ATX variable power supply

[MattQ]

I'm trying to make a variable voltage power supply from an old ATX power supply I have laying around. The problem I'm having is finding voltage regulators that can handle both 1) high power and/or 2) regulation from 0-12 (or 0-24) volts. Any recommendations on regulators that meet these criteria, and can handle 10 or so amps? My plan was to bring out the regulated +12, +5, and +3.3 connectos, while making an additional variable voltage output. I'm thinking I'll skip the -12 volt connector because I've read that it can't handle high current, and what fun is a 300 watt ATX supply if it can't handle high current? On a less important note, without making a ringing choke or switching power supply (I'm worried that adding these might add unpleasant harmonics at my output), is there an easy way to generate 24 volts from the ATX supply to increase the versatility of my supply?

 

[Mosaic]

NO.

You can get away with around 16VDC variable, but exceeding that will prob. blow caps etc. I have a benchtop ATX rigged to give me variable regulated VDC. However, you lose the overcurrent shutdown capability. I can pull a full 20A from the 12VDC rail with this. The 12VDC rail now varies from about 8 thru 16V. For the lower range of 1 to 8 V, I use the 5VDC rail.

There are a number of sites to hack a PSU...just a matter of adding a Pot. and changing a resistor on the PWM switching controller. No other parts.

 

[EN0]

Why do you need that high of current? Normally anything at that level would utilize a fixed power supply, since variable power supplies are used more for experimentation; powering applications that only require an amp or two.

 

[4pyros]

Isn't most of the power on the 3.3 volt rail? Andy

 

[Mosaic]

I work with Peltiers so I need many AMPS.

 

[EN0]

Mosaic,

I wasn't questioning why you need that kind of amperage, but rather the OP. I realize that you were providing an example of why that current level might be necessary, but I only indicated that usually variable power supplies are not used for gargantuan current levels. Most hobbyist or experimenters use several amps for their projects, which usually suffice. If the OP expounded on what this high current PSU will be used for, I'm sure we would be able to provide more help.

 

[MattQ]

To be a little more clear, I was considering high current to be 20 or so amps, which is high in comparison to what most variable power supplies output, which is usually limited to 10 amps.

EN0 -- There are lots of situations where low voltage/high current is necessary: quickly charging large capacitors, for driving DC motors, battery chargers, or for driving high power LEDs in parallel (as I'm currently doing) ect. There is also the challenge of designing a high current variable DC supply. While these projects usually require some kind of Buck voltage control with current regulators, I would enjoy both the convenience of a single power supply, and the challenge of the design.

4pyros -- The supplies I have been looking at have almost the same current rating both the 3.3v and both of the 12v rails (but yes, you're right, the 3.3 is a slightly higher current rating), but because the 12 volt rails have a significantly higher power rating, I would rather use them for my variable voltage source.