Repurposing old, large, desktop PSU

[Harry Bloomfield]

I have a desktop system, which I am scrapping, but wish to make use of the PSU. The PSU, has numerous cables coming out of it, and rated 750w. In the past, I've found that just adding a small amount of load, a resistor, got the PSU to run, but not this one. The difference being, that rather than the mains being switched on and off, this PC had a start/stop button, on it's front panel. How do I bypass this, or which colour wires should I be shorting, to get the PSU to fire up please?

 

[Jurassicspark]

Model number of the PSU?

You will see the large connector with 24 pins is the main power connector from the PSU to the motherboard. You're interested in the green wire, which is the PS_ON (power-on signal) wire.

Find the ground wire (black wire) there are several ground wires, so you should have no problem finding one.

Use a small piece of wire to short the green wire (PS_ON) to any of the black wires. This should trigger the PSU to turn on.

Once the PSU is on connect a load to prevent the PSU from shutting off after a short period due to no load.

If you can't find the green wire then if a schematic is available for your power supply you should be able to trace the PS_ON pin on the main IC. (I doubt you'll find a datasheet or a schematic diagram.

 

[RandomGrinch]

The pinouts are common for the 20 + 4 pin motherboard connector, or the 24 pin connector.
If you have a 20 + 4 pin connector, connect pins 14 and 15 together of the 20 pin section.
If it's a 24pin connector it would be pins 16 and 17.
However, as above, modern PSU's may need a decent load on them to continue to power on.

Some info here...

https://www.electronics-tutorials.ws/blog/convert-atx-psu-to-bench-supply.html

 

[Harry Bloomfield]

Some info here...
https://www.electronics-tutorials.ws/blog/convert-atx-psu-to-bench-supply.html

Got it, and it's working, without need for any load on it's 5v output, thanks....

Idea was/is - A power supply to replace the battery, plus charger, for the 8Kw diesel heater (CDH) I'm using to provide warmth in my garage, workshop area. The CDH, can over heat, damaging the PCB, if the 12v supply is suddenly lost, but the risk here of l, loosing mains is slight, and even reduced by the time the heater is in actual use, so I thought run it on a mains powered PSU. A surplus desktop PSU. It needs around 12amps, at 12v, during it's ignition startup phase, then that drops to around 2amps once running. Connected between one yellow, and black, it ran, but failed on too low a voltage, at the first try. I joined three yellows, three blacks, and that worked fine.

I installed it on my work bench, with an hot air duct pipe, all the way along the rear edge of the bench. I've drilled a series of 1" hole in the pipe, bending the hole in, so as to funnel hot air out all the way along it. It got far too hot, with the hot air just blowing out in one place.

Rather than run it on expensive diesel, I'm running it on kerosene, jet fuel, Jet A1 to be exact at 92p per litre, from a local aero club. It's running absolutely fine on that.

 

[Jurassicspark]

Just saying, if you want to play around and have a various range of voltage output you can adjust the voltage by altering the feedback circuitry.

That's what I have done to power up any device ranging from 12v to 30V. Comes in handy if you dont have a charger for something.

Note that the current output will decrease linearly by doing this.

 

[Harry Bloomfield]

Just saying, if you want to play around and have a various range of voltage output you can adjust the voltage by altering the feedback circuitry.

That's what I have done to power up any device ranging from 12v to 30V. Comes in handy if you dont have a charger for something.

Note that the current output will decrease linearly by doing this.

Yep, I've done that, with telecoms 50v 50amp SMPSU's, to tweak them down to 13.8v.