Resolved Another power supply question

I used to know the answer to this one but since I've had my handy Power Supply tester I've never needed to try it.
My question is in two parts:
a) Which pins should be shorted on a 20xpin ATX power supply to make it run? Online info says pins 14 and 15 (I guess that's 14 plus any ground?), but they're not working for me. Whereas it runs with my 20xpin-7xLED tester connected.
b) Is there any downside to leaving a power supply running for a few days with these shorted pins?

I ask because I've had a weird issue with an intermittently squealing AGP GFX card, so to test a theory, I've got the computer running with a separate power supply driving the card, while the main ps drives everything else. It works fine, so long as my tester is bridging the 20x pin plug, but I'd like to free the tester for other use.

BTW, as far as the card-squeal issue goes, it seems that the extra power may have done the trick, as it's been running squeal-free for 36 hrs. So maybe my 400W main power supply might be a little under-equipped to run this GeForce 7800GS, though its specs aren't all that demanding.

 

I would think from your own explanation that the 400W PSU may not be sufficient for your PC demands. Can you get a larger output PSU to try? Neil.

 

I shouldn't have mentioned the GFX card issue; it's obviously diverted attention from my main question about which pins to short on the power supply. No worries, I've sussed it myself, it's the green wire that should be grounded, ie pin 16.

Yes, retiredlearner, the 400w power supply is a bit light.

 

Understand there are not industry standards for color coding the wires so green on this PSU may be orange on another. This is not really a good way to fire up a PSU because it does not place any load on the supply, and that can often lead to voltages being unstable, and out of tolerance.

The "minimum" requirement for that card (assuming it's the 256Mb version) is 350W (with a single card), but of more importance is the current on the +12 rail, and we don't know that. If your 400W is from a major maker, it should be fine, but if generic, I would consider a new supply under normal circumstance. But considering you are able to resolve your problem by splitting the load with two supplies, I would get a new supply anyway.

 

Thanks Bill. So if the wire color can vary, is the pin assignment and\or label always the same? Like, this one I'm shorting is pin16 and it's labeled "Power on ".

Regarding the temporary PSU being 'balanced', it is feeding the GFX card, of course (which is 256MB). If I were to keep this arrangement, how would it be if I powered some of my two optical and two IDE drives from the second supply?

The main PSU is an Acbel; I don't know how good a brand it is, but it's one of the more expensive units from my supplier, and it's very quiet. Prior to this second-hand GeForce 7800 GS I was running a GeForce 6800, which never caused any squeaks.

You say the power requirement for the 7800 is 250W. I did a small amount of research before I installed it and couldn't find any hard and fast figures for that particular card, just ball-park estimates for generic equipment. But if it definitely chews up that sort of wattage it obviously needs a much stronger single PSU.

 

Yes. The pins are the same, as defined in the ATX Form Factor Standard. That's what allows consumers to buy any ATX power supply and connect it to any ATX motherboard and install them in any ATX case.

The biggest problem with using two supplies is to make sure they are connected to a common ground. This can be done by making sure they are connected to the same power source, or by running a ground wire between them.

I said 350W.

 

350W, so you did. No wonder it was squealing Probably asphyxia setting in.

Re the joint grounding, that's not happening right now. The rig is still working but perhaps I should look at that. Whats the best way to common-ground the two PSs?

 

Plug them into the same source (wall outlet, power strip, or best yet, UPS).