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I'm designing a circuit board to which I'll be able to connect multiple LiPo batteries (2-6S) and charge them in parallel without bothering user about balancing those packs firstly. So the charging process would be done in two steps:

  1. Balancing LiPo packs
  2. Charging them, as in normal parallel charging routine

In normal routine I'd charge all batteries separately to the same voltage and then connect them in parallel to prevent high "balancing" current from flowing. Now very last thing to do in my project is to create a circuit which can do this automatically using only power from other batteries, in other means:

circuit which will be charging lower voltage lipos from those with higher voltage unitl they reach all the same voltage

from which point normal charging can begin. But I'm struggling to create such circuit.

Firstly I have tried by using high power resistor but soon abonded this idea because I wouldn't have much control over current. Another idea was to use a light bulb, but that would generate much heat and for different voltage lipos I'd neeed to use different ligh bulbs My next idea was to use some kind of current limiting circuit, so that I'd control max current. This is what I found:

Current limiter with low voltage drop out

Current limiter with low voltage drop

https://hackaday.io/project/20825

But still I'm not sure about voltage drop in such circuit and it shouldn't be more than 0.15V.

My very last thought is to use some of the lipo charger power to charge individual lipos, using current limiting circuit as shown above. Which of those attemps would be the fastest one?

Do You Guys have any experience in designing such circuits? I will really appreciate any ideas!

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