Converting an ATX power supply into a bench power supply

So I’ve needed a good bench power supply in order to have something I can quickly hook up to the circuits I’ve been planning on (and started!) building.

It turned out that I had a 230W old ATX PSU lying around, so I converted that. There are already basic instructions for this on the net, so I’ll just detail the, fairly minor, differences in my situation. No photos because I don’t have a camera.

The one major difference I had was that the wire colours differed on mine. After giving up looking for them on the PCB, I found a page that gives the pinout for the PSU connection to the motherboard, and used that to work it out from the plug I’d chopped off. Of course, that was still the hard way. After doing all that I found the colours were actually written on top of the supply, with the corresponding voltage and amperage rating.

The other major difference was that my PSU doesn’t seem to need a load on it all the time, so a high-wattage resistor is unnecessary.

So now I have a very handy PSU sitting on my work desk, allowing banana plug connections to +12, +5, +3.3 and GND. Due to a miscalculation about the amount of sticking-out on the inside of the socket, I can’t put the -5 or -12V lines on without doing something about the fan.

One thing to be aware of, my PSU appears to be quite underpowered when it comes to the voltage (not just the crappy wattage). The voltages seem to be about 30% down on what they should be. The 12V actually produces more like 9V, and the 5V closer to 4V. Given these PSUs aren’t supposed to be too consistent anyway, you should be running them through a voltage regulator, say bringing a 12V input down to 5V or so to drive the circuit, that will give plenty of extra to play with.

(PS: fr1st ps0t!)

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