Page 1 of 1

5v rail on computer psu for power

Posted: Mon Jul 23, 2012 4:50 am
by Andynerd
I have an old external CD drive I gutted and it had a single wall to molex converter. I was wondering if the RPi could run off of it. I'm just worried the +5v noise might damage it.

Re: 5v rail on computer psu for power

Posted: Mon Jul 23, 2012 5:16 am
by Wolfram23
If it's a terrible PSU, then maybe don't do it, but it should be ok. Many people power their RPi off a PC's regular USB connections. I guess it depends how you hook it up.

Re: 5v rail on computer psu for power

Posted: Mon Jul 23, 2012 8:54 am
by dukla2000
Andynerd wrote:... it had a single wall to molex converter. ...
It is not clear to me quite where the molex is getting +5V from - the wall or a PC? But overall it doesn't matter where the Pi gets its +5V from as long as it is clean and sufficient.
I am not that keen on powering a Pi from a PC USB port (but obviously can and has been done) - my Pi takes a feed direct from my desktop +5V rail as per your thread title onto the GPIO pins. To some extent I guess it depends if you know what you are looking at when your PC cover is off.

Re: 5v rail on computer psu for power

Posted: Tue Jul 24, 2012 11:11 am
by AndrewS
dukla2000 wrote:I am not that keen on powering a Pi from a PC USB port (but obviously can and has been done)
According to the specs, a regular PC USB port should only be able to supply 500mA, whereas the RPi needs 700mA. So in theory it shouldn't work.
But of course we all know that specs are flexible / not always followed correctly ;) So it might work, but it's not guaranteed to work. It's something I've not tried myself though.

EDIT: Strictly speaking, a PC USB port should only supply 100mA to a 'passive device' such as the RPi. Devices with an active USB data connection can then negotiate up to a maximum of 500mA :geek:

Re: 5v rail on computer psu for power

Posted: Wed Jul 25, 2012 1:21 am
by haitek
I'm running mine from the USB port on my PC, works well. I have compared it with a wall wart 1A phone charger with no difference in performance...