Easy Variable Voltage Power Supply




Introduction: Easy Variable Voltage Power Supply

About: I love electronics and all about DIY.

Sometimes, to supply the necessary voltage in a project, i needed to buy a lot of batteries, or i had to look for a proper power supply for hours and it is not necesary, beacause now i have that awsome variable voltage power supply that can supply from 1,25 to 29 volts and 500mA, but if you decide to make your own, it would be able to deliver 3A.

It is easy to make and only cost me 4$.

Step 1: Materials

-A 30-32v power adapter. (Mine is salvaged from an old printer)
-A DC-DC buck converter. (1$ on ebay)
-A LED panel voltmeter. (2$ on ebay)
-An audio spring terminal. (0.40$)
-A potentometer, the same value as the one of the converter, mine is 10K (0.60$)

Step 2: No Project Box Needed

I know that kind of power adapters have a lot of empty space inside that we can use to place our components, so i'll open it to se if it can be the project casing.
If you use a transformer with a rectifier circuit, you'll need a different box.
As you can see un the pics, there's enough space for all the components.

Step 3: Electrical Connections

The wiring is pretty easy, you can see it in the diagram.
What you'll need to do first, is replace the small multi-turn potentiometer with the big one, it'll make the voltage controlling easier.
Then connect the voltmeter and the spring terminal in parallel at the converter output.

Step 4: Preparing the Case

Open three holes in the case. one for the voltmeter, other for the terminal and one for the potentiometer.
Then glue them all to the case and cover the connections with tape to avoid short circuit risk.
I didnt have any knob on hand, i recomend you to use one for a better appearance.

Step 5: Final Steps

Now solder the 30v output of the adapter to the converter input and cover it with more tape.
Then close the adapter with everything inside and glue the case with a strong glue as epoxi or cyanocrylate.

Step 6: Ready to Use!

You've done!
The power supply is ready to power all your projects.
I hope you have enjoyed this instructable.

Feel free to ask me anything you didn't understand or propose upgrades.

6 People Made This Project!


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115 Discussions

Hello was just wondering does the AC adapter HAVE to be 30-32 volts? Im just making sure because i dont wanna fry anything, and it was an oddly specific value to give. 30 volt AC adapters arent available in any of the stores I've been in, im assuming theyre somewhat rare. Would something like a 48 volt or 24 volt adapter be suitable?

I need a circuit diagram for the adapter u use with component specification... I intend to print the circuit and make one PCB for this project rather than using an adapter.

If I wanted 4 0-10V analog outputs, could I attach 4 potentiometer, DC-DC, voltmeter, output module to the same 48V power adapter?

Is it possible to replace the 2 wire digital voltmeter with a 3 wire one without adding an extra power source? My voltmeter needs a 5V current to light up

5 replies

You can use a 7805 regulator, but make sure it doesn't overheat.

But then does that mean that the input has to be greater than 5V? Because I want to be able to mesure 1V for example, and my voltmeter needs 2,7-5V to light up

Then,you would need another 5v power supply.

Also, one last thing: the amps written on the adapter is the max amps it can support, so it won't necessarly be that much current in the DC-DC converter?

You can use your 3 wire meter just fine. The 3-wire meter I have has a red wire for its "+" power, black wire for its "-" power, and white wire for its reference voltage. Connect the red wire to the power supply "+", connect the black wire to power supply "-" and connect the reference to buck converter "+" output.

* This will work as long as your meter can take the power supply's voltage. Mine can be powered by anywhere between 5V and 30V, my power supply was 19V.

Could I use binding posts instead of the audio spring terminals?



1 year ago

hi my cars fan stopet working and they dont have the fan controller, so i got a potentiometer and am wondering as how i would hook up the car battery to the potentiometer the potentiometer to the DC motor? please answer me. i need help

1 reply

Although fan speed is controlled by a resistor in series with the fan motor, those fans draw a serious amount of power. You would need to find the ratings of the fan speed switch in your car to find out what values they used. A 10W to 25W potentiometer can be purchased after finding out what values produce minimum speed for your fan. You could get several 10W 100 Ohm and 10 Ohm resistors and experiment. No resistance will be maximum speed, obviously. To use a much lower power resistor you will need to use a transistor with a heatsink or an encapsulated fan speed controller module. Like this one available on Amazon: ELEGIANTFurmores3317 This is a 90W PWM motor speed controller that will run from 12V and cost about $7 US.


I would like to build this power supply, one of my uses will be as a car battery charger, what would be the best way to add an amp meter to the device that can let me know what the battery is taking? Also would that be a cheap addition?

Thanks for your assistance

3 replies

You can't use this powersupply as a car battery charger,not only it wouldn't handle the curren needed, you also need current limiting to charge a battery.

Thanks, for your prompt response, I was hoping that I could have a more versatile unit with this project than a standard battery charger, but it looks like I will just have to get a battery charger.

But you can totally build your own car battery charger. Buck converters with amp control are not expensive and are used for DIY chargers.

very good idea!
i dont found pcb??may be send this
thank you


You mentioned that I could make the power supply to deliver up to 3 A if I make my own. How could I do that? Would I have to get an AC power adapter that can supply that much current?

Thank you

1 reply

Yes, the power adapter has to be able to deliver at leat that current.