Voltlog #82 – DIY Adjustable Analog DC Electronic Load

In this episode I am building an analog adjustable dc load with parts easily obtainable from ebay and banggood. The advantage of such a dc load is that you can understand how it works, modify or repair it if necessary far easier than you would with a digital one. I was able to push mine up to 60W dissipation, but it is recommend to stay under 50W to protect the mosfet.

Constant Current Analog DC Load PCB Module

PZEM-031 100V 20A LCD Panel Meter

Metal Box Enclosure 170mm x 130mm x 75mm Blue

10 Turn 10K Potentiometer

Brass Standoffs Kit
M3 Screw Kit
KSD9700 NO Thermal Switch
Cooling Fan 12V
JST XH 2.54mm 3 Pin Connector
4mm Banana Plug High Current M5
2.1mm DC Jack Panel Mount
Rocker Switch
Screw Terminal 3 Pin
16AWG Silicone Flexible Wire

Reverse Engineered Shematic – Copyright Adrian Carstea


fredlllll says:

usually people use isolating heat transfer pads, cause the back of the mosfet is connected to the circuit, is this one isolated?

Ton Bovee says:

hi, Tx for the diagram. Do you know what is the function of the IC 1A LM393N?

Hugatry's HackVlog says:

Another great dummy load video! That panel meter looks great with nice layout and decent precision. If it had (m)Ah instead of Wh, I would have ordered one straight away…
Anyway, awesome project!

The Radio Shop says:

Very nice project. Thanks for showing this. Just may build me one of these. Good job!

Jack Zimmermann says:

Very nice build! I really like the matching color of the LCD and the case.

standishgeezer says:

Great job! Always like your very thorough explanation of the build and your tips (such as the pinout on 10 turn pots – that one caught me out some time ago).

John Cherry says:

Nice project, explained clearly.

ton bovee says:

great job Voltlog, Tx again . I learned a lot from this video I just installed a temp switch my unit is fail safe now . 80 C. added a second mosfet ! (You need to match them, I added a series resistor for each to divide the load better. This increases the fail save situation as well Silicone glue is great stuff.I did not know this type of glue. I took the larger tube. I suggest keep it in the fridge for storage and it lasts! This DC load is easy to modify and so easy to use. Got 2. Keep it going

squalazzo says:

very well done 🙂
i think i’ll do 1 for myself 🙂
oh, correct the box link, add “box” to the description, otherwise you have car wheels 🙂
the KSD9700 NO Thermal Switch link is wrong, too

codebeard says:

Nice project. Is there a reason you didn’t have a sense wire for the load negative?

MindFlareRetro says:

Great project. Can you simply trim the length of the post on the 10-turn pot so the knob mounts flush with the enclosure?

tengelgeer says:

Damn, again I bought all kinds of stuff during/because of your video. Damn eBay addiction :p

iceberg789 says:

i have the same power bank i guess.

Robin Cerny says:

hm… I actually have exactly the same Panelmeter laying around and didn’t had an good Idea…
Now I have one 😀

Actually I was also thinking about to modify the Meter like you did, but didn’t had the time to think more about it :/
Thanks for your work! And your Video (:

jjensen2492 says:

Well done! Looks good and is a very valuable tool. Thanks for showing us.

Joseph Nicholas says:

Hi, very nice build. I would have been nice to see what the board circuitry does since there are a few ic’s on the board. If memory serves, one is an op amp. Removing the mosfet and connecting it to the heat sink is a great idea and leaves the door open to increasing the draw by adding more mosfets. But why mount the heatsink and mosfet upsidedown?

blackbrayn says:


.rpv says:

Very nice project!, the only thing I’ll do different it’s to leave the fan on the wall of the box.

Neil Hall says:

Nice project. Have you stopped working on the dark load project?

Robert Gibbons says:

Nice affordable project! Thank you.

Mauro Sedrani says:

+VoltLog Great job!

Chris Moen says:

Excellent and very clear discussion. Now I have your great advice on how to build this unit.

MrBrymstond says:

I believe I would have applied the Thermostat on top of the plastic part of the mosfet not allowing any conductive thermal paste or cream to touch the conductive parts of the mosfet if it’s supposed to be isolated and maybe it would also act more accurately as a bonus. Just a thought.

Mike Novo says:

At first I wasn’t sure I liked the blue project box and preferred the plastic one. Now after seeing it in this vid, the quality looks pretty good for the price. Your skills are also improving. Dremmel did not jump around as much as on the plastics. The extra height for the PC heat sink is the top seller for this project. Nice work!

David Watts says:

This was great mate. Who needs a fail safe anyway 🙂

Maurice Bauer says:

How accurate can you adjust the load ? Down in the 10mA ?

Jon Vannatto says:

Any comment on recent news on Eagle moving to a paid subscription model? Moving to KiCad or sticking with Eagle?

juliusvalentinas says:

Very bad idea to use thermal switch that is under 230VAC, the case is wired to live AC. You need to use insulated one !

That much thermal paste in not desirable, as if it squeezes on the pins there can be a short circuit if the paste is conductive.

Orkhan AmirAslan says:

Nice build, @VoltLog. I always use regular screw for newly bored holes, once it screws/unscrews without a problem, I switch it to standoffs (even plastic ones).

MrMac5150 says:


Digger D says:

Another nice video but this DC load is very reminiscent of #38 😉 One day (some day soon I hope) I would like to design one that has PC logging, uC controlled of course, with constant resistance, power, current and the ability to run it with different wave forms. Meanwhile I have the one you showed in #38 which does a decent job but lacks logging.

dormstories says:

Where did you source the panel meter from?

Surging Circuits says:

Well done. Did you consider holes in the cabinet to allow air flow and heat escape?

1an Email says:

Great information on a simple solution for electronic load! I will build this device as it appears to work well in your video, but will use a different panel meter and fan speed controller.
Maybe you will consider testing this cheap ebay fan speed controller for inclusion in future projects. I was going to build one for myself but at this price just ordered one from ebay. http://www.ebay.com.au/itm/262723958505

tablatronix says:

great build

DrRunCMD says:

Wow! excellent video my friend! I had bought the same dummy load circuit from ebay and now have found a schematic for the board! Thanks.
What I have done is used an entirely different mosfet for my setup. I used a IXFH50N50P3 which can handle up to 960W. But for heatsink I used a Fischer Electronik LA 6/150.

Works well up to maximum 150W so say 30V 5A.





Works very well. Oh yeah, I subscribed too! 😉

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