NiMH charger for 20+ cells

Projects General Guidance
1

Hello, guys!

I've been building an electric longboard around some NiMH batteries left after my Honda Civic Hybrid battery reconditioning. You know, the big fat battery that powers the engine. It is made out of 11 "pairs" or "sticks", 6500mAh 12cells each. The awesome part about them - they can give out 100A quite easily.
Anyhow, I'm half-through in building the board and I think it's pretty lame to use bench power supply to charge the battery in such a mobile project. So I thought of building a charger for it. The general advice my engineering friends gave me was "don't go for arduino, go for special NiMH charging ICs". Okay, I've researched a bit and found out that there are exactly none ICs that support >20 cells nimh. Famous MAX713 only supports UP TO 20 cells, and I'm planning to use 2 "sticks", that makes 24cell battery.
I need your good advice, people. I'm more of a programming guy and had C- in physics, so I kinda feel lost about this task.
Maybe I should just stick with MAX713 x2 for each stick?.. Although, sticks are connected in series so that would mean some kind of tricky switch needed.
Thanks!

2

I built an arduino based charger for cordless drill battery packs, but not for anything as large as you are using.

AFIK it depends on what rate you want to charge them. If you are just going for a slow charger e.g 10 hours or more, then all you need is a constant current source, and a timer, with possible some over voltage detection.

If however you want do use slope detection or bubble charging, it gets a lot harder.

I tried slope detection, but found it virtually impossible to do without a smooth power source, because the dv dt is very small and the ripple on a transformer based PSU was greater than the voltage reduction at top of charge.

Actually, cell temperature is, from what I read, now favoured above slope charging.

Bubble charging is probably a good idea and could be programmed into the arduino fairly easily, but the external hardware required is non trivial for large battery packs I.e large power FETs to effectively short the batteries for a few milliseconds per second.