ishibu
Posts: 1
Joined: Tue Sep 17, 2019 7:12 am

Pi Zero W - Powered over USB data port

Tue Sep 17, 2019 7:21 am

Hi !

I got a "problem" (?) with my Raspberry Pi Zero W ; I don't know if it's a real problem or if it's a normal case, then I would ask you before doing bad things...

My Pi has a USB hub plugged into the USB data port, and a power supply plugged into USB power port.
The hub is powered by another power supply.

When I unplug the power supply, the Pi stays "alive". It's always powered by the USB data port.

Is it normal ? Are there any risks ?

Thanks !

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alphanumeric
Posts: 2080
Joined: Tue Jan 19, 2016 2:17 pm
Location: Sydney, Nova Scotia, Canada

Re: Pi Zero W - Powered over USB data port

Tue Sep 17, 2019 1:07 pm

The Pi can be back powered via the DATA port. Thats so you can use it in USB gadget mode.
Power coming back from the USB HUB is IMHO not desirable. Not in this instance anyway.
I'd either just power the Pi via the HUB, or get a HUB that doesn't back power the Pi.
The two power supplies are going to fight each other trying to regulate the +5V to what they want it to be.

PhatFil
Posts: 1373
Joined: Thu Apr 13, 2017 3:55 pm
Location: Oxford UK

Re: Pi Zero W - Powered over USB data port

Tue Sep 17, 2019 1:15 pm

To avoid this issue with my pi3-nas, and stop the hub psu maintaining power on the Pi board I simply snipped the +5v line at the hub pcb, being an older hub with an old square usb B? socket it was a simple task easily undone if needed, with a smaller usb micro device it may be easier to hack into the flex line the odds are good its colour coded red and black for power if not have a good supply of solder and shrinkfit at hand and you will get there..

alphanumeric
Posts: 2080
Joined: Tue Jan 19, 2016 2:17 pm
Location: Sydney, Nova Scotia, Canada

Re: Pi Zero W - Powered over USB data port

Tue Sep 17, 2019 1:24 pm

What do you have connected to the HUB? If it isn't anything that requires lots of current just unplug the power supply feeding the HUB. Power "should" then come from the Pi Zero.
This is what I use with my Pi Zero's, https://shop.pimoroni.com/products/thre ... connector
No issues with a keyboard mouse, thumb drive, and ethernet running.

hippy
Posts: 5976
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Pi Zero W - Powered over USB data port

Tue Sep 17, 2019 1:26 pm

The way I solved the problem of a Zero being powered by both a power supply and a hub / PC / other equipment was to find USB cables whose connectors could easily be exposed and have the power wire cut.

Those can be clearly marked and can be used with any equipment without having to modify any equipment.

It is never a good idea to have two power supplies connected at the same time. They will both fight with each other with unknown outcomes. One or the other, or both, could be damaged.

Not only is there the problem of the Zero always being on, being back-powered by the hub or PC it connects to, but that the Zero may try to back-power the PC or whatever it connects to, or parts of its circuitry, with unpredictable results.

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