Cell voltage after capacity test

Adrianablett

New Member
Joined
Feb 27, 2021
Messages
15
Hi

Just a quick one.
Just finished capacity test on my 150ah 4s 12v pack.
Charged to 3.65v, rested for over an hour before I did the capacity test.
These are my results off the bms, one cell seems quite a bit lower than the others.
My question is do the cell voltages look ok or do I need to be looking at the cell that hit 2.5v first.
I am happy with the capacity result, was just wondering about the cell voltage difference.
Thanks in advance guys
 

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Gazoo

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What was your cells delta when your battery was fully charged and did you parallel top balance your cells? Unless you paid for capacity matched cells then it's normal to have runners and sleepers. Parallel top balancing can help but then your battery's delta when discharged could be more.

After I parallel top balanced my 8 EVE 280ah cells my delta at the top was 100mv's and at the bottom 500mv's. Or .1 volts and .5 volts respectively. Not the best but not the worst and I get 272ah's capacity from the pack. Your battery exceeds the advertised capacity so I would be very happy with that.

Also it's a good idea to test the BMS's high and low voltage disconnect. Charge until the highest cell exceeds 3.65 volts and discharge until the lowest cell voltage is just less than 2.50 volts.
 

Just John

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One cell will always have less capacity than the others. The drop off below 3.0v is very, very steep. If those are 150Ah rated cells, you got what you paid for, and I see no problems with the cell voltages.
 

Horsefly

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I agree with @Gazoo and @Just John but would add that you should set up your system so that your regular cycling is charging to something like 3.5V per cell (which will then settle to 3.4V), and cutting off at around 3V per cell. That keeps you mostly between the knees. Then you will never see one cell getting out of whack with the others, while still getting >90% of your cell capacity.
 

Gazoo

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My cells charge to apx. 3.385 volts per cell using the dumb charger that's built into my UPS. The cells absorb the charge until the current is 0. I get 265ah's capacity discharging to 2.5 volts. Agreed keeping the cells somewhere between the knees is the way to go for cell longevity. :)
 

Adrianablett

New Member
Joined
Feb 27, 2021
Messages
15
Thanks for all the info guys.
Yes all cells were top balanced before capacity test.
I'm happy with the result, i was just asking to check really but I'm happy with the test.
As mentioned, I was also planning on running them in the middle ground for longevity.

Thanks again.
 
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