How to Convert an Old ATX Source to a DIY Lab Source

DIY projects (Do It Yourself, do it yourself) can be very diverse, but there is always a common denominator and that is that you need to feed whatever you are riding. Whatever your need, a PC power supply would almost certainly do what you need if it had the right connectors, right? Well then we are going to teach you how to do it yourself.

How to transform a PC ATX source into a DIY source

Generally, when you change the power supply to the PC it is because the previous one has been damaged, but it may also be that you have changed the source because you have directly changed the PC, because you have bought a new graphics card and the previous source did not have enough power, or simply for more convenience when going from a normal source to a modular one. Be that as it may, as long as the source is ATX it will be valid for this project, since these types of sources have standardized voltages that are the ones that will be used in the projects (+ 12V, + 5V and + 3.3V).

As a general rule and as we said, as long as the source is ATX it will be worth to convert it into a DIY laboratory source, but we would recommend that you do not use non-standard sources and that they have at least 300 watts of power. By “non-standard” we mean those “rare” fonts with specific form factors that come with some OEM PCs, no more, no less. Generic fonts can serve you perfectly for the purpose that concerns us today.

For this project you can use the power supply’s own housing if you want, although the ideal would be to have a 3D printer with the appropriate dimensions and connectors. In any case, you can use the inside of the source as is, with its plug connector and power switch without problems and thus take advantage of the different voltage outputs to have several connectors in your project.

Identify the cables that interest us

The first step is to identify of all the cables of the source which are the ones that interest us; let’s assume that you use an old and non-modular source, but for modular sources it would be the same but obviously with the cables connected. The only cable that interests us is the one with the 24-pin ATX connector, which you will have to cut and keep the following cables:

• You will need at least 6 of the 8 ground pins.
• At least one + 5V cable.
• The + 5VSB cable, since although it supplies 5V the same as the previous one, it continues to supply them even if the source is off, so it is used, for example, to charge a USB device even if the PC is off.
• At least one + 3.3V cable.
• The two + 12V cables.
• The PS-ON cable; Like the + 5VSB there is only one and it is the one that, when it closes the circuit with ground, starts the operation of the source.

These are all the cables that interest us in the first instance and unless you intend to create a much more advanced DIY ATX source, the rest of the source cables can be safely discarded.

Prepare the wiring of your ATX DIY source

Having seen which cables we are interested in, the first thing you should do is disassemble the source and select the cables that we have listed before, discarding all the others. The ideal is to unsolder them, but if it will not be enough to cut them and tape them at the cut end so that they cannot short or condemn them with hot glue, your choice is left.

In the end, you should end up with the following clean cables:

• 2 of + 12V.
• 1 of + 5V.
• 1 of + 5VSB.
• 1 of + 3.3V.
• 6 grounding.
• 1 PS-ON.

Now depending on how you want to mount your ATX DIY source, you will need to create a support for the connectors (that is why we told you about the 3D printer), but you can also drill one of the sides of the source and make them come out there. Obviously you can add switches or other elements to your liking, it depends on how handy you are and the desire and materials you have.

Now, to connect the external devices we will need other components called bananas, so in the source we will have to install female banana connectors of 4 mm in diameter. You need 1 banana plug for the ground connection and 5 more for the different voltages, but you can add the ones you want (the cables that we have marked before are the “at least” but you can use the ones you need).

In the same way, it is ideal to have the following materials:

• A switch, although you can take advantage of the source itself.
• Two status indicator LEDs (red).
• Two 220 Ohm resistors.
• A 10A fuse holder with its corresponding fuse.
• An LM317 voltage regulator. It is usually sold already with a heat sink installed and with a potentiometer, since it allows the voltage to be regulated from 1.2 to 37V.
• If you want, a voltmeter with a display that allows you to read the voltage of the regulator.

Internal connections

This would be the connection diagram, so prepare the bananas and the materials because you will have to solder.

Let’s explain how this scheme works: the grounding is shared between all the connections and the power supply circuit, so you can use each of the grounding wires for each of the other wires: you don’t need to have only one connecting each and every one of the elements that must be grounded.

The resistors and one of the LEDs will let us know if there is current in the VSB socket, while the other LED is for the 5V socket and will indicate whether or not we have turned on the power supply through the PS-ON cable. For safety, a fuse is added to the ground connection and the rest of the connections go direct. Finally, with regard to the LM317 circuit, the board used has two input pins: the 12V cable goes to one and one of the earth leads to another. The two corresponding connectors and a voltmeter are connected to the output if you want to see the voltage selected on the regulator’s potentiometer.