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Wont work with a welder. You need a transformer that will take 120 volts up to 10k to 15k volts. I use a oil burner ignition transformer I bought from walmart's online for 48 plus tax.
Using a microwave transformer is way too dangerous. You can find a transformer that has high voltage and less amps. It's not the volts that kill you it's the amps. Do your homework....search for safe practices....it may save your life