Stepper- Motor test, fehlerhaft

Quote
Triffid_Hunter
Basically, a computer power supply provides a regulated 5v, and all the other rails are unregulated but closely linked to the 5v due to winding ratios in the transformer. Because of this, if you draw many amps from 12v (or any other rail) but leave 5v unloaded, you will get unacceptable voltage drop. However, if you load the 5v, the other rails remain far more stable.

It's exactly the same principle as attaching a high power light or heater to a generator so it doesn't choke when the fridge or other inductive load kicks in.

As far as I know, the 3.3v rail undergoes secondary regulation and is sourced from 5v or 12v so it's basically out of this part of the equation.

Quote
nophead
Most PC PSUs do not work properly unless they have some load on the 5V and possibly the 3.3V rail. It is because the rails are not individually regulated. If you only load the 12V rail and leave the 5V rail unloaded it has to throttle back to prevent the 5V rail being over voltage. That leaves the 12V rail under voltage, typically about 10V.

I haven't seen one shutdown but it is conceivable that it may. If you follow the RepRap instructions they recommend adding a dummy load resistor to the 5V rail.