2 chargers vs one?

[Garry]

On one of the RC car forums I'm on, theres currently a thread on charging 2 packs of six NiCD or NiMH cells at once. The obvious answers are either one charger capable of charging both the packs separatley, or two stand-alone chargers. However, one member thinks its fine to use one charger that'll handle more than 12 cells, just wire up the two packs in series.

I've tried to explain that this is dangerous as the packs have been discharged at different rates, and would probably lead to overcharging/venting, and possible explosion.

Can someone point me to an article, guide or post to support the 2 chargers vs one theory?

[Chrislong]

OK,

Think of it like this.

You have two empty glasses infront of you, one pint glass and one half pint (i.e. 4300's v2 2000's MAH).

Fill the glass's up seperate, so you can stop filling them when the water reaches the top.

Fill them up at the same time, the half pint glass will overflow before the pint glass is full.

An electronic techy here mentioned to me that water flow is a good way to think about electrical flow. The difference in this instance, is that half pint glass won't explode like cells will as the Delta peak will be miles out.

Chris

[Col]

All true, no doubt Chris, but does the same still apply if charging 2 identical types of cells (I have 4 packs of Dans old 3700's and have wondered if it's possible to charge 2 packs at the same time from the same charger)

[Jony]

If the packs are very well matched, then you'll be fine. After you can charge all the cells in one pack at a time.

But I'd be very cautious - it likely that the packs are no longer that closely matched, even if they were the same when new. If they're a long way out you might run into trouble. If you have a fancy enough charger that you can identify the voltage(s) at which the cells peak, then you could compare the peak voltages of the packs. If they're peaking at near the same voltage and taking the same capacity you might get away with it.

[Col]

Cheers Jony - it all makes sense. I'm not ever gonna charge 2 packs at once though, just wondered if it was possible!

[mark christopher]

dont want to point out the obvious if a manufacture says thier charger can do 12 cells it has to do it.
if both packs are the same capacity/type ie gp 3700 and they are discharged and equalised the same you will have no more trouble than charging 6 cells in one pack