Make a Portable Spot Welder




Introduction: Make a Portable Spot Welder

What is up guys, In this instrucable I am gonna show you how to make a portable spot welding machine from and old microwave transformer and other scrap materials.

Step 1: Modifying Transformer

Hey guys, hope you are having a great day so far, so the first core element of a spot welder is a powerful transformer which we are gonna need to modify and replace a primarly coil with this 5-10 mm thick copper cable.

I clamped transformer into the wise and use a angle grinder to cut through the welds and then with a chisel lift a bottom part of the transformer .

After that I removed both coils from the steel core and try to be extremely careful when removing the first one because we are gonna still need it later on.

As you can see, when I punched the secondary coil out my core seperates but that is not such big of a deal, just carefully hammer back down the primarly winding and that is it.

Now , lets use our thick cable as a new secondary coil but this time we are gonna do just one revolution, which is gonna lower the output voltage and increase the amperage up to 100 amps.

After that I weld the cap back on and we are ready to test it out.

So I connect the transformer to a 220 v and hooly shit this thing is actually really powerful, it took just a few seconds to make a nail red hot.

Step 2: Enclosure Build

Now, lets continue with making the enclosure for the transformer.

I used some 4mm thick plywood, cut it down to a needed length and drill some holes for the switch and wires.

And yea, while we are working on the enclosure I leave my new printer to make a handle and legs for the spot welder.

After that I assembled everything together and we can proceed to the next step.

Step 3: Making Copper Tips

So last thing is to make some copper tips and I found the best way to do it is by getting a T- profile plug from a home improvement store and drill two holes for the screw that are gonna hole the main copper tip in place.

Then I press the plug hardly in a wise that is it. I also cut a few cm long copper rod, make a chamfer on one end, secure it into the plug with two screws and the spot welder is finished.

Step 4: Results

As you can see with the spot welder we can melt down lots of thing, mostly anything in the right size that is made from steel.

If you want to actually weld something together then you need to press both sheets very strongly together to make a strong bond between both materials.

Thank you for reading this instructable, if you have any questions, please leave them in the description below and also don't forget to check out a video tutorial at the end. Thanks :)

Step 5: Watch a Video



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    15 Discussions

    great instructable have you thought of dipping the transformer once made in varnish to make it quiet ?

    1 reply

    That is a great idea but I don't have any experience with varnish.. Do you think it would serve as a great sound-absorbing material?


    7 months ago

    Can it be modified as an arc welder?

    1 reply

    Yes, for sure! Just need to do a bit more turns instead of just one and that is it.

    Hey there,

    thanks for the 'ible! I really like your tip design! I'd just be worried that the thread would wear out rather quickly, did you face that problem yet?


    8 months ago

    Actually I have similar ideas to make both a typical spot welder but with extra heavy wire terminals to use independently in other areas. If you want some really easy to make spotting terminals, buy a copper or brass rod and you can turn them on a drill press or lathe to make any size point you need. Thumbs Up!

    2 replies

    Thanks for the tip :) And I found brass doesnt work fine as a tip because it has a much higher electrical resistance than copper, so copper is the best way to go. :)

    Yeah, I've been wondering about this as well. If you compare the resistivity of copper (1.68×10−8 Ohm/m) and aluminium (2.65×10−8) you see, that you would just have to slightly increase the radius of the according aluminium conductor to achieve the same resistivity as the copper conductor -- which might still be cheaper and less heavy. The reason copper would still be better, is apparently (I read that somewhere (dunno if true)) that any bar of the same resivitity as any compareable copper bar will have a higher inductance, thus effective AC resistance. This sounds quite logical to me, so accepted it for now. For the tip(s) specifically you want a very high conductivity (because it is the thinnest "piece of conductor"), while being not too soft (because good spot welder excert quite some pressure and you are producing some heat to boot), so most professional machines use some copper-alloy.,,,,,,,,,,