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USB hubs

Thu Oct 18, 2012 2:28 pm

I know this is a n00b question, but I do not have my pi yet but should be getting delivered today!
I am wanting to get a hub for my Pi and ideally would like to power it off the hub. I have a 7 port powered hub, but it is a cheapo one (looks just like this ... 40?item=66) and do not know how much power it supplies, so first Q is how to test it?

2nd, if I got a powered hub, I am assuming I would have 2 connections to the RPi from it correct? The one off the hub to the micro usb port on the Pi, and one from the Pi usb port to the input of the hub. Is that correct?

The devices I would be putting on the hub would be the Edimax wifi adapter, usb HDD (it is powered with an adapter not off usb), possibly a bluetooth adapter, and possibly a game controller eventually.

Thanks for the help!

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Re: USB hubs

Thu Oct 18, 2012 8:10 pm

You should have only one connection from your hub to the Pi and that would be the USB connector. You will need to have a separate power supply for both the Pi and the hub.

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Re: USB hubs

Thu Oct 18, 2012 9:39 pm

I believe the RPi can draw up to 700mA from the power supply (partly depending on what is being supplied to the USB devices plugged in to it). However the USB standard states that a device should only draw up to 500mA which means that, even if you could sort out the appropriate connectors at each end of a cable between the hub and the RPi, you would be pushing the capabilities of the hub to provide enough power.
Secondly, (and this may well not apply to cheap USB hubs) a part of the initial USB handshake is to have the device request how much power it needs from the host (or hub in this case) - the host can opt to supply that amount or not form the connection and probably not provide power to that port.
My advice is to use a separate power supply for the RPi and use the hub the way it is intended - to provide the host (RPi) access to multiple devices (not RPi).

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Re: USB hubs

Fri Oct 19, 2012 11:33 am

I have a Belkin 4 port powered usb hub (F5U234) that powers my Raspberry,
I have my Edimax wifi, keyboard and mouse plugged into the hub, my Pi is plugged into the hub from its usb port
and also has another connection from the hub to the micro usb power connector on my Pi and this seems to work ok
the hubs power supply is rated at 2.6A,
hope that helps

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Re: USB hubs

Fri Oct 19, 2012 11:41 am

you can use the HUB to power the RPi
USB on hub -> micro USB on RPi
you can also use it to extend the USB port available
RPI USB -> HUB uplink USB port [usually type A socket]

if you have a Revision 2 board you may be able to get away without the usb - micro usb power and just backpower the RPi from the USB ports
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Re: USB hubs

Fri Oct 19, 2012 1:15 pm

Yeah, I just got the rev 2 yesterday. I'll try backpowering it from the usb port and see how it works.

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Re: USB hubs

Mon Nov 12, 2012 4:17 pm

So the first hub I got was defective. I just got the Belkin F5U234. It powers it fine, but have to have two cables going to it. Is there any way to make it backpower the Pi?

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