Battery Pack Burnout

[scwhiteley]

Hello!

I recently built a portable stereo that runs off a battery pack consisting of twelve AA size NiMH batteries (14.4V) It has worked like a dream, that is, until today.

The stereo worked this morning, then as of this afternoon, it did not. I opened it up to see what was causing the trouble, and it appears that something caused two of the batteries to overheat, hot enough to melt the ends of the plastic battery holder.

I tested all the batteries with a voltmeter, they all checked out except two, which registered a slight negative charge.

It probably is worth mentioning that I've been charging the pack as a whole unit, with a charger designed to charge a 14.4V battery pack.

So what do you suppose happened? Perhaps a short somewhere? possible, but unlikely. Is the charger or my charging method at fault? Who knows?

 

[Hero999]

I've heard about this happening before but with lead ac id batteries.

What's probably happened is that two of the batteries weren't fully charged and the others were so they discharged first until the point of being reversed.

You could replace the two bad cells but then you have the problem of them being strong and the rest weak.

What you should do, is charge all the batteries when before they run completely flat. Cell reversal becomes more of a risk as the number of cells in series increases.