So I have built a Benchtop Power Supply out of an old computer power supply to power and test misc. gadgets I have created. I would like to attach 2 salvaged USB ports from a junked computer to the 5v rail in order to charge devices from my Power Supply as well. The 5v rail is is capable of 25amps on this specific supply. I plan to attach a USB hub to the port which would extend the total ports to 7. I am questioning the wires from the main port's ability to hold up to current that may be drawn. If I was to attach 7 devices to the USB for charging I would estimate anywhere from 5 to 14 amps that could be drawn. If it makes any difference, I have spliced the 2 data wires to each other on the main port. I'm fairly new to tinkering with electronics, and this power supply is my first real project I've decided to try, so any advice is appreciated. I will include pictures of what I'm working with to hopefully provide any information I may have missed. I will have of course properly mount and protect all the wires once they're connected, but if I am current that this could draw too much current for the wires to handle. Is there any easy solution to solve this issue? Homemade Power Supply

Salvaged USB Ports


  • \$\begingroup\$ Possible duplicate of AWG for connecting a USB \$\endgroup\$
    – Unknown123
    May 14, 2019 at 8:34
  • \$\begingroup\$ Note that a USB hub of 7 ports is not a suitable way to get charging level currents out of 7 ports. Such USB hub most likely comes with a 5V @ 2.5A power source. A decent hub will have internal current limit switches at 500mA per port. Obviously you cannot draw 500mA from 7 ports at once as it would overrate the power supply. In addition, even if you tried to supply higher current to the hub from your power supply, it will probably smoke the circuit board in the hub that was designed to only distribute 2.5A. \$\endgroup\$ May 14, 2019 at 10:41

1 Answer 1


Current capabilities of conductors are generally defined by the wire gauge. Look up what gauges your wires are, and search the internet for a current/gauge table. You will find out if your cables are able to withstand the current. Are the 5V cables connected directly to the usb ports? If so, the maximum current is defined by what the port can hold. You should be able to find a datasheet for a generic USB port to find its capacity. If there is some sort of circuit between the USB port and the cables, then yeah, it depends on what the circuit is designed for.

Good luck on your starting adventure with electronics! Remember to work safe if working with high voltages (unplug cables from wall sockets etc) Only touch anything if you're SURE you're safe.

  • \$\begingroup\$ Before touching anything that may be live, check it with a multimeter... Found circuits that stay live because previous people "cross-connected" circuits. \$\endgroup\$
    – Solar Mike
    May 14, 2019 at 8:41
  • \$\begingroup\$ I will be wiring the stock wire from an old windows computer, that was already connected to the USB port, directly to the 5v rail if I determine this is safe. And yes, I always make sure to unplug devices before touching anything. Luckily I also learned about capacitors before taking my first computer power supply apart. I learned how to discharge them, but apparently they can deliver quite a shock if your not careful! \$\endgroup\$
    – ICEMAN
    May 14, 2019 at 8:53

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