Abstract: In view of the non-supplying of softener quality incidents in the drop pump of the XQG-RBD1401Ea1 heat pump washing and protecting machine of our company. The injection pump does not operate because the reverse impulse voltage generated by the injection pump motor exceeds the withstand voltage of the solid state relay after it is turned off, according to the analysis. Without the circuit for absorbing the reverse voltage, which leads to the breakdown of the solid state relay. By adding a resistance-capacitance module to the pump wiring harness to absorb the peak voltage, the controlled solid state relay is added with a varistor at both ends for clamping voltage, so that the reverse voltage is reduced by rectification. After the rectification, the reverse voltage is within the withstand voltage range of the solid state relay, and the whole machine is qualified.

Key words: Heat pump washing and protecting machine, Drop pump, Reverse voltage, Solid state relay