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I'm wanting to put together some LiFePO4 battery modules using 4S 10AH cells for running a lantern, and later possibly using multiple modules to make a pack for ebike/scooter use.
Resistive balancing seems easy, but I'd need a higher balancing current than if I was using a charge shuttling scheme since I'd want to balance it while it was still on a charger so I'm not bleeding capacity off.
I figured I could use a charge pump IC since that would handle the switching, but that raises a question. Are the charge pumps (from maxim etc...) bi-directional or are they built so current can only flow out of the output pin(diode/mosfet for rectifying etc..) ?
If they were bi-directional then I could use a single IC to equalize 2 batteries, and only 3 would be needed to balance 4 cells. If they arent bi-directional, then would using one in a doubling configuration work to pass the charge 'up' the stack, and one inverting to pass charge "down" the stack work? Or would there be issues if the voltage of the battery its trying to pass to is greater than the voltage on the cap?
Or are there any suggestions for easy to implement bi-directial switches? Could I AC-couple the gates of 2 common source mosfets to my gate drive source with a bleed resistor so they will default to off in case of a stuck drive? This seems easier and faster than any scheme implementing GDTs or optoisolation.
Thanks! Edit: answered my own question, drawing out the circuit from the maxim datasheet. 2 batteries in series, a doubler passing charge up from the bottom, inverter passing charge from the top, and you end up with 2 ICs hooked up exactly the same way. The exar SP6661 also looks to do the same, but doesnt have a shutdown pin like the maxim chip does, but its 1/3 the price. Might be worth investigating both with a prototype.
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Using charge pump ICs for battery balancing.
