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ludo75
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Location: Wonderland

power an usb hub

Tue Dec 06, 2016 6:45 pm

Hi boys and girls.
I noticed that when i pulled the power plug from rpi, the usbhub continued to power the rpi, since that happend would it be possible to power a hub like this with 1 or 2 usbpower thingys
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wildfire
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Location: Dundee, Scotland

Re: power an usb hub

Tue Dec 06, 2016 7:36 pm

Not a good idea, back feeding power via a hub could cause issues, use a proper PSU or a powerbank and leave the hub to worry about the devices connected to it.

After saying that, you don't mention which model of Pi you have.
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ludo75
Posts: 31
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Location: Wonderland

Re: power an usb hub

Tue Dec 06, 2016 8:21 pm

4

wildfire
Posts: 528
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Location: Dundee, Scotland

Re: power an usb hub

Tue Dec 06, 2016 9:31 pm

ludo75 wrote:4
No such Pi model, maybe in a year or so. Seriously each Pi requires different power levels, A zero or A/B can probably live of a USB Hub, the 3B would likely draw current outwith USB specs.
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W. H. Heydt
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Re: power an usb hub

Tue Dec 06, 2016 9:50 pm

The first thing to be aware of is, if you are using two power sources, they will not have exactly the same voltage, so power will flow from one to the other in ways that you don't intend...with potentially disasterous consequences. This is, by the way, why hubs are not supposed to backpower, and good quality ones don't. For any hub, you should *know* whether or not it will and adjust your practices accordingly.

It is possible to backpower *some* models of Pi starting with booting the Pi. Ones that can do that are the A+, Pi Zero, and Model B Pis. Ones for which this won't work (because the power won't be fed back from the USB ports to the rest of the board until the LAN chip is up and running) are the Pi3B, Pi2B, Pi2B2, and--if I'm not mistaken--the B+. Also note that it is going to be an exceptional powered hub that will provide enough backpower current to fully power a Pi2B or Pi3B.

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