User avatar
Dyfatty
Posts: 7
Joined: Thu Aug 09, 2012 11:13 am

My Rpi needs no power unit !

Fri Aug 31, 2012 6:34 am

I was watching a program from 4OD via Raspbmc (which works very well) and decided to pull the plug for the evening. I switched hdmi inputs on my tv to watch regular stuff and then pulled the power feed to my Rpi. The lights did not go out!. And the network led kept flickering.

I switched my tv back to the Rpi and it was still working with a perfectly good picture with no power supply.

A miracle ?
No. Power was coming via the powered USB hub. Should this happen ?

itimpi
Posts: 1090
Joined: Sun Sep 25, 2011 11:44 am
Location: Potters Bar, United Kingdom
Contact: Website

Re: My Rpi needs no power unit !

Fri Aug 31, 2012 7:33 am

Dyfatty wrote:I was watching a program from 4OD via Raspbmc (which works very well) and decided to pull the plug for the evening. I switched hdmi inputs on my tv to watch regular stuff and then pulled the power feed to my Rpi. The lights did not go out!. And the network led kept flickering.

I switched my tv back to the Rpi and it was still working with a perfectly good picture with no power supply.

A miracle ?
No. Power was coming via the powered USB hub. Should this happen ?
Not on a well designed USB hub as technically back-feeding power down a USB connection is against the USB standard! Having said that many hubs, particularily cheaper ones, tend to do it. Also it should only work on the very newest Pi's which have zero ohm resistors in place of the F1/F2 polyfuses (or an equivalent mod one by the user) used on initial Pi's as the polyfuses stop enough power getting in via the back feed method to run the Pi reliably.

User avatar
Dyfatty
Posts: 7
Joined: Thu Aug 09, 2012 11:13 am

Re: My Rpi needs no power unit !

Fri Aug 31, 2012 8:03 am

The hub is a Belkin Hi-Speed USB 2.0 7-Port Mobile Hub Hub - 7 ports.

I do not know how much current the hub can supply.

If the hub voltage is slightly higher than the power unit I assume that the Rpi will take juice from there?

User avatar
RaTTuS
Posts: 10504
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK
Contact: Twitter YouTube

Re: My Rpi needs no power unit !

Fri Aug 31, 2012 8:06 am

look at the polyfuses on the RPi are they 0ohm?
if so then the hub will backpower with no issues [YMMV] if they are not 0ohm then you will get problems

as long as the hub has a good PSU then you'll be fine
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

Wendo
Posts: 142
Joined: Sun Jun 10, 2012 8:27 pm

Re: My Rpi needs no power unit !

Sat Sep 01, 2012 3:43 am

Also, if you just pull the power out of a running system you will eventually corrupt the file system. Like every OS, you should shut it down before powering it off

XBMC even has a shutdown option

User avatar
Dyfatty
Posts: 7
Joined: Thu Aug 09, 2012 11:13 am

Re: My Rpi needs no power unit !

Sat Sep 01, 2012 3:42 pm

Thanks for the replies. The power unit that came with the hub is rated at 5.0 v at 2.5A. and can be used for charging up to 2 mobile phones at once but no tablets ! How much charging current do tablets take !

Should be plenty of current available for the Rpi , but I will stick to using my normal power supply rated at 1 Amp.

Must get into the habit of closing the pi down correctly. I always do with my PC.

itimpi
Posts: 1090
Joined: Sun Sep 25, 2011 11:44 am
Location: Potters Bar, United Kingdom
Contact: Website

Re: My Rpi needs no power unit !

Sat Sep 01, 2012 4:25 pm

I do not know about all tablets, but the iPad comes with a 2A charger.

rasbeer
Posts: 242
Joined: Wed Mar 07, 2012 8:35 am

Re: My Rpi needs no power unit !

Sat Sep 01, 2012 8:06 pm

I have an Android (Allwinner A10) tablet that came with a 1.5A charger.

Return to “General discussion”