Andynerd
Posts: 3
Joined: Fri Jul 20, 2012 10:36 am

5v rail on computer psu for power

Mon Jul 23, 2012 4:50 am

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.

Wolfram23
Posts: 73
Joined: Thu Jul 19, 2012 6:50 pm

Re: 5v rail on computer psu for power

Mon Jul 23, 2012 5:16 am

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.

dukla2000
Posts: 190
Joined: Tue Jan 10, 2012 12:02 am
Location: Reading.UK.EU

Re: 5v rail on computer psu for power

Mon Jul 23, 2012 8:54 am

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.
Daily driver: Pi3B, 64GB Samsung Evo+ @100MHz, DVB-T, onboard WiFi for internet, BT/USB dongle for KB/mouse, 250GB HDD via USB for media, Raspbian Jessie Lite with Openbox desktop.
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AndrewS
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Re: 5v rail on computer psu for power

Tue Jul 24, 2012 11:11 am

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:

haitek
Posts: 23
Joined: Wed Mar 14, 2012 7:16 am

Re: 5v rail on computer psu for power

Wed Jul 25, 2012 1:21 am

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...

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