NiCd charging.....reverse cell?

OK, so I'm charging a 12V NiCd battery pack that is sealed and where I can't get to the individual cells...

It's a little old and when I charge it for a good while and take the charger OFF , the voltage shows 11.7 ish. After a few minutes it starts to climb and ends up around 13V.

Shouldn't this be the other way around?

Is this something to do with a reversed cell?

Anyway, it isn't holding charge very long anymore...

Any clues for a cure if there is one?

Help...

thanks

Symes

Hi there Symes,

I think you should test the charger first by measuring the
output voltage to see if it looks ok.
If any batteries are bad, you'll have to take the pack
apart to find out. Measure the voltage across each cell.
If any are less than 1 volt you know they are bad (after
a night's charging).
You'll have to replace the bad cells by removing them and
soldering in new ones.

I had two packs bad, i replaced every cell in one pack
because all were bad, and it was almost brand new!
Purchased at Home Depot, Ryobi brand.

Take care,
Al

Al,

thanks,

Charger looks good.

The problem now is whether to crack open the pack and be able to get it back together again!!

Thanks for the info though!

kind regards,

Simon

P.S. I had that with a DeWalt (Black and Decker) 18V NiCd too...

Hi again,

He he, i know what you mean. I only replaced 6 of the
8 cells required in my pack. Almost couldnt get it to
fit back together, but it's ok now i guess.
If you open the bottom you could always seal it up
somehow.
Get out the duct tape if nothing else works /ubbthreads/images/graemlins/smile.gif

Take care,
Al

So now my question is.... for a 12V rated pack, discharging through a resistor (8 ohm, 20W and toasty hot!!), what should I let the voltage get down to under load before I consider the pack discharged and then recharge it to attempt revitalisation....

If all the cells are working properly, a 12v (10 cell) pack would be dead at 9 volts.

What I would do is:
trickle charge for a day or so
connect a medium load (car tail light bulb)
connect a volt meter
watch the voltage and record it every minute or so

If you've got a bad cell, the voltage will drop little by little, then it'll take about a 1 volt drop (within the space of 1-2 minutes). Then it will continue the little by little dropping. If a cell is bad, this drop will happen way before the overall pack voltage drops to "dischaarged" levels.

But, with your voltage RISING after coming off the charger we can likely stop right there. Buy a new battery. Don't charge it till it's dead. And it will last many years.

My dad gave me a pack from a drill motor and the way I checked it out was to measure each cell (he had drained it with the drill already) and mark the ones that were either low or reversed then I charged each cell individually and let him drain it again. The cells that were again way too low or reversed I consider bad because they let the pack drop too fast to make it useful. I figure if over half the cells are bad in a pack you may find it better to invest in a new pack unless it is an expensive name brand or higher output pack.