There's starting to be lots of good info out there, but I opted for a balance of MYOG/Off the shelf. I think I'm ~$10-$15 into this project, so WAY cheaper than any of the off-the-shelf USB charge systems
referenced here. I'll keep this short on details because there are a few good articles you can read elsewhere on the theories involved. Plus my EE skills are quite limited.
I bought a $3 regulator module
from ebay. The only required items remaining were 1x bridge rectifier, 1x capacitor. I thought it would be nice to leave all my connections alone to limit wear and tear (connections are always where your failures begin!) so invested in a small switch, where I can toggle back and forth between
- AC headlight/taillight
- OFF
- Regulated USB
Skip this if you want a simpler system. Just means you'll have to switch your wires when you go between illumination and charge modes.
I went quick and dirty and after shielding the leads, just jammed the Bridge Rectifier and Capacitor into the input leads of the prefab China Buck regulator module. Seems to work from prelim testing. Voltmeter says i get 5.08V = Perfect. I intend to get a few images that give a sense of output current after some more testing.
The case turned out a bit hasty/janky. I may redo it soon, but from discussion on the web it seems the actual USB port is likely to be one of your main failure points in waterproofing. I would argue that no matter how tight your case/wiring is, USB charge device just plain isn't waterproof, so keep it in your Hbar bag and call it a day.
