Extreme lipo battery balancer

Projects General Guidance
1

I have a battery pack made up of 2x 5 cells in series (3.7x5x2=37v) and then another 2x 5 cell in parallel for a total of 20 cells. Each pack (of 5 cells) has a balancing plug on it that looks like this: http://eflight.hedlunds.net/bilder/koppling.jpg (just expand the idea to 5 cells)

So what I want to do is have an Arduino cycle through each cell while the pack is still "live" and do two things: measure the voltage and if need be, patch in a resistor across that cell to bring its voltage back into line with the rest of the pack (and it would be nice if I could do this simultaneously). Because the pack will always be "live" it kinds rules out any common ground ideas I had using shift registers... I'm really at a loss of how to accomplish this in a nice way. Any ideas?

2

im looking to do exactly the same thing.

no point starting a new thread though. BUMP!!!!!

3

measure the voltage and if need be, patch in a resistor across that cell to bring its voltage back into line with the rest of the pack (and it would be nice if I could do this simultaneously).

As it would take a fairly large number of individual resistors to load any specific cell, you probably should consider power MOSFET as the load device. One per cell - they are capable of high current (~30A) and high dissipation (> 100W).
An RC network in conjunction with PWM could form the DAC to control the MOSFET.

You may wish to model the basic idea using SPICE:
http://www.falstad.com/circuit/

Ray