Quick circuit for LED “high beams”
November 8, 2008
his has come up twice in the last week; I want high/lo beams, and I think Wiley needs them too. Different reasons — I don’t want to be rude to peds and other bikers, and Wiley (I think) just needs to conserve power.
The thing to note is that LEDs in the amber-orange-red family are much more efficient at lower temperatures, and more efficient at lower currents. For a given amount of heat sinking, you get more light per watt. In Wiley’s case, he has 4 LEDs total, and he wants to run them from 8 AA NiMH batteries. If he runs 2 1Amp BuckPucks, with two lights in series on each, those batteries will drain pretty fast.
So, first, just go for half the power, because 12 watts from 8 AA batteries won’t last long.
Second, by default, run all 4 LEDs in parallel. 250 milliAmps per LED will still produce pretty good light. When they need to be brighter, run them in series-parallel. A DPDT toggle works.
On-off-on toggles are not the best choice, because the current regulator will run at a high voltage when its output is disconnected from the diodes, which is too high for the LEDs when they are turned on again (this is a bigger problem if there is a capacitor on the regulator output). Either a on-momentary or an on-on will do.
It’s also possible to use a second 2PST toggle to turn a second BuckPuck on, or a 4PDT on-on-on to give you low/medium/high output.
I’m not 100% sure how the two current regulators work in parallel, but it’s worth a try.