Solar Powered iPod/USB Charger?

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

SiLo (author) 10 years ago
Thanks for the quick response, that answered a good bit of my questions.

I think these 2V @ 100mA Solar Panels (60x60mm) will do the trick with 3-4 of them in series for a 6V-8V source at 100mA.

Alternatively, I could go for setting them up in 3x3 grid in parallel (3 per path), giving ~6V supply @ 300 mA. Unfortunately, at this rate it gets a bit costly at $3 a panel, almost into the area of going for the $40 version they have at their site. Of course, the point is to make my own for the joy of creating it myself.

For the applications I think I would be using this, I'd imagine that the slow charge of 100mA would be more than fine. All it would take aside for the panels is the regulator and a diode (although the regulator might just have the diode functionality in itself).

Thanks for the heads up about the resistors on the terminals, I would have been really stumped without that.
LasVegas10 years ago
1) Yes, it will charge. A little slow though. You should have the iPod turned off to prevent drain while it's charging.

2) When you're considering short current, it's the internal resistance of the supply that would limit the current. Ohm's law still applies.

Yes. you would need regulation. I recommend looking at Maxim components. They have a number of components that will take fluctuating input (2.5-18v, I think) and output a constant 5v.

Also, to build a charger for the 5th Gen iPod, you must add a 10K resistor from the NEG supply to the DATA+ and a 10K resistor from the POS supply to the DATA-. This tells the iPod that it's connected to a charger.