Having created for my personal use low voltage/high amperage transformers myself to use for house repairs when need it and already knowing the danger of using too much voltage with hundreds of amperes (where the total power would rise well above 1.5kW) I wonder about this circuitry long term usability. I know from personal experience that melting metal using such a transformer is generating a lot of heat that goes back to your transformer isolation. And my transformer would be 1.75 V in secondary or as high I ever went was 2.25 volts. So reading this diagram that has hundreds of amperes at 12V seems highly unlikely. That would be over 2kW easily and using this more then 1 minute would definitely destroy the transformer at least. I use my transformers for maximum 5 minutes then I let them cool for 30 minutes on the cold concrete.