Abstract: A water pump protector unit which includes electrical circuitry through which an electric motor is energized. The pump protector unit is primarily adapted for operation of a capacitor-start induction-run electric motor which operates a water pump. The electrical circuitry includes components for energization and deenergization of the start winding of a capacitor-start induction-run electric motor. The electrical circuitry senses the phase angle between the voltage and the current applied to the electric motor. When the phase angle indicates that the electric motor is operating without a load, the circuitry deenergizes the electric motor. Thus, the water pump is protected against damage which may occur when the water pump is operated without pumping water. Preferably, all of the components of the water pump protector unit are housed within a single cabinet.

Abstract: An electrical circuit for providing electrical energy to an electric motor which operates a liquid pump. The motor and the pump are adapted to be submerged in the liquid which is pumped by the pump. The circuit disclosed herein senses the phase angle between the current and the voltage applied to the electric motor. When the phase angle indicates that the motor is operating without a load, the circuit deenergizes the electric motor. Thus, the motor and the liquid pump are protected against damage. Recognizing that harmonics may exist in the current flow through the motor, the circuit provides for obtaining a filtered signal proportional to the fundamental frequency of the current flowing through the motor. Thus, an accurate measurement of the loading of a motor is obtained. The circuitry of this invention also provides an accurate method of compensation for applied line voltage variations, so that a change in the applied line voltage does not produce a false indication that the motor loading has changed.

Abstract: A water pump protector which includes electrical circuitry through which an electric motor is energized. The electric motor operates a water pump. The circuitry senses the phase angle between the voltage and the current applied to the electric motor. When the phase angle indicates that the motor is operating without a load, the circuitry deenergizes the electric motor. Thus, the water pump is protected against damage which may occur when the water pump is operated without pumping water.