# OMAPS - One More ATX Power Supply conversion

## 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!

Updated the packaging a bit so it looks sexier and wife acceptance factor increases ... used a ready made unfinished wooden box from Michaels.
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weatherjack4 years ago
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!
4 years ago
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.
1 year ago
so when you have two plus's you subtract the smaller from the larger to get the volts? and if you have one plus and one minus, you add both together to get the voltage? what about two minus's like -12v and -5v? also, if i wanted say, 17v, i use one lead in the +5 and the other lead in the -12 jacks? does it matter what lead? red or black? what about if Im connecting them to something? would it matter what voltage went to neg and what went to pos? also, no ground in those scenarios?
abizar (author)  zacker1 year ago
Zacker, what are you trying to power? In general stuff like light bulbs, LEDs, etc. a ground is not required as long as the polarity of the device is respected. The + terminal of device needs to be connected to the more positive (or less negative) voltage. So, if I was using the -12V and the -5V terminals. I would attach the -5V to the positive terminal of the stuff I was powering and the -12V to the negative terminal. The device would think it is being powered by +7V! If I was using the +12V and +5V, then I would connect the +12V to the positive terminal (as it is more positive than +5V) and the +5V to the negative terminal. The device would still think it is being powered by +7V.
This will not work if the device really needs 0V (ground). For example, if it is connected to something else which is at 0V from another power supply. Hope this is not too confusing!
1 year ago
Its a little confusing, ill just have to read it a couple times to get it to sink in...lol thanks for explaining it.
I am looking for something to power an electrolysis tank for rust removal. I basically need like, 12V with about 2 Amps. A lot of people will try and go with as many Amps as possible but the more seasoned guys say 2Amps works well, it just takes a bit longer. I used me 12v car battery charger set to the 30 Amp "Quick" Charge setting but after 3 Hrs. it shut its self down. Most people leave these going for 8 hrs. or more depending on size of items being cleaned or amount of rust... in the three hrs. I ran mine on the 30 amp setting, its got almost all the rust off and old vise. So Im thinking if I can run this at 12v with anywhere in the 2 amps and above, it would be good. But then Im seeing all these PSU's being turned into bench power supply's and now, not only do I want to make this for the Rust Removal, but I may as well use it for a bench power supply too.. lol its just confusing, all these Volts and numbers and - / + and stuff... Like the pin outs on this PSU, some wires are +12v or +12VC DC or +12 VB DC or VA DC or worse, +12 VD DC / SE... lol
TM76774 years ago
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 (author)  TM76774 years ago
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.
4 years ago
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!