Find all your DIY electronics in the MakerShed. 3D Printing, Kits, Arduino, Raspberry Pi, Books & more!

Makezine_COTM_Transformers-BadgeManekinen’s spot welder uses a limit switch connected to a moving electrode to trigger the weld current for up to 4 seconds (as set by a pot) while giving the user time to clamp on the electrodes. It produces 2.6V at 1kA.

One cool aspect of the project is that he repurposed the transformer from a Technics SU-V670 stereo amp, and rewound the secondary winding, allowing him to power the welder from wall current.

[Reposted from last year; H/T Michael Colombo.]

John Baichtal

My interests include writing, electronics, RPGs, scifi, hackers & hackerspaces, 3D printing, building sets & toys. @johnbaichtal



  1. blake says:

    Well, those output numbers are greatly exaggerated, try a few hundred amps at half a volt.
    You’ll get 2.6v open circuit, not shorted. That transformer is only good to 1000va max (probably half that, hard to tell the size from the video) the limit of the core. A larger transformer from a 1500+watt microwave would be better, with spot welding you want vary high power for a short time. What he has hear works, but it takes far to long (heats and warps the metal). In industry most spot welders are capacitive discharge allowing for tens of thousands of amps for a fraction of a second.

    1. Keith says:

      Blake, I don’t think you’re quite understanding the electronics point of view as well as the welding aspect. The current anf voltages specs he quoted are completely relative and I’m sure he did get those specs under certain conditions. All that is somewhat irrellevant in the big picture that he built a nice fully functional spot welder that makes quality welds. You also mention warpage due to the time constant of the weld. I’m not sure how much welding you’ve done, but warpage is inherent in welding, not to mention his demonstration displayed quality welds with minimal warpage on light gauge material. The welds looked to be high quality to me. You also need to understand, if you build or buy a unit with much higher current capacity, you stand a much greater chance of blasting a hole in the work rather than bonding two pieces together. You don’t use a jack hammer to shoe a horse. Even though a jack hammer is a wonderful tool, it’s not the right hammer to apply shoes to equine. I plan to look at his design further and incorporate much of his ideas into my design. If you want to spend thousands on a big complicated commercial welder, go for it. For my needs, I was cheap and simple.

In the Maker Shed