ATX Bench Power

See, it works!

Finished product

With many devices these days, power comes in the form of DC 5 or 12 Volts. It seems that battery chargers are especially bad because they require upwards of10 Amps and don’t include a wall-adapter.

An easy solution to this problem comes in the form of a standard computer power supply (ATX). These devices have several nice qualities and only a couple caveats: They are capable of providing plenty of current: 10-15A 12V, 10A 5V, etc. are small in size, and generally efficient.

However, they also require a couple of considerations: cooling needs, voltage levels (12V is really more like 11.5V),and Switching Noise. Switching Noise comes from the way they are designed to be small, efficient, and cost-effective. Switching-Mode Power Supplies generate a given voltage by turning on-and-off a higher-voltage source so that the average of the output is the desired voltage. This is then filtered to smooth the result enough such that it is appropriate for the application.

Computers don’t require voltage sources that are all that clean, they are almost always run at 3.3V and lower, and have extensive power filtering on the motherboard and peripherals themselves.

Anyway, enough justification for the choices made, on with it...

First, though, as a disclaimer: Do not follow these instructions! I have no idea what I’m talking about. If you follow these instructions, you’ll die, you pets will talk and the world will cease to be. I take no responsibility for the idiotic things you do.

Step 1: Disassemble the power supply:

Be careful for latent energy in the capacitors!

Be careful for latent energy in the capacitors!

First, you want to find the screws that hold this thing together. They are often in a bit of a strange place, on this model they are on the top, far away from where the case separates. Notice that the sides are held in by the lip punched into the steel. Also, you may need to cut-off the ends of the long wires at this point (the connectors that attach to your motherboard, CD-ROM disk drives, etc) as they will no longer be needed.

There are a couple things to pay attention to about your power supply. You'll want to check to see if the main power connection and the fan have removable connectors on the main circuit board. If they do, you're in good shape. If not, it's still possible to continue, but it'll be a little more challenging.You'll have to carefully solder them once everything is installed in the box.

The next step is to remove the "IEC" socket and switches (On/Off and 110/220) from the case. You may have to do more or less than I had to, depending on the specifics of your salvaged power supply. I had to desolder the wires from the IEC socket to the On/Off switch, and the wires from the switch to the harness that connected to the mainboard. The 110/220 switch was mounted fully on the inside of the case and was left alone.

What was required on my box

What was required on my box.

Now, we need to prepare everything for mounting in the new wooden box. Because these power supplies are produced in mass quantities, the manufacturers do whatever they can to save money. This usually includes using single-layerPCBs. What that means it they have to move the ground plane off the PCB. This means that the metal case is the ground plane. So, we have to keep it. In this case, I measured exactly how little case I could get away with and broke out the Dremel. Here is all the parts you need from the case (not including the main board):

All you need from the case

All you need from the case

Step 2: Preparing the box

Now, we need to find a wooden box to encase the power supply. I found mine from the local craft store. In the next image you can see that I've cut holes for ventilation, the switch and IEC socket. We also need to re-solder the wires from the socket to the switch. Make sure that the HOT wire (black) goes through the switch.

Ventilation, switch, and wall power

Ventilation, switch, and wall power

Power wires soldered back on

Power wires soldered back on

Glue the mounting plate into the box. Make sure that the plate won't chafe the wires leading to a short, and that the wires can reach. I used super glue (CA)to glue the plate to the box. I was happy to note that it bonded to the metal pretty well.

Mounting plate glued down

Mounting plate glued down

Step 3: Installing the Power Supply

Screw the power supply mainboard onto its mounting plate. Make sure you mechanically and electrically attach the ground wire to the plate. During this step, it is imperative that you make sure the ground wire doesn't short anything out. Now is also the time to attach the wires to the mainboard.

Wiring the input to the mainboard

Wiring the power input to the mainboard

I glued the 110/220 voltage switch to the side of the inside of the box, using CA again.

The 110/220 switch glued to the case

The 110/220 switch glued to the case

Now, we strip and gather the 12V wires (yellow, usually) and an equal number of ground wires (black) and attach either spade lugs or something else convenient.


Spade Lugs installed

Get your hands on some banana plugs to use. They're available at RadioShack, but they suck, so try to get them somewhere else. Drill some holes on the front and mount them.

Mounting of the 12V wires

Mounting the 12 volt wires

Mounting of the 12V wires In order for the power supply to work, the "PS_ON" wire must be tied to ground. This is usually the green wire, but you should probably check for yourself. Also, now would be a good time to "Smoke test" your installation. Sometimes, switching power supplies need to have a non-inductive load to turn on, such as a light bulb or something.

Step 4: Finishing up


Airflow baffle

These switching power supplies are really efficient, but often need some active cooling. I decided to make a baffle plate to mount the fan in it. I traced around the fan and cut it out, and center punched the screw holes. I think it fit nicely. The writing on the lid is the voltage and amperage rating copied off the original case.

Below, I've included a a photo of the whole device. Everything seems to fit really well.

All done (only12v included)

All done (only 12v included)

See, it works!

See, it works!

1237 Words