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About backfeeding

Posted: Mon Apr 29, 2013 12:47 am
by LukUndTrug
So I know that my RPi (Model B, 512MB, rev. 000f) can be backfed over the internal USB hub via an external, powered hub. But I also heard, that operating the RPi this way is not very safe if the powered hub does no good job at overvoltage protection. The thing is, I don't know how much of that applies to my revision or how much of that is outdated information.

I know that my Hub (LogiLink UA0085, powered) will backfeed into the RPi. (I don't have it yet myself, but other users have reported that it does)

What I don't know is: is it still backfeeding if I connect the RPi's micro USB power port to a Hub port? (i.e: will the 'correct' power line drown out the 'incorrect', backfed, line and thus make the whole operation safe again? I have seen this looped setup a few times [with this precise hub even], but I don't know for sure.)
Or is it actually completely safe to operate my RPi using only backfeeding by now due to some hardware changes I didn't catch?

I have not found *definite* information regarding that and I'd very much like to not have to have two separate power plugs (for the RPi *and* the hub).

Thanks to anyone who can help me out!

Re: About backfeeding

Posted: Mon Apr 29, 2013 3:53 am
by SirLagz
LukUndTrug wrote:is it still backfeeding if I connect the RPi's micro USB power port to a Hub port? (i.e: will the 'correct' power line drown out the 'incorrect', backfed, line and thus make the whole operation safe again? I have seen this looped setup a few times [with this precise hub even], but I don't know for sure.)
Yes, It's still backfeeding unless you cut the red power line going from the Pi's USB A port to the Hubs USB B port.

It's not 'safe' to backfeed as theres no circuit protection in case of a short of a surge, but If your power supply is not a dodgey china jobbie, then you shouldn't have issues backfeeding.
I'm backfeeding one of my Pis now with a Linksys power supply and a cheap 7 port hub

Re: About backfeeding

Posted: Wed Aug 27, 2014 8:41 am
by HenryF
SirLagz wrote:
LukUndTrug wrote:is it still backfeeding if I connect the RPi's micro USB power port to a Hub port? (i.e: will the 'correct' power line drown out the 'incorrect', backfed, line and thus make the whole operation safe again? I have seen this looped setup a few times [with this precise hub even], but I don't know for sure.)
Yes, It's still backfeeding unless you cut the red power line going from the Pi's USB A port to the Hubs USB B port.

It's not 'safe' to backfeed as theres no circuit protection in case of a short of a surge, but If your power supply is not a dodgey china jobbie, then you shouldn't have issues backfeeding.
I'm backfeeding one of my Pis now with a Linksys power supply and a cheap 7 port hub
But you can assure me that if I cut the red line the hub will still provide data from my devices to the pi?
Thanks
HenryF

Re: About backfeeding

Posted: Wed Aug 27, 2014 8:47 am
by RaTTuS
HenryF wrote:....

But you can assure me that if I cut the red line the hub will still provide data from my devices to the pi?
Thanks
HenryF
nice 16month necro
yes cutting the red wire [as long as the power line is red as it is in 99% of all cases] will still provide data
you need the ground and data line to be connected as they are all used but the power will just stop power back flowing

Re: About backfeeding

Posted: Wed Aug 27, 2014 2:30 pm
by 123splat
Rat,
So what is wrong with a necropost if it gets the poster's question answered?

Re: About backfeeding

Posted: Wed Aug 27, 2014 2:47 pm
by RaTTuS
123splat wrote:Rat,
So what is wrong with a necropost if it gets the poster's question answered?
nothing much really TBH
I suppose these are found via the power of google ;)