So i'm building a pretty high powered LED light for my mountain bike for riding at night. its three LuxeonIII LEDs wired in series. each has a forward voltage of 3.9V. so in series i need a voltage of at least 12V to turn them on. I also have a buckpuck current driver that provides a constant 1A to the LEDs to keep things regulated. It needs at least as much voltage as the total forward voltage and up to 32VDC.

now, my intention for this project was to use cordless drill batteries. i have some 19.2V craftsman EX batteries. theyre nicad and i presumed theyd work fine. but they dont

using the buckpuck or wiring directly w/o it, the 3 LEDs in series will not even turn on w/ the drill battery. If i wire the drill battery directly to ONE LED, it turns on, but is very dim.. the battery is fully charged and i tried two different batteries. multimeter shows the voltage is like 21VDC on the batteries.

thinking my LEDs were messed up, i hooked up a (4) AA battery back to one LED, and it lit up great. tried again w/ the buckpuck and it worked great, too.

then i found my friend's old R/C car batter packs and they worked fine for one or two LEDs (not enough voltage for all three in series).

so wth? if this drill battery can power a drill why cant it drive an LED? any ideas?

3/3/2006 9:26:25 AM

does the drill have any mechanical mechanism (redundant?) that is activated when you plug the battery into the drill casing? Maybe something is pressed or a connection is made or something when you put the battery into the case. Maybe to prevent a battery from shorting out, for example, when dropped into a bucket of metal nails.

3/3/2006 9:45:50 AM

^ well if he used the multimeter and checked the voltage while the battery was out of the drill I wouldn't think that would be the case

3/3/2006 9:50:03 AM

oh, didn't see that part.
So you're trying to put 21V through a single LED? what kind of resistance you put in there with it?

3/3/2006 10:09:28 AM