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how to best maximise capacity after top balance

c3auto

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Jul 21, 2021
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Hi all

I am building a 2x 8S battery banks using 16x 3.2v 320ah cells. (8S,2P)
I have top balanced half the cells doing the following:
series charge in 8s configuration to 28v, then parallel them to 3.6v (my DC power supply only shows to 1 decimal point so didnt do up to 3.65v) until the DC charger shows 0.00 charge current.

I am now doing the second batch

Once I do them, what's the best way to then build the 2 banks?
They have been top balanced but the resting voltage seems to differ quite a bit after a few days (up to 0.03v)

For the 16 cells to get maximum capacity is it better to order them from 1-16 in resting voltage state and take the bottom half and make the battery bank, then take the top half and make the other battery set?

Or does it not really matter?
 
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If you really want to maximize the capacity you have to measure the capacity for each cell. And then split the in two strings so you have the lowest possible capacity deviation in each string.

But I don't think that anybody does that - too much effort, for too small benefit.

0.03V voltage deviation for fully charged and resting cells is not something that you should care about.
 
Thanks for your responses, i am building 2 banks (probably used the wrong terminology above). I think it is 8S, 2P (2x separate BMS).

Would arranging them based on resting cell voltage so there is least deviation be a similar thing or would it not be indicative of capacity?
 
Thanks for your responses, i am building 2 banks (probably used the wrong terminology above). I think it is 8S, 2P (2x separate BMS).

Would arranging them based on resting cell voltage so there is least deviation be a similar thing or would it not be indicative of capacity?
Not indicative of capacity.
Like @brum said, you would need to know actually capacity, then I’d split down the middle and put the highest 8 together and the lowest 8 together. Each battery would have the capacity of the weakest cell in that battery. But in reality, the gains would probably be minimal. And zero if you can’t measure capacity.
I’d likely just build the two batteries with whatever cell split is convenient. Resting voltage would be as good a way to split them as any, I suppose.
 
Thanks all.

Unfortunately I overcharged my 2nd batch (set DC power supply to 3.6) but when i measured it with a meter on the battery terminals it was 3.69..
Amp draw was about 0.3amp and it was possibly about an hour it sat past 3.5v.
Hopefully it hasnt damaged it too much.

Im thinking of making a bank with this 2nd batch that I over-charged, and the other batch the second bank
 
To maximize capacity, flexibility and cell visibility, build 2 separate batteries with separate BMS
I don't think that will maximize capacity but I agree it adds to flexibility and visability of each cell. I have a 3P16S pack and while I do not have individual cell voltages the voltage of the the 3 cells in each group of parallel cells is enough visability for me.
 
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