The PSU has 2 12V rails listed in its specs on the side, however both show continuity between them when I tested it with my multimeter. I then tested continuity between the positive from the fan and 12V1 and it also showed continuity. The fan is rated at 0.7A. This is a higher load than the 22 Ohm 10W resistor I was originally going to use (0.55A). Should this provide enough of a load? Would it be necessary to put a load on one rail or the other if they are both connected internally anyway?
When I started it up with no other load connected, the grey wire came to +5V which I believe means power is OK. Is this a good sign that it likely doesn't need an extra load?
Finally, should I also put a dummy load on the +5V rail?
Extra Info:
I was able to dig up these specs, although they aren't from the manufacturer so it's hard to tell how accurate they are. They do suggest that extra load might be required though.
Min Load:
- +3.3 – 0.3 A
- +5V – 0.5 A
- +12V1 – 1A
- +12V2 – 1A
Although given that both 12V rails seem to be connected I'm not sure if that means 1A each or just 1A for both.
Best Answer
The problem is that most of the output voltages are generated directly from different windings of the same transformer, so it is not possible to regulate them independently.
If you only load the +12V output the controller will increase power to the transformer to compensate for voltage drop in the rectifiers etc., but this causes voltage on the other unloaded outputs to increase. If the +5V output exceeds its maximum permitted voltage the crowbar will trip and shut the PSU down.
Loading the +12V output down more will only make it worse. To prevent the +5V output from rising too high you need to draw a reasonable amount of current from it, typically 2-3A.