Clever spot welding machine circuit

1. This spot welder has three levels of power adjustment and a fine adjustment knob. The circuit design is clever and the production is not complicated. Its working principle is capacitor energy storage and discharge type. After the power is turned on, the pulsating DC half-wave voltage obtained through D2 is clipped and stabilized by D3, and then sent to the SCR1 main trigger circuit and the other to the SCR2 auxiliary trigger circuit. The main function of the auxiliary trigger circuit is to adjust the charging voltage of the C6 and C7 capacitors (control the output power) by adjusting the fine-tuning potentiometer W3 or the coarse-tuning switch SW2. The voltage on C6 and C7 passes through R9, W3., SW2 A voltage divider is formed, and the voltage signal picked up at the center tap of W3 is sent to the base of comparator BG2 for comparison with the clipping voltage sent to its emitter. If it is less than its value, BG2 is cut off. At this time, SCR2 is turned on under the control of the relaxation oscillator composed of BG1, and C6 and C7 are charged through D1 and SCR2. When the voltages on C6 and C7 reach the set value, BG2 is turned on, the relaxation oscillator composed of BG1 stops working, and the charging of C6 and C7 ends. D4 is a clamping diode, used to force BG1 to stop oscillating when the welding button AN is pressed.

2. Transformer B1 uses a 4cm×5cm iron core, B2 uses the same core area, the primary winding is 98T with Φ2mm enameled wire, and the secondary winding is 8T with 0.6mm×8mm flat copper wire.

3.Adjustment