Spot welder
Over the years I have seen a few ways of doing spot welder for battery packs: A bank of electrolytic capacitors One or more super-capacitors A modified microwave oven transformer A car or motorbike or LiPo battery But besides the power source, some sort of control is needed, as you are basically shorting the output of your power source and you do not want that to last long. The simplest thing to do is to use a pushbutton, but that is not very precise nor repeatable, so something like an electronic timer can work best. But if you want to provide more than a single pulse a microcontroller can be the best choice for a precise and repeatable switching of the power. And switching the power can be another source of trouble, especially if the switch is the high-current side. A spot welder can rush hundreds of Amperes and you need something more than a pushbutton to handle that. Some designs use a bank of MOSFET transistors to do the job (power dissipation is not huge due to th