ATX PC Power Supply to Electronics Variable Supply

I was in need of a 5v power supply for my microcontroller circuits as the supply I have was not working with them for some reason and I was not happy keep using batteries. There are many write-ups online so if your interested, do a google and don`t trust this. This is just a log of what I am doing and have done so far. This is a work in progress although I do now have it working as a +5v, -5v, +12v, -12v supply. I hope to include a 3.3v supply and also a variable pot to have a true range of supplies.

This is the inside of the PSU and looking at other examples, mine seems jam packed with components. It made it hard to decide where to mount my switch and sockets. Not ideal but it is going to have to be on the side of the unit but I prefered this to other examples where people had been in similar situations and taken the plugs to an additional piece of angle iron bolted to the top of the supply. At least this it will all be contained.

The main jist, is that when you take a few hours ::) to untangle the mass of wires, there is:

red: +5v
white: -5v
yellow +12v
blue: -12v
black: gnd
gray: DC-OK (power on)
green: PS-on (turn-DC on)
Purple – VSB+5v (standby)

Here is the 10w, 10ohm resistor connected across the 5v supply to ensure there is always a load so the supply does not shut down with nothing connected.

And once I`d added a few posts to the case along with the Power On LED:

And here it is providing a voltage as close as dandy to 5v:

Still quite a bit to do but that is where I left it this evening. Clearly the top is not down fully but I want to finish it before I start to use it. I need to differentiate between the various voltages, also I am ultimately going to have +12, -12, +5, -5, +3.3 volts, and also ground. That totals 6 binding posts but I think because of the large current this can provide, I guess you could run multiple sources therefore is it worth having a couple of grounds?

Then I need to think about this variable voltage pot. Again lots of stuff on the net regarding that but it would then make it very useful! Once finished it should give me direct: 24v (+12, -12), 17v (+5, -12), 12v (+12, 0), 10v (+5, -5), 7v (+12, +5), 5v (+5, 0) and then fully variable 0-11v.


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One response to “ATX PC Power Supply to Electronics Variable Supply”

  1. Ron Rickett says:

    Chris, a few questions for you if you can find the time to answer.

    I have a PC PSU that I would like to use for something and noticed that you think you can get 24v from the two 12v rails. How would you do this, a bridge rectifier circuit maybe?

    I got here via your YouTube video on the 8mm shaft brushless motor with ER collet chuck and might be able to use the PSU with a 24v scooter motor that I’ve had for some time.

    Do you think the PSU will supply enough current to obtain the max torque of the motor and do you think this motor would have enough torque to drive small cutters (say, 5mm diameter) through mild steel?

    I am quite keen to get a small CNC system up and running at minimal cost using Mach3, with maybe a CAD/CAM front end in the future. I would be most grateful for your input.


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