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Pi runs off usb...

e14 Contributor

Is it OK that my Pi runs off the power from usb connecting my powered usb hub? Is my Pi overpowered when connected to normal power supply + usb hub?

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  • richard moore wrote:

     

    Is it OK that my Pi runs off the power from usb connecting my powered usb hub? Is my Pi overpowered when connected to normal power supply + usb hub?

    RasPi only uses as much 5.0V power as it needs, so the answers are YES it's OK and NO it won't be overpowered.  If you have two power sources for RasPi, they both supply current.  The current from each source depends on the exact voltage of the source and the amount of cable and fuse resistance between the source and RasPi's 5.0V plane.

     

    It is technically possible that the two power supplies could fight with each other over voltage regulation, resulting in extra 5.0V ripple.  I think is unlikely because of the resistance of the cables and especially polyfuse F3.  I haven't heard of anyone reporting it for RasPi.

     

    A USB hub is not supposed to provide upstream power.  However, many hubs do so anyway so RasPi decided it was easier to allow a downstream hub to power RasPi than try to stop them from doing so.  If you power RasPi this way you lose the protection of polyfuse F3, but you also avoid the problems of polyfuse F3.

  • in reply to johnbeetem

    Aha! That sounds like the answer I was hoping for. I will stop worrying now!

     

    Thanks

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