Title pretty much says it all. Sure, I could have just bought a decently powered headlight that runs on 3x AA batteries and call it a day, but that would've been too easy
Anywho, here's what I cooked up:
I had a 12V SLA battery lying around that I got at a surplus store a while back, I figured that it would work well since it was meant for deep cycle use and has a 7 AH capacity.
The battery is mounted in a bracket I made out of some metal from an old computer PSU and some steel strapping they sell that the hardware store, boy that stuff is really useful. The rear reflector is held on with some freakishly strong double-sided tape. Mabye one day I'll put an LED light there too.
Well, something has to keep that battery charged. The dynamo generators they sell on ebay were around $30. I figured it couldn't be too hard to make your own, so I took a decently-sized DC motor and pushed a small LEGO wheel onto the shaft. Using a bench grinder to spin the shaft, it kicked out about 40V unloaded.
Trying to connect a load to it and take proper measurements proved to be a bit of a challenge, so I just made a little regulator for it with an LM317 to keep it under 15V. I figured it wouldn't kick out enough power to overheat the IC, and if it did, the IC has a built-in thermal shutdown. I bolted a heatsink onto it anyways and put the assembly in some ABS pipe for protection:
The output of the LM317 is connected to the battery through a 10 ohm resistor, I'll spare you the fancy math, but it keeps the current to the battery under 0.5A.
Let there be light!
Now all I needed was a headlight to run off the battery. I found a 21 LED flashlight at the surplus store for $6. Problem was, it was designed to run off 3x AAA batteries, which is about 5V max, and my battery is 12V =/
Here's a picture of the light:
It came in a camo green. Since my bike is mostly black, I painted it black. It's the cheesy camo so it wouldn't even look good on one of those army bikes I see around the forum.
The solution to the battery problem was of course another regulator. But burning off 7V @ 750mA in a linear regulator (7805) would get warm to say the least, and it ain't too efficient either.
That's where the switching regulator comes in:
This little fella can drop 12V to 5V and source up to 1A without breaking a sweat. In addition, I was able to use a variable resistor so I could adjust the brightness of the headlight. Of course, the price for all this is that a switching supply is a fair bit more complex than a linear one. Oh well, making your own PCBs has a certain zen to it.
And in the end, success! ...at least so far.
I still have to do some testing to see how rugged this setup is. All I know is it's certainly unique!