Power Through USB Hub


9 posts
by rodent » Mon Sep 26, 2011 3:05 pm
What is the possibility of powering the device through a powered USB Hub?

Kill a few birds with one stone as it were - power for the Raspberry and provide extra USB expansion?
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by obarthelemy » Mon Sep 26, 2011 3:15 pm
Not possible, and already widely discused.
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by davehiggins21 » Tue Feb 07, 2012 12:43 pm
Could you buy a 7 port USB hub with decent power supply (should be able to buy a reasonable 5V 2A power supply with universal plugs if you can't find a hub with decent power supply) and power the Pi from one of the ports on the hub using a USB A to Micro USB cable then connect the Pi to the hub via a USB A to USB A cable for the data connection which still leaves 5 ports available on the hub.
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by grumpyoldgit » Tue Feb 07, 2012 12:55 pm
I'm sure you would be setting up some sort of loop there. It could form a tear in the space/time continuum. My view would be that you want to give the Pi it's own power to guarantee what it is going to get.
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by Raccoon » Mon Feb 27, 2012 4:14 pm
That sounds possible.

@grumpyoldgit since the micro usb port only contains the pins for power, it is not possible to use it for data transefer, so in theory, you should be able to power it through one and then plug a male to male usb cable to be able to use the other ports for things.

However you have to keep in mind that the model A requires 500mah and model B requires 700mah, so make sure the usb hub is capable of supplying sufficient power. From what I"ve seen, most hubs only give out 500mah, if you can find one that can give 700mah or higher (the rasberry pi will only take as much power as it needs) you should be ok.

Also make sure to check how much power the devices you plan on using require, usb memery sticks should be ok, but portable HDD"s will have problems, however external HDD"s have their own power supply.
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by joshhodgson » Mon Feb 27, 2012 8:08 pm
Powered hubs tend to still draw current from the host, and taking this power from the host and pumping it back could grow risky.
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by Chromatix » Mon Feb 27, 2012 8:32 pm
This *has* been widely discussed before, and it *is* possible and actually pretty easy.

All you have to do is power the hub, and then provide a connection not only from the R-Pi to the hub (for data), but from the hub to the R-Pi (for power).  There is no "loop" to be worried about, it's all at the same voltage and with the same polarity; a properly designed hub will not feed power back along the data cable anyway.

With a typical 4-port hub, you will then be left with three powered ports on the hub and the remaining low-power port on the R-Pi.  I strongly suggest using the former and not the latter.
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by BlueClogger » Tue Feb 28, 2012 2:13 pm
As has been discussed before, this is possible.  The limitation might be that each USB outlet on the hub can only supply 500mA.  I'm going to use a 2A 7-port powered hub with a split (2xUSB-A to 1xMini-USB) cable which came with an external USB 2.5" drive, combined with a Mini-USB to Micro-USB adapter (available from ebyuer).  This should give me 1000mA to the Pi and still leave 1000mA and 5 ports for other devices from the hub.  All I need now is a Pi to see if it works or blows up!
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by digital_addict » Tue Feb 28, 2012 3:36 pm

@ BlueClogger +1



With the concerns over the “Loop” it should be noted that when you purchase your power hub, you will be provided with a cable with 1 type a plug and 1 type b plug or other (not a). This links the output of the Pii to the input to the hub, thereby avoiding any contention.



IMHO this thread has now run it's course.

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