Can the length of the USB cable be the cause of a non-working external hard drive?

Question

I have this old external hard drive, 80 GB, nothing too fancy, that is powered entirely by USB. The problem is that it keeps disconnecting itself.

I remember that I tested it with a short cable (15 cm, more or less) and it worked fine.

Now I'm using a one meter cable and it keeps disconnecting. And I can't find short USB cables anywhere!

Could be that the hard drive is not receiving enough power from the USB? It is connected to the back USB ports of a desktop PC, so I didn't think it could be that, but now I have my doubts.

Solution

A cable that is too long could reduce the power delivered to the device to the point where it does not work. The longer cable will have more resistance than a short one, which creates a voltage drop and reduces the current to power the device. I don't know if the USB spec requires all devices, especially high-power devices like hard drives, to work at the full 5 meter cable limit.

Although I'm surprised it took only a one meter cable to see a difference. I just connected my 120GB WD Passport (1 year old) with a 1 meter cable, and it works okay.

Comments

[Daniel R Hicks]

Is it possible that something untoward has happened since you last tested with the short cable?

[Daniel R Hicks]

(One possibility is that the USB connector on the drive is flaky and only makes good contact if the cable is positioned a certain way.)

[Zequez]

Mmm, I bought a cable recently so it's brand new. And it's a Wester Digital Passport (support.wdc.com/product/download.asp?groupid=201&lang=en) so no, it's a normal external hard drive.

[Keltari]

have you tried swapping the cable? what about trying it on another machine? the drive and/or cable could be defective.

[Zequez]

I tried with many cables and in many computers, the only cable that worked fine was this one that was 15cm length, but it wasn't mine.

[Zach]

If you have a powered usb hub, you might try plugging the drive into that. Or just buy a smaller cable to test with.

[woerndl]

Your direct answer is factually incorrect. The cable length can play a major role for any devices powered via the USB cable.

[fixer1234]

This is a good answer, but it only "suggests" that the cable length is the underlying reason. You could turn it into a great answer by making it definitive with electrical measurements (e.g., voltage at the drive or round trip resistance of the cables' power conductors).

[woerndl]

Absolutely, thanks for your positive feedback. I was thinking about measuring the consumption and voltage drop, but didn't have the resources to do so.