5 Replies Latest reply: Dec 30, 2012 10:28 PM by lhnorman RSS

Pi runs off usb...

fatdragon New Members

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?

  • 1. Re: Pi runs off usb...
    viktor19466 New Members

    I don't understand what you want to say by "OVERPOWERED" , but i would recommend you not to give to much stress infact buy an external powered usb hub for sake of your's pi health.

    If you mean that wether it's net wattage cosumption increases then answers is off course yes.

  • 2. Re: Pi runs off usb...
    fatdragon New Members

    Hi,

     

    Thanks for reply. I have not been clear. I have an externally powered hub. It is this that powers the Pi via the usb! I am worried that with the normal power supply plus the power from the usb it might add too many volts...

  • 3. Re: Pi runs off usb...
    John Beetem Level 15

    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.

  • 4. Re: Pi runs off usb...
    fatdragon New Members

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

     

    Thanks

  • 5. Re: Pi runs off usb...
    lhnorman New Members

    Thanks. I was about to ask the question about the powered hub when I found your answer. I never even plugged in the micro-usb power because as soon as I plugged in the powered USB hub, everything booted and worked just fine.