Small and Simple Homemade Variable Power Supply

Power supplies are necessary when you want to make an electronic project, but they can be really pricey. However you can make one for yourself pretty cheaply. So let’s get started.

First, you will need components. There are three key part of the build. The DC DC step-down converter, the voltage meter and a charging supply from an old laptop. You will also need a potentiometer (with or without a cup(not necessary)), a toggle switch and some jumper cables. The value of the potentiometer need to be specified before purchase. You can find it in the wiring diagram of the converter.

Parts:

• LM2596S-PSUM DC DC step-down converter (any step down converter could work, but the pin layout may be different)
• VM028-330-R voltage meter (any other type would do)
• Old laptop power supply
• Potentiometer
• Toggle switch
• Cables

The first step is to solder jumper cables to the positive and negative in terminals of the converter. You should see the polarity on the PCB (IN+ = input positive, IN- = input negative). Then solder the other end of the positive cable to the middle pin of the toggle switch. Pick an other jumper cable and solder that to one of the remaining pins of the switch. Now, you need to connect the voltage meter with the output pins of the converter. You may pay attention to the polarity again (so the red cable should to go to the OUT+ and the black to the OUT-). Now we need to connect the output of our laptop supply with the input of the converter. I was lucky, and I could remove the female connector from my old laptop but you may need to cut the cable and solder to position (the positive terminal to the toggle switch and the negative terminal to the IN- pin). If you are lucky, or you’ve bought a female connector then repeat the previous instructions but with the connector.

Now plug in the power supply and grab a screwdriver, as you need one to control the voltage level. As you can see my power supply delivers 20 volt to the panel and as you can see I can adjust the output with the rotation of the inbuilt potentiometer. However it can’t go any higher then the input voltage, in this case 20 volt (19.7 volt). From this point the supply is usable but you may find hard to adjust the voltage with a screwdriver so in the next step I will show a solution for that.

Now, first of all you need to remove the inbuilt potentiometer. This can be a bit hard as it has 3 legs. You should grab it with a plier and as the tin starts to melt you should pull it out. Then you need to solder 3 cables to the holes of the gone potentiometer. Then connect these cables with your new potentiometer. And this is it, you’ve finished the project. You may find hard to accurately control the voltage level. So, you can cut a wheel from wood and glue to the potentiometer. With it you should be able to rotate it more slowly, and accurately.

For more protection you can build a housing around the device. Be aware that the converter can deliver a limited amount of power, after you reached the limit the board may damage itself. I hope you’ve found this instructable helpful. Let me know if you have any porblem. Happy soldering!