Introduction: Computer Power Supply to Bench Power Supply Adapter

Picture of Computer Power Supply to Bench Power Supply Adapter

There are a lot of ways that you can re-purpose 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 the power supply itself. 

Another option is to make an external adapter for your power supply. Any ATXpower supply can be plugged into the adapter. The adapter then connects the appropriate wires to a series of output jacks that can be easily accessed to provide power for your projects. This design lets you utilize the power supply without having to modify it. 

Step 1: Materials

Picture of Materials

Here are the materials that you will need for this project.

ATX Computer Power Supply
20 Pin (or 24 Pin) Female ATX Connector (these can be purchased online or salvaged from an old motherboard)
Plastic  Project Housing
Jumper Wires
8 Female Banana connectors/ Bind Posts
JB Weld
Heat Shrink Tubing
Crimp-On Spade Terminals
12V DC Power Outlet (optional)
USB Extension Cord (optional)

Drill and Bit Set
Sharp Knife
Soldering Iron and Solder
Colored Markers

Step 2: Background: Computer Power Supplies

Picture of Background: Computer Power Supplies

A computer power supply converts the AC power from the wall outlet into smaller DC voltages that power the various components of the computer. They regulate 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
A power supply 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 tun 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 that is 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 a later step.

Step 3: Identify the Wires on the 20 Pin (or 24 Pin) Connector

Picture of Identify the Wires on the 20 Pin (or 24 Pin) Connector

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. This allows you to power any circuit that might control the ON/OFF signal. 

The gray "Power Good" indicator. This wire 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 4: Solder Wires to the Female ATX Connector

Picture of Solder Wires to the Female ATX Connector

Next you need to attach a wire 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 5: Cut a Slot in the Housing for Then Female ATX Connector

Picture of Cut a Slot in the Housing for Then Female ATX Connector

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 6: Drill Holes in the Top of the Housing for the Banana Jack Terminals and the Power Switc

Picture of Drill Holes in the Top of the Housing for the Banana Jack Terminals and the Power Switc

I am using 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 were drilled I inserted the switch and the power terminals and fastened them in place. 

Step 7: Glue the Female ATX Connector to the Side of the Housing

Picture of Glue the Female ATX Connector to the Side of the Housing

To hold the main connector in place I used 2 part J-B 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. Then let it sit overnight to fully cure. 

Step 8: Connect the Green Wire to the Power Switch

Picture of Connect the Green Wire to the Power Switch

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

Step 9: Attach the Banana Jack Terminals to the Top of the Housing

Picture of Attach the Banana Jack Terminals to the Top of the Housing

I attached the banana jack terminals to the top of the housing in two rows. The red terminals would be for the positive 3.3V, 5V and 12V connections.  The black terminals would be for ground. 

I inserted the post of each terminal into holes and tightened them in place with their screws.

Step 10: Connect Spade Terminals to the End of Each Wire

Picture of Connect Spade Terminals to the End of Each Wire

The output terminals need to connect to multiple wires. The easiest way to keep this neat and organized was to make the connections with crimp spade connectors. So I attached a spade connector to the end of each wire. 

Step 11: Connect the Wires to the Appropriate Terminals

Picture of Connect the Wires to the Appropriate Terminals

I connected the black wire to the first black terminal. Then I connected 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. On the far left, I connected the 3.3V wire (orange). Then I connected the 5V wire (red), the +12V wire yellow, and the -12V wire (blue).

Step 12: If Necessary Add a 10W Resistor to Meet the Minimum Load Requirement

Picture of If Necessary Add a 10W Resistor to Meet the Minimum Load Requirement

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. Then 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 13: Add a 12V DC Power Outlet (optional)

Picture of Add a 12V DC Power Outlet (optional)

In addition to the banana jack connectors, you can add other kinds of connectors as well. I added a 12V DC outlet. Start by drilling a hole in the side of the housing that is 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 14: Add a USB Power Outlet (optional)

Picture of Add a USB Power Outlet (optional)

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. Then 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, you need to 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 then glue the USB connector to the side of the housing. I recommend using J-B Weld just like you used for the 20 pin power supply connector. 

Step 15: Add Labels for Each Pair of Terminals

Picture of Add Labels for Each Pair of Terminals

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

Now your power supply converter is complete.


KasunJ (author)2017-03-11

i have an idea to make a great power supply with a ATX psu.using two buck boost converters(for two channels) and rotary switch for 3.3v , 5v , -5v and -12v.

will this work?or anything else?

and why always that 5v rail has maximum current output.huge that 12v rail.

sergeike made it! (author)2016-12-25

I did it with what I had. So is really different.

SherylinRM (author)2016-11-19

Great idea.

Another option for having something to power is to use a 25 watt light bulb.

Yes you can use an AC bulb in a DC current.

Actually they last longer that way.

Anyhow, it lights up [not as much though] and provides the PSU with something to do so it won't shut off.

Also reminds you that the power is still hot in the terminals.

Great ible.

Thanks for this :)

alevi made it! (author)2016-10-20

Working great! thanks !

made a case from of thakita driller box.

pota1 (author)2016-08-09

And i only have 4×5 watts resistor but it only has 0.22ohms of resistance will this work?

You might want a larger value resistor just in case

pota1 (author)2016-08-09

If i put no load will it blow up?
Bcs i dont have anything to test it with.
And if a circuit needs 12v 5 amps
But the powers supply outputs 18 amps will my circuit blow up?

No. It will not blow up without a load resistance. The amp output rating is a maximum. It is the voltage that is held constant. The current changes to allow the voltage to be constant.

It will not blow up. Threse power supplies are volltahe regulated. So they will output the same voltage regardless of the load.

Johnrosspt (author)2016-05-27

hello am a beginner. my question is what is -12 volt and what it does? I understand+12v but not -12v.
please help me to understand.

Positive and negative voltages are relative to the common reference which is "Ground." In this project, all the black terminals are connected to Ground. So the +12V output is 12 volts higher than Ground and the -12 volts terminal is 12 volts lower than ground. By combining positive and negative voltages you can actually make a lot of different combined outputs. For instance you could connect to the +12V output pin and the -12V output pin to get a 24V signal.

How much amperage will I get from connecting +12V and -12V? The one indicated on +12V or -12V?

That depends on the model of power supply that you are using.

I have an old power supply. It has 8A on +12V and 0.5A on -12V. How much will I get combining them getting 24V? You can see the attachement, it's my power supply.

Generally speaking, electronics projects are limited by the weakest components. So you probably shouldn't exceed the 0.5A

LoneWolf0 (author)2016-03-10

I love the look of this project! I sadly just tore apart my last psu for parts, but hopefully I can get a new one and make this.

MSargent99 made it! (author)2016-03-01

Great project! And I found it just as I was needing a higher current power supply from some of my other Arduino projects.

I make just a couple minor modifications -

I added a small 78S09 voltage regulator circuit to give me a 9V 2A output so my supply has: 3.3V, 5V, 9V, & 12V outputs.

I also added fuses for each output.

I added a small 5v fan inside direct connected to the 5v line just in case the internals get a little warm and it adds just a small enough load so that hopefully I won't need the 10W resistor for a load. But will see.

And finally I added a small green LED to let me know when it is on. But that wasn't really necessary, I forgot just how loud the fans in the old ATX power supplies really are.

Last thing I need to do is to attach my labels and then it will be totally finished.

Thanks again for a great Instructable project!


waynesworldlydrawerings made it! (author)2016-02-04

working great! thanks again!

Eric20136065 (author)2016-02-03

One of the best tutorial i've ever seen, super useful and easy!

waynesworldlydrawerings (author)2016-01-23

SUPER useful, can't wait for rest of my parts to make this. Good reference on power supply details:

I wasn't able to get the female 20pin ATX connector off my motherboard....and couldn't find a source for a cheap part of that type so instead picked up an ATX motherboard power extension cable from Amazon and I'll chop off the male end....connect wires and set. THANKS for re-posting from Make here!

psargaco (author)2015-12-26


I am preparing to implement a mix of this and other ATX power supply projects and I'm wondering if I should aggregate all the same colour power wires to guarantee a higher current. For example, my power supply has a 20 pins connector where pins 1, 2 and 11 are all orange, therefore 3.3 V. Pin 11 actually collects 2 wires. I'm not planning on drawing large currents, but I'm thinking that with all the orange wires connected the power supply would be more flexible. Maybe it doesn't make sense.

For the USB outlets I'm consider the two 4 pins connectors which also come out of the ATX. Finally, for the variable 12 volts I'm planning on using the 2 yellow, 2 black pins connector.



Yonatan24 (author)2015-11-07

Very well written 'Ible, Really helpful as a guide for the project I am building now



Yonatan24 (author)Yonatan242015-11-10

My ATX power supply doesn't have an On/Off switch, So when I plug it in, It doesn't turn on, I've connected a "pull-up 10 Ohm 5 Watt resistor" between the "PS-On" and the "Ground-Black" and the ATX power supply turns on and works as it should.

I saw that you mentioned that the resistor should get really hot but my resistor doesn't heat up at all (I'm not complaining ;) ) Is there a reason why this is happening?

RafałZ3 (author)Yonatan242015-12-14

To be honest, you don't have to connect anything between green PS_ON and black GND wires. Just short them together or if you want to be on the safe side, connect it through small 1/4W resistor. The only dummy load should go between either +5V and GND or +12V and GND based on your ATX (check which line gives most amps)

Yonatan24 (author)RafałZ32015-12-14

Why do I need a "dummy load" between the +5V and GND? What will it do?

RafałZ3 (author)RafałZ32015-12-14

And yes, if you connect it between GND and 5V (or 12V), it will get hot.

RafałZ3 (author)RafałZ32015-12-14

And yes, if you connect it between GND and 5V (or 12V), it will get hot.

Razor 911 (author)2015-10-27

how do you bypass the power suply i saw a guy once just bridging two wires on the power suply plug and it made it fully electrical and operational

RafałZ3 (author)Razor 9112015-12-14

Connect green wire with ground and voila!

DIY Hacks and How Tos (author)2015-10-27

Check the above pin out diagram. The PS-ON pin (the green wire) that I have connected to the power switch can just be jumpered to ground to turn it on without all the other stuff.

Mesut.DD (author)2015-10-18

good power supply

MohitS17 (author)2015-09-08

I built my power supply with the similar instructions as yours using only the 12Volt output to power my Car Airpump (12V 14Amp max).I joined all 5 12V wires (Yellow) together and same for the ground connections to get the max current on the 12V rail which is rated for 17A on this supply.

With no load connected, the SMPS turns on and works fine but as soon as i connect the Car Airpump it trips (shuts itself down) not sure why ?

Now if i connect the same Power supply with a Digital Ampere meter connected in series, the Air Pump works perfectly. Could you help me understand the possible cause for this behaviour and how could i go about fixing or diagnosing it.

That is weird. The only thing that I can guess is that some power supplies have a minimum current requirement. That is why sometimes you need to attach a resistor to dump some extra current. Your circuit might be right on the threshold and the current meter might push it over the line into the operating range. Try hooking up a variety of loads to see how it reacts with different current requirements.

Thanks Jason. I agree with your suggestion. Since i'm not an electronics person, would you be able to roughly suggest the possible value of the resistance this digital ammeter could be introducing (a range of resistance would also do). I can then purchase these resistance and experiment with them individually as you have suggested.

You can try using a 10 ohm 10 watt resistor like the one that I talk about in step 12.

Update - Just tried with these 2 resistors - 4.7 ohm 10 watt & 10 ohm 25 watt across the +12 & ground (i had them lying around) and the SMPS still tripped as before. I went ahead and bought another SMPS, it worked right out of the box without any resistors. Thanks for your help.

Chipmunk03 (author)2015-07-25

About a year a go i made one too. Now I want to improve it to an adjustable power supply sing a LM317.

Be careful not to exceed the power rating of the LM317

could you please give some insight on how to make a variable-voltage version of this? there are some good instructables for variable PSUs, but none (that I can find) that use a computer's power supply

The simplest method is to use a LM317 variable voltage regulator. This will let you set the output voltage but you are a little more limited on output current.

the LM317 has an output current limit of 1.5 V. does this mean that if my circuit has a current running through it of greater than 1.5 V, it can damage the regulator?

Yes. Each LM317 has a max current of 1.5 amps. So you shouldn't exceed this. But you could set up multiple circuits. For instance, the power supply could drive multiple lm317 circuits with different voltages.

whoops; I just noticed I used "V" instead of "A."

and okay. the LM138 has a max current of 5 A. this should be more than enough current--right?

That should meet most of you needs.

jerrad.karpowich (author)2015-07-20

few questions.
1. -can i use one of each wire or should i bunch them togeather. not worried about full amps being used just wonder if its a fire hazard.
2. - why would my voltage act like a dying battery. i checked and 12v was down to 10.9 but slowly climbing up.

now i did use a 10k pot to adjust the voltage but i dont see it doing that to the supply

One of each wire should be fine. I am not sure what you mean by "act like a dying battery. Could you be more specific.

yea turns out i think the pot im using is messed up i tap it and the voltage changes. this is what i get when i use scrap parts. lol

yup thats what it was. i replaced and it works like a charm :)

Tiezane (author)2014-08-12

I tried to make this, and as long as I hold the power button down, it turns on, but the instant I release the button it shuts back off. I tried adding the 10 Ohm, 10W resistor to the 5V, to the 3.3V, and to both lines, and nothing helped. Bad power supply, or is there something else I can do?

Are you using a momentary button?

About This Instructable




Bio: My name is Jason Poel Smith I am a Community Manager here at Instructables. In my free time, I am an Inventor, Maker, Hacker, Tinker ... More »
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