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Raspberry Pi Forum backpower / backfeed test
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  • backpower
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Related

backpower / backfeed test

drandy
drandy over 9 years ago

I've just bought a Unitek Y-2142 powered USB hub (AMD chipset) (£5 from Maplin). The hub is a 3+1 hub. There are three usb2 ports + an iPod2 charging port which happily powers my pi. Having looked at the list of powered hubs on elinux (and failling to find this brand), I am a touch worried about backpower / backfeed (hopefully different names for the same thing). I've google the problem and came accross a test you can do at stackexchange power supply - Powered hubs, backfeeding and safety - Raspberry Pi Stack Exchange and was wondering if its a good test. The test envolves unplugging everything from the pi (inc sd card) and connecting the pi to the hub using one of the pi's fullsize ports to the 'input' port of the hub. If the red led on the pi lights up when the hub is powered up then there is backpower (and an unlit red led indicates no backpower).


Thanks

Andrew

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  • clem57
    0 clem57 over 9 years ago

    Which Pi version are you using on hub

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  • rew
    0 rew over 9 years ago

    The thing is: there is a fuse on the raspberry pi, and you may be circumventing that fuse if your hub powers the "upstream" port into the 'pi. This may even happen if you connect the "charging" port to the pi's power port: There is a fuse between the pi's power port and hte pi itself, but there may be a parallel connection between the pi's "fused 5V" and the hub through the dataconnection cable.

     

    So what "disadvantage" do you get if that fuse gets bypassed? IMHO: not so much. The hub would have been happy to provide power (fused or not, current limited or not) to normal devices, so why get in a huff if that device happens to be a pi, which also has an extra fuse?

     

    The decision to put a fuse on the pi is because some users can be expected to prod metal things at the device (intentional or not). If you just take a bit of care to prevent short circuiting the pi, you'll be fine.

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  • drandy
    0 drandy over 9 years ago in reply to clem57

    I've got a pi 2

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