MattMade
DIY Maker Blog by Matt Morawiec
Jun 29 2016

DIY Bench Power Supply

Convert an old ATX PSU into a bench power supply!

•Intro

It is not uncommon for those who work with electronics to need regulated power sources at common voltages, such as 3.3v, 5v, and 12v. Power bricks supplying these voltages are common around the house, but their outputs are normally limited to no more than one amp or so. An old ATX power supply from a computer, which is sure to be found in storage in and old PC, can supply plenty of current for more ambitious projects with ease, usually up to 20 amps or more on the 12v rail! Today I will convert this computer ATX power supply to a bench power supply that we can use for all future projects!

Get the Parts

  • ATX Power Supply: Grab it from an old computer! Or buy one for cheap on ebay!
  • Soldering Iron (+ solder): The most used and most important tool.
  • Connectors of your choice: I used 5mm bullet connectors, but you can use any type of connector so you can tap into any of the supply rails at any time.
  • Misc Tools: Wire cutters, wire strippers, scissors
  • Misc Materials: Wire, heatshrink, zip ties, braid wrap

The Original Power Supply

The power supply I decided to use came out of an old computer that was too outdated to be used. It is rated for 350 watts and up to 18 amps on the 12v rail! Sweet!

Original PSU

Without modification, the power supply has a bunch of clunky and proprietary connectors on all of its output wires, making it very hard to draw power from! Lets take care of that...

Snipping the Connectors

I simply cut off all of the connectors while leaving the wires as long as possible.

Original Connectors

These can go in the trash can...

Organizing the Wires

Now I am left with dozens of loose wires. I organized them by color and used heatshrink to bundle them up.

In general, here are how the colors relate to the function of the wires:

Black: Ground
Yellow: +12v
Red: +5v
Orange: +3.3v
Blue: -12v
Green: On/Off signal
Brown/Grey: Misc. Measure with a multimeter to find out :)

Wire Organizing

I set aside one black wire (ground) and the green wire. This is used to wake the power supply up and to let current pass through to the outputs.

On/Off Wires

There will be a few odd colored wires that can be cut off or isolated for later use. (for example the blue wire is usually -12v (yes, negative :D)

At this point it would be smart to cut all the wires of the same color to the same length for easy soldering.

On/Off Switch

In order to control when the power supply is on or off, I simply wired a switch between the aforementioned green and black wire. When the green wire is grounded (when the switch is "on") the power supply will turn on.

On/Off Switch

I just mounted the switch to the enclosure with some glue.

Voltage Meter / Status Indicator

I wanted to know when the supply was on as well as the health of the system. I used a small voltage meter readout I had lying around and wired it to a spare 12v output. This was mounted to the top of the enclosure and lights up whenever the supply is turned on.

Voltage Indicator

Output Wiring

Next was to get usable output from all the loose wires. I stripped the ends of the wires of one color and tinned them together with my soldering iron. Then I attached female bullet connectors and heatshrinked them with the corresponding color (I had to use green for 3.3v because I didn't have orange heatshrink). I also attached a special connector to the 12v rail for use with my Li-po charger.

Connectors

Test Time

Now that all the outputs were organized, it was test time! I tried powering my charger and monitored the five volt rail with my multimeter. It works!

Testing

Now I have a fully functional bench power supply! Perfect for almost any DIY project!

Completed PSU

Extra

I also used some braided tubular mesh to protect and organize the wires further. Looks good!

Braided Shielding