I would like to modify an old power supply to have a USB A female adapter so that I could use it to charge any device.
I plan to split out the power lines from an adapter that is:
Input: 100-240V – 1.0A 47-63Hz
Output: 5.0V 3.8A max
I know that some devices like the data lines to be high, but for now I'm focusing on the power required and any pitfalls there.
Am I correct in calculating that I could add four USB female jacks to this power supply and there would be enough power to charge most devices with them. I just need to connect each jacks pins to the correct lines.
Would there be any issues with this that I am missing?
EDIT: Upon further reading I've noted that a 600mA fuse on each line would be good protection if a device draws too much.
Also decoupling capacitors for each line would protect lines from each other.
Best Answer
Many devices won't properly charge from a 5V supply, they need a USB host (or power controller) to supply the correct command first.
The original USB spec (USB2.0) gave only 100mA per port until the device identifies itself and provides it's power needs to the host.
Then the current is limited to 500mA. USB3.0 increased this to 1.5A, again through negotiation. Some devices adhere to this spec so won't charge (at more than 100mA) until a host tells them so. Later specs (as well as deviations from the spec) again increase the available current through negotiation for battery charging by using the data lines as power lines to increase the current capacity of the wire.
Basicly this means that sometimes pluging some devices into a wall wart (PSU) will only change very slowly (if at all) unless that PSU has a USB host or power controller inside it.
I have an Asus tablet that certainly behaves like this.