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For connecting external hard drive I want to use an active USB hub.

I found some USB hubs which seem also to power the upstream ports.

While this is under normal circumstances very bad I was wondering if this is actually a nice feature for powering also the Raspberry Pi device just via the Type A connector where I connected the USB hub.

Is this possible? Or can I power the Raspberry Pi only via the micro USB port?

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  • Look at Tobias Kienzler's answer to the question linked above.
    – Krzysztof Adamski
    Mar 26, 2013 at 8:55
  • Not sure why under normal circumstance that would be bad? They are designed to do that. And yes it will work as long as the hub can provide a minum of 1A per port. Both the mini and large usb connectors are only connected to 5+v and GND - For various reasons it is better to power using the micro usb port at all times - but not mandatory
    – Piotr Kula
    Mar 26, 2013 at 12:46
  • @ppumkin: Back-feeding power by USB hubs can be bad for various reasons. One example is in raspberrypi - if you unplug your mini-USB cable to power off device, it will still be running since it will get power form the HUB. It would be even worse if you have older revision on the board with polyfuses on USB since it will probably blow them after a while. And I think it will be OK if you have 500mA per port and connect two of them. And even one can be enough if you don't have to power anything but RPi itself.
    – Krzysztof Adamski
    Mar 26, 2013 at 14:17

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From the Raspberry Pi wiki:

Back-Powering; (powering the Raspberry Pi from a USB hub through the uplink/data port, single cable) Back powering is possible on the Raspberry Pi.

Revision 1.0 boards have to be modified to back power, this is due to the 140ma "polyfuses" that are installed in the USB port circuit.

Revision 1.1 boards do not need modifications to back-power, they have replaced the polyfuses with 0ohm resistors in their place.

Revision 2.0 boards do not need modification, they have neither resistors nor polyfuses. It is advised that short (12" (.3 meter) or less) USB cables be used for back-powering a Raspberry Pi. Cable resistance plus connector resistance can quickly reduce operating voltages below the proper range(5.25V to 4.75V).

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