how can I test the voltage of my PSU?

[mule43]

To the best of my feebleminded recollection it mostly has to do with the fact that PSUs are designed to be run under a load and if not run that way they will overheat and burnout. As well, even to do a short test, a load is required to give accurate results.

I use this simple 25 watt generator by Antec:

Switching power supplies, which is what is used in computers, need to have a load for them to start regulating. The size of the load will depend on the supply. If you look at power supply ratings you will often see a minimum current rating listed. THis minimum value is what is need for the supply to start regulating. For supplies that do not have a minimum rating they usually have a small load resistor built into the circuit so there is always a load on the rail.

I could see where a switcher without a load could potentially burn up but that will depend on the actual design of the supply.

[mule43]

Anybody tried this with a multimeter and a rheostat before? It would proabably work if you had a University lab to work in.

Yeah we have tested supplies this way. One problem with a rheostat is that for any kind of big load you need one BFR. For example lets say you want to test your 5 volts at 15 amps you would need a load resistor of .33333 ohms (V/I where V is volts DC and I is current in amps). Now we also need to know what power the resistor needs to dissipate whic is figured with Power = V * I which gives us 75 watts. That is a fairly large resistor or rheostat and it will get hot.

The best load I have found was when we needed to test supplies that would put out 100-200 amps at 5-20 volts or so. What we did was take about 100' or so of 16 gauge wire and use it as the load, worked pretty well