Hi I'm working on powering my Sony external hard drive disk.

I want to power the drive from the sector and link it to the RPi without drawing any current from it (and also because i'm a afraid of backpowering the pi, even though I'm not sure of what it exactly is, if you guys could tell me some more about backpowering I'd appreciate)

I made a picture of what I did because English isn't my native language so I think it'll be more self explanatory : electric diagram

When I tested it, the drive turns itself on but I can't get the data on the RPi (nor on my computer).

Can you tell me what do to ? How to get the data on the rpi without powering the drive from the rpi usb port ?

I looked at a Y cable I have which is doing what I want and saw it was like this : enter image description here

But in this case, isn't there any risk of backpowering ? And doesn't the Y cable become useless in my case since the drive draws current from the rpi too ? Are Y cables only designed to draw power from 2 usb sources instead of one ? Correct me if I'm wrong but in this diagram, the HDD draws power from the RPi AND the sector, doesn't it ?

I thought they would be perfect for what I wanted : one usb cable for the power, one for the data

I know I could simply use a powered usb hub but I want to learn by myself how things work, thanks in advance guys for your responses

  • Yes, the latter solution risks back-powering the Pi. (Back-powering is when power enters through the USB host port to the Pi to power it, so that even if you disconnected the main power supply it would continue to run.)
    – Fred
    Commented Mar 24, 2014 at 16:36
  • What is this sector ?
    – Piotr Kula
    Commented Mar 24, 2014 at 18:26

1 Answer 1


You have to use the solution that is right in the middle of both.

Use the layout as per the first image, but also connect the ground to the pi. So the ground goes to both the Pi and the external power supply.

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