We purchased a 2.5" Seagate external hard drive. For power and data transfer it has a USB 3.0 cable, like this Amazon USB Cable. It works great on the USB 3.0 ports on the PC but the Smart TV does not deliver enough power through the USB port to work. I have tried it with a USB extension cable like this Powered USB Extender with an extra plug dedicated to power connected to a phone charger and it worked. I need that cable else were have the parts so i was looking to make a similar cable out of an old USB extension cable and a old phone charger. Would I be able to connect both the power coming directly from the port and the charger together or would I only be able to connect the power to the charger? I ask this because I also want to use the cable with other devices that do not require extra power.

  • \$\begingroup\$ I wouldn't do that, given these powered extenders are cheap and hassle-free. And messing with it without adequate knowledge/experience is risking to screw some expensive equipment. \$\endgroup\$
    – Eugene Sh.
    Dec 22, 2017 at 20:04
  • \$\begingroup\$ Do not directly connect the phone charger output to the power from the computer port!! The USB 2.0 type cables that have two Type A connectors are only meant to be used in two USB ports on the same host computer where the power to both ports comes from the same power supply. \$\endgroup\$ Dec 22, 2017 at 22:05
  • \$\begingroup\$ Go buy another Y-cable and call it a day. \$\endgroup\$ Dec 23, 2017 at 7:15

1 Answer 1


Here is the USB 3.0 cable pinout.

If you could somehow split out the 5V power/ground lines and connect them to an external power supply, I don't see why it wouldn't work. I don't think you should connect the signal ground to the power ground, but someone else more knowledgeable than me should weigh in on that.

I don't think the host would care if zero current is being drawn, as long as current draw stays under the max allowed. If for some reason it failed to detect the device, then you could add a dummy load resistor on the host side to fake it out.

Ensure data lines stay twisted and shielded to avoid signal degradation.

  • \$\begingroup\$ -1 Actually, it should be -3: 1. You MUST connect power ground to ground wire in the cable. There is no other ground in the USB link. 2. You don 't need USB 3.0 cable to feed a HDD out of USB 2.0 port - standard u-USB plug will do the job. 3. You don 't need any dummy resistor to load the host port - host doesn't check any actual draw anyway. \$\endgroup\$ Dec 23, 2017 at 7:14
  • \$\begingroup\$ I referenced USB 3.0 because the OP did. Looking at the 3.0 pinout there is ground for Power and ground for Signal. I realize 2.0 only has 4 lines but I was referring to the 3.0 pinout in the link above. The standard usb ground line must be passed through to the host in addition to being connected to the 5v power supply ground. \$\endgroup\$ Dec 23, 2017 at 14:19

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