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With my PI I'm trying to use the F4U018 Belkin 7 port hub (yes - the one on the problem list). Its one of three I have around, all of which happen to be on the problem list - I don't want to shell out for another one.

The RPi/Hub is working fine when not powered, however when it is powered the ethernet (amongst other things) stops working (Stops getting ipv4 addresses, although still gets ipv6).

Oddly the RPi will try to boot when the hub is powered, and is plugged into one of the normal usb ports, and there is no power at all supplied to the RPi through the normal micro usb. I assume that this power isn't enough to properly run the RPi as it isn't stable in this configuration.

So: I assume that the issue is that there is power "travelling the wrong way" down the cable (from the input port of the hub to the RPi USB port).

Is there a way to prevent this? - A USB cable that won't carry the power? Some way to stop the PI taking power from these ports?

A fix for this may help with a number of the other issues seen with Powered Hubs.

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Uhh, I didn't think the Pi could be powered this way. –  Jivings Jun 24 '12 at 14:33
    
Me either, but it definitely has a go at booting. –  Jon Egerton Jun 24 '12 at 14:38
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There's no reason power can't travel into the USB hosts - no diodes etc, but there is a polyfuse which will limit the current, which is why it won't boot properly. Check out my answer here: raspberrypi.stackexchange.com/questions/340/… –  Alex L Jun 25 '12 at 4:47
    
@AlexL: True, and I've read this (but the PI can't be powered this way due the to the polyfuse). What I wondered was, since this additional power appears to be the factor causing my issue, whether it was possible to stop it. –  Jon Egerton Jun 26 '12 at 10:49
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2 Answers

up vote 3 down vote accepted

This is what a diode is used for: restricting electricity to flow in one direction.

More about Diodes

A 5.1V Zener diode applied inline with your usb cable should keep electricity from going toward the Raspberry Pi.

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That sounds promising. Where would this best be implemented, as some sort of extra adapter on the usb cable, or is there scope for it to be soldered to the RPi board? –  Jon Egerton Jun 29 '12 at 8:15
    
I would not solder it to the board, but instead splice it into the USB cable. I would also get some breadboard so you can easily experiment with it. –  Kyle Macey Jun 29 '12 at 14:10
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did as was suggested and put a zener diode in line on the 5 volt + USB input(USB a) 5 watt and bingo no more problems,USB still works fine. thank you for this tip –  user3130 Nov 1 '12 at 18:43
    
@davidwhale cool! –  Kyle Macey Nov 2 '12 at 3:33
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For the record, a Zener Diode is NOT the correct component. A Zener (or breakdown) diode will conduct in the reverse direction if the applied voltage exceeds the rated breakdown voltage. If you attached a powered hub with 5.15V supply, then a 5.1V zener would conduct, and you'd have the same state as without the diode. What is required is a standard power diode, of the 1N400x or UF400x variety. Given that the point of the polyfuses is to prevent the USB devices overloading the RPi, and this is not going to happen when a powered hub is connected, it seems reasonable to up these to 1 amp rating and power the pi through the USB hub with a diode in the Hub preventing the in reverse from occurring.

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