So, I’ve got all these hobbies and interests that require a few different voltages.  I’ve got a lot devices that require 12v DC and it looks like half of those come standard with car adapters.  I also play around with some servos, some LED projects and some other stuff that require less than 12V DC and a few that need more.  What’s a guy to do?

Yes, I could have taken the reasonable approach, that I’m sure most of you would have taken, and just purchased a variable bench power supply or a few separate specific converters. Yeah, yeah, yeah, whatever.  I took it on as a personal goal to convert a standard computer power supply to a variable output DC desktop test rig.  Easy, right??  Kinda.

Let me get it out right up front that the reason I took on this project, as with most of my projects, was for the sheer satisfaction of turning out a functioning product.  Once I was able to get the wiring down right, the rest was a snap.  And, more importantly, almost everything I used for this project was laying around in various states of non-use so the total cost was almost nill.

Here’s a side shot of my Frankensteined power supply.  I was able to pull out all the standard voltages.  I also threw in a cigarette lighter plug (the only real cost) so I could charge up some of my devices that ONLY came with that type of plug.  (Some of my RC gear).  As you can see by my lousy handwriting, I fused up the cigarette lighter adapter (came with) and the main +12v plug since that will be the most used.  Future additions will include fuses for all voltages and an amp meter.  Maybe even a potentiometer or two…

The biggest time killer on this project was trying to figure out what wire colors corresponded to what.  I used some standard references on the Net but they were only partially helpful.  Leave it to HP (actually, it was a Compaq branded PC) to not play by the ATX standards.

This should give you some insight into how the power supply needs to be hooked up.  I switched the Green and White wires for the on/off switch and put a load between the +5v and ground.  A couple of banana jacks, a couple of LEDs (don’t forget the resistors!) and walla, she is done!   Worked like a charm!  Actually, I put both LED grounds together which somehow caused the system to start and then fail.  After putting them to different grounds I’ve never had another problem.