There are a lot of ways that you can repurpose and reuse old electronics. For instance, a computer power supply can make a great bench power supply for your workshop. There are already a lot of tutorials online that show how to convert an old computer power supply into a bench power supply, but most of these designs require you to permanently modify it.

This design for an external adapter lets you use the power supply without modifying it. Any ATX power supply can be plugged into the adapter. The result is a high capacity power supply that can output 3.3V, 5V, 12V and -12V.

Before we begin, here is some background information on computer power supplies.

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A computer power supply converts the AC power from the wall outlet into smaller DC voltages that power the various components of the computer. It regulates the voltages by rapidly connecting and disconnecting the load circuit (switched-mode power supply). Most modern computer power supplies follow the ATX convention: They output +3.3V, +5V, +12V and -12V on a series of color coded wires.

Computer power supplies have a number of safety features that help to protect you and the power supply itself. Here are a couple that you need to know about:

  • Turning on the Power Supply It is designed to not turn on unless it is connected to a computer motherboard. This is controlled by the green “power on” wire. Connecting this wire to ground (any black wire) will allow the power supply to turn on.
  • Minimum Load Requirement Many power supplies require a minimum load current in order to stay on. Without this load, the output voltages may vary significantly from the specified voltages or the power supply might shut itself off. In a computer, the current used by the motherboard is sufficient to meet these requirements. If your power supply has a minimum output requirement, you can meet this by connecting a large power resistor across the output terminals. This is discussed in the steps below.

Steps

Step #1: Identify the Wires on the 20 Pin (or 24 Pin) Connector

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  • The wires on the main 20 pin (or 24 pin) connectors are color coded. These are the same for all ATX power supplies: 3.3V wires are orange; +5V wires are red; -5V wires (if they are present) are white; +12V wires are yellow; -12V wires are blue; ground wires are black.
  • The green wire is the "power on" sensor. This wire is internally connected to 5V with a pull-up resistor. If you connect this wire to ground (any black wire) the power supply will turn on.
  • The purple wire is the +5 "stand by" power. This outputs a 5V signal even if the rest of the power supply has not yet turned on, allowing you to power any circuit that might control the ON/OFF signal.
  • The gray "power good" indicator is at 5V if each of the output wires is operating at the correct voltages.
  • To make the connections easier to identify, I used colored markers to color code each slot on the 20 pin connector.

Step #2: Solder Wires to the Female ATX Connector

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Next you need to attach wires to some of the pins on the connector. I connected to the 3.3V, 5V, +12V, -12V, Ground and the "power on" wire. Solder the wires to each connector. It is easier if you select pins that are a little spaced out from each other. I also used the same colored wires to help keep track of them.

Step #3: Cut a Slot in the Housing for the Female ATX Connector

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In order to attach the connector to the housing, you first need to cut a slot for it. It is easiest to do this at the edge where the two parts come together. Hold the connector up to the side of the housing and mark the edges. Then using a sharp knife, cut along the outline.

Step #4: Drill Holes for the Banana Jack Terminals and the Power Switch

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  • I used four pairs of Banana jack connectors for the outputs, so I marked eight locations evenly spaced on the top of the housing. Then I drilled holes that where just big enough for the mounting screws. I also drilled a hole for the power switch on the right side.
  • Once all the holes are drilled, insert the switch and the power terminals and fasten them in place.

Step #5: Glue the Female ATX Connector to the Housing

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To hold the main connector in place, I used 2-part JB Weld. This compound comes in two parts; squeeze out an equal amount from each tube, then mix them together thoroughly. Apply the mixture all around the connector and let it sit overnight to fully cure.

Step #6: Connect the Green Wire to the Power Switch

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In order to turn on the power supply we need to connect the green wire with the ground (one of the black wires). I used a small push button switch to make this connection. Solder the green wire from the 20 pin connector to one side of the switch, then solder the second green wire to the other side of the switch. To help keep them insulated, I cover the connections with heat shrink tubing.

Step #7: Attach the Banana Jack Terminals to the Housing

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  • I attached the banana jack terminals to the top of the housing in two rows. The red terminals are for the positive 3.3V, 5V and 12V connections; the black terminals are for ground.
  • Insert the post of each terminal into the holes and tighten them in place with their screws.

Step #8: Connect Spade Terminals to the End of Each Wire

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The output terminals need to connect to multiple wires. The easiest way to keep this neat and organized is to make the connections with crimp spade connectors. Attached one to the end of each wire.

Step #9: Connect the Wires to the Appropriate Terminals

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  • Connect the black wire to the first black terminal, then connect the other black terminals to the first one with short jumper wires. I also connected the wire from the power switch to the nearest black terminal.
  • I connected the rest of the wires in ascending order according to their voltages. Begin with the 3.3V wire (orange) on the far left, then the 5V wire (red), the +12V wire (yellow), and the -12V wire (blue).

Step #10: If Necessary, Add a 10W Resistor to Meet the Minimum Load Requirement

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  • Many power supplies will not stay on unless the output reaches a certain minimum power requirement. To test if your power supply has this requirement, press the power button and wait for a few minutes. If it shuts itself off, then you know that your power supply has a minimum output requirement.
  • To take care of this, you can add a power resistor between the 5V terminal and ground. In most cases, a 10 watt 10 ohm resistor will work. In very rare cases, you may also have minimum output requirements on the 12V pin and the 3.3V pin. This will require additional power resistors.
  • These power resistors create a lot of heat, so if you add a power resistor, make sure that your project housing has adequate ventilation. In some cases you may even need to add a small PC fan to help dissipate the heat.

Step #11: Add a 12V DC Power Outlet (optional)

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In addition to the banana jack connectors, you can add other kinds of connectors. I added a 12V DC outlet. Start by drilling a hole in the side of the housing big enough for the barrel on the DC outlet. Then connect the center terminal on the 12V DC outlet to the +12V terminal (the yellow wire) from the power supply. Connect the outside terminal on the 12V DC outlet to one on the ground terminals (black wire) from the power supply.

Step #12: Add a USB Power Outlet (optional)

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  • Another optional connector that you can add is a USB outlet. This will let you run any device that is powered by a USB port. To add this kind of connector, I recommend using a USB extension cord. Cut the cord in half — we want to use the piece with the female connector on the end. Next, separate the internal wires at the end. Strip the insulation off of the ends of the red and black wires and add a spade connector to each one. Connect the red wire from the USB cable to the red wire from the power supply. Connect the black wire from the USB cable to the black wire from the power supply.
  • Once the wires are connected, mount it to the side of the housing. Trace the outline of the USB connector onto the side of the housing, then use a sharp knife or a rotary tool to cut it out. You can glue the USB connector to the side of the housing. I recommend using JB Weld, just like you did for the 20 pin power supply connector.

Step #13: Add Labels For Each Pair of Terminals

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  • To help keep track of the different voltage outlets, I labeled each pair of terminals. You can print out a simple label and attach it to the top face of the housing between the positive and negative terminals.
Jason Poel Smith

Jason Poel Smith

My name is Jason Poel Smith. I have an undergraduate degree in Engineering that is 50% Mechanical Engineering and 50% Electrical Engineering. I have worked in a variety of industries from hydraulic aerial lifts to aircraft tooling. I currently spend most of my time chasing around my new baby. In my spare time I make the how-to series "DIY Hacks and How Tos."


  • JPalm

    Very useful

  • Scott Perry

    This might be a stupid question, but how do you connect to this? I admit I don’t know much about these “banana jacks” but I was just wondering how you would connect something like an arduino or anything else to this? Thanks.

    • Jason Amri

      if you take a look at this: http://imgur.com/gmHlsi5 you can see that the binding post has holes that you can insert a wire into and screw tight. These wires could connect to an ardunio and many other things.

    • Aristarco Palacios

      Tadaaa!!!

  • Chad Krause

    How many amps can you pull from the +12v rail? I was thinking of making this for a lipo charger

    • Pitariu Darius

      +12 13A ; -12 1A

    • Arcanek

      That depends on your power supply. They have different wattages. You’ll have to look at the nameplate for the specs.

  • Nici Schmidi

    I used an Old shoebox big enough to fit the power supply so now its portable

  • Palmer O’Neal

    12 volt rail on my supply supplied 20 volts so I turned it into a variable supply for 13-20 volts. All the other rails are messed up as well 3volt=5 5volt =8.something

    • Dave Ferreira

      Hey Palmer, I’d be interested in seeing your variable circuit. Did you just put a panel-mount pot in series with the connectors? Did you put a meter on it? Thx.

  • Scott Perry

    I wound up trying my hand at this, with a few tweaks. I used a toolbox to put the psu in, and bored holes in the removable tool tray to hold the binding posts. Works ok so far. Only mistake I made was putting the posts too close to each other. Other than that, works great. Nice project that becomes a useful too.

  • John Ellsworth

    I really like your take on using a motherboard connector to make this work with with any (atx) power supply. A little more work up front, but well worth it in the long run as it is super easy to swap supplies if one fails. Also can serve as a quick tester for all those old supplies I have taking up space. Now the question is….buy a atx connector or take the time to desolder one from an old motherboard…

    • Aristarco Palacios

      I’ve tried to desolder connectors from motherboards and always end up ruining them. They require a lot of heat and I almost always melt the plastic before the solder :(
      I for one, would prefer to buy it.

  • Chamika Manchanayake

    great

  • Laura Taylor

    Hi, I am in the process of making this, but I have a question. Can I have more the one 12 volt outlet?

    • Aristarco Palacios

      As long as the sum of all the 12V outputs’ currents don’t exceed the maximum current for the 12V supply, you can have as many as you can. If your supply has a +12V 10A output, you can have 5 outputs of 12V @ 2A each or 20 outputs of 12V @ 500mA each, for example.

  • chuck

    Very nice! I’ve used PSU’s but not taken much time to “improve” them – like with a switch, binding posts, USB etc. I was looking to build a few with kids to power various projects we are working on… Arduino, and some automotive stuff, so was hopping for ideas on how to make them a little nicer… and safer. You win:o)) !

  • Thanks for this! BTW I designed a 3D printable custom enclosure for this project, here: http://www.thingiverse.com/thing:665797.

  • DreadPirateZed

    For power supplies with a minimum-load requirement, how about lights (LEDs or older low-voltage incandescent bulbs) in place of the power resistor(s)? Same heat dissipation/power usage, but you’d get something useful (light, and a visual indication of ON status) along with the waste heat. Of course, it would require a few more holes in the enclosure and sockets/mounts, but it might be worth it.

    • Aristarco Palacios

      I was about to suggest the same. Maybe a pilot light might make a good load resistor. And look retro-cool. :)

  • Scott sutton

    Cheers for this it was helpful, I do have one suggestion though. In looking at the wires etc I would make a plug board or other such apparatus so you could easily connect and disconnect different voltages. At first glance and because I do not have the components on hand to make it proper I thought a simple board with finishing nails through it on the one side only sticking out enough to solder the wire to the end of the nail and on the other side enough to connect an alligator clip jumper wire too. say in two rows the top positive, the bottom negative 12v grouped together 5v together and so on (or vice versa) then label them presto you have a bench top power source no loose wires easy to connect and disconnect you can also set it up so the green trigger wire is connected properly too. when I thought of this I was having a flashback to grade 7 electronics class lol where we used a similar method to connect led lights to a board as some simple game. of course you could do it much cleaner with the right components adding switches even some sort of control dial to adjust the Voltage and even hard wire an old multi meter to it for that added macgyver feel lol

  • Sajjad Haider

    I have a power supply in which no green wire is exist. FOLLOWING colors of wires are Red, orange, black, purple, white, brown, gray nd sky blue. I want to make 12v charger

    • Arcanek

      Sounds like you have an old supply. The pre ATX supplies didn’t have this feature.

    • Aristarco Palacios

      Are your connectors like these?:
      http://www.cosam.org/images/a1200t/at_mb_power.jpg
      If so, your supply is a bit old and it needs to be turned on and off with a switch, not a pushbutton.

  • Sajjad Haider

    Plz tell me how to make

  • webaugur

    For our makerspace classroom I designed a laser cut case that slips over a standard ATX supply and hides all the wiring, etc. It has a ground terminal for a wrist strap that ties to chassis, three voltage taps, and a switch to connect a DC barrel jack to one of three voltages. We have had tons and tons of old computers donated most of which we just strip for parts. So we had a massive stack of ATX supplies looking for a purpose.

    • William Turner

      raaaaaagggghhh I need a freakin 3d printer I am jealous!!

      • Alex O. Martinez

        That was made wtih a laser cutter!

  • Idahoser

    I would also take a look at Anderson Power Poles instead/in addition to the 5-way binding posts. Very good connectors, common in ham radio.

    • webaugur

      Very common in a lot of 12VDC connections. US FIRST Robotics also standardizes on the 45A Anderson Power Poles. Same connector arrangement as the ham radio standard. Our makerspace happened to have a west mountain radio battery analyzer we were able to use with our US FIRST team’s battery packs without modification.

  • Aristarco Palacios

    I like the idea of having a USB output to use some devices like mobiles, just remember some brands require pull-up and pull-down resistors at the data lines to operate correctly. Like the iPhoney.

  • Nick Salmon

    Are all the different coloured wires at the same potential i.e. all yellow wires can be joined together, all orange …, etc.? This would allow me to get the full potential via each coloured connection.

  • Armin Willis

    I’m trying to run my power supply with a 12-volt car stereo in my garage. When I turn on the power supply and connect it to the stereo, the power supply shuts off. The 12-volt pin produces good voltage and it will run a 12-volt PC fan, no problem. There does not appear to be a short in the stereo unit—it shows several thousand ohms between the power wire and ground, which is roughly the same resistance as the fan. Do you know why the power supply is shutting off? By the way, the same thing happened when I tried to connect a 12-volt, 1 amp wall adapter to the stereo. The adapter will no longer produce sufficient voltage.