I'm constructing a custom(cheap) power supply, with digital current meters and such. I'm using 2 ATX power supplies to build it. I'm using 1 for the standard -12, -5, +3.3, +5, +12 outputs. I've modded the other to output ~0 - ~24V(off of the 12V line). I've tested both of them separately, and they work great.
My concern is if I have 2 separate GNDs. If I change the voltage on the one power supply, would it affect the other power supply?
I had the 1 atx power supply stay to same because it is easy to use the standard ATX powers supplied.
I wanted something that I could change as well. So I did a little research on the circuit inside the ATX power supply. There is a voltage divider that controls the output voltage on the power supply. It is on pin 1 of the TL494 chip (guessing on actual chip). You also have to change the Over voltage protection on (I think) pin 4. I placed a small circuit turn pot on the Pin 1 with a resistor. I tested it, and I was able to get 0 - 24V on the 12V line. I estimate that I would be able to get 5amps out of this variable control.
I also added some Amp meters and 1 voltage meter. Here is an image my ideal design.