Computer Power Supply

[StLBeer]

Has anyone taken an old PC power supply and used it for powering other things?

I have an old microATX 145W power supply that I'd like to use it for powering small electronics projects. It's not that difficult is it?

[astx813]

Not difficult at all. For specifics on the voltages, Google ATX pinout. Or just look at the picture below. I can tell you that to turn it on, you need to short the PS_ON pin to ground. In plain English, that means take a paperclip and stick one end in the connector so it's touching the green wire. Stick the other end into any one of the black wires, or just touch it to the outer shell of the power supply. If the fan starts spinning, you're set. If not, either it's broken, you've tripped a breaker, you've electrocuted yourself, and/or your house is now burning down.

Honestly (and legally), do be careful. You can get an unpleasant surprise from these things. I recommend the first time you do the paperclip routine, you rig it with the power supply unplugged, then plug it in. That's just me. If there's no green wire (or more than one), it's not using the industry standard color codes. The pinout will be standard, so just refer to a diagram like this one. Good luck!

[StLBeer]

Thanks for the pin outs. This PS has the v1.0 20 connector plug. I found that out last night.

A little more research and I found a tutorial on this from Murray State IT department. In that document they short out the green PS_ON# to COM through a 10 Ohm, 10Watt wire wrapped resistor. This provides the load needed to initiate the PS start. PWR_OK is not used. The resister is pretty big so I wire tied it to the inside of the case where it is in the airstream of the fan. I did not use the +3.3VDC or the -12VDC, half of the COM, and about half of the +5VDC lines, so I chopped them short and insulated them to prevent a short, then stuffed them out of the way.

A SPST toggle switch was wired up then I put some binding posts on the top of the case, soldered the COM, +12VDC, and +5VDC connections to the binding posts.

viola! A power supply capable of max 5.5A at +12VDC and 66W, and 14A at +5VDC for 66W.

The only thing weird about this is I bought an illuminated switch. With the green PS_ON# wire connected to the positive side of the switch and a COM line connected to the negative side of the switch, it works just fine. If I then add a +12VDC to the accessory side to illuminate the switch, it does that, but then shuts down the power supply. Does anyone know why this would happen?

At any rate, this took just about 2 hours to put together after I got the parts from RadioShack. This is great for those small electrical projects where I need 5 or 12 volts DC and a cell phone wall wart won't cut it! Like building a pulse width modulator for an electric kettle.

Here's the post I found:
http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM#More_Current

[astx813]

Hmm, well, you've surpassed my experience at this point. I only learned the PWR_ON short to COM a few years ago so I could quickly test power supplies on the computers at work. I've never even bothered with the resistor, but I don't think I ever ran it my way for more than an hour or so.

Not sure why it would kick off the power supply when you connect the +12 to your switch. I'm assuming when it stops, the illumination goes out, too? Are you sure the power supply isn't defective? I did have power supplies that would work find when I shorted the power pin, but as soon as I connected anything that drew a load they'd cut off. I might try getting +12 from a different "rail," ie the yellow wire on one of the smaller 4-pin connectors.