them. Bottom or top balancing will work fine as long as you don't discharge the cells to less than 30% SoC. If you want to discharge them further, bottom balanced ensures all cells are at about the same voltage when at low SoC, so you have less danger of over-discharging one which is at significantly lower voltage than the others, which may occur with top balancing and somewhat different cell capacities. Of course, if you go a bit further than you should, you will then over-discharge all of them if they are bottom balanced. Staying away from the exponential parts of the charge and discharge curves is safest, so charge to the knee of the curve, and discharge to 30% SoC, or 25% at lowest. Top balancers require charging up into the exponential part of the voltage vs Ah curve, but should shut off the charger to prevent overcharging a cell. I recommend at least having LVC and HVC to protect cells.


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## Elithion (Oct 6, 2009)

tomofreno said:


> Yes. If you are going to leave them sit unused for months it is said to be better for the cells if they are at 50% charge.


Yes. Good point.



tomofreno said:


> ... just check the cells with a dvm with 3 decimal place display (mV). If they all are within a few mV of each other there is no need to balance them before install.


Yes. Correct. I may add: if just a few cells are off, you can use a supply or power resistor to bring them to the same voltage; BUT, you must measure the voltage after a 15 minute rest period, to let the voltage settle ("relaxation effect").



tomofreno said:


> Bottom or top balancing will work fine as long as you don't discharge the cells to less than 30% SoC.


Not exactly;
Top balance: do not bring them to less than 30% SOC when driving
Bottom balance: do not bring them to more than 70% SOC when charging
Middle balance: both of the above
The better the match between the cell capacity, the further you can risk it (20 % / 80 % ... 10 % / 90 %). But you have no idea of the cell capacity match, so stick to 30 % / 70 %.



tomofreno said:


> Top balancers require charging up into the exponential part of the voltage vs Ah curve, but should shut off the charger to prevent overcharging a cell.


Not exactly. When using a properly set CCCV charger on a top balanced pack, the charging current will naturally decay exponentially as the cells top off; therefore, there is no need to turn off the charger. See:
http://liionbms.com/php/wp_charging_stages.php

The only reason to turn off the charger is if the pack is not top balanced. In that case, you do need a BMS to detect when any cell is full.
________
WEED VAPORIZERS


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## JRP3 (Mar 7, 2008)

Elithion said:


> Not exactly;
> Top balance: do not bring them to less than 30% SOC when driving
> Bottom balance: do not bring them to more than 70% SOC when charging
> Middle balance: both of the above
> The better the match between the cell capacity, the further you can risk it (20 % / 80 % ... 10 % / 90 %). But you have no idea of the cell capacity match, so stick to 30 % / 70 %.


My cells all came with a sheet showing measured capacity. Bottom balancing and doing a few cycles can verify which cells fill up first. You can then shut your charger off when the smallest capacity cells fill up first and safely go to 90% SOC with them. You'll never get more range than your smallest cells anyway.



> The only reason to turn off the charger is if the pack is not top balanced. In that case, you do need a BMS to detect when any cell is full.


Or set your charger to shut off when your smallest capacity cells reach around 90% SOC, that gives you a 10% leeway. This assumes an adjustable charger of course.


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## JRP3 (Mar 7, 2008)

tomofreno said:


> If you want to discharge them further, bottom balanced ensures all cells are at about the same voltage when at low SoC, so you have less danger of over-discharging one which is at significantly lower voltage than the others, which may occur with top balancing and somewhat different cell capacities. Of course, if you go a bit further than you should, you will then over-discharge all of them if they are bottom balanced.


I can tell you with the Curtis 1238 controller that would almost be impossible. Near the end of my low voltage event, 1.77 per cell average, the controller cut back power so much I was barely doing 10mph and barely moving by the time I pulled into the driveway, and the cells jumped back to about 2.45 and climbing after I stopped. I think the car would have stopped completely before the pack hit 0 volts under load.


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## dimitri (May 16, 2008)

JRP3 said:


> Or set your charger to shut off when your smallest capacity cells reach around 90% SOC, that gives you a 10% leeway. This assumes an adjustable charger of course.


This sounds great in theory, but not so much in real life. You have no idea when the smallest cell is at 90% SOC because there is no linear relationship between voltage and SOC, until you reach the "knee". Only by reaching the "knee" you can decide to turn off the charger. But once you reached the "knee" voltage shoots up too fast for charger to detect it on a pack level, so you have significant risk of overcharge, especially if the charger is not so precise in the first place and swings its presets based on ambient temperature or moon phase, or political situation, who knows 

In reality the cell is not at 90% SOC at the "knee", its more likely at 95%-97%, so your safety margin is pretty thin. If you pull the charger below the "knee" to increase the safety margin, then you might be charging your pack to 70% or 80%, you simply don't know how much you are leaving on the table.

Considering extra $1200-$1500 you pay for adjustable charger that you can't even trust half the time, all these debates become a moot point.

All these management technics have pros and cons, none of them are perfect for everyone since there are so many variables in every DIY EV project outside of just battery pack. Battery management decision is tied to a number of other design decisions, so each case is different.

Gotta love the guy who's advise is to just watch the video and all your problems will be solved. You should start your own religion, you already have your messiah picked, you are half way there. Don't let technical details and experience sidetrack you


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## dtbaker (Jan 5, 2008)

dimitri said:


> Only by reaching the "knee" you can decide to turn off the charger. But once you reached the "knee" voltage shoots up too fast for charger to detect it on a pack level.


this is exactly why I think the best choice for ME is top balancing... to give the best chance of cells hitting the knee and starting to climb mostly together to have the best chance of raising the pack voltage to the charger setpoint and making the safe switch to constant voltage and finishing gracefully.

sorry this has become a religious argument, but I have enjoyed the information and perspectives.


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## dimitri (May 16, 2008)

dtbaker said:


> sorry this has become a religious argument, but I have enjoyed the information and perspectives.


I'm glad this is helpful, but honestly its been covered over and over and over and every time we get to the same point, where everyone has different ways of doing it and they start arguing which is better, forgetting that you have to look at the overall picture and compare apples to apples.

One guy says "just stop your charger when first cell is full", simple, right? But how do you stop a charger that is not adjustable? Well, the guy giving this advise forgot to mention such little detail and the price tag of his charger, how convenient for the guy on recieving end of such advise who already bought non-adjustable charger.

Same for the other advise, "just set your controller to cut power at specific voltage". Hmm, how do I do this with my old Curtis again? Ahh, the guy forgot to mention that his controller is 2 generations ahead, doh.

Same story every time. You have to take a holistic look at all your components, their capabilities, how they tie together. Then decide how to manage your pack with all those components and whether BMS investment is worth it for you.


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## dtbaker (Jan 5, 2008)

dimitri said:


> Same story every time. You have to take a holistic look at all your components, their capabilities, how they tie together. Then decide how to manage your pack with all those components and whether BMS investment is worth it for you.


exactly.
I have a simple (cheap) pfc-1500 charger that is pre-set for 38 cell nominal charge curve to bring up to 38*3.65. There are other curves I can switch to, but the simple two-stage up to a conservative finish is what I have to deal with.....


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## Guest (Aug 26, 2010)

Too bad for the folks who do not do their homework before committing to such purchases. Or to use OLD outdated controllers and expect superb results. I understand that and know many have done just what you described. I guess then that the BMS is a cheaper fix for a total screwup. A way to save the day and save face so to speak. I have a modern controller that will limit my voltage and amperage and I'd be sure to buy a NEW charger specific for lithium that can stop the charge when requested and it can be done for under 1K. No need to spend $4k on a charger. The charger algorithm will do this for you. If you purchased a DUMB charger and expect perfection, well you got what you purchased, a DUMB charger. If your going to invest you best be ready to invest in more than just batteries and BMS. Controller and Charger are more than likely going to be required too. 

But if you have a DUMB system then I would suggest you find a real good BMS system. 

Pete


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## dtbaker (Jan 5, 2008)

gottdi said:


> Too bad for the folks who do not do their homework before committing to such purchases. Or to use OLD outdated controllers and expect superb results.


ok boys, back to neutral corners. 

I expect LOTS of us have old (but not dumb) controllers like Curtis that do a fine job of amp limiting, and are set up to be very forgiving on voltage sag because they were designed for lead. Not adjustable = less expensive (not dumb)

same on chargers.... I made a decision to go with a fixed nominal voltage setup on a charger that offers 10 different Li specific curves, but not variable field settable voltage setpoints. again Not adjustable = less expensive (not dumb) After all, I am HOPING not to have to change this car's batteries for 10 years, why do I need adjustable voltage?

my original post was along the lines of: here is what I have to work with, here is what I am thinking, have I missed any considerations I need to know about before I decide what to do.


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## Guest (Aug 26, 2010)

Your charger is configurable from the algorithms you request for it. Not user configurable but configurable none the less and not a DUMB charger. Set it for the limits you need and your good to go. Since your using a Curtis I will still say OLD School and Semi DUMB. My old 7 volt controller was DUMB but good for what it was but I had to watch my batteries. Sure you can use the old stuff but should you? If the BMS will let you get away with the old stuff then yes the BMS might be a good thing. 

No need to go back to the corner. I am not totally against BMS but if you have the proper newer stuff you may just not need them. Nothing wrong with promoting that either. So in your words then maybe all of us should go back to the corner and use the facts for each situation. 

Pete


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## JRP3 (Mar 7, 2008)

I did say you need an adjustable charger to do what I suggest. Though I have found some variability with the PFC charger, as long as I'm charging from the same mains voltage and at the same current output it's accurate enough for daily use at 80-90% SOC which is fine for me. I've learned it's behaviors and can deal with it. Where I run into problems is when charging from different circuits at different voltages and currents, then I have to watch it. It doesn't happen that often so it's not a huge problem.
There are certainly drawbacks to a user adjustable charger, including the price, but there are also advantages, including adjusting my current draw from different circuits and being able to increase my pack voltage without having to buy a new charger. Nothing is perfect and there are always compromises.


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## octagondd (Jan 27, 2010)

JRP3 said:


> I did say you need an adjustable charger to do what I suggest. Though I have found some variability with the PFC charger, as long as I'm charging from the same mains voltage and at the same current output it's accurate enough for daily use at 80-90% SOC which is fine for me. I've learned it's behaviors and can deal with it. Where I run into problems is when charging from different circuits at different voltages and currents, then I have to watch it. It doesn't happen that often so it's not a huge problem.
> There are certainly drawbacks to a user adjustable charger, including the price, but there are also advantages, including adjusting my current draw from different circuits and being able to increase my pack voltage without having to buy a new charger. Nothing is perfect and there are always compromises.


My take from reading, viewing, discussing. I don't actually have my TS batts yet, so take it with a grain of salt.

Initial Top balancing has a problem when nearing the end of the discharge cycle as was shown in the video. Most of us can manage this by monitoring our discharge as we drive and most of us are not trying to push our batteries past 70-80% DOD. This is not wise as far as investment is concerned. But, what happens when you need to go a little further, or your car didn't charge while you were at work so you figure you can take surface streets to limp home? You may be risking a cell or two since the system voltage is not telling of the individual cell voltages.

Initial Bottom balancing is tougher to do, but I cannot see a problem on either the charge or discharge side, in fact it would seem that you actually have a better idea of the voltage of each battery with a bottom balance than with a top balance because of the different sizes of the batteries.

I am not trying to choose sides or proclaim any one King, but just trying to see the data, analyze it to the best of my knowledge and then decide. If there is some data I am missing, then please let me know. I don't hold to theories for the sake of being right, I just want the facts.
Dave


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## dtbaker (Jan 5, 2008)

octagondd said:


> Initial Bottom balancing is tougher to do, but I cannot see a problem on either the charge or discharge side,


you are missing the problem at end of charge, IF there is not a good shunting BMS or a BMS watching voltage on every cell capable of shutting down charger.

If the charger cannot be shut down by BMS when the first cell hits limit, or the shunt(s) cannot carry full charge current, then you run the risk of overcharging the short cell that hits the limit before the others.

If you have a BMS that CAN watch every cell, and shut down the charger when any one cell hits the HV limit, or give major warnings when any one cell hits the LV then you can use any balancing you want and probably be fine. Just a personal assessment of whether that nice BMS is cost effective in your case.


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## JRP3 (Mar 7, 2008)

I should add that I'm using an amp hour counter as well, Dimitri's EV Display. That allows me to set my charger a bit conservatively, and if it shuts off a bit prematurely the ah counter will show it and I can put in a bit more charge if I need it. It also shows me when the pack is getting low, regardless of momentary load or voltage. So even if your controller can't cut power on low voltage as long as you can read a gas gauge you'll know how much your pack has left.


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## octagondd (Jan 27, 2010)

dtbaker said:


> you are missing the problem at end of charge, IF there is not a good shunting BMS or a BMS watching voltage on every cell capable of shutting down charger.
> 
> If the charger cannot be shut down by BMS when the first cell hits limit, or the shunt(s) cannot carry full charge current, then you run the risk of overcharging the short cell that hits the limit before the others.
> 
> If you have a BMS that CAN watch every cell, and shut down the charger when any one cell hits the HV limit, or give major warnings when any one cell hits the LV then you can use any balancing you want and probably be fine. Just a personal assessment of whether that nice BMS is cost effective in your case.


Not sure what you mean? If all bottom balanced cells start at 3V then they are all pretty much at 3.65V together when the charger goes to CV, correct? Do you mean if for some reason a cell has half the capacity of the others?


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## JRP3 (Mar 7, 2008)

No but they aren't all exactly the same capacity, that's the problem. My cells range from 110-114ah. Near the ends some will fill or empty first, depending on how they are balanced. If you can get a pack all within 1 ah then it's not much of an issue, but that might not be possible.


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## JRP3 (Mar 7, 2008)

dimitri said:


> Same for the other advise, "just set your controller to cut power at specific voltage". Hmm, how do I do this with my old Curtis again? Ahh, the guy forgot to mention that his controller is 2 generations ahead, doh.


Don't all controllers have a low voltage shutoff point?


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## Tesseract (Sep 27, 2008)

JRP3 said:


> Don't all controllers have a low voltage shutoff point?


Dimitri is clearly making a distinction here between controllers that just shut down if the battery pack voltage is too low (e.g. - Curtis, Kelly) and those that actively limit power drawn from the pack to maintain it at a minimum programmed voltage (e.g. - Soliton1, Zilla).


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## JRP3 (Mar 7, 2008)

In either case though the controller will protect a bottom balanced pack from damage.


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## dimitri (May 16, 2008)

Actually my point was that old controllers have some preset LVC, not precise enough to match desired pack LVC for a given number of cells. Controller LVC might kick in too late, after smallest cell already been reversed. Of course knowing controller LVC up front, you can design the pack size such that pack LVC will match controller LVC. Which goes back to my original point of taking holistic look at all components.

But to Tesseract's point, there is a difference between controller abruptly cutting power in the middle of the road when LVC is reached, vs. "smart" controller reducing the power to stay at LVC, giving driver a chance to get off the road safely.


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## dtbaker (Jan 5, 2008)

JRP3 said:


> Don't all controllers have a low voltage shutoff point?



The old controllers have a very low cutoff designed to accomodate huge voltage sag from lead batteries..... like down around 1/2 nominal voltage! so no, old controllers cannot practically 'protect' a li pack.


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## JRP3 (Mar 7, 2008)

dtbaker said:


> The old controllers have a very low cutoff designed to accomodate huge voltage sag from lead batteries..... like down around 1/2 nominal voltage! so no, old controllers cannot practically 'protect' a li pack.


Actually it probably would. A 3.2V cell sagged under load to 1.6 will not be damaged, other than a deep discharge and will quickly spring back once the load is removed. A bottom balanced pack will mean no single cell goes much below that. Obviously you don't want to do this regularly but that will protect your pack if it happens.


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## GEO-NL (Apr 6, 2010)

Hello,

I'm a starting ICE to EV convertor and will connect my first TS package for the first time soon....
But this thread has made me a bit confused....in how to start off with my package and how to go on with the BMS i bought.

To explain the package:

50 x 200ah TS cells
Manzanita pfc-20 charger
A BMS bought in europe(will post some info also)
I also have soliton 1

The instruction for the initial charging was:

The new 3.2V LFP cells delivered from the warehouse are partially charged. However *before the first use*, it is essential *to charge each cell to full capacity*. The initial charging should be done with the charging current set to less than 1C (typically 0.5C), till the voltage level of 4.0 V is reached.

What is the best thing to do...balance each cell to 2.8v before i connect the complete package, and then charge it to full...(without the BMS)

And afther this first cycle connect the BMS..


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## GEO-NL (Apr 6, 2010)

I thought that this BMS sytem would give me some safe handeling of charge and discharge current.

_Real Time Battery Management System (RT-BMS)_
_The Real Time Battery Management System (RT-BMS) is an advanced battery management solution for any_
_type of lithium-based cells. Unlike other management systems, the RT-BMS provides the battery management_
_during the complete charge and discharge cycle. Each cell is managed individually and the master_
_control unit manages the whole chain of cells._
_If we consider a 100Ah traction battery with a cell capacity variance of ±2.5% being charged at 100A for 1 hour,_
_a balancing current of up to 5A is needed, provided balancing is enabled throughout the whole_
_duration of the charging cycle. Leaving the balancing only for the end of the charging cycle requires either_
_a higher balancing current or a longer charging time. With a 200Ah battery, for example, a 10A balancing_
_current is needed when charging at 200A, or a 2-hour charging time when charging at 100A._
_The RT-BMS solution allows to manage each cell with balancing currents up to 5A. For example,_
_operating large-capacity LiFeYPO4 cells built into a 32-cells pack with a nominal voltage of 100V requires to_
_release ~640W of balancing energy (= 5A [balancing current]× ~4V [cell voltage] × 32 cells). Although this_
_may seem to be quite a large amount of wasted power, a individual balancing of the cells at 5A requires only_
_~20W of energy to be released from each managed cell._
_The RT-BMS is designed according to the concept of single real-time balancers managing and balancing up_
_to 192 individual cells. The individual cell-balancing units are controlled by the central Master RT-BMS_
_Control Unit._

Besides controlling the cell balancers, the Master Control Unit of the RT-BMS is designed to provide for the
communication with the charger, motor controller, and other devices, as well as on-line transmitting
of voltage levels, cell temperature, charge and discharge current, and signal data status for user display.
The individual cell balancers are also used for data recording the battery discharge cycle. In the same way as
while charging, during discharging the Master Control Unit monitors the status of each individual cell
(temperature, voltage, internal resistance, total current, differences in relation to other cells, etc.). If userdefined
limits are exceeded, warning is signaled. The Master Control Unit can also provide additional
warnings of approaching conditions, such as a near-to-full discharge, over current, high temperature, etc. It
can control the various indicators (remaining charge, drawn current, etc.) either on its own, or it can relay this
information to other systems via CAN data bus—to displays or motor controllers, for example. The Master
Unit also collects stored data for later analysis. It is also able to identify the damaged or defective cells,
thereby preventing potential emergencies or failed discharges.
The whole RT-BMS system is compatible with all current types of traction cells (Pb, A123, LiPol, LiFe,
LiFePO4, LiFeYPO4, etc.) – with the exception of the NiXX cells – i.e. all types of rechargeable cells with an
operating voltage between 2.7V and 5.0 Volts.
The RT-BMS Master Control Unit is able to communicate with a PC (parameter settings, transfer of online
or stored data) . The link is via galvanic-separated USB module.

*RT-BMS sofware configuration parameter*










*Cell settings*

*Cut-off voltage *– the lowest voltage level. When this level is reached on any of the cells, the “Main Current” signal (B3 connector) will turn off. We recommend setting of 2.60V for the TS cells.
*Low voltage *– the low voltage level. This voltage level indicates that cells are near to full discharge. We recommend setting of 2.75V for the TS cells.
*Nominal voltage* – the balancing voltage during charging. As soon as the voltage of any cell reaches the Nominal voltage, the balancing of the respective CBU module starts working. We recommend setting of 3.65V for the TS cells. (Additionally after Nominal voltage is reached during charging, the “Charging Current 2 – Full Power” signal (B6 connector) will turn off. (The charger should reduce the charging current to small power – i.e. the finishing power)
*Charge Voltage* – the highest voltage level. When this level is reached on any of the cells, the “Charging Current 1 – Main or Small Power” signal (B5 connector) will turn off. (The charger should shop charging immediately.)


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## GEO-NL (Apr 6, 2010)

*RT-BMS software information*
RT-BMS is provided with monitoring and management software. The software is available for a free-of charge download to the BMS owners. It is a Windows software. Information about the displayed values is as follows (from top-left to bottom-right):

*Voltage(V)* – the total voltage of the battery pack as calculated by BMS Master unit.
*Current(A)* – the current drained from the battery pack. Positive values (+) are for discharge. Negative values (-) are for charge.
*Capacity (%)* – the total calculated capacity of the battery pack. Is it necessary to make at least one or two charge-discharge cycles to have this value calculated by the BMS.
*Low Cell (V)* – the voltage of the lowest cell in the pack.
*High Cell (V)* – the voltage of the highest cell in the pack.
*Temperature (C)* – the highest temperature of the pack – the temperature of the warmest cell.
Status information

*Online (Green)* – the software is communicating with the BMS Master.
*Running (Green)* – the BMS master is running (not in the stand by mode).


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## dtbaker (Jan 5, 2008)

looks like the instructions are to top balance before installation... although i would not go to 4.0v. The best way to do this that I have heard about is to wire all cells IN PARALLEL with a power supply capable of a Constant Voltage that can be set to something slightly above the 'knee' of the voltage curve like 3.65 or 3.7v. After current drops to less than 1 or 2 amps, disconnect power supply and leave cells in parallel for a day or two to completely balance.... THEN install and wire in series.

I bought an inexpensive but decent power supply (Mastech) for $149 that I plan to use for the initial top balance charge, and then subsequent cell balancing as needed.


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## JRP3 (Mar 7, 2008)

I don't think it's necessary to charge to 4.0 volts. The cell has already been fully cycled at the factory to test capacity and resistance. In use it's not recommended to go much above 3.8 volts. I think they just mean that the cells are not shipped fully charged and they need to be charged before using them, but not necessarily charged to 4.0 volts.


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## GEO-NL (Apr 6, 2010)

dtbaker said:


> looks like the instructions are to top balance before installation... although i would not go to 4.0v. The best way to do this that I have heard about is to wire all cells IN PARALLEL with a power supply capable of a Constant Voltage that can be set to something slightly above the 'knee' of the voltage curve like 3.65 or 3.7v. After current drops to less than 1 or 2 amps, disconnect power supply and leave cells in parallel for a day or two to completely balance.... THEN install and wire in series.
> 
> 
> 
> ...


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## Elithion (Oct 6, 2009)

GEO-NL said:


> _Real Time Battery Management System (RT-BMS)_...


You are referring to the GWL power BMS, from the Guernsey Channel islands (a tiny country off the coast of England).
You can find info on that BMS and all other Li-Ion BMSs in this comprehensive list: http://liionbms.com/php/bms_options.php
________
BONG PICTURES


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## GEO-NL (Apr 6, 2010)

Elithion said:


> You are referring to the GWL power BMS, from the Guernsey Channel islands (a tiny country off the coast of England).
> You can find info on that BMS and all other Li-Ion BMSs in this comprehensive list: http://liionbms.com/php/bms_options.php


 

Yes that's the one i bought..

But after this discussion and the tv show of Jack.....i'm getting a bit confused. 

This is the first time i install a batterypack and also BMS..
And i had the impression that this BMS would secure the overcharge as well as undercharging. So if you install things right i won't kill cells during charging and driving...

........


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## dtbaker (Jan 5, 2008)

my take on the initial balancing is that it is best to do it even with a BMS to reduce the chances of low cells hitting HV limits while the rest of the pack is at full current.... the bms shunts might handle shunting 1-3 amps, but probably not 10-12 amps . You want to BMS to handle things when all the cells are 'nearly' full and current has cut back to just a couple amps.


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## octagondd (Jan 27, 2010)

dt-

I am coming around to see the top balance side of things. Some how I ignored the end of charge problem which I think Jack washes over because he sets his CV point at like 3.5V/cell. If the CV is at 3.65V what happens if 37 cells are at 3.5V? One cell is at 9.2V. Top balancing helps to keep the cells together near the CV point which is what is critical during unmonitored charging.

The one problem I have with Jack's example is it seems he was trying to drive his LFP cart using Voltage meters which may work for LA but not for LFPs. I don't know if he had an amp counter in there or not, but I think most of us who are planning on going without BMS are planning on using an amp counter of some sort so we can personally manage the discharge.

What I am looking for now is some real world data from people without a BMS on the balance of their cells over time. Maybe I will start a thread on it.


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## dtbaker (Jan 5, 2008)

octagondd said:


> What I am looking for now is some real world data from people without a BMS on the balance of their cells over time. Maybe I will start a thread on it.


I have been unable to find any such recorded info.... but plan to record MY pack performance and balance history, and will probably add to my build website. I will be added a section to cover the 'upgrade' from floodies, and then a performance page as well. I have installed a Cycle Analyst for the express purpose of counting aH, and the side benefit is that I now have an accurate way to count aH per specific test mile section of road I plan to use for comparing any body mods, and even overall lead-acid versus LiFePO4 performance in my car.


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## JRP3 (Mar 7, 2008)

I'm running bottom balanced without a BMS. My SE/CALB cells range in capacity from 110ah-114ah. Four months after my initial bottom balance I checked again and they were all within less than 0.08 volts of each other. I rebalanced again with a more accurate meter so they were all within 0.004 volts of each other and I'll check them again in December. I've pulled 5.5C from the cells occasionally and had one low discharge event to an average of 1.77 volts per cell yet they've remained well balanced at the bottom. I do undercharge the cells to be safe. The PFC voltage trim is a bit less accurate than I had hoped. If I need a full charge I'll flip the charger back on for another 15-30 minutes while I monitor closely, but not very often. I like the safety bottom balancing gives me while driving in the event of low SOC but as long as you stay away from the top and bottom I think you can get away with top, bottom, or middle balancing, without a BMS. I do have an adjustable charger, PFC-30, so I can change current draw and cutoff voltage as temperature changes the resistance of the cells. If I did not have an adjustable charger and wasn't using a BMS I'd probably top balance the pack. I'm using Dimitri's EV Display for amp hour counting which makes life easier being able to see how much charge goes into and out of the pack.


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## octagondd (Jan 27, 2010)

I just posted the thread. We'll see if anyone has anything to share. My big concern is, 6 months down the road, how will I know if a cell starts to go down while driving to work? The pack voltage could look somewhat normal, the amp counter could look correct, but when I plug in to charge, the rest of the cells will get more than their normal share of voltage before hitting CV mode. The amp counter would probably show less then normal amps going back in, so that would throw a flag before I get back in and start driving, but maybe it wouldn't be enough to make me concerned.


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