Testing ATX power supplies

[mikey76]

Is it safe to test an ATX power supply that is NOT under load? Will the voltages measured at the plugs be meaningful if it is not under load. Will the switching regulators perform correctly with NO load?

TIA

mikey

 

[L3]

I don't think you can power up an ATX PS without a load, can you?
If you can, it's certainly safe, if you test safely.

 

[Mark R]

Some will power up with no load, although most will require a small load - however, the voltages will not be representative of voltages during normal running - one of my PSUs, when connected to an empty mobo (nothing else) only offers about 10.7 V on the 12 V line, once a decent load is put on the 5V line, then then 12V rises into the normal range.

Only the 3.3 and 5V lines are regulated on a typical ATX supply - the 12 V, -5 V and -12 V lines are generated by additional windings on the 5 V transformer - unless the 5V line is under adequate load, these supplies will be extremely weak.

 

[blahblah99]

Without any load, your 12V and 5V lines may be higher than what you may expect.. with a load on it, it will drop to around 12V and 5V. If a power supply is well designed, the output will be regulated those voltages up to the specified load.

 

[anxman69]

I might be misunderstanding this ... but if you mean, "Test an ATX Power Supply" as in, get it to turn on. You can just stick a wire between two of the joints to short it out and it will turn on. I forgot which but I believe it's the green wire near the clip and any of the black grounded wires.

I soldered a switch in to one of my power supplies to get it to turn on whenever I want which is also a good way to see if a power supply works.

cya l8r

 

[kluge]

To test if the power supply runs at all, I'd obviously first test it without load. If you want to see how it performs, test it under load. I hope that's what you meant.

 

[mikey76]

kluge....that is about what I meant. To give a little more detail, I was concerned that powering up with out load might cause the voltages to be exceptionally high, perhaps damaging filter caps.

Sounds like it is safe.

Thanks all


mikey

 

[Jerboy]

Originally posted by: mikey76
kluge....that is about what I meant. To give a little more detail, I was concerned that powering up with out load might cause the voltages to be exceptionally high, perhaps damaging filter caps.

Sounds like it is safe.

Thanks all


mikey

Without a few amps of load on 5V line, your PSU probably won't fire up properly. Get a 1ohm 30W resistor and use it as dummy load.

If you don't have 30W resistor, you can use a five to ten watt resistor in water with caution.

 

[Evadman]

Just pickup a PWS tester. Comes in handy. I got mine for $8 from Golbal computer supply in naperville ( tigerdirect )

It puts a 50 watt load on the 3.3 - 5v rails. Then it has points to test out all the voltages.