ATX Power Supply for RPi


11 posts
by qwertymodo » Fri Jan 25, 2013 6:43 pm
Is it possible to use the 5V rail from a typical PC ATX power supply to power the RPi? Are there any concerns I should take into consideration if I want to power it this way?
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by Mobius » Fri Jan 25, 2013 7:33 pm
I suppose that the biggest concern is making sure that you wire the connector to the Pi properly. You might want to put a voltmeter on the ATX power to see what the no-load voltage is. If it's a switching supply then it should be pretty close to 5 volts even unloaded. If it's over 5.5 volts I would hesitate to hook it up even though I think the polyfuse is rated up to 6 volts and there is a 5 volt zener diode that is supposed to clip the input.
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by YoungInSurrey » Fri Jan 25, 2013 7:40 pm
I've bought the following to use on a couple of old ATX power supplies. It comes with a big resistor too.
The main issue is that the breakout board is as big as the Pi and the ATX power unit is huge too.
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by YoungInSurrey » Fri Jan 25, 2013 7:41 pm
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by qwertymodo » Fri Jan 25, 2013 7:42 pm
I would think that a PC power supply would be pretty consistent with its voltage levels... according to the specs on the product page, the PSU I have can source 5V@12A, so at least power consumption isn't going to be an issue :roll: If nothing else, I'm already going to be constructing a simple PCB for power connections, GPIO breakout, and GPIO level shifting, so if I have to use the 12V rail instead and throw in a 7805, so be it.
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by Arjan » Fri Jan 25, 2013 8:02 pm
Hi,
Most likely you will need a dummy load. I've used the following article http://gathering.tweakers.net/forum/list_messages/885613. It is in Dutch, but Google translate would help you.
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by rpdom » Fri Jan 25, 2013 9:34 pm
I have used the 5VSB (Standby) wire from an AX power supply to run my Pi with no problems. The voltage was pretty stable and well within the tolerance of the Pi. No dummy load was required on any of the other lines, as only a small part of the PSU was active.
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by techpaul » Fri Jan 25, 2013 9:37 pm
Consider look at this spec for ATX power supplies on this page

Basically you could power a Pi using the 5V Stanby rail (5VSB) as this must be able to supply 5V 1A with max of 2A (short peak of 2.5A) THIS IS WITH THE PSU IN STANDBY MODE.

However to turn main rails on you need to work with PS_ON# (Low active pull-up and driven from 5VSB) to turn PSU on and PWR_OK to monitor power is up then you need dummy loads to draw

12V at least 1A (12W)
5V at least 0.5A (2.5W)
3V3 at least 0.5A (1W65)

So you need a total heater of 15.15W to run the Power Supply, this is minimum current so the control circuits can work and minimum efficiency of power supply
Just another techie on the net - For GPIO boards see http:///www.facebook.com/pcservicesreading
or http://www.pcserviceselectronics.co.uk/pi/
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by qwertymodo » Fri Jan 25, 2013 10:36 pm
Hmm, ok. I'll have to look into it some more. I definitely need the live rails, because I will be needing the 12V rail as well, since I need a 9V source for a piezo contact mic preamp (12V rail -> 7809). I'll definitely use that breakout board as a reference, but I'm already building a board, so I may as well just put it all on my own board. The PTC resettable fuse is a good idea, but the DP breakout doesn't seem to need a load, so I may take my chances with just the fuse. I will be driving other things with the power supply, so it's not going to be JUST the Pi.
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by Mobius » Fri Jan 25, 2013 10:48 pm
Why not just find a 12 volt wall plug that sources a couple of amps and use regulators for 9 and 5 volts? Much more compact than an ATX supply and no need for "dummy loads". Not sure about where you are, but around here just about every thrift store has a big bin of orphan wall plugs of different voltages - usually for $1 US each.
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by qwertymodo » Sat Jan 26, 2013 2:08 am
I'm building a project inside of a rack mount server chassis, which already has the ATX power supply. For this project, the ATX PSU is definitely the best option.
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