Re: Observation on using 12v Lifepo4 batteries in serial/parallel (probably applicable to lead, too)

Dean Gillies

I'm still not convinced a balancer will help. 

I suspect your batteries will not show much imbalance if you check them at lower states of charge. The balancer only has time to do its job at the top end when the voltage of one battery kicks up before the other.  Maybe you can check this and log the imbalance at different states of charge. If your batteries are out of balance across the entire SOC range then maybe there is a case for an external balancer.

Series-connected lead batteries will definitely not self-balance, and will get progressively worse on each cycle.

Series-connected lithium batteries may try to self-balance, it depends upon how the cell balancing is configured. The cell-balancers provide an amount of bypass current which effectively does not (over)charge that battery, but will contribute charge to a second (lower voltage) battery.  The problem is that the bypass currents are very small, and only start when the first battery is almost fully charged so there is not enough time to bring the second battery up quickly enough.  So in practical terms the effect will not solve an imbalance problem.

Solar top balancing will help but timing is a problem. My bank takes about 4-5hours to fully balance after the pack reaches the balancing start voltage, and this only really happens in practice when on shore power.

Dean Gillies
SV Stella *****,  Amel 54-154

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