Hello
I realise this has probably been posted to death but I am getting mixed information from Googling this issue.
Basically I got a USB hub today off eBay, I plugged it into the Pi and noticed the Pi suddenly powered on without my power plug plugged in..
It seems that the powered USB hub is back feeding power into the Pi through the standard USB slots.
Is this safe? I read somewhere that it isn't because it could potentially fry the Pi?
My Pi is a Model B if that's any help.
Thanks!
Chris
-
ChrisMayhew
- Posts: 3
- Joined: Thu Sep 12, 2013 5:20 pm
-
FTrevorGowen
- Forum Moderator
- Posts: 5621
- Joined: Mon Mar 04, 2013 6:12 pm
- Location: Bristol, U.K.
- Contact: Website
Re: Back Feeding Power
This happens with about 50% of low-to-medium-cost hubs. As long as the hub's PSU is "of good quality" (ie. produces a clean. stable, 5V) then you're unlikely to "fry your Pi". However you're by-passing the Pi's polyfuse and over-voltage protection circuits so there is an "increased risk", but many forum members do use this "USB hub feature" (which, strictly speaking, is "against the USB specs.").
Trev.
Trev.
Still running Raspbian Jessie or Stretch on some older Pi's (an A, B1, 2xB2, B+, P2B, 3xP0, P0W, 2xP3A+, P3B+, P3B, B+, and a A+) but Buster on the P4B's. See: https://www.cpmspectrepi.uk/raspberry_pi/raspiidx.htm
-
ChrisMayhew
- Posts: 3
- Joined: Thu Sep 12, 2013 5:20 pm
Re: Back Feeding Power
Thanks for the reply.FTrevorGowen wrote:This happens with about 50% of low-to-medium-cost hubs. As long as the hub's PSU is "of good quality" (ie. produces a clean. stable, 5V) then you're unlikely to "fry your Pi". However you're by-passing the Pi's polyfuse and over-voltage protection circuits so there is an "increased risk", but many forum members do use this "USB hub feature" (which, strictly speaking, is "against the USB specs.").
Trev.
Well I am not taking the risk, I've just ripped open the cable and cut the red cable and it's no longer powering the Pi now!
I assume I only needed to cut the red to stop all power backfeeding?
I've tried a USB keyboard and it still works
-
FTrevorGowen
- Forum Moderator
- Posts: 5621
- Joined: Mon Mar 04, 2013 6:12 pm
- Location: Bristol, U.K.
- Contact: Website
Re: Back Feeding Power
Fair enough. I'm not a fan of doing it either. Cutting just the red cables fine, and others have chose to do similar. As part of my testing of USB hubs I made an "Isolating and Back-power Indicating Adapter" as shown here**: http://www.cpmspectrepi.webspace.virgin ... esChk.html .ChrisMayhew wrote: ...
Well I am not taking the risk, I've just ripped open the cable and cut the red cable and it's no longer powering the Pi now!
I assume I only needed to cut the red to stop all power backfeeding?
I've tried a USB keyboard and it still works
Trev.
**towards the end of the webpage.
Still running Raspbian Jessie or Stretch on some older Pi's (an A, B1, 2xB2, B+, P2B, 3xP0, P0W, 2xP3A+, P3B+, P3B, B+, and a A+) but Buster on the P4B's. See: https://www.cpmspectrepi.uk/raspberry_pi/raspiidx.htm
-
ChrisMayhew
- Posts: 3
- Joined: Thu Sep 12, 2013 5:20 pm
Re: Back Feeding Power
Thanks mate, Looks like a good little device.FTrevorGowen wrote:Fair enough. I'm not a fan of doing it either. Cutting just the red cables fine, and others have chose to do similar. As part of my testing of USB hubs I made an "Isolating and Back-power Indicating Adapter" as shown here**: http://www.cpmspectrepi.webspace.virgin ... esChk.html .ChrisMayhew wrote: ...
Well I am not taking the risk, I've just ripped open the cable and cut the red cable and it's no longer powering the Pi now!
I assume I only needed to cut the red to stop all power backfeeding?
I've tried a USB keyboard and it still works
Trev.
**towards the end of the webpage.
I'll see how the modified cable goes but it seems to be okay so far