I will make a simple and Powerful spot welder using a few capacitors that can weld all the nickel strips effectively and powerfully without any controller or programming. capacitor pins take a copper wire from seven core wire solder the capacitors solder all the capacitors in parallel configuration now for a pack of four capacitors DC filter it will look like this I designed the PCB for easy assembly of the circuit. let's put all the components on the pcb according to the circuit diagram thank you and after spending some time with the soldering process i clean the pcb with isopropyl alcohol and here our pcb looks nice and now the capacitors we have assembled are clean first it needs to be connected to this filter circuit and soldered with the PCB now our circuit almost ready and all we need is a 909 volt Step-down Transformer Connect the transformer output wires to the filter connector and fix the connector with a screwdriver use small bolts for the output terminals use two mm of enameled copper wire to apply some flux to the ends of the welding probes and then pre-solder the copper ends then use 4mm multicore copper wire to solder with these copper tips. make it safer then connect welding rods with output terminals, connect Transformer to AC Source with nut bolt and now ready to test I am using this 18650 lithium battery and 0.3mm nickel strip for testing, as you can see it can weld strongly nickel strip to battery now let's test it on another battery, as you can see the nickel strip can be perfectly applied to the battery.