DIY Lab Bench Power Supply [Build + Tests]




About: I am creating step-by-step, do it yourself project videos. My goal is to create something cool or useful from wood, plastic materials, electronics, etc. As I am huge DIY enthusiast, expect variety of differ...

In this instructable / video I will show you how you can make your own variable lab bench power supply which can deliver 30V 6A 180W (10A MAX under the power limit). Minimal current limit 250-300mA.
Also you will see accuracy, load, protection and other tests. They should give you better idea, to easily decide, is it worth making it yourself.

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Main Tools You'll Need:

Main Materials You'll Need:

Other Things You'll Need:

M3 screws, nuts, wires, crimp terminals, banana plugs, alligator clips.

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Step 1: Preview

Front, back and the inside shots of the power supply.

Step 2: Components

All components that you will need and some close up shots of them.

Step 3: Making Front

In the front we need to make holes for the display, two potentiometers, two banana sockets and for the power switch.

For smaller holes metal drill bit works just fine, but for bigger holes you will need a step drill bit to drill the holes without cracking the box.

Step 4: Finishing Front

I would say this is the hardest part of the build - make a square hole at the top of the box. My solution was to drill many small holes, cut out bigger pieces and then sand to the right size. I works well, but it takes a lot of time.

If you know better solution, I'm all ears. It must be the easier way?! Right?

Step 5: Back

Now on the back, we need to make many holes for the fan, that it could exhaust the hot air and square hole for the AC socket. Nothing hard, just a lot measuring and drilling.

Step 6: Component Placement

We should plan the inside layout for the components. You want like AC connectors of the power supply to face the back and potentiometers of the 300W step-down module to face the front.

Also try to position those two components that the air from the bottom front would go through all the heatsinks.

Step 7: Rubber Feet

With screws in place, now we can find space to make additional holes for the rubber feet in each corner.

Step 8: All Wires

With all components in place now we can measure required wire lengths (how everything connects - later).

Step 9: Modifying the Module

But before connecting everything, we need to de-solder existing small potentiometers on the module (on my module you can see only one potentiometer, because I already de-soldered one).

We need to add extension wires that will go to the new multi-turn potentiometers.

  • The middle wire from the module goes to the bottom connector on the potentiometer.
  • The top wire goes to the middle connector
  • The bottom wire goes to the top connector.

This way you will get that rotating potentiometer clockwise voltage or current increases and counterclockwise decreases.

Step 10: AC Wires

AC, AC, AC, be really careful with it, or it could kill you. Always connect ground wire, it's a great safety feature.

For quick connection to the onboard AC socket and power switch at the front, I used these wire crimp terminals. On them, I added some heat-shrink tubing for the insulation.

Step 11: Wiring

4 wires goes from the 36V power supply. Thick (16AWG or thicker) wires go to the main 300W step-down module and thin wires to the additional step-down module. With this done, don't forget to power on the additional module and adjust output voltage to 12V.

Step 12: How Everything Connects

As from this wire mess it's really hard to follow, I added simplified view how everything connects together.

  • We have connected live AC wire which goes from the onboard socket through the power switch to the power supply. The neutral wire goes to the other terminal and ground wire to the ground connection.
  • Two thick wires go to the main step-down module and two thin wires to the secondary module. To it, comes wires from the fan and two thin wires from the display.
  • The third thin wire from the display, which is usually yellow, goes to the red positive banana socket. To this same socket goes positive output of the main step-down module.
  • Finally, black thick wire from the display goes to the negative connector of the main step-down module, and red thick wire to the black negative banana socket.

And that’s it, the circuit is complete. You additionally can fine tune voltage and current readings on the meter with two integrated potentiometers.

Step 13: Final Touches

With caps on, display wires in and all screws isolated, we are done.

One more thing that we could make are banana plugs for easy testing.

Step 14: TESTS

Few accuracy, load and other tests.

Step 15: TESTS

Few temperature and short-circuit tests.

Step 16: THE END

So, what can I say, as all parts cost only around $35, I think it gives good value considering the accuracy and performance of the power supply.

For me, this device will hugely ease up testing of all sorts of electronics for my future projects.

So if you are looking for a cheapest way to get above average accuracy and performance, DIY power supply like this might be the answer for you.

I hope this instructable / video was useful and informative.
If you liked it, you can support me by liking this Instructable / YouTube video and subscribing for more future content. Feel free to leave any questions about this build. Thank you, for reading / watching! Till next time! :)

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    34 Discussions


    4 days ago

    I also made the same item in a different way :)


    11 days ago

    Great! It is always nice to see that there still can be found people who want to do things with their own hands, respect! As you probably have found out, the cooling fan and air distribution inside the box could maybe be thought again by placing all PCB units so that the air flow is in the same direction as the heat sinks. Then the smoke gets out easier and does not glog the holes...


    Very nice looking job.

    I’m planning to build something similar and you’ve given me some ideas.

    A couple questions/comments if you have a moment?

    1) I’d strongly suggest you add a fuse. At least to the 110V input. You can get IEC sockets with a fuse holder built in, and they usually have a cute red switch (remember that the current in the 110V line won’t be 6A). Id consider a fuse between the 36V supply and the variable supply. I’d also consider a fuse in your output to the red binding post. Even if both your supplies are current limited. (Put the meter on the output side of the fuse, or best attach it right to the binding post). If you use a 10A fuse, I don’t think it will add much resistance and thus current induced droop and ripple (a smaller fuse would have higher resistance). You could use bulkhead fuse holder(s) and install them on the back... with bulkhead socket holders you won’t need to disassemble everything...

    Why all these fuses? Even if the supplies are current limited, if a short develops - (either at your load, or inside your box due to a wiring short or failing component.), you can see from the big letters on the box 180W. That’s a lot of heat inside your box. Something will get very unhappy. Smoke will blow out the cluster of fan holes in the back. Uses slow blow fuses, rated just below the current rating of your supplies.

    2) you might add some kind of schematic. For instance, I wasn’t sure if the on/off switch is on the input of the 36V supply, on the output of the 36V, or the output of the buck regulator. I wasn’t sure if ground carried through from the iec socket to the black terminal post or not. Your description of wiring the panel meter was confusing. Lots of bench supplies have a floating output (black/negative is not grounded) and then they add a third green terminal that is grounded. You can tie green to black if you want your load grounded. The green terminal also makes a good spot to plug in your ESD strap.

    3) if it’s on the input, make sure the switch is rated for 120V. If anywhere else, make sure it can handle the current.

    4) if it were me, I’d put a main switch on the back for the 110V.

    5) if it were me, I’d add a toggle switch on the output of the regulator on the way to the red post. That way you can shutdown your load and adjust the voltage without having to pull the leads out.

    6) those meters are a royal pain because the current measurement is in the return path (the black lead, not the red lead).
    That means that any current that goes from the supply to the load on the RED wire, but somehow finds its way back to the power supply via a path other than the BLACK wire won’t register... this would be more often a problem if you decided to add a second output with a meter - say both 5V and 3.3V to a project. Most loads would have a common ground. So, you don’t know which black wire the current will go back on...

    If anyone knows of a source for these meters that measures current in the POSITIVE lead TO THE LOAD, please let me know!!! I want some!

    7) finally, I’d put some capacitors right across between the two output terminals. Make sure they are rated in excess of the maximum voltage. I might use a 100uF (or 10uF), a 1UF and a 0.1F.

    2 replies

    RicksterInstructables thank you for this feedback! The power button disconnects live AC wire from the main 36V PSU. I now added input and output notes on the photo.
    Again, thanks, that's some valuable tips/information, appreciate it! :)


    Reply 17 days ago

    I think that the article explains things very clearly - one of the best I have seen!

    I agree about the fuses. I too would buy an IEC connector with switch and fuse built in. I think the last capacitor value in your comment should be 0.1 uF a.k.a 100 nF? If you do put capacitors there, a 47k or 100k resistor in parallel is needed to discharge them reasonably quickly.

    For protecting the power supply from already-charged capacitors I would add a 3 Amp diode across the OUT+ and OUT- (reversed, i.e. cathode to the OUT+) on the 30V module. The diode protects the supply from negative voltages from equipment previously tested, then connected the wrong way around.

    For ultimate safety it is best to shroud the mains wires and connections in fiberglass sleeves. That way even if the box burns or melts, people are still protected from touching the mains. It is a requirement in some countries, I believe.


    18 days ago

    This is very nice and neat ! Bravo !
    I would like to know how the power supply is behaving when the load is important ? For instance, if you want to power a 5V 3.5A device, does the voltage remains stable ? And if yes, to what extent (1%, 5%, 10%) ?
    I recently bought a PSU and its voltage drops (from 5V to 4.6V) when you draw more than 2A... so the device is not properly powered and shuts down.
    And I am looking for a strong and reliable power supply for developing and prototyping systems.
    Thank you for your answer !

    3 replies

    Reply 17 days ago

    Thanks! I tested with 10.03V - no load, 9.91V - 4.5A load. I would say it is good, just a little drop. :)


    Reply 18 days ago

    yeah static tests on this unit look great but voltage regulation is also important.


    Tip 17 days ago

    I made a similar PS but with a slight change.

    On the 300W step down i isolated the + feedback resistor and added an extra jack on the front and ran the feedback resistor to the extra jack.

    In normal use i just short the extra jack with the Positive jack and have your basic Lamda PS.

    In sensitive testing i run 2 wires to the + side of the load eliminating the voltage drop in the wiring.

    it adds an extra measure of accuracy and ends most discrepancy in readings.

    1 reply

    Reply 17 days ago

    Sounds good if you need the best accuracy, thanks for the tip!


    17 days ago

    Very nice job. Clean and tidy !! One question. What is the CC low current control capability of the DC CV/CC Buck converter? How low can you set the current level? I have seen similar converters that could only go as low as 30 - 40 mA. Still too much for say - a single LED. There is no CC specification on it's product page. Thanks !!

    1 reply

    Reply 17 days ago

    Thanks, this buck converter is not suited for a very low current. Minimal current limit is 250-300 mA. I will add this info in the instuctable.


    18 days ago

    Interesting build!
    If I may make a suggestion: I would replace the M3 screws covered with electrical tape with nylon standoffs, as they are inherently insulated. :)

    1 reply

    Tip 18 days ago

    Excellent! Thank you! I've been thinking about buying one of these (but maybe bigger/higher amperage - for ham radio equipment), but I might try this first. I would echo RicksterInstructables' suggestion and add fuses. You don't need them until something goes wrong...

    Only one comment/tip of my own, regarding the rectangular hole in the box. (You did say, "If you know better solution, I'm all ears.") Search amazon (or your favorite source) for "nibbler metal cutter" or "nibbling tool". I'd recommend the non-powered tool if this is your 1st time using one. You'll still have to go behind with sandpaper or a wider file, but loads faster and easier than all of those small holes.

    1 reply

    Reply 17 days ago

    Thanks! Yes, I guess a fuse is never a bad idea here. But on the 36V 5A PSU, there is some sort of a fuse (pictures). Correct me if I am wrong.
    Thanks for the tips! I think my box is way too thick for a "nibbling tool".


    18 days ago

    Very nice! I like how easy it is to set the voltage/amperage, and it packs quite a lot of power too! A dedicated 5v supply might be a nice addition. Also, the ability to set the voltage/amperage while the output is off, then turn the output on. This would be good just in case you misadjust the dials with something connected- this way you wouldn't burn it out.
    As for cutting the square hole, an oscillating plunge cutter would do a nice job. Lacking that, a Dremel would get the job done with the right attachments.

    1 reply

    Reply 17 days ago

    Thanks! I mean it's just two old school rotating knobs. They have 10 turns of rotation and they doesn't turn very freely. So it's hard to mess something by accident.
    You set desired voltage, lower current to minimum, connect device, and rise the current. I do like this if it is current sensitive device like a LED chip.


    18 days ago

    Very good job! Only thing that would make it better is to make a dual output but that would be easy based on your work here.