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Cause of USB Power Problems

o_o

Member
Aug 1, 2013
44
0
0
#1
I have recently noticed that sometimes the USB Power given out by a USB Port is not sufficient to power/use a connected device. I am curious to know if the cause of this is the Motherboard or the Power Supply?

I have this problem in two of the devices I interact with: A Laptop at home, and a Desktop at work. The Laptop is my own, but the Desktop belongs to the company I work for. I think both of these are about 4 years old. I have various devices like an external HDD (powered solely through the USB Port) that do not seem to work. (I can get them to work sometimes though, but if I have too many devices like a USB to DVI, mouse, keyboard etc, they either don't connect or drop off.)

Do you think that the power supply on these machines is weak i.e. putting out less current e.g. on the 5 V rail, or is it a problem on the Motherboard voltage controller/regulator?

I am looking at the problem hypothetically. I am looking to build a new computer and if I know the answer to this, I can focus on getting a better component be it the Motherboard or a Power Supply.

I'm just curious. Thank you all
O. O.
 

Cerb

Elite Member
Aug 26, 2000
17,485
0
86
#2
USB 2.0, by design, should kill the port if anything tries to draw over 500mA per port. I'm 99.9% certain everything is working as designed.

Since you don't mention doing so, can I assume you are not connecting the HDD with the correct Y-cable, but using a regular double-ended cable? If so, you need a cable that will draw power from 2 ports, which USB 2.0 HDDs would come with. USB 3.0 HDDs often don't, since USB 3.0 is allowed to carry higher current, but that only works when functioning as USB 3.0. So you may need to get your own, if it is a USB 3.0 drive to be used with USB 2.0 ports.
 
Last edited:

o_o

Member
Aug 1, 2013
44
0
0
#3
USB 2.0, by design, should kill the port if anything tries to draw over 500mA per port. I'm 99.9% certain everything is working as designed.

Since you don't mention doing so, can I assume you are not connecting the HDD with the correct Y-cable, but using a regular double-ended cable? If so, you need a cable that will draw power from 2 ports, which USB 2.0 HDDs would come with. USB 3.0 HDDs often don't, since USB 3.0 is allowed to carry higher current, but that only works when functioning as USB 3.0. So you may need to get your own, if it is a USB 3.0 drive to be used with USB 2.0 ports.
Thank you Cerb I'm sorry I did not notice your reply. Yes, my HDD was a USB 3.0. I did not know that USB 2.0 is limited to 500mA, whereas a USB 3.0 can go up to 900mA. I think that was my problem.
 

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