Bike light design help for newbie

Hopefully my image posts...new to this. If not I'll modify, otherwise I've covered everything within the image. I'm a visual guy and I think this explains it better than I could verbally.

Thanks to everyone for the help.

Li-ion packs are lusualy listed as multiples of their single cell nominal voltage of 3.7. Max capacity is 4.2 volt. Some longevity is gained by undercharging. Seven cells at 4.2 volt would be 29.4 in series, less than the maximum for the buckpuck. Good there. As long as the fully charged pack is less thatn the 36v maximum for the puck.

If the puck is rated to drive into the Vf load of 3 MC-E's (3 x 3.4 @ 700 mA) = 10.2 Vf total, all three will be driven at 700 mA all the time until the battery's low voltage cutoff (I assume it has one as well as a max voltage out/short protection).

The highest output bin is a bright white and will give about 470 lumens at 350 mA x 1.7 (factor from current versus poutput chart)= almost 800 lumnes under controlled laboratory conditions. you will run them hotter (losses 10-30% or more if they get really hot) plus a 10-20% lens/reflector loss. Say 25% overall as a bit on the high side if you don't get silicon smeared on the lens cover, for about 600 lumens each out the front, or 1800 total.

You may wish to consider lower output but warmer colors in the side beams. I think you might like levels, but don't know if your selected buck puck will take a variable resistor to accomplish that. If you shut the light off I suppose you could run switch them from series to parralel with wiring and switch to accomplish that and reduce the current to 700/3 = 233 mA for about 70% of the 350 mA output, or 70/170 = 41% of max ouput.

I suspect the buckpuck won't tolerate a no-load situation without failure and a power pulse to the LEDs would be bad, so the changeover would from series to parallel or reverse would have to be with battery disconnected.

Look through older design threads when buckpucks were cutting edge. The topics by category sticky thread at the top may help.

This is NOT a good road light BTW.

LiIon Batteries are rated at the average voltage of 3.7 volts, so you get 7.4, 11.1, 14.8, 18.5, 22.2, 25.9, 29.6.

So a "28" volt battery is 8 cells which has a maximum output of 8 x 4.2 = 33.6 volts.

Another Buck puck capable of analog (varistor) or digital dimming:

http://www.cutter.com.au/products.php?cat=Recom+Drivers

Check datasheet link. That would let you tame it if riding with others.

There's a few ways to wire an MC-E. Each MC-E is 4 dies.

4s: 4x Vf, 1x current
2s2p: 2x Vf, 2x current
4p: 1x Vf, 4x current

The forward voltage of each MC-E die is around 3.5v at 700 mA. You're using 3 MC-Es. It's a good idea to wire them identically, but you don't have to.

The buckpuck will output less voltage than the battery has. So you have options. The closer the output voltage is to input, the more efficient the buckpuck will be. Battery voltage drops as they discharge though.

4s. 3 MC-Es worth of dies will take 42v! Only 700 mA though
2s2p. 3 MC-Es in 2s2p takes 21v and 1.4 amps.
4p. 3 MC-Es in 4p takes 10.5v and 2.8 amps.

Electrically it'll work. Heatsinks and optics and wiring next!

Thanks for the help everyone! Sorry for my delay in responding, but I was traveling for work most of the week. I really appreciate the help on the electronics. I still need to learn more about electrical draw when hooked in series vs. parallel. I had made assumptions about this which I can tell are incorrect based upon the responses.

If I decide to take the plunge and get this thing going I'll be sure to post pics. The biggest challenge I'm having is the housing which needs to have an integrated heat sink, a place to mount the reflector/optics AND a way to seal the front with, hopefully, something strong like gorilla glass (not a fan of acrylic). Additionally, I really want this to be solid. I don't want it looking goofy, which I personally think the "bright luxeon" on instructables does.

Fun project, though! And great forum too!

I forgot that the Vf for the MCE was for a single die.

Oh well that's why it's a forum to help catch that sort of thing.! lovecpf