Cells in series and parallel at the same time for balancing and use ?

[crozen]

Hi,
I have a LiFePO4 4S 12V "100Ah".
One cell has much less capacity than the others. It has 70Ah while the others 90Ah. I'm fine with it but i was wondering if i could do something. I know that the best solution would be to buy another cell with more capacity.
My issue is that the weak cell always reaches 3.62v (that's my limits) much faster than the others. Also it discharge much faster than the others.
I'm not using often the battery and the weak cell always drops in voltage firstly. I want to do something to use all the capacity from other cells and store the battery much longer.
So, i was wondering if it is possible to wire both in series and parallel to keep them balanced constantly ?

Here is my 4S wiring and i drawn the parallel wiring.

Will it work ? What will happen if i put the 12V charger ? ?

Thanks.

 

[TacomaJoe]

If you try that it will fail. The original jumpers will now be shorting out the cells. If you remove the original jumpers leaving the cells in parallel, the voltage to use is 3.6V not 12V!

 

[Rocketman]

No that wiring will NOT work. It will short-circuit. And let all the magic smoke out of the batteries all at once…

You could get another battery cell (like a 25 or 30Ah cell and hook the new one in parallel with the smaller cell - those two cells hooked up in parallel make what is called a “super-cell”, then this super-cell gets hooked up in series with the three other cells.

Did that make sense?

 

[crozen]

If you try that it will fail. The original jumpers will now be shorting out the cells. If you remove the original jumpers leaving the cells in parallel, the voltage to use is 3.6V not 12V!

You are right. I see what you mean.

 

[crozen]

No that wiring will NOT work. It will short-circuit. And let all the magic smoke out of the batteries all at once…

You could get another battery cell (like a 25 or 30Ah cell and hook the new one in parallel with the smaller cell - those two cells hooked up in parallel make what is called a “super-cell”, then this super-cell gets hooked up in series with the three other cells.

Did that make sense?

I have a cell of 50Ah capacity (not new, real capacity is 45Ah).
This wiring ?

At least, all to 3 others cells will now be used at full capacity right ?

 

[Rocketman]

Yes, that wiring look right. Cell #1 is most negative, so cell #3 is your super- cell.

I would label your cells 1,2 3a,3b,4. And yes #3 will be larger than the others - you your battery should have the full amp-hours of 1,2,&4.

 

[crozen]

Yes, that wiring look right. Cell #1 is most negative, so cell #3 is your super- cell.

I would label your cells 1,2 3a,3b,4. And yes #3 will be larger than the others - you your battery should have the full amp-hours of 1,2,&4.

Should i do a top balancing of the 3 cells and the super cell too ?

 

[Rocketman]

Yes you want them to all be at the same top, otherwise you may not get all the amps out that should be available.