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When building a solar powered USB charger should i use a 50mA panel or a 100mA panel?

 also is 5.4 volts a safe voltage for usb charging? im following this instructable: https://www.instructables.com/id/How-to-make-a-Solar-USB-charger-simple/
would it make a difference to use the 100mA panel over the 50mA one?


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orksecurity7 years ago
Amperage: Well, how much current will whatever you plug into it need in order to recharge? The bigger panel can supply more current, but if the device isn't drawing more than 50mA this is a difference that makes no difference.

Officially, USB provides up to 500mA, though no single device is ever supposed to draw more than 100mA. (An unpowered hub typically supplies 100mA per device, plus consuming 100mA itself, which is why 4-way hubs are typical.)

5.4 volts is out-of-spec high, though probably not enough to damage anything.

Note that the panel's rating is probably valid only when it's in full sun. If it's in partial shade or haze, its output can be expected to drop considerably.


No, a USB device can ASK for up to 500mA.
CPninja (author)  orksecurity7 years ago
is there any way to lower the voltage to a safer amount(maybe with a schottky diode?) without increasing the amount of light needed to keep it working?
Like Ork says, the panel is only going to supply 5.4 V in full sun, anything else and you'll be below that. IMHO 5.4V is likely to be an open circuit voltage anyway, and you'll see less in practice. Try it ! measure the output voltage across a fixed resistor.

Solar panels are rarely specified into a load, they are more commonly stated as open circuit volts and short circuit amps.
CPninja (author)  steveastrouk7 years ago
ok thanks.