Adapting a DeWalt charger to charge AA battery packs
 

With a 3 year old I had a bunch of NiMH AA's lying around, so I decided to build a quick and easy Optronics MR16 20W 10 degree halogen headlight. I used two AA 6-pack holders in series and overvolt the lamps. The light seems pretty good, but I haven't gotten it out on the road yet so this is based upon garage checking. I'm curious to see how it compares to the dual 2xAA Ultrafire Cree Q5 setup I have on the other bike.

I happen to have a DeWalt DW9180 charger lying around unused. It is labeled for 1-hour charging 7.2-18V. The output is listed at 2.8 Amps DC.

Would it be safe to crack this open and run it to my AA battery pack so I don't have to take the AAs out and put them on 3 separate 4 battery chargers? It sure would be handy.

Incidentally, I found an optronics head that I like much better, but it is an h3 setup. ANyone know where I can get a 25 watt or less H3 bulb?

Couldn't wait for the forums.

FAIL.

I plugged in the battery pack, the dewalt charger showed OK flashes. I stuck with it in the garage while I tinkered on something else. After 30 mintues, the flashing light went off. The normal sign of done is a solid red light.

The batteries were HOT. The charger's overheat sensor must have gone off and shut it down.

Bad idea. Generally drill packs are made with C cells (or 2/3 C cells). Charging AAs at that current will fry them.
Also, the more batteries you charge at a time, the less accurate is the charge on every cell. If you can, buy the 10 cell charger from batteryspace.com But if you want to charge as a pack, buy a 12v pack charger from there.

Also, that charger may be intended for NiCad. NiMH requires more sophisticated circuitry. NiCad cells are brutes, they can take abuse (though they don't perform nearly as well as NiMH). NiMH chargers can charge NiCad cells, but not the other way around.

I was going to say the same, most power tools are nicad so the charger isnt going to do a good job with nimh. There are nimh pack chargers available that you can get.

Cordless tool chargers are usually running the raggedy edge of frying the cells anyway; tool users like 15 minute charging. It's not even good for the batteries that they're designed for. In fact I wish the tools came with a slow charge mode; generally I don't mind charging overnight, especially if it means the batteries will last twice as long. But the manufacturers don't want the battery to last a long time, they make a lot of money selling new batteries.

There is a certain point where charging slow doesn't help and can actually cause missed end of charge (with NiMH). My old Makita 9.6v had a 1 hour charger and those batteries lasted 10 years.
Charging via a set timeisn't good anyway, good chargers set charge current at .5C to 1C.

1 hour charge would be good. All the drills I've looked at, and the one I've had for nearly 20 years now, has a 15 minute charger.

GOOD chargers are pulse chargers with microprocessor-controlled, negative-delta-V end of charge sensors. You're right, you don't want to charge too slowly, but keeping the batteries from getting hot to the touch is good.