I have a raspberry pi being powered by a cellphone charger (1A)

I try to connect and HDD but the power is not enough. I don´t have a powered USB hub BUT i do have other power supplies. So I tried powering the HDD by myself.. but I cannot.

I tried:

I have a Y USB cable, I shortcuted the red wire from the endpoint that goes to the power suply and the HDD. So it does NOT backpower my PI. I tried 1A and 2A in the charger here. Nothing works

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I also tried using the 2A adapter to power the Pi and connect the HDD to the USB thinking that 2A should be enough for everything. But it is not

I checked the specifications of the HDD and it says 5V and 1A so .... No clue why it fails.

IF I plug the HDD to my desktop PC it has no problem working. But in the Pi it starts and stops all the time making ugly noises

Any clue ??

  • Just snip the red wire inside the cable going to the pi. Connect the other plug to you power supply. This way both the Pi and the HDD share a common ground, but the HDD gets its power from the separate power supply.
    – Gerben
    Commented Feb 11, 2014 at 16:18
  • If you want to write that as an answer Ill gladly select as an answer
    – javirs
    Commented Feb 12, 2014 at 7:40

2 Answers 2


You COULD do this but I do not recommend it.

Firstly there are NOT 2 data lines - you need at least a common ground.

If you REALLY can't afford a powered hub (I recently bought one for less than $10 - without power brick) you would be better to connect power to the GPIO +5 and GND pins.

This bypasses the polyfuse (which is what is limiting the current), but will power the Pi and external peripherals. Provided the Power Pack is capable for supplying the current (while maintaining the voltage, which many newer chargers do not) this will work.

EDIT You could use a Y cable, but you would still need to isolate the external power from the Pi (otherwise this is the same as connecting to the GPIO connector).

You could cut the +5v line in the cable, but I use an adaptor which lets my Pi feed any peripherals (through a Schottky diode), but prevents any powered hubs etc feeding power to the Pi (bypassing the polyfuse).

power isolator

  • I guess that both back powering and powering via GPIO enables the protections the raspi have so they are NOT recomended.
    – javirs
    Commented Feb 11, 2014 at 14:11
  • I would like to see something like power the HDD with its Y cable without powering the raspi and then power the raspi as usual
    – javirs
    Commented Feb 11, 2014 at 14:11
  • I extensivelly edited my question, can you please check my updates ??
    – javirs
    Commented Feb 22, 2014 at 10:40
  • I cutted the red and ... it does not work more more than some seconds ...
    – javirs
    Commented Feb 24, 2014 at 7:42
  • IF you have what you claim, AND the power supply is adequate it should work. Try the same configuration (power, Y cable) on a PC. If you want any further you will need to measure the actual voltages, not just go on what the label says.
    – Milliways
    Commented Feb 24, 2014 at 7:59

Problem could be too long and/or too thin wires. Here is how I made it and it works fine: Wiring diagram showing interconnections between single 5 Volt 2 Amp PSU, an RPi and a separate Hard Disk Drive with only a USB connection to the latter Photograph showing the answerer's implementation of their answer Idea is almost like yours, but I used cable with thick wires inside on part which connects power supply and green connector; cables between green connector and HDD and between green connector and RPi are standard usb cables, but I made them as short as possible.

So make sure that voltage is not dropping in cables too much, and it should work fine.

Update: With system like shown above I was experiencing random HDD disconnects caused by EMI (suggested by dmesg log). Adding ferrite ring on power cable which goes to RPi resolved it. Ferrite ring on power cable to eliminate EMI

  • Welcome to the Raspberry Pi part of the Stack Exchange. I have "tidied-up" the wiring diagram slightly to emphasis the removal of the +5V power (Red) connection from the original RPi to HDD lead. It might also be worth pointing out that the Black wires are 0V(Ground) and the Grey/Green ones represent the USB Data Lines...
    – SlySven
    Commented Feb 5, 2016 at 17:27

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