Converting a computer ATX power supply to a really useful lab power supply

Step 7 Testing the power supply

24) Plug the power cord into the back and into an AC socket.
25) Flip the main switch on the PSU (on the back). The fan will come on.
26) Check to see if the LED light comes on. If it has not, then power up by flipping the switch you placed on the front.
27) Plug in a 12V bulb into the different sockets to see if the PSU works, also check with a digital voltmeter. It should look good and work like a charm!

Comments

[TroyMacDonald]

So I've wired up everything exactly as this and other posts said, but I'm not getting any voltage out of my terminals and while the Standby LED comes on, the Power On LED never does. Using my multimeter across the additional Power toggle switch, I get just over 5VDC in the ON position but thats it. The fan comes on briefly - about 1 sec - then turns off. Any suggestions on what to check?

[abizar]

Many of these powersupplies will atomatically shut down if there is no load or zero current draw. Try it again with a 12 or 24 volt bulb across the 5 v terminals. If this does not work then you have a short across the output, I would re-check the wiring make sure that the black wires have not been connected directly to any of the other outputs. The power supply will shut down in case of a short, remove the short and it should work again.

[TroyMacDonald]

You were right about the short circuit thing going on, but it wasn't really modified wiring, it was the all the extra wires I clipped down....when I put the lid back on they apparently were shorting to the housing. A little electrical tape on the inside of the metal housing fixed it up and the thing works like a charm!

[weatherjack]

I have been thinking about building one of these. I am an amateur electronic hobbiest. I still cannot figure out he +/- o equal certain voltages eg. +5v and -12v makes 17v, guess I am thinking +5-12=7? Anyone can shine some light? I feel pretty silly for asking but.. Knowledge is King!

[Synck]

Voltage is the electric potential difference between two points. So if you have the points +5v and +12v the potential difference between them is 12-5=7v. If you have the points +5v and -12v the potential difference is 5-(-12)=5+12=17v.