Advice on potiental mod

Hi All

New to the forums, but very impressed with all of the designs I've seen here.

I'm looking to build a bike light based loosely on Elektrolumens tri-star. I'd like to use 5 W luxeons and I'd like to use a high efficency potentiometer to be able to adjust current draw on the fly. The light output at the full 15 watts is great for descents, but more than is necessary for climbing. Given the relativly linear power - lumen relationship of leds ( especially in comparison to incandecent lights) it seems that you could reduce the current a fair amount to prolong battery life while climbing, then on the descent where brightness rather than battery life is the priority, switch back to the full 15W.

I figure I could buy the tristar and mod it fit on my bike without too much difficulty. Where I'm running into problems is figuring out what kind of potientiometer to use. I've seen some pretty nice digital power regulators here, but haven't yet seen something that has multiple power levels. Is anyone aware of anything like this?

Obviously I'm very new to this whole modding thing (my background is medical not electrical engineering) Beyond the basic physics equations of V=IR etc, I'm pretty much in the dark (sorry about the bad pun), so any advice or information would be greatly appreciated. Thanks in advance.

Jeff

If you have not already done so, you could read the Vari-Needle thread. http://www.candlepowerforums.com/ubbthreads/showflat.php?Cat=&Board=UBB14&Number=319508&page=&view=&sb=5&o=&fpart=2&vc=1

Well, the simplest option, if you can live with three distinct power levels, would be to make the LEDs individually switchable. Since the three optics seem to be aligned pretty well, all you should get is a dimmer beam. But read the TriStar comments - ISTR that someone put 3*5W in a 6D maggie and things got pretty warm after a while...

Seriously: if you're going for that power and price level, you'll want to spend some thought towards cooling.
Electrics/electronics will depend on your power supply. Easiest (for me...) option seems to be to go for a custom battery pack, holding 4 SLA cells (a bit heavier than NiMH, but much more forgiving) and powering the LEDs through a small resistor (LEDs in parallel, individually switchable, 1 resistor per LED). This means you'll have to build the charger yourself, but SLA chargers can be very simple.
Second option would be to use NiCd/NiMH R/C racing packs (and matching charger) at 8.4 Volts and slightly larger resistors.
Everything else will either be very wasteful (i.e. generate a lot more heat) or somewhat complicated (switch mode power supply).

Bye
Markus