Solar Powered iPod/USB Charger? Answered
I know you can buy these suckers for some $60-$100, but I prefer to make my own so that it'll be (hopefully) cheaper and definitely more fun. This is my first major project as well, although I have toyed with breadboards and other test environments with ICs, capacitors, transistors, and LEDs to create some effects.
Right now I'm just thinking about the power system itself, of course the idea is solar power so I've been looking at the solar cells that Clare electronics has. The CLA289-ND and CLA292-ND seem like they might be pretty decent cells for the job.
The iPod (5Gen) uses a USB interface for charging, so it'll need a steady 5V source along with 100-500mA. At this point, I have two questions:
1. While USB starts at 100mA, it can ramp up to 500mA maximum. If the charger only provides 100 or 200mA, will the iPod still charge? Even if slower, it's better than nothing.
2. The solar cells I mentioned state a short circuit current of 50 uA. Does that mean I'd need 5,000 of these to get 500 mA? If so, then I'd better look for a more powerful solar cell it seems. It seems I am misunderstanding something here since Ohm's law would seem that 8V input should mean a current of 8/R. Taking the pure ideal case of "no resistance" (assuming R = 1), that gives 8 amps. Of course, that doesn't sound right either. I'm sure I'm messing up something here, it's been a while since electronics class.
I also assume that the solar power voltage will definitely be spiky with the varying amount of light that it may have. There would definitely have to be some kind of regulation with it before giving it to the iPod.
If anyone could give me a little tip on how to construct the power cell or what solar cells I should use, I'd greatly appreciate it. I got the idea from this related article: How To Make Your Own USB Car Charger For Any iPod Or Other Devices That Charge Via USB