Power supply for Raspberry Pi from USB hub?

[Ettore_M]

So, as I'm waiting for my R-Pi (It'll be dispatched "the week commencing 09/07/2012"! ), I'm stocking with the things that are needed for my R-Pi to get started with it. Keybooard, check. Mouse, check. SD card, check. Analog TV cable, check. But I don't have a USB power supply. "Really?", you'll say. "You don't have a cell phone charger?" Actually, I have one, but I don't think it's a good one, as it's rated on 5V, 500mA. So, I don't think it'll work (On R-Pi FAQs, it says I need a 1A charger).
So, as I was looking on Ebay for one, I found a 7-port USB hub with a supply of 5V, 3A, and I started wondering: Could I use the USB hub as a power supply for my R-Pi? Did anyone of you try this?

Sorry for the long post. I'm a newbie, so I'm shooting with questions..

Hector

P.S. Here's the hub: http://www.ebay.com/itm/280522733324?ss ... 1423.l2649

[davidmam]

If it is a cheap hub that doesn't regulate each channel to 500mA then yes, it will work. It is how I run mine (though with a 4 port hub)

..d

[greypower]

I am using this hub to provide power to RPi. BUT the power supply gives 5.37 volts, which is slightly above tolerance for the Pi - however no problems yet !! Also this provides a +5v supply back into the Pi from the Pi to hub USB (data) cable, which is enough to cause the Pi to start reboot when you disconnect the hub-to-pi usb power connection - I will let you search the forum with "cut+the+red+wire" where you will find this (general) topic discussed. However this hub is easy to take apart and modify so that this feed-back does not occurr (by cutting a pcb track). Apart from all this, the hub seems to run well with wireless adaptor, usb disc and memory stick attached.

Good look with your Pi.

[Ettore_M]

Thanks a lot for the answer, greypower!

BUT the power supply gives 5.37 volts, which is slightly above tolerance for the Pi - however no problems yet !!

Maybe this "5.37 volts" problem could be solved with the construction of a 5V regulator (7805, etc.) from the power supply to the hub. Or it wouldn't provide the same current output as before?

Also this provides a +5v supply back into the Pi from the Pi to hub USB (data) cable, which is enough to cause the Pi to start reboot when you disconnect the hub-to-pi usb power connection

Are you reffering to this as a problem? Or is this the expected behavior of the R-Pi? Excuse me if I misunderstood that..

I will let you search the forum with "cut+the+red+wire" where you will find this (general) topic discussed.

You're right about this, but I can't get the search to work. It always shows me the message "The following words in your search query were ignored because they are too common words"! Can you post the link to the thread?

However this hub is easy to take apart and modify so that this feed-back does not occurr (by cutting a pcb track). Apart from all this, the hub seems to run well with wireless adaptor, usb disc and memory stick attached.

That's good, because I want to build a case for my R-Pi with mounted usb hub and one power supply for both the R-Pi and the hub.

Thanks again!

Hector

[greypower]

1. My psu gives 5.37v, yours may give a different value.

2 7805 would not work in my case - not enough volts to drive that ageing part!! Don't know if you could use a low drop out part. Maybe a simple voltage divider perhaps - but you may not need to. Depends on the current you will draw which solution is best (sorry if that sounds like the "sucking eggs" treatment!!)

3. search - sorry , don't use the + sign.

4. Yes there is a problem with this "power feedback". All sorts of "spurious" events seem to be caused by this (quite a few posts on this). Some people have chosen to "open-up" the Pi Hub-to-Hub data cable and cut the red (+5v) wire or modified the hub in some way. It is easy to mod this hub if you feel confident enough. Else "cut the red wire" in the cable

p.s psu supplied with this runs cool, but not tested for regulation (I'm just hoping its OK! - seems to be)

Cheers