Hello everyone,
Yes that is an ssr relay I was using in the box triggered by the arduino nano I had. I ended up soldering the entire battery pack (40 Li-ION cells) successfully as well as adding a bms and creating my very own battery pack! The spot welder works great, i think by taking in everyones advice i significantly increased the quality, but i think the biggest change that really made the difference was using the two trigger method with very very short trigger times (5ms for first pulse, then 10ms for second). This avoided sparks/burning holes through the thin nickel strips. Also, the thicker tips were sturdier and I think provided a better welding contact, but i did make them a dull fingertip kind of shape instead of pointed or sharp. Pretty cool how you can make a pretty expensive and "precise" piece of machinery from an old microwave and some cheap parts

 

Recently I followed an instructables on building my own MOT spot welder, and the build went great. I am getting power from a normal home outlet, which is 120V and 15A, and I am getting out around 2 volts, so around 900A for the output of my second winding. I used a large gauged stranded wire for the second winding, and at the end of it, tied so smaller gauge solid wire that is around 2 mm thick as the soldering tips. I started out using it and it was going alright with decent and clean welds, and an occasional spark, with the nickel plate burned with a hole through by one of the copper tips. Now, everytime I try and weld with it at least one of the tips makes a spark, the surrounding weld has a black burn mark, and the nickel strip is burned straight through making a hole, so nothing ends up sticking to the battery well. I have tried reshaping the tips I am using and re-positioning them in so many different ways, but cant get a clean weld anymore. I have also tried changing the pulse time from 10-30 ms with the arduino im using as a timer, but shorter or longer pulses does not prevent the sparks and burns from happening. Any one have any idea why this could be happening and if I just got lucky with the weld I did on roughly 30 batteries?

 

You can use tungsten tig welding tips ( just buy one and cut it up) i use this for 3 years now and its a big difference it almost doesn't show pitting ( make it into a little bit dull point 1.5 to 2mm flat spot on the tip) and use a momentum switch or a pedal ( can do Arduino or something) pedal works fine for occasionally making a battery pack etc..

 

I came a cross this post because I have a similar problem, and a strange non-sense issue. I tired it with two turns in the secondary and doesn't work perfectly, but when I make it 3 turns I feel it more powerful which is against the calculation. I wish if I can get any explanation as it should be more powerful with two turns.

I'm on 110v for the primary, and two turns get me 1.3v while 3 turns 2.2v which should get me less current but it doesn't seem right.

Thanks