DIY Spot Welder Doesn’t Look Like It Will Immediately Kill You

We love hacks that involve mains voltage, but most of the time, for safety’s sake, we secretly hope for that one macabre commenter that details every imaginable way the questionable design choices will result in death. This spot welder may still be dangerous, but it looks like they took some precautions to make it non-lethal, and that counts for a lot.

After their extremely questionable high speed belt sander, this one is, refreshingly, extremely well done. It starts of as a dead standard microwave spot welder build: take apart microwave, try not to die from large capacitor, remove coil, modify coil, and hook up.

After that, it gets to some nice heavy metal music fabrication. Aside from a slightly shocking number of fresh OSHA reportable hand injuries (wear gloves!) the build goes together well. A lot of planning obviously went into it, from the actively cooled transformer to what appears to be a resettable timer circuit for the weld duration, not to mention the way that it just fit together so well at the end. There were some neat ideas as far as home mechanics go that we’ll be using in some of our projects.

In the end, the proof is in the spot-weld. The timer is set, pedal gets pressed down, and when tested, the sheet metal breaks instead of the weld. Video after the break.


30 thoughts on “DIY Spot Welder Doesn’t Look Like It Will Immediately Kill You

      1. You thank them again, and explain that it’s really unfair to ask them to believe it’s homemade, because after all, you ARE a professional, [hack.]

        I have to be satisfied with, You MADE THIS? And it works?!? LOL
        Even Jesus had NO hometown respect… so THEY got no miracles.
        Fix everybodies’ stuff, except the unbelievers. Tell them, it’s part magic. They have too little faith. It could break the machine that works so very well, for everyone else.

  1. Doesn’t really look too different to a regular low end spotwelder you could buy.
    I’ll be that commenter, but the only thing that I don’t like and think is an issue is the power cable looks way too small, and with vent holes everywhere the fan is going to push more air out of them then around the big transformer. I’d think a box with the grate being on the fan and transformer ends only would really help improve the cooling, and a thicker heavier duty cord should take a bit more use and abuse before getting too warm, as it lacks the forced air cooling of the transformer.

      1. For the typical 1kw that would be 8,3A, and since this is a cheap transformer with a rather crappy power factor, you’re going to have even more current going back and forth that cable, since the apparent power is anything from 1.4 to 2x as much…

        Oh and did you see the “shims” he took out before the HV winding? Those have a very god reason to be there, see “shunted transformer”, this increases the current even more.

          1. Too deep, can’t reply directly.

            No, the capacitor in the microwave is there to act as a voltage doubler. The klystron looks like a mostly resistive load.

            AKA the A is correct on second thought, without a constant resistive load the power factor will be bad. Microwave oven transformers aren’t designed to be used without a load, they’ll draw too much no-load current and overheat. It may sound strange, but it is because the self-inductance of the primary is too low. The shunts are to increase the self-inductance a bit without adding more primary turns, and a load on the secondary reduces the total flux.

            So I’d add primary turns before using a microwave oven transformer like this.

  2. Forgive my ignorance, but what is he spraying on the round plate at about 1:24? Is it for preparing the surface for weldment, or just paint to register the square tubing’s desired position on the plate?

      1. If the welder knows what he or she is doing and the material is clean, the correct process and settings are used spatter should be minimal and any that occurs should easily be knocked off with a chipping hammer. The tubs of “goop” for dipping a hot “gun” in are handier, safer and cheaper than sprays and there is less cleanup to do on the metal prior to priming/painting.

  3. Nice build, the only things I would change is add a second transformer core in parallel for more current and machine the tips accept commercial available spot welder tips. Tips often need to be take out or changed out for different kinds of work, plus they are not just generic pure copper, they are usually a harder alloy.

    Something better to hold the tip would help too. You really want the tips to come into contact with their faces parallel to the sheet metal and line up with each other. The cathead bolt arrangement will just make that tough to align.

  4. Wait how exactly will this kill you? Spot welders work at only a handful of volts, no where near the needed amount to overcome your body’s resistance and shock your heart with the nessesary amperage. TIG welding we get shocked all the time and it’s no big deal

  5. If you have an electric drill, bits and a MIG welder you already have a spot welder. Or rather a plug welder. And you can take those to the material instead of taking the material to the tool. Overall that thing looks like a brake rivet press.

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