Hello
I am building a custom pc in old oem computer case, so i have to use certain form factor power suply, and it can't be anything more standard than what i could find already. I need to rate if the power suply is up to the task for long term use.
atx standard specs say
Supply (V) Tolerance Range, min. to max. (V) Ripple, p. to p., max. (mV)
+5 ±5% (±0.25 V) +4.75 V to +5.25 50
−5 ±10% (±0.50 V) −4.50 V to −5.50 50
+12 ±5% (±0.60 V) +11.40 V to +12.60 120
−12 ±10% (±1.20 V) −10.80 V to −13.20 120
+3.3 ±5% (±0.165 V) +3.135 V to +3.465 50
+5 standby ±5% (±0.25 V) +4.75 V to +5.25 50
But i have no idea how to test it in real life.
for instance
My test computer 12V rail have idle voltage of 12,2V, but it sags under load (graphic card benchmark) down to 11,9-11,85V and sensor sweep on pc makes it looks like a very ugly graph, many dips and raises. This is the kind of load power suply will experience, and was measured from inside software on the pc itself, so it might not be very accurate. But i am still concerned that under bigger load it may even fall out of atx specs or die.
Power suply didn't get even a little bit warm under load mind you, and i was benchmarking it for over an hour. And 2 of oem special sauce wires were not even connected (i suspect they are for fan speed controll).
Test system i was using also might be at fault of wrong measurments, because it is an old computer that liked to kill power suplies in the past.
By the way the power suply in question is made by delta and it is 300w fujitsu branded part, I also have 250w model. I have no schematics or specyfication sheat other than the label on them.
Is there even a point hooking up a scope to my test system as it is and looking at the ripple and noise, or should i have linear load like some dumb 300w resistor or bulb? I mean cpu and graphic card are not really a good electronic load candidates, they are very spiky power consumers, very inconsistent. Then again if we consider fluctuations under load as ripple, it would be already out of atx specs by the factor of 2, still in range of min/max voltages though.
I don't really have a way to directly measure power draw on each line . I can measure power draw of entire system with a clamp meter, but the power draw on each dc line is different and spreaded, so even scoping cpu 12v socket or atx plug, or molex connector can bring in different data.
What do you think, how should i unpack this problem?