Spot welder from microwave transformer

  1. steve_s Member

    UK Derby
    Has any of you guys made a spot welder using a microwave transformer with any success ? got any pics or materials list ?
    Iv watched a good few youtube vids seems to be a fair few different methods.
    I'm wanting to join some 0.9 mild steel and it don't want a great slugs of weld on it
  2. bourbon Member

    Lichfield UK
    There have been threads on here about using micro wave bits. The overwhelming opinion is, DON'T DO IT.
    daleyd and like this.
  3. The_Yellow_Ardvark

    The_Yellow_Ardvark perkele

    I tried it a few years ago.
    1. It is a long winded way to do any type of welding.
    2. Yes it can be done, but it is also dangerous.
    3.The results vary from use to use.
    4.The transformer body gets hot and the metal hardens, so it looses efficiency.

    It was a fun thing to waste time, that's about it.
    slim_boy_fat likes this.
  4. eddie49 Member

    Portable spot welders normally run from 2 to 3 KW - I didn't think you could get that much out of a typical MOT ?
  5. I'm not sure if a microwave transformer would have a duty cycle long enough to do more than 1 spot weld at a time at the current needed for two 0,9 pieces. You may have to suck it and see. They are safe to make and this is a link to someone called Poroldchap. He's an old school TV engineer and is my sort of man cave bloke. He knows his stuff and will have a go at anything, just like me. Even when the 'experts' say you shouldn't/mustn't do it.

  6. I use one to do batteries with a special double pulse cycle timer that on the first short pulse softens the metal to bring it into good contact, then a longer pulse to do the final spot weld. Works as good as any commercial unit and is fully programmable for pulse time and interval between pulses. Makes battery pack a breeze to do.
    Hopefuldave and julianthegypsy like this.
  7. Member

    Essex England
    I wouldn't
  8. Ed. Member

    A few years ago I started making one out of a Microwave transformer but halfway through the project I decided to use a transformer from a 140A stick welder instead, I figured that the 600W microwave transformer wouldn't have enough grunt to do the welding I wanted to, so turned that one into a battery charger and the welding transformer works well for a spot welder. It can turn a 10mm bolt into a glowing mess in about 25 seconds.

    Added an electric timer, circuit breaker, cooling fan and an electronic relay, and to join 2 x 6mm stainless rod takes about 3 seconds/spot, used 2/0 welding cable for the secondary coil. The small Microwave transformers are good for light work such as battery tabs etc., but for heavier plate you need a larger tranny. If I was to do one again I would use a tranny out of a 180A or 225A welder, I used the 140A one only as I picked it up for $10.
    SteScouse, oddbob and Seadog like this.
  9. oddbob

    oddbob Member

    East Midlands
    I did the same as Ed, with a 140 buzz box,having played with a microwave jobbie and realised how gutless it would be. I had the advantage of having a dead cheap Chinese spot welder to use the arms and clamping mechanism from ...that was about three years ago, I use it regularly and it's still going strong.

  10. Why do some think it's dangerous or shouldn't be done? We would never discover anything if we had had H&S looking over our shoulders. You can be safely dangerous but dangerously safe is somewhat boring.
    steveo3002 likes this.
  11. The_Yellow_Ardvark

    The_Yellow_Ardvark perkele

    Mine was dangerous to those who did not know what they were doing.

    But I knew it was safe for me to play with and have fun.

    Not something I would be willing to do with other people near by.
    Alan Reynolds likes this.
  12. Natural selection then takes over. :)
    Hopefuldave likes this.
  13. Screwdriver

    Screwdriver Member

    UK London
    I bought a dead spot welder and fixed it. :dontknow:
  14. Ed. Member

    Your cables look nice and thick, here is a pic comparing my two transformers and also one pic after the wrap.

    I only had 70mm Square cable so did a double wrap of 3 turns so ended up with 4.68V.
    • both transformers size comparison B.jpg
    • Transformer wrapped with 2 Layers of 70mm 4.68V B.jpg
    oddbob and Hopefuldave like this.
  15. oddbob

    oddbob Member

    East Midlands
    I used 95mm2 flexible cable (600 odd strand copper), two turns (that's all I could manage with that cable!) that gave me around 2.5 volts. Sadly, I didn't take any pics of the build, but, as you will know, it's pretty straight forward to do. I also had every intention of fitting a timer, but, three years on, I still just rely on a 20amp microswitch tripped by the clamping mechanism.

    I originally tried it with the sliding shunt still in, hoping to have a variable amp machine, but it reduced the output to next to nothing even with it positioned right out.

    It's far more powerful than the burnt out Chinese thing it replaced, has never overheated (two axial fans working away) or tripped the mains.

  16. Yay! an alternative to the light dimmer :) That's the way to do it.
    skotl and oddbob like this.
  17. graffian

    graffian Seer unto the end of his beard

    I made a microwave tranny spot welder and made the steering box covers for my landy.

    Someone saw it and gave me a spot welder;-)
    DAPPH likes this.
  18. skotl

    skotl Forum Supporter

    Edinburgh, UK
    My guess is that people are concerned about the microwave components (which I would be, too!) but for this kind of projects it's just a transformer, so I don't see any additional risk due to it coming from a microwave :dontknow:
    Seadog likes this.
  19. Seadog

    Seadog Forum Supporter

    NE London - UK

    Why? They haven't used beryllium for yonks.
  20. Bsmith Member

    Leyland UK
    How about 2 microwave transformers in parallel for spot welder ?
    Alan Reynolds likes this.