Introduction: Easy Variable Voltage Power Supply

Picture of Easy Variable Voltage Power Supply

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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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!

Picture of 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.


AjayG50 (author)2017-08-21

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.

ahub1201 (author)2017-03-08

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

Tian XiZ (author)2016-06-11

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

pinomelean (author)Tian XiZ2016-06-11

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

Tian XiZ (author)pinomelean2016-06-15

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

pinomelean (author)Tian XiZ2016-06-15

Then,you would need another 5v power supply.

Tian XiZ (author)pinomelean2016-06-18

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?

Dragon940C (author)Tian XiZ2017-01-03

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.

BADyoyo2 (author)2016-12-04

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


drogus (author)2016-11-28

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

JosephP36 (author)drogus2016-11-29

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.

starbeam (author)2016-02-15


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

pinomelean (author)starbeam2016-02-16

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.

starbeam (author)pinomelean2016-02-16

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.

EddieDigits (author)starbeam2016-08-12

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

esafb52 (author)2016-07-22

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

thomaszoega made it! (author)2016-07-15

nice, cheap and easy!!! thanks for the idea!!!

CarlosM224 (author)2016-03-20


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

pinomelean (author)CarlosM2242016-03-20

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

HIKAMAT TAMATTA (author)2015-12-12

can i use a 40-45 power adapter?

RC32 (author)2015-03-02

How did you decided to use a 10k potentiometer?

pinomelean (author)RC322015-03-02

Use the same value as the one that came in the board.

ZeeshanR3 (author)pinomelean2015-12-06

Can I use LM317 with a 5kpot at the output of adapter instead of DC-DC converter??????
Please reply fast

pinomelean (author)ZeeshanR32015-12-07

Yes, but the lm317 will need a heatsink.

eletrofss (author)pinomelean2015-06-01

Actually the pot is just a simple resistor divider, 1k or 50k generally work well so.

ZeeshanR3 (author)2015-12-05

I just want to know that why are u using dc-dc buck converter??????

ricjoh made it! (author)2015-12-04

I made this! Unfortunately is't really easy to tear out the vias on these cheap boards when de-soldering the trim pot. I ended up finding a schematic for my buck converter and wiring in my 10k pot directly to the output power and through a 330 ohm resistor to pin 4 (feedback) of my power converter chip (LM2596).

Schematic I used:

JohnW51 (author)2015-09-15

What variable output DC-DC converter did you use? Most of the ones I see are quite a bit larger than the one in your photos.

AfiqG1 (author)2015-09-14

Hi. I got the same version of this project. Can i change the power adapter to car power supply ?

kaostias made it! (author)2015-08-23

I made it, great idea. My Power suply gives only 12V, and my potentiometer has a 4-32 range, so mine only has 4-12 range (Enough for my purposes). Also my power suply had no space, so i put the project in an old transformer, I'll work on the project boxing when i'm done with the led project i'm gonna manage.

kaostias (author)kaostias2015-08-23

Hint: Do not test Intensity without a circuit or you'll burn the device. I've just finished it and i have to buy another DC-DC converter

DanielS54 (author)2015-06-18

Can I use this?
You could send the link of what you use you

kaostias (author)DanielS542015-08-23

Yeah, you can. If you see on my comment above, i used a 12V one, but you just have to get the cable and test with a polimeter which cables have 32V. (in my case black (generally negative) and green were 5V and another black (doesn't matter which one) and green had 5V. I removed the 5v one and worked with the most powerfull one.

eletrofss (author)2015-06-01

@tru-dhillion yeah i know what kind of vape.....
Obs: you do'nt need a pwm controller, the PS already has one.
I build electronic vapes all the time, it isn't really hard if you know a bit.

Tru-dhillon (author)2015-05-29

Anyway of connecting a PWM? I was considering building this as a vape station.

MechEngineerMike made it! (author)2015-04-13

Hey, I was inspired by this project enough to make my own little version. I used a slightly more expensive voltage regulator than yours, but mine had a screen built in. I designed a 3D printable case for it too because I didnt want to try cracking open the adapter case. You can check it out here if you're interested:

MechEngineerMike (author)2015-03-14

Nice project, this looks like something that would be really handy to have. Your graphic on step 3 looks good too, what program did you use to draw it?

I used photoshop, but any drawing program would do.

andrew.larson.14289 (author)2015-03-08

Could I use other terminal? Like a Weidmuller?

jongscx (author)2015-03-06

I love that you're reusing the plastic casing of the PSU... Brilliant!

RC32 (author)2015-03-02


Can you tell me how does it work, what we are actually doing. Please provide a detailed explanation.

Thank for help.

pinomelean (author)RC322015-03-02

The little board is a switching converter, you can look for the theory behind it. What you have to know is that you can put a voltage on the input, and the output will go from almost 0v to the imput voltage minus 2v, just by turning the potentiometer.

RC32 (author)2015-03-01


Thanks for the inscrutable, it was a very nice instructable.

I have a question, my printer adapter has an input of 200-240V but in the you uploaded it read as 100-240 V; will my printer adapter work?

Another question, can you give the link from where you bought the components, because when I searched it on ebay it showing product costing more than you specified.

pinomelean (author)RC322015-03-01

If you live in a country that has an outlet voltage of between 200 and 240V

MMelfe (author)2014-04-24

very good Instructable, but i have one question, i would like to use my old laptop charger but in output signal have 4.97A, can i use that DC-DC buck converter which his max A is 3A without problems?

luzzyf (author)MMelfe2015-01-03

Yes, no problem. Your circuit will only draw current (amperes/A) as needed from your 4.97A PSU. In fact, having more current capacity than required by the circuit is ideal as long as your load does not draw more current than the safe limit of ~2.5 A (the 3A limit of the buck converter's LM2596 IC should never be reached - especially not without a heat sink).

yoyolo (author)2014-10-12

Where could I solder an amp meter to this board?

yoyolo (author)2014-10-12

Any way to get an on off switch on there?

dkime (author)2014-10-09

what if i wanted ac output? specifically 9-12v at 1500-2000ma?

pinomelean (author)dkime2014-10-09

This circuit only works for dc, for ac you'll have to find something with a variable transformer, there i can't help you.

About This Instructable




Bio: I love electronics and all about DIY.
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