Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I'm facing a low power USB port issue on my desktop PC. I have a USB 2.5" external harddrive and it does not work with any of the USB ports on the computer case except for one.

Also if I use a extension cable with that port, the HDD will not work. I measured the voltage of the USB ports and they gave me about 4.60-4.70V. I updated the BIOS to the latest version. My motherboard is an AUS M4A785TD-V Evo and my power supply is Xilence 700W.

Is there any way to increase the voltage of the USB ports?

share|improve this question
does the port work with other devices? – user78429 Jun 5 '11 at 15:30
bckbck, obviously, I cannot say for sure, but it probably works fine with many devices that require less power. I got the sense that the external drive he is using might be powered solely by the USB port, making power critical. A mouse will use a lot less, and probably work fine. – KCotreau Jun 5 '11 at 16:03
A)How are you measuring the voltage? B)Have you tried another PSU? Also, it is very silly that you didn't think about or didn't mention about 'B'. – barlop Jun 5 '11 at 16:32
@bckbck yes wireless mouse and keyboard, and other usb devices are working on my pc. They require less power than usb hdd. – zforx Jun 6 '11 at 14:35

I doubt you can change it on your computer. You should probably buy a powered USB hub. Google "powered usb hub" without the quotes.

share|improve this answer
I know external powered usb hubs but I want to know why my pc does not give 5V on usb ports. – zforx Jun 5 '11 at 13:39
The specification for USB is +5 DC volts. I don't regularly (by that, I mean never have) measure the voltage on USB ports, but 4.7 seems like it may just not be working right, and the hardware is bad. I would probably call ASUS and ask them about it, and if it is a problem, as I suspect, have them RMA the board. Does the external drive have its own power source? – KCotreau Jun 5 '11 at 14:05
External drive does not have it's own power source, and it is working with my laptop which give +5V when I measure it's usb ports. – zforx Jun 6 '11 at 14:31

They make usb Y cables that use 2 usb ports to properly power the drive. It draws power from 2 usb ports. image description here

share|improve this answer

USB low voltage can impact a hard drive. I have an Apple (Fujitsu make) drive my brother gave me. I put it in an external USB 2 enclosure and used a USB connector with a Y (double USB ends)to plug into an nGear powered USB hub and then to my computer. The drive would mount and unmount and I could never complete a clone of my internal drive. I ended up just plugging it directly into one of my Mac Mini's USB port (just using one of the USB ends) and I didn't have any further problems. This leads me to believe that hard drives are especially sensitive to power sources as the Y connector didn't seemingly provide enough juice (even double plugged in with a powered HUB). Also, my 2012 Mac Mini has USB 3.0 which I understand provides more power (in the range of 900 mA verses 500 mA for USB 2). This boost may have helped things.

share|improve this answer
Welcome to Super User! This is really a comment and not an answer to the original question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. – DavidPostill Oct 13 '15 at 14:19

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.