![]() ![]() There should be no danger in turning on an ATX power supply at zero load. That being said, the outputs may be out of regulation, hunting (overshooting and undershooting their setpoints), or absent. None of these things are 'dangerous' per the definitions of safety used by regulatory agencies like UL. What this means is unless you apply some load, you won't be able to determine anything useful by probing it while disconnected from the PC. How much 'some load' is will likely vary from model to model, but if you don't want to shell out for a full-blown PSU tester as Kruug suggested, try loading each rail with power resistors to 10% of its label-rated maximum, then test with your multimeter. If the behaviour is still bad, you may indeed have a defective power supply. Switch mode power supplies (typical PC PSU) will blow up with no load. The fan counts as a load. Take out the fan and watch the voltage go up until it smokes. I know, I fix the things and have blown up many with no load. Switch mode means it takes the AC in, converts it to DC, then switches it to high voltage, high frequency, then steps it back down again, then converts back to DC. This is far more efficient as transformers don't perform as well at lower frequencies and lower voltages. It's not like mains power or a battery which can sit around doing nothing. I would say from experience that one in four can be blown up in this way, most likely not much to do with cheapness or quality of design as just about every PSU brand (nearly every brand is different) has a different circuit for it, and even the same brands scarcely keep the same circuit for long as they always source the cheapest components available at the time. The underlying technology has hardly changed since the the days of XT computers, nothing really 'modern' about it. You won't find any more modern fancy components in newer PSU's. To turn on an ATX power supply that isn't connected to a motherboard use a wire or paper clip to short the green wire (PS_ON) to any one of the black wires (COM. I would like to use a power supply to run a few pc components for purposes other than typical computer usage. That is, I would like to use it without the go-between of a motherboard, and just plug my things directly into the power supply, so that I might run small fart fans and such 24 hours a day. How do I activate the power supply without the remote function of the pc case power button to turn it on? Could I just hotwire it in some simple way, so that it will be fitting of the humble country folk that I am? Wrote: > I would like to use a power supply to run a few pc components for > purposes other than typical computer usage. > That is, I would like to use it without the go-between of a > motherboard, and just plug my things directly into the power supply, so > that I might run small fart fans and such 24 hours a day. > How do I activate the power supply without the remote function of the > pc case power button to turn it on? > Could I just hotwire it in some simple way, so that it will be fitting > of the humble country folk that I am? > You connect PS_ON# to an adjacent COM (a.k.a GND) pin. Those pins are on the main power connector. It helps to have some minimum load on the power supply, and a very few power supply labels tell you what that minimum load is. A supply should regulate properly with a minimum load on it, staying withing the stated output when loaded. These pictures are looking into the end of the PSU cable. PS_ON is the one you want. The first picture is for a 20 pin connector, and the second is for a 24 pin connector. ![]()
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