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I read recently (I don't remember exactly where) that you could power the Pi from a "cheaper" USB powered hub. I just tried this, and it works.

On checking the Pi schematics, it seems the USB port Vcc pins are directly connected to +5V, whereas the 5V Power micro-USB goes through the poly fuse.

I don't know what the specifications of USB powered hubs are supposed to be, but if they are just feeding +5V to the USB port Vcc (as the Pi itself does) this makes the poly fuse a joke for anyone using a powered hub, and all warnings to people attempting to power their Pi through the P1 port a bit academic.

PS I know similar questions have been asked before. I further tested and the Pi voltage between TP1 TP2 was 4V45, while the 3A PSU supplied 5V25 (off load). I assume this means that the Hub feed is via some circuitry (probably a diode), so if the Pi is using its own PS it should reverse bias the diode, and be "safe". Powering the Pi via the Hub (mine at least) is below the minimum recommended voltage.

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2 Answers 2

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Some hub backfeed power to the Pi.

Either buy a hub that is verified to work, or open the usb cable and snip the 5V line, preventing backfeed.

Make sure you have 2 usb cabled between the hub and the Pi as illustrated below. One for power from the hub to the Pi. One for data from the pi to the hub. raspberry hub wiring

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  • I still think the above is an exercise in futility. 1) The comment "Cable with no data Lines" is pointless, as the micro-USB as they are NC on the Pi. 2) In the configuration above, if there was an overload, opening the poly-fuse the Pi would still be powered. 3) I do not regard cutting a cable as a satisfactory solution. The Pi should have provided isolation - the omission of the poly-fuses without providing other isolation such as diodes is an error. If this was the design decision the USB should be powered from 5v, not through the poly-fuse.
    – Milliways
    Nov 21, 2013 at 8:16
  • First, it's not my image. Indeed the red cable can have data lines. They're just not used. I don't thing the Pi has a bad design. It's the powered hub that shouldn't backfeed power. At least some PCs have the same problem as the Pi (electronics.stackexchange.com/questions/75654/…). You idea of having the usb power bypassing the fuse wouldn't the meet the USB safety requirements. So the Pi wouldn't pass the USB requirements, maybe even fail CE certification.
    – Gerben
    Nov 21, 2013 at 16:57
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I use a powered hub and I don't have any problems with it. I use the CyberPower 7 port hub.

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  • But are you using the original Raspberry Pi B which this referred to. The Foundation has fixed the problem in B+ and later.
    – Milliways
    Mar 1, 2016 at 21:48

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