Introduction: Hack an Old Pc Power Supply Into a Lab Bench Power Supply

Picture of Hack an Old Pc Power Supply Into a Lab Bench Power Supply

In this tutorial i am going to show you how to convert an old PC power supply into a relatively chip bench power supply. This could be very useful for any beginners that enjoy making diverse circuits projects for a number of reasons. In the first place the costs are minimal since you probably already have all the parts needed in-house.

Secondly, it's has all the commonly used voltages, it has 3.3V 5V and 12V levels. In addition, the voltage levels are pretty stable since they are used in PC's.

Step 1: All the Parts and Tools Needed Ar:

Picture of All the Parts and Tools Needed Ar:


- 1 PC power supply

- some wires

- a switch that has at least 3 input's and 1 output

- a digital voltmeter and ammeter

- pliers


- soldering iron

- multimeter

- screwdriver

- something to cut trough the metal

- and others which I've probably forgot to add :))

Step 2: Construction

Picture of Construction

!!! ATTENTION: do not attempt to disassemble or touch any of the circuits inside the power supply case unless it is disconnected from the wall and even if you've disconnected it wait 15 minutes for the capacitors to completely discharge (anyway, try not to touch them at all) !!! HIGH VOLTAGE (just like the movie except this time is for real)

The first thing to do is to start the power supply and see if is working. In order to do so, you will have to short the green wire that goes inside the big connector to ground (ground can be any of the black wires). The motherboard does the same thing in order to start your computer when you press the power button. Once you're done with that start the power supply an measure the voltage between a yellow wire and ground and you should see 12V if you've got a good one.

Next, open the case (!!! REMEMBER TO UNPLUG IT FROM THE WALL !!!) and identify the wires you need (3.3V 5V 12V) by looking at their colors and the picture from above. Firstly solder the green wire to a black wire to ensure the starting part is don. Then cut a red and a black wire from the connector since you won't be needing them anymore and mount pliers to them, those would be the external wires (+ and ground). Inside the case cut all the wires but make sure you leave 2 red 2 black 1 yellow and 1 orange wire 15 cm long (don't cut them too short in case you need them later; also don't cut the green wire which should be connected to ground).

Now cut the metal and mount the switch and display assembly to the most spaced area of the case. And finally the fun part, look at the circuit diagram above and wire the parts the same way. Start by identifying the pins. The display should have five wires, the thinner ones are used for power and the other three ones for measuring.

Once all the solder is done make sure you insulate all the wires to avoid any short circuit and reassemble the case. Now you can test your build. :))

Step 3: The Final Product

Picture of The Final Product

You can see the voltage levels in pictures. Sadly, I don't have any load on it so you can't see the current level.

By the way, this are differential power supply's so you also have -12 and -5V that you can be useful when working with operational amplifiers.

Feel free to ask me anything about this project.


harvsch (author)2016-09-07

Make sure that the rotary switch is a "break before make" configuration. Switches used in audio work are often "make before break" to avoid popping noise when the switch is moved from one position to the next.

If a "make before break" switch is used it will short the supply Voltages to each other when the switch is rotated. Sparks or damage may be the result.

caisa16 (author)harvsch2016-09-08

mine work's pretty much ok, i guess it depends on switch

caisa16 (author)2016-08-17

that switch has 1 or 2 common pins (depending if is 1 or two channels) and all the other pins are for selection

the switch makes a connection between common and one of the other pins (it is better if you have a multimeeter and check using continuity mode) , you first need to understand how this switch works (you can search online for a diagram) and then connect the the red wire with crocodile clip on the common pin and next connect the other 3 wires (3.3v 5v and 12v) to any other pins on the same channel

let me know if u need more help (i will also post some more pictures)

josé antonioc3 (author)2016-08-04

sorry for my next question

i am not an electronic

where in the switch do i solder the cables. ¿can you show us manypictures?


russ_hensel (author)2016-04-01

Welcome to the club: Just a note to let you know I have added this instructable to the collection: Encyclopedia of ATX to Bench Power Supply Conversion >> Take a look at about 70 different approaches to this project. This topic is one of the more popular of all instructables.

caisa16 (author)russ_hensel2016-04-02

thanks for letting me know, i had no idea about that collection. I'll take a look.

Henmarsh (author)2016-03-30

Sorry but this is unintelligible. 'Then cut a red and a black wire and mount pliers to them, this would be the two external wires'?? Dangerous too - even after disconnecting the PSU from the mains you don't mention that the capacitors inside it can still retain a dangerous charge.

caisa16 (author)Henmarsh2016-03-31

I've completely forgotten about the capacitors. Thanks bro!

By the way, this is my first instructable.