A Microwave Oven Transformer Spot Welder

I need a reliable and maintainable spot welder to solder the 18650 batteries of my Powerbucket. This is my version of this basic tool.

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The power part of this spot welder is classical. It implements an MOT Microwave Oven Transfomer) with a 2 turn secondary winding made of heavy gauge wire. The current is fed to 2 bars made of 15 x 15 mm square brass tubes. The electrodes are made of machinned heavy gauge copper bus bar.

The power control board is based on a Cortex M0 processor controlling a TRIAC. The firing moment and duration are synchronised on the cycles of the mains. This insures repetability of the welding.

The duration of the welding is set by a potentiometer. The welding cycle is started by a push on a button or a pedal.

You will need 2 electronic boards to build the Spot Welder:

1 - an XSBO processor board - described here #a Break Out Board for an eXtremely Small Proc.

2- a TRIT board - all the files are provided in this project.

NOTE: I can provide the XSBO board populated, tested and programmed with the spot Welder application.


Precompiled Spot Welder application

hex - 21.80 kB - 04/04/2017 at 10:08


This ZIP contains the Schematic, PCB drawing, BOM and gerber files of the mother board

x-zip-compressed - 369.19 kB - 04/04/2017 at 09:56


  • First Welding Tests

    Michel Kuenemann07/02/2016 at 21:45 0 comments

    I made the first "serious" welding test on 3 18650 cells tonight.

    The blue part is a piece of heavy gauge copper bar in a thermo sleeve. It serves as a weight to control the welding pressure. Each arm can move independently (to some extent...).

    Close up on the welding electrodes

    The electrodes are made of machined copper bar. The electrodes are perfectly perpendicular to the surface to be welded. The gap between the electrode is 1.6 mm.

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Enjoy this project?



Marco wrote 04/04/2017 at 08:50 point

Hi Michel,

very nice and clean job!

Could you provide some Infos to the pcb?

I'm very interested in rebuilding this project!

  Are you sure? yes | no

Michel Kuenemann wrote 04/04/2017 at 09:52 point

Hallo Marco,

Danke sehr für Ihr Interesse an diesem Projekt.

I have put all the necessary files into the "file bag" of the project.

If you need more details, please ask.



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Michel Kuenemann wrote 02/16/2017 at 08:26 point

Hello Loïc,

Thank you. The Spot welder works very fine. It's an "easy to build", cheap and valuable tool.

The first string of 1000 cells has been put into service by November 2016. Check the project out here #A 110 kWh Powerbucket.

 I will build the second string as soon as I find the cash for the cells...

See You


  Are you sure? yes | no

Loic Cuenot wrote 02/16/2017 at 08:06 point

Nice ! 

So how are things going on this welding part ?
Are your new batteries on their way?

  Are you sure? yes | no

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