One other note: During the charge cycle a nimh or nicad pack will often dip a little (go backwards) in voltage, but then begin steadily climbing once again. This tends to happen more often in the first hour or so of the charge. That's the trick with chargers that allow you to set the m/v threshold setting. It needs to be just high enough to keep the charger from being falsley tricked into thinking the charge is done, but not set so high that the charge won't trigger it's self to shut off once the pack drops a bit in voltage when it's peak is reached.
This voltage drop isn't constantly falling once peaked. In other words, the pack will in general just drop so much in voltage and then stay right around that level regardless of the charger constantly pumping amps into it. You're charger has missed it's shut off trigger because the m/v setting was too high, and now you've got a potential fire on your hands or will at least destroy the pack if it is charged too long.
This is less of a risk with a low and slow charge rate, because even if the charger doesn't shut off the amp rate is so low (close to a trickle rate) that it probably won't overheat the battery even if it's still charging it for hours. That's another reason why a low and slow charge rate is better- it's less risky should the charger not shut off and it's sitting on it for a long time.
If the m/v threshold setting is set too low then now you've got a different problem. The charger will set terminate several times during the charge even though the pack hasn't peaked, due to the random slight drop in pack voltage as it goes through the charge process. I tend to set the m/v on my chargers low enough to put up with that, and just check the charger within the first few hours or so to make sure it hasn't shut off early. An easy way to tell is just to put the pack back on the charger. If it's already peaked then within an hour the charger will shut off again. If you still aren't sure stick it back on the charger a second time. It's rare for it to false peak a few times in a row. On the other hand, if the pack is hot it probably has peaked and you are overcharging it. It's only likely to get hot from overcharging if the amp rate is higher than say a 10 hour charge rate, though.
Normaly I set my threshold at 5 m/v per cell for a nimh and maybe 10 to 12 for a nicad. Most chargers consider this a "per cell" setting, meaning you put in 5m/v and they'll do the math for you for the total pack voltage drop that has to occur to terminate the charge. I've also found that a real slow charge rate (like 10 to 14 hours) might require me to adjust the m/v setting down a digit or two, or also might require me to raise it by a digit or two if I'm charging extremely fast like less than an hour. Higher charge rates will cause the per cell voltage drop to be increased and real low ones to decrease.
I would think that trying to charge a nicad pack on a nimh charger might cause this false termination without the pack being peaked, since I'd think nicads will drop more in voltage during the charge process as well like they do when peaked than a nimh. Putting the pack back on the charger two or three more times to make sure it isn't false peaking should correct that. Once it gets over that "hump" or dead spot in battery chemistry that is causing it to drop a bit in voltage it should continue to the end of the charge. Just be sure you are watching the thing and checking it's temperture with your hand. Again, keep it in a fire proof place and use this information at your own risk. Injury or fire could result and I don't have that kind of money.
That's most of what I know about nimh/nicad charging. Charge it slow most of the time. Once in a while a fast charge (about an hour or less) is healthy for it to break down resistance caused by crystals that form. Drain the pack completely dead two or three times a year with a car light bulb or something. Don't let a completely dead pack sit for weeks because the cell polarity can switch and now negative becomes positive and vise versa. If the pack seems bad drain it dead and then charge it fast (hour or less). Drain it again and then slow charge it for 10 hours. Sometimes that will recover bad cells or balance them if they are in different states of charge. Excercising a pack by draining it dead once in a while was the old tool used on nicads to prevent memory problems. Newer nicads don't suffer that fate from what I hear and neither do nimhs, but excercising a pack still helps it to flex it's muscles and thus hold more capacity which equals longer run times. In fact, it's a good idea to cycle a pack about 3 to 5 times when it's new. Charge it/drain it 3 to 5 times at a slow easy discharge and charge rate. If you have a charger that shows capacity you'll be surprised to see how much more it holds after this.
One more time...Use any of the above at your own serious risk of death, disaster, or other things most people find to be a negative.
