Simple capacitor spot welder

Spot welder circuit view

Schematic of a simple capacitor spot welder. The circuit was tested. Works well.

Discharge energy is adjusted by changing the supply voltage (10...20V dc) obtained from the bench power supply.

The P-channel MOSFET (eg. IRF9540 ) is used to turn off the SCR. The P-MOSFET doesn't need heat sink.

In most applications the 33R 10W resistor also doesn't need heat sink. 

In the prototype the SCR was THOMSON TK1204 type.

Capacitors bank C contained 12 x 4700uF/25V 105'C. The capacitance can be increased for higher discharge energy.

The LED and 2,2k resistor warns that capacitors are charged and discharges them after switching off the power supply.

The 1N4002 diode protects the bench power supply.

Bold lines mark high current path and the connections should be done using a thick copper wire or plate.

Use protective glasses while testing/ using welder.

The circuit is presented for educational purpose only.