Here is a little mod so you can use your PSU without the motherboard. Useful for powering fans and other components you might normally power in a computer.

Material List:
[ ] Power Supply Unit
[ ] Fan or other computer component
[ ] 6 inch wire
[ ] Wire stripper/whatever you choose to use to strip the insulation

PSU


Fan


Wire


The first step is to plug in the fan to the PSU.


Next step is to jumper the 20/24 pin so that the PSU will run without the need for the motherboard.

You'll need to strip the wire so that there is about 1 inch of bare wire on both ends of the wire.

One end will be inserted into the pin #14 or usually the green wired plug.

The other end will be plugged into any of the black wired plugs, I chose the one next to the green one.


Finally, we can plug in the power cord.


Then flip on the power switch, if it has one, mine doesn't. And POWER!!

Very nice Prof!
This is a very handy mod,especially if you are running multiple fans and a pc fan controller.
As a footnote,I have found some old dell pc psu's use a grey wire instead of a green one,but it is still the same pinout.
And some psu's will require more current drain than a single fan, plug in an old hard drive to stop the psu from cutting out after 0.5 sec on certain psu's.

Cheers P

Thanks. I know plenty of people have old PSUs they are not using. Why not put them to use?

Nice pictures to go along with the instructions.

And just a reminder to anyone doing this, you put a switch in place of that wire to turn the power supply on and off. This way you don't have to use the power supply switch or unplug it all the time.
Just a simple switch will do the job so you can leave the psu plugged in all the time, and stash the psu inside the pj somewhere.

Yeah, for powering about two fans my PSU worked fine, but when I popped in a third fan, it went for 1/2 a second and cut off. The fix I used was to switch the voltage on the back (little red thingy that slides back and forth) from 115v to 230v, worked fine for me.

don't forget with a combination of different color wires will give you different voltages if needed. but check the amperage on end results, like a +12 and a -5 will give you 7v and +12 and +5 gives 17v and so on.

joe, if you join the lines you do not average the voltages - you short them out! What you want to do is connect something between +12V and +5V i.e. treat +5V as if it were the ground. That would give you 12-5V = 7V. connecting between +12V and -12V you would have 24V. (12 - (-12))V. Between +12 and -5 you get 17V, and so on.

Don't use those voltage combinations for high loads though - the PSU isn't prepared to sink current through the current sources. It might work, but don't use it for more than a fan or so. Use a variable voltage stabilizer like the LM317T (cheap) if you want to obtain other voltages. It should work better if you use the negative voltage sources, since those are obviously designed to sink current - i.e. using +xxV as positive and -yyV as negative to get (xx+yy)V is fine, but using +xxV as positive and +yyV as negative to get (xx-yy)V is not too great for the PSU - use it only for light loads.

Also, I've seen many PSUs that do not turn on unless they have a minimum load on (some of) the output lines. Usually connecting a hard drive to the PSU does the trick to test it. Try adding appropriate light bulbs (not LEDs, those are a minimal load) to the different voltage lines if that happens. High power resistors would also work - but make sure the value is appropriate for the curernt you want (or your PSU needs) to sink. Ohm's law is useful here - to sink I amps, at V volts, you need R ohms according to: R=V/I. To figure out how many watts power is that, multiply amps times volts.

very nice, definitely useful.

Found a diagram for a typical 20 pin ATX powersupply:



Just thought i'd post it.

Awesome find! That has to be the most concise pin-out maps for a ATX power supply ive seen! Great find!

I'm a little lazy so I bought this contraption:


You just plug it to the end of your PSU main cable. They also make one for modular PSU, which has the opposite gender plugs. They're available for both 20 and 24 pins.

If anyone wants a link to that, it's right here. And for those who feel weird playing with
wires, click here.

And yes, I realize it's a DIY site. Some people feel uncomfortable messing with
wires tho...

Does anybody know if it would be possible to power a portable DVD player with an old computer PSU? I bought one on ebay to harvest the screen, but it came without power. The player requires 12v, 3a.

Provided the power supply can pump out 3A - sure. I have an old DVD player that broke. Tore it open and found the power supply was bad. I had an old one sitting around so I just circumvented the internal power supply and now I have an ugly DVD player with a scruffy old power supply sitting on it. It works though.

Usually you can find adapters around the house that go to .5 amps pretty commonly for phone chargers. On a 12V rail, a power supply usually puts out more than 12 amps, and thats on older models as well. Obviously you have those 4 pin connectors as well, but I'm unsure as to how much they provide or if it is all included in that 12 amp estimate. It would be relatively easy to output 12V through the 4 pin connector, you just need to make sure that it outputs those 3 amps you need. Its also DC so make sure that is what your DVD player asks for. I think the PSU will output what ever requires the amps to where ever they are needed, but that is a guess. And don't take anything I say like gospel because I have learned my electronic stuff all from experimentation and some of the things I use to fill in gaps of areas I don't know. Their are much more knowledgeable people here that deal with electronics that would be better suited to answer your question.

I did this same thing only with a computer so that I can use two psu at the same time. Just that one of the psu's is only for my video card. 9800 runing bf2 for 2 years now. Needed to do this because psu wasn't giving enof power.

Thanks for the tip. i will have to look into this some more.

So if I wanted to say power a few fans and an LCD (7"), would a computer power supply be feasable? What wattage would I be looking for? The instructions say it takes 12v, and about 9 watts. what about amps? It says nothing about it. Of course I should probably wait to actually take delivery of the monitor. Might be stamped on the side.

So what would happen if you had a ATX power supply. Cliped the green and black wire and connected them together. And put it inside a computer and put power to it. Would it run the computer soon as you plug power to the PSU?.

I have been rebuilding this computer in a CNC saw grinder. The motherboard went bad and they wanted 2000 for a new Mobo. So I just gutted everthing and put a shuttle PC in its place. It works like a charm. Except turning it on and off. The shuttle pc is inside the cabinet and you cant get to the on off button. So would clipping the green and black wire make it turn on soon as i fire up the machine?

Also the LCD panel I put into this machine runs off 12v. It used to have a old CRT that ran off 220v but it got burned so bad after years of use you can always see 2 screens at once. Is it possable to run the LCD off one of the 12v leads on the PSU? So I do not need to run anything special and it turns on and off with the computer.

Thanks Smackre,

You probably figured this out by now, but it would be a lot easier if you just extended the power switch for the cpu than to mess with the power supply.

Just as an aside, (If you're not using a spare ATX PSU that happens to be lying around) you can still buy AT PSU's at Newegg for under $20. AT PSU's come with a built-in power switch, for those of you who don't like monkeying with wiring. Problem is, you won't be able to use them on any modern motherboards and they seem to max out around 300w.

Personally, I'd deal with ATX because of the higher wattage and flexibility, but there's another option.