Supplying USB Power


9 posts
by dandrum » Tue Nov 06, 2012 11:28 pm
Based on what I've read, I was expecting my Rpi to power on when I plugged in the micro USB plug connected to a 5V power source. Plan was to do that as the last step. To my surprise, it powered on when I plugged in a std USB plug to one of the 2 USB ports on the Rpi and plugged that into my powered USB Hub. I was so surprised, I unplugged it immediately. (1). Whats up? (2). Did I screw anything up?
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by itimpi » Tue Nov 06, 2012 11:56 pm
No - it means your hub back-powers (many do although technically it is against the USB spec). If you have a rev 2 board or a rev 1 without Polyfuses on the USB sockets you can successfully power your Pi in this way.
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by dandrum » Wed Nov 07, 2012 2:13 am
itimpi wrote:No - it means your hub back-powers (many do although technically it is against the USB spec). If you have a rev 2 board or a rev 1 without Polyfuses on the USB sockets you can successfully power your Pi in this way.


Yes, I have a Rev 2 board. Then I guess that means that I can forget using the micro USB power input as long as I'm using the powered hub?
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by Burngate » Wed Nov 07, 2012 10:50 am
dandrum wrote:
itimpi wrote:No - it means your hub back-powers (many do although technically it is against the USB spec). If you have a rev 2 board or a rev 1 without Polyfuses on the USB sockets you can successfully power your Pi in this way.


Yes, I have a Rev 2 board. Then I guess that means that I can forget using the micro USB power input as long as I'm using the powered hub?

Yes, so long as the hub can provide the Pi with enough amps whilst also powering whatever else you have attached.

If you also power it from the micro USB connector, there's the possibility of the two power supplies fighting. This may or may not create a problem.
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by jools » Wed Nov 28, 2012 7:49 pm
if you're looking for a powered usb hub that will power your Pi a treat I discovered that one I already had works a treat. It's avaiable from 3 suppliers on amazon for £8 or less:-

http://www.amazon.co.uk/TRIXES-Speed-Po ... B00504BBB8
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by Wheel_nut » Wed Nov 28, 2012 8:55 pm
That Hub, like most unbranded "Powered" Hubs only provides a 1.0A Power Supply. I have bought and returned three such hubs because the PSUs supplied ranged firom a puny 400mA to 1.0A though the seller specified either 2A or 3A.

Caveat emptor.
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by jools » Mon Dec 03, 2012 8:24 pm
Well I bought 3 more based on my experience and they all work fine with a keyboard, a mouse, edimax wireless dongle and a portable DVD drive!. Incidentally I should have said that for Model B Rev1 you will need to duct power from one of the USB ports to the micro USB power connector on the Pi (the cable costs about £1) but with the Rev2 you don't need this: you can duct power via the common USB cable only.
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by jools » Mon Dec 03, 2012 8:29 pm
Also the link I gave: the spec says 1.0 amp, and it isn't 'unbranded' ??
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by Wheel_nut » Mon Dec 03, 2012 8:40 pm
Jools, The 7 port Hub you linked is a GENERIC item sold by a reseller Trixes. It is available from a myriad of sellers on eBay both in the UK and Hong Kong/ China for ~ £3-85. I have bought three of these and returned two of them because they were specified to have 3A and 2A PSUs but came with 1A PSUs like yours. To Trixes credit, they specify the PSU as a 1A unit.

Whereas 1A may be adequate for your rig, it will almost certainly NOT suit everybody's needs and hence my "Caveat emptor" warning. A 7 Port POWERED Hub should come with a 3.5A PSU or at least 2A allowing for some "diversity".
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