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I am putting together all the bits I need to start playing with my Pi, and one question I have is how to power it using the least cables as possible.

Given that I have ordered a small mains powered USB hub to attach all the kb/m/wireless etc to, it seems silly to need a 2nd mains socket to power the Pi itself.

It is possible to just connect a Micro USB cable from the hub to the power input on the Pi? Or will this cause some weird loop thing whereby the Pi attempts to see itself as some USB connected device?

stuffe
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  • I'm doing this now, using this hub: http://www.microcenter.com/product/371801/4-Port_SuperSpeed_USB_30_Powered_Hub Each port only gets 900mA though, not sure how the RPi likes that, but it works and I haven't had anything disconnect so far. I had to plug everything in a certain way in order to get it to work. The order seems to matter. The hub is plugged into the bottom USB port on the RPi, while the wireless keyboard receiver is plugged into the top port. Also I have the OS on a USB stick plugged into the hub as well. I will be switching over to an SSD (USB) to see if things speed up. – b01 Feb 24 '13 at 22:46

5 Answers5

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This can be done (I have done it with two different Belkin hubs). However, it requires a good powered USB hub, cheap hubs may not be able to supply enough power to the Pi to prevent problems with the peripherals (keyboard and network problems are the most common), or for stable operation of the Pi itself.

If I remember correctly the micro USB connector used to power the Pi does not use the data lines, so it will not recognize it as a USB device.

I would suggest setting up the Pi with a separate power supply first and then try powering it through the hub, This order will help debug any issues you may experience.

Steve Robillard
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    I have tried connecting to 2amps hub and it worked, but keyboard/mouse/flashdrive/wifi sometimes refuses to work or disconnects after some time, so it depends on the power consumption of all your peripherals. – Tomas Adomavičius Oct 25 '12 at 00:10
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Yes it is possible. As seen on http://www.raspberrypi.org/wp-content/uploads/2012/04/Raspberry-Pi-Schematics-R1.0.pdf at Page 1 - A4: Data lines are not connected.

Additionally here's also a blog entry about it and how to add power to a cheap unpowered USB hub: http://pihub.blogspot.co.uk/2012/06/raspberry-pi-power-supply-and-powered.html

Mose
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  • THe usb hub conversion looks good but I am not sure if it all that greatly done. Are you supposed to cut off the original power lines? Do all the ports get this adiditonal power. It would need a bit of tweaking but yea.. cool +1 – Piotr Kula Oct 25 '12 at 11:51
  • The blog post describes to cut the original power line from USB-Host to USB-Hub. It's not always necessary but some hubs can cause problems with "powering back". This is problem is also mentioned here: http://raspberrypi.stackexchange.com/questions/3281/raspberry-pi-usb-hub-failure – Mose Oct 25 '12 at 12:02
  • Oh yea fine then. I just skimmed it did not find that. Because that is what i was worried about :) – Piotr Kula Oct 25 '12 at 12:03
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It should work fine. Note that some powered USB hubs will also let power into the RPi through the fullsize USB ports, but on the Revision 1 boards not enough current can flow due to the polyfuses.

Revision 2 boards can be backfed just fine if the USB hub is happy to supply enough current

You can solder a wire across the polyfuses on the Rev 1 boards if you wish to use this trick

Rev 2 board is easy to identify as it has 2 mounting holes in it

John La Rooy
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    Thanks - can you provide details on how to know which revision I have and what to solder? Also, how much is likely to back feed in this way, would it obviate the need to use the Micro USB power input? – stuffe Nov 02 '12 at 11:36
  • I feel like an idiot, but what does 'backfed' mean and how does one identify the 'polyfuses' so that a wire can be soldered across them (and is that safe?) – Chris R Mar 23 '13 at 23:31
  • @Chris, it just means instead of using the USB 5V power to power devices you are powering the host (by the hub) instead. My polyfuses are green with the number 14 printed on them. They are bewteen the USB ports and the LEDs. It's safe to solder a wire over them - thats effectively what they did on the rev2 boards. – John La Rooy Mar 24 '13 at 04:51
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Sorry, not enough reputation to add comments. I've got powered USB hub. Noname, grabbed it on sales years ago. It has 4A output power adapter. Not sure how much current it supplies to each USB port. I was very surprised when my R Pi Model B turned on when I plugged hub into it. So, I have WiFi adapter, mouse and keyboard plugged into hub, HDMI cable connected and TP1-TP2 voltage shows 4.75V when playing movie in omxplayer.

Denis The Menace
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Study the Schematic. 5v to USB is directly connected to the 5v rail which is connected via a fuse to the power in. Should work perfectly if you can modify the hub to back power the pi.

neel
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