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Old 07-10-2018, 08:47   #1
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LifePO4 Battery Balancing Issues

Hi Iím new to LifePO4 and have 4 Calb 180ah Cells in series.

I ended up purchasing the zeva bms and tried charging the cells. They were all very closely balanced at first but during charging the 2 cells in the center quickly rise by over .1 volts or so.

Iím concerned because I donít want the cells to go over 3.65 per calb specs. And it looks like the bms is not able to balance them sufficiently.

Also I added another balancing devices that work independently of the bms. I was told they balance non stop if the cells are out of balance. They seem to work but still not enough to keep them balanced.

Is this normal aka center cells receiving more charge is normal or is my new cells have differing resistance?
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Old 07-10-2018, 10:52   #2
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Re: LifePO4 Battery Balancing Issues

You probably need to ask Zeva since this relates to the behavior and operation of their BMS.
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Old 07-10-2018, 19:29   #3
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Re: LifePO4 Battery Balancing Issues

Perhaps the Zeva was not programmed for LiFePo4? Or perhaps your second balancing system is confusing the Zeva? Is it wired up correctly? - Just guesses. Tanglewood probably has the best answer.
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Old 07-10-2018, 19:34   #4
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Re: LifePO4 Battery Balancing Issues

Hi thank you both.

I guess it was a false alarm or maybe the extra balancers are helping. I slowly got them up to full by charging up until they started going over 3.65 (the two center ones) then let them settle and balance.

Then discharged them for several hours on a 130watt load. Now it is charging fairly balanced.

My best guess is they were new so needed top balancing?
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Old 08-10-2018, 08:10   #5
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Re: LifePO4 Battery Balancing Issues

Yes you must manually balance the cells - or at least verify already well balanced as part of your commissioning process.

Keeping charging voltage to 3.45Vpc or thereabouts will be much better for longevity than following the vendor reco.

Also will likely mean never need to worry about re-balancing, nor the BMS active balancing, becomes redundant.

This will only sacrifice a few % AH capacity.

Between 3.45V as your 100% and 3V as your 0% SoC, you will likely still get ~180AH for many many years.
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Old 08-10-2018, 12:08   #6
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Re: LifePO4 Battery Balancing Issues

John, I am a little confused about this point, because I read something about the BMS not being able to balance well without having voltage go up to 3.45vpc or 3.65vpc which is when it does its job top-balancing, which does nake some sense. The OP may have noticed that the BMS balanced better when the voltage went higher to whatever..

Perhaps that type of balancing is just done a couple of times a year, carefully avoiding overcharging, particularly when there is a BMS.

I
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Old 08-10-2018, 12:17   #7
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Re: LifePO4 Battery Balancing Issues

Johnct

It looks like one approach you suggest is quite simple. No BMS, but top balance each cell. Then use 3.45vpc / 13.8v as 100% and 3vpc / 12.0v as you 0%.
for 180ah capacity.

Thanks, it's simple, just treat them right. Dont store them fully charged, but at 30-60%, don't float them which adds amps to the bank which damages capaciry, dont charge them when it is below 0F, remove them to warmer areas when temps likely to drop to -teens several times during the winter.
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Old 08-10-2018, 13:19   #8
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Re: LifePO4 Battery Balancing Issues

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Originally Posted by rgleason View Post
John, I am a little confused about this point, because I read something about the BMS not being able to balance well without having voltage go up to 3.45vpc or 3.65vpc which is when it does its job top-balancing, which does nake some sense. The OP may have noticed that the BMS balanced better when the voltage went higher to whatever..

Perhaps that type of balancing is just done a couple of times a year, carefully avoiding overcharging, particularly when there is a BMS.
A BMS can just be protective, does not need to include balancing, nor any cell-level functionality.

Staying below the shoulders can mean little need for any balancing, active or manual. Many users have found never needed for years at a time.

So does going to high voltage make sense just to get active balancing?

Really you should read the main thread to get an overview, make up your own mind. . .
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Old 08-10-2018, 13:22   #9
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Re: LifePO4 Battery Balancing Issues

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Originally Posted by rgleason View Post
dont charge them when it is below 0F, remove them to warmer areas when temps likely to drop to -teens several times during the winter.
No need to remove unless much colder. Just don't **charge**.

And the yttrium in Winston's supposed to allow colderÖ
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Old 10-10-2018, 05:32   #10
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Re: LifePO4 Battery Balancing Issues

Johnct wrote:
"Really you should read the main thread to get an overview, make up your own mind. . ."

I am inclined to bottom balance and top balance at 3.45 or 3.5vpc by hand and then maybe check at times.
I guess a very simple BMS with LVD and HVD and some alarms would be good. Should it have cell monitoring?
I was looking at Orion Jr but that does it all, including cell balancing and is perhaps overkill.
Any ideas for a simple BMS?

Also, which is the main thread? I trt to follow them all. Its a treasure of information.
Thanks
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Old 10-10-2018, 05:38   #11
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Re: LifePO4 Battery Balancing Issues

http://www.cruisersforum.com/forums/...nks-65069.html

, make sure to give both Maine Sail and Ocean Planet your close attention.

Choose top or bottom,

If you do both, whichever you do last is what counts
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Old 10-10-2018, 05:40   #12
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Re: LifePO4 Battery Balancing Issues

Pretty sure all BMS, as in a hardware unit, have cell-level functionality including active balancing.

Does not mean that part must be put to use.
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Old 10-10-2018, 05:49   #13
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Re: LifePO4 Battery Balancing Issues

https://marinehowto.com/lifepo4-batteries-on-boats/

Good information here for lithium owners.
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Old 10-10-2018, 05:51   #14
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Re: LifePO4 Battery Balancing Issues

Quote:
Originally Posted by dogboyaa1 View Post
Hi thank you both.

I guess it was a false alarm or maybe the extra balancers are helping. I slowly got them up to full by charging up until they started going over 3.65 (the two center ones) then let them settle and balance.

Then discharged them for several hours on a 130watt load. Now it is charging fairly balanced.

My best guess is they were new so needed top balancing?

When starting with a new pack you would be well served to capacity test each cell. If the cells are not well matched, from the factory, you will definitely want to stay away from the knees or you can certainly have balancing problems. It has become more difficult to get well matched cells these days than it was 6-8 years ago..

The fastest way to top balance is to wire the cells in parallel and charge to 3.60V to 3.65V and allow current to go to 0A but you'll need a variable power supply to do this.

Another issue may be terminal torque or oxidized connections. A Flir or other infrared camera, during bulk charging, can spot this or a volt drop test between the copper bus bar and the physical battery terminal can also show this.
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