Charging a Sansa with solar panels

[Unmensch]

Hello,
this is not exactly a rockbox issue, but I hope to find someone with enough knowledge to answer my questions here.
I want to solder a solar-panel to a female usb connector and to charge my Sansa with this.
Therefore I need to know how much Voltage the solar-panel has to supply. For the amperage I think 500mA should be good, but feel free to correct me if I'm wrong.

Help would be highly appreciated.

Greetings Steven

[saratoga]

The USB spec requires 5v.  Supplying less may or may not work. 

[Hillshum]

Aim for 5v and at least 500mA

[CyberSnipa]

I made an USB solar charger and it works, however make sure you put some sort of a current restrictor somewhere between the panel and the plug so that the current only goes one way. I didn't in mine and it sucked the juices out of my G1 phone so quickly that it was counterproductive. Otherwise, it's a great tool that you can take anywhere and charge your devices for free. And as long as any device has a USB connection then it should work.