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How to power up ATX PSU without MB

Last response: in Components
March 21, 2006 10:27:00 AM

I have an extra PSU lying around that I wish to utilize. Is there anyway to power it up without connecting it to a motherboard?

Thanks in advance.

More about : power atx psu

March 21, 2006 10:42:18 AM

hold the 20-pin cord to your tongue and it should fire right up!
March 21, 2006 10:46:44 AM

you have to put a toggle switch on the power-on leads on the atx header, and maybe put a dummy load on the +5v.

see here for the atx pinouts and here for a dummy load example.

Usually 1/2 A is good for the dummy load, so 10 ohms should do it (5 ohms for a 1A if yours is stubborn)
Related resources
a c 158 ) Power supply
March 21, 2006 10:55:07 AM

That's just GREAT advice... :roll:

Chokfullonutz: The PSU receives a signal from the mobo to turn on, but there is a way to bypass that signal requirement. What do you want to do with the PSU?
March 21, 2006 11:27:39 AM

@ merlin

Don't know, sounds dangerous. Post some pics of yourself after powering up with your tongue and I’ll consider trying it myself. :p 
March 21, 2006 11:30:00 AM

Thanks that helps a lot. I bookmarked the link that you provided :)  .
March 21, 2006 11:35:17 AM

Since my main PSU is 350W and I have a spare 300W lying around I was thinking of powering the case fans and maybe HDDs(2) and optical drives (also 2) off the spare.

Main reason for trying this is my GF4200 is getting old and most new cards require a small nuclear reactor to power them :) 
I don’t want to spend extra $$$ for a new PSU. Use the main PSU just to power the MB and video Card.
a c 158 ) Power supply
March 21, 2006 11:43:34 AM

List your specs...i'd be willing to bet that either this Fortron 400W or this Fortron 450W would be enough to power your rig. $40-$50 is a great deal to get a relieble, quiet PSU and avoid having a monstrous looking case setup.
March 21, 2006 12:20:51 PM


Intel P4 (northwood) 1.8@2.6 Ghz
MB: Abit BD7II Raid
Ram: 2x512MB PC333 (2,2,5,2)
Video: GF4200 64MB (soon to be replaced)
HDD: IBM 120+80
Other PCI stuff: sound blaster live, Firewire adapter, TV tuner, Winmodem
3 Case fans

It’s a wonder that my 350 Manages all of this.

Anyway I’m making a custom case (more of a hobby than anything else and not related to the PSU issue) therefore space is not a problem. Those PSUs might not be available here (St. Petersburg Russia) while there are good PSU’s available for 60-70$ (400-500w range) I really don’t want to spend money on that since I already have an extra PSU.

Got a 250W AT PSU too but cannot figure what to do with that. Any ideas?
March 21, 2006 12:34:25 PM

I just straightened a paperclip and stuck one end in the green wire hole and the other end into any of the black wire holes.
March 21, 2006 12:43:39 PM

having an external spare psu is good for testing fans, opening drives with cd's still inside etc.
March 21, 2006 1:35:48 PM


Simple but effective :D 

I think I'll use a switch or relay as suggested in the link that dolittle provided as I don't need the second PSU running 24/7 and don't want to open the case to switch it off.
March 21, 2006 1:36:43 PM

Any other ideas or mods ?? I am sure there is something I can do with my 250W AT.
a c 158 ) Power supply
March 21, 2006 1:39:57 PM

DD: I never said that having a spare PSU was a bad thing. The point that I was trying to make is that having a single internal PSU for daily operation makes for cleaner looking, neat setup.

Chok: Nice OC :wink: - is it running that constantly? Your PC is yours to setup however you want. My recommendation is to get a good, inexpensive PSU to run your rig on a daily basis. A good 350W should be sufficient to run your rig, if you would feel more comfortable with more power, then either of the PSUs I linked would be good options for your PC.
March 21, 2006 1:50:46 PM

Expanding on DiscoDuck's mention, I have an AT power supply as benchtop tester similiar to this, is handy if you are into electronics.
March 21, 2006 7:15:24 PM

Yup stable as a hmmmmmmmmmmm....................... (what is really stable???)
It actually does even more 2.7+ but I prefer 100% stability. Gotta love them ABIT mobos. (From my BP6 days I have been an ABIT only type of guy)

My PSU (350w) handles everything as it is now with no problems whatso ever. What I am worried about is the new video card that I am gonna buy. Anyway 2 PSUs is not an extra cost to me as I already have them and admit it, you cannot beat the cool factor of having 2 PSUs :D 
March 21, 2006 7:18:38 PM


wow man that's just neat!!!!! I am into electronics (not hardcore just small projects repairs etc). This will be my next project after I finally finish(maybe hopefully :(  ) finish my new case. I might not really need something like that too often but the task itself would be a nice reward. Should be easier with my AT PSU too. :D 
a c 158 ) Power supply
March 22, 2006 12:01:36 PM

Two PSUs does have a certain :cool: factor. If you do it, then just make sure that you secure the PSU properly - would suck to have it fall and damage something. Out of curiosity I would still try it with the 350W PSU and then so some stress testing....
March 22, 2006 12:08:07 PM

At one time i was using my bench testing psu to power a really great set of 2.1 powered speakers for a pc, lost the power brick during a move. It provided ample 12v power to the speakers with the appropriate adapter connected to a molex connector. just had to turn it on manually with a switch under the desk to power up the speakers.
March 22, 2006 12:19:01 PM

Me bad. Should have mentioned that I am planning to get a new setup later this year so anyway I’ll have to buy a new PSU. At least this way I will just need a quality PSU in the 400-500W range and the old 300W PSU instead of having to buy a 3 MW psu or nuclear reactor (Anybody know if N. Korea is still selling? :twisted: ) to power it.

Won’t have to worry about the second PSU falling as it is going to be at the bottom of the case.
March 22, 2006 2:49:01 PM

@DD - yea I feel your pain, I have made several AT bench PS and end up giving them away. I just spoke to a coworker yesterday and he needs one to power a dlink that needs 5v@2A, so there goes my current one (and my last spare AT power supply!)

I am thinking, I have a 20 to 24 pin ATX adaptor I am not using so I was going to fabricate it into a breadboard w/ the switch and banana plugs so I can plug into any ATX PS since there is no shortage of crappy units and what else do you do with the cheap PS that comes w/ the case?

But after some thought maybe I should splurge and get a 24 -> 20 pin ATX adaptor and use the 24 pin plug, so I can wire it for dual-rail so I will not have to upgrade when I get my dual-core breadboard :lol: 
March 6, 2011 8:57:32 PM

Cinder said:
I just straightened a paperclip and stuck one end in the green wire hole and the other end into any of the black wire holes.

Yep, that's all it takes to turn on an ATX PSU. Pin 16 (the green pin) is pulled up to 5V DC by the PSU, and must be 'pulled down' to turn on the PSU. A good SPST momentary switch between pin 16 and either 17, 18 or 19 (the black pins) will do the trick nicely.

FYI...if you compare the price between a 30-amp 12v DC Power Supply, and a 400-Watt ATX PSU, you will see that vendors overcharge by about $60 for the commercial power supplies! I've used an ATX PSU before (via homemade hobby case) to power 12V CB's, car stereos, etc. Just grab a yellow and a black wire and you have 12V car power...for about $25...(free, if its an old PSU!)

There's TONS of usage for an old 400+ Watt PSU!!!