Getting an ATX power supply to run outside a PC

Hey everyone,

So I recently bought an old ATX power supply off a friend of mine, and it took me hours to get it running, so I thought I’d do a quick post to help you guys do it in future.

So first thing everyone will tell you is to ground the green wire to turn it on! And this is true, the green wire (or the DC_ON wire) is your main switch for the power supply. And when you ground it, this should turn the power supply on, but only after you do a load of other stuff!

Some power supply’s (like the Dell n220p-00 I have) have smaller thinner wires of the same colour as most of the positive outputs and ground. So you will have one for 5V, one for 12V, one for 3.3V and one for Gnd most likely. These are sense wires and they must be connected to the same rail as they are coloured with (red for 5V, yellow for 12V, orange for 3.3V, and black for Gnd), they sense the rail constantly to check for shorts on that rail or if the rail is somehow broken. This is a great advantage when you have it running, but if you don’t know about it then it is a pain to get running. The solution is to take each of these thin wires and solder it to an output wire of the same colour. Then ground the green wire and it should now turn on!

Some power supplies have multiple ground sense wires and some also have the sense wires the same thickness as the normal outputs, so if all yours are the same and it doesn’t work automatically, check where the wires go on the PCB. If it is an odd one out, it’s probably a sense wire.

Also some require a constant load on the 5V line! For this I used a 100R Power resistor (10W) between 5V and Gnd!

Be really careful when taking these things apart! Honest, even when they’re unplugged you should let them sit for 2 days or so before messing with them. I made the mistake of assuming that because it was unplugged it was safe, boom, I shorted a capacitor and was across the room. Not fun.

Take care guys!

Tom Cousins