Cell balancing circuit should stay on

A pack might be abused over a number of charge/discharge cycles. Then a borderline cell deviates measurably from its siblings. (Example, nicads are known to have 'memory effect'.)
Then one day the pack is charged optimally. I can picture the borderline cell returning to normal behavior.

Hi,

it depends on cell current. Without current I see no need for the balancing circuit to be continously ON.

But when there is charging current you may need the cell balancing circuit.
The same is true for discharging current.

But neither charging nor discharging current will be continously.

Klaus

Depends on the size of the battery and load currents - for larger systems where the losses associated are a small %, leaving it on would be fine;

for smaller systems there may be some slight eff gain in operating only when required.

The problem is you can never balance a 90Ah call with a 100 Ah cell over the whole range. Top balance, or botom balnce yes, but not both. Decide which is most appropriate and only fire up the balancing circuit when appropriate IMHO.

Warpspeed said:

The problem is you can never balance a 90Ah call with a 100 Ah cell over the whole range.

Click to expand...

Except that you can - if the terminal voltages are in the correct range e.g. 2.8 - 3.3V for LIFePO4 then each cell - if at 3.3V - then each has reached its max state of charge - if the balancer takes energy from the higher energy cells and shifts it to the lower ones ( which is what our's do ) then offset cell sizes can be handled - both during charge and discharge - of course the BMS must still disconnect the battery for cells over-voltage and under-voltage.

If you want to maximize the lifespan of batteries one uses a battery balancer all the time for charging and discharging to sense individual low cell voltage rather than the whole string.

Just like electrolytic capacitors it is impossible to make them all perfectly the same so there are tolerances and mismatches on capacitance and ESR. When the quality is good or you are lucky to get them from the same batch, then a balancer is only needed just before they go out of balance. But it is always best to use them from the start this way the weakest cell does get stressed out by premature full charge then over-voltage or premature fully discharged and undervoltage fatigue and rapid wearout. The mechanism for imbalance is like thermal runaway and even if balanced within 0.1%, the weakeast cell always dies first. No sexual jokes please (lol)