A small improvement on the ordinary refrigerator motor starting circuit

The ordinary refrigerator motor starting circuit is generally composed of a secondary winding and a thermistor (PTC) in series. This motor starting circuit has two disadvantages: (1) the PTC is in a high-temperature blocking state for a long time, which greatly shortens its life; (2) when the secondary winding stops working, the PTC is also in a power-on state, wasting energy in vain. In response to the above problems, a delay circuit was designed to improve the motor starting circuit. The actual use effect is satisfactory. The circuit is shown in the attached figure.

The 220V mains is stepped down by capacitor Cl, half-wave rectified by diodes D1 and D2, filtered by capacitor C2 and limited by voltage regulator DW, providing a DC voltage of about 12V to the delay circuit. When the motor power is turned on, because the voltage on C3 is zero, the compound tubes T1 and T2 are turned off, the normally closed contacts of relay JK are still connected, and the main and auxiliary windings of the motor are powered on and started. R2 charges C3, and after a delay (slightly longer than the motor starting time), the voltage on C3 rises to about 1.8V, T1 and T2 are turned on, relay JK is powered, and the normally closed contacts jump open, thereby completely disconnecting the starting circuit from the mains. After turning off the power of the refrigerator, the +12V voltage disappears quickly, T1 and T2 are turned off, and relay JK returns to the normally closed state to prepare for the next start-up. By changing the parameters of R2 and C3, the length of the PTC working time can be adjusted, which is generally set to 10 seconds.

During production, Cl uses a 0.68μF/400V CBB capacitor, C2 uses a 220μF/25V aluminum electrolytic capacitor, and C3 uses a tantalum electrolytic capacitor with low leakage (220μF/25V); Dl and D2 both use 1N4007 silicon rectifier diodes, D3 and D4 use 1N4148 switching diodes, and DW uses a 12V/0.5W voltage regulator tube, such as 1N5242; Rl uses a 470kΩ/0.5W carbon film resistor, and R2 preferably uses a 680kΩ/0.5W five-color ring metal film resistor; Tl and T2 use 9014 or 3DG6 low-power transistors; JK uses a JQC-3F relay.