This is my version of a DIY ... spot welder controller. It is intended for use with a modified microwave oven transformer, but may suit other applications too. I have included the PCB Gerber files, ...

This Spot Welder can be used to weld 18650 batteries. It uses a 12V car battery as welding current supply. Typically one 60Ah 600A battery delivers enough current to get good welds with 0.15mm - 0.2mm ...