NiCad Battery bank Balance circuit (1.2v 32Ah x 20 cells)

rjenkinsgb said:

You can do, it will speed up the overall process.

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ronsimpson said:

Thanks for the data sheet. So which type of battery do you have? There are three in the data.
KPM?KPL?KPH? Then there are numbers to indicate size like 100?

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TJP said:

Row 1 - 10 cells total voltage - 16.64v - draws 1.5(3) amps

1.665, 1.666, 1.666, 1.663, 1.666, 1.658, 1.660, 1.668, 1.662, 1.664v

Row 2 - 10 cells total voltage - 16.59v - draws 1.5(7) amps

1.658, 1.672, 1.652, 1.658, 1.654, 1.661, 1.658, 1.665, 1.655, 1.660v

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rjenkinsgb said:

I'd reduce the current (PSU setting) somewhat, the cells should not be rising to that voltage if they are in good condition.

The metal in the plates may have crystallised from being unused for years, meaning the cell internal resistance may be rather higher than it should be.

Under normal working conditions the "active" metal is amorphous, which makes it more reactive with the electrolyte. If left unused, the metal gradually crystallises (the same way that galvanised steel develops crystal pattern in the zinc coating over time), which changes how the cells react.

The cure in normal NiCDs is to deep discharge each cell individually to a fraction of a volt, then recharge.
As long as the loads are connected directly to each cell rather than an overall battery, there is no possibility of voltage reversal and it does no harm, just allows the plates to slowly react at their own rates rather than being forced.

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TJP said:

1.665, 1.666, 1.666, 1.663, 1.666, 1.658, 1.660, 1.668, 1.662, 1.664v

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ronsimpson said:

It looks like you do not need a balance circuit.

for those that don't want to dig through the datasheet.
View attachment 134392

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TJP said:

Why is it not necessary to balance the cells?

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rjenkinsgb said:

NiCd (and many other rechargeables) "leak" a small amount of current, especially when at or near full charge, so all cells in a battery pack chain get a steady trickle charge which automatically equalises them.

Lithium battery types are an exception, as they have near zero leakage so no self-equalisation.

It looks like those particular cells have a higher full charge voltage than the ones I found data on at the start of this thread, so the approx. 1.66V per cell is fine, and they have already balanced to +/-20mV of their average voltage.

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