Bench Top Power Supply





Introduction: Bench Top Power Supply

About: I am a Senior in college studying Mechanical Engineering. My interests include woodworking, 3D printing, electronics and building computers

I finally found the time to make my own bench top power supply from and old computer power supply. This has been done many times before and this is my take on it.

What you need

  • Computer Power Supply
  • Screw drivers
  • Wire cutter/Strippers
  • Ring terminals
  • Soldering Iron (If your right terminals aren't crimp type)
  • 4 screw terminal posts (I made my own, Instructable here)
  • Heat shrink Tubing
  • Switch
  • Drill

And as always be careful around power supply's. They contain capacitors that can cause serious harm to yourself if not handled properly.

Step 1: Identifying Wires

For the first step we need to take the case off from around the power supply.

Now you need to identify the wires

  • YELLOW = 12 Volts
  • RED = 5 Volts
  • ORANGE = 3.3 Volts
  • BLACK = Ground
  • Green = Power On

I cut all the other wires back down to the board and wrapped the ends with black tape to prevent them from accidentally touching anything else.

I then sorted the yellow, red, orange and black wires into separate groups.

I set the green wire and one black wire aside for the switch to turn on the power supply.

Step 2: Adding Terminals

Now i selected around 6 wires from each color and trimmed the rest down close to the board and covered with black tape.

The six wires from each color were then soldered into a ring terminal and then covered with heat shrink tubing.

The green wire and the one black wire were wired into the switch.

I then attached my screw post terminals to the ring terminals.

Step 3: Drilling Holes

Mark out on your power supply case where you want your terminals and switch to be. (Since my power supply was smaller and more compact I didn't have much choice where they would fit)

Drill out your holes and test fit your terminals and switch.

Step 4: Button Everything Up

Put your post terminals and switch in there holes and reassemble the case. Now plug in power and test your voltages. You now have a cheap desktop power supply.

I would of liked to have added an led to signal when the power supply was turned on and this could easily be done with an led in series with a resistor connected to one of the voltages.

Thank you for taking the time to read my instructable, have a nice day!

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thanks for all the details - like color code of the wires etc. This let me build a DC power this afternoon. Plus I added two DC-DC step down adjustable modules with LCD display, so I can get variable voltages apart from the ones provided.

It's dependant on the supply.. Most switching supplies, will shut-down if there is no load across the +5V rail to GND.. I think a lot of the newer ATX supplies have this already covered, but a lot of the older ones, (right back to the original IBM-PC 5150), if there was no load, would simply stop working within seconds if there was none. (something about the feedback circuit that regulates the voltages.. If no load or overload, the supply simply shuts-down.)

BTW Joshmt2012, Love the "DefCon" switch application! (flip cover toggle)

good power supply

Excellent. One of the cleanest designs i've seen!

Hi, is the power supply limiting current? and if so by how much from each voltage? And it would not be better to take off all the wires and just put one of each of thicker diameter to reduce cluster arround posts?

1 reply

How much current is allocated for each rail (voltage) should be written somewhere on your psu. I believe (correct me if im wrong) you should use more wires than one since with one wire you would be using a specific rail and put load only on that while psu are designed to share the load.

I made one. love it. I used color coded terminals though. I don't want to forget or permanent marker to wear off so that's the only change I made. good job.

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awesome! You have some pictures of it? And I printed a new base plate for the terminals with the voltages on it I just haven't gotten around to installing it

Great idea! I will suggest two things though. First, I would love to see this mounted into your desk, that would be awesome! Secondly, I want to warn anyone who attempts this that capacitors in the PSU can kill if your not careful. Please use the appropriate safety equipment or you could get badly injured or even killed!

1 reply

same point I made capacitors in PSU and in old TVs arent safe to mess with and that includes old monitors

Might I suggest that you go old school, and instead of adding an LED and extra wires, you select a power switch with a built-in light up indicator.

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This is a possibility depending on how the switch is wired. Since you arent actually running 12v through the switch to turn the power supply on you have to add the power into the switch. The switch i used has a built in light but its wired to use the incoming voltage to power it, this doesnt work because if you add one of the 12v wires you are basically creating a short. I hope that makes sense how i explaned it

Green should be your ground so you can add another terminal to give you the option to ground some projects

The green wire is what tells the power supply to turn on, so it has to be connected to a "black" ground. So the green and a black are wired into the switch to do that.

oh ok, I also had an earth wire in mine which was connected to the metal frame