PSU as Bench power supply: problem

[fpal]

I want to test various computer parts with my ATX power supply.

I looked into operating a power supply outside the a computer. So at the 20 pin connector I connected pin 14 PS_ON# green wire to pin 15 gnd black wire.

When I power the supply and turn on the switch at the back, the power supply does operates (the power supply fan operates).

When I attach an old drive to the power supply it does not provide power.

When I attach a small fan the power supply operates.

It seems that any kind of substantial load stops the power supply. So I thought faulty supply. But, when I connect the power supply 20 pin connector to an old motherboard that has a CPU installed, the power supply works fine.

What's going on? How do I get the power supply to work outside the case?

[Gabriel Torres]

Hi

Your power supply is faulty OR your drives are burned, activating the PSU short-circuit protection. Before condemning the PSU I would test the drives on another PSU.

The procedure to make a PSU work outside the case is exactly this one you described, you are doing it correctly.

Cheers,
Gabriel.

[fpal]

Thanks Gabriel,

But there's something not quite right or that I don't understand.

I have an old motherboard with only a CPU+fan installed into which I connected my PSU. The PSU worked fine (when I momentarily shorted the ATX power switch pins on the board, the PSU turned on and I was able to turn it off by shorting the pins for over 4 seconds) plus the PSU was able to power my HDD (could hear it spinning).

Again, I don't understand why this same PSU doesn't work standalone. There must be something the motherboard is doing to make the PSU operate properly other than shorting the PS_ON# pin to ground.

Any comments, much appreciated.

[Gabriel Torres]

Hi,

I just remembered about something. Some power supplies need a minimum load to turn on (in fact all PSU's need this, but the majority have a resistor inside the PSU that acts like a phantom load to allow them to be turned on without any load). Maybe that is exactly what is happening. Try hooking a fan or any other stuff that will draw current at one of the PSU connectors to see how it goes.

Cheers,
Gabriel.

[fdsafdsa]

1. Provide a load:

• Usually a spare drive is enough.

2. On the 20 pin connector:

• Short pin 14 (should be green wire) to pin 15 (should be black wire next to green wire)

Here is a good link about the ATX supply, with connector pinout/illustrations, etc. Also has an explanation of why you need to short pin 14 to ground.
http://www.bluemax.net/techtips/ATXP...pplyWiring.htm

With a drive attached for a load, you should be able to use this as a general bench supply for almost any project, assuming you only need PC voltages (+/- 5, +/-12, etc.) and you don't excede the current rating for any supply voltage.