Abstract: An electronic motor protection system which protects electric motors against various fault conditions such as over-temperature (12) of the individual windings of the motor and low voltage (18, 20). The system has a power supply compatible with 24, 120 or 240 VAC input voltage using only two input terminals. According to a first embodiment, line voltage is inputted to a transformer (T1) while the combination of a zener follower (Z1, Z2, Q1) and series regulator (U1, Q2, Q3) provide independent DC voltage supply levels or voltage rails (VR1, VR2) for control circuitry over a wide range of input voltages. A dead-band voltage range is provided by a circuit section (20) which works in conjunction with a 240 volt, low voltage cut-out circuit section (18) to prevent the possibility of chatter in 240V motors and excessive voltage from being applied to 120 volt motors.

Abstract: A thermally actuatable auxiliary switch (10, 10', 100) used with a refrigerator compressor system (60) has a generally U-shaped bimetallic element (12) mounted at one end on a base plate (16, 16', 102) and with a movable contact (28) mounted on the high expansion side (12a) of the bimetallic element in alignment with a stationary contact (32) mounted on a stationary contact support (18, 18', 116). A thermal generator (34) in the form of a PTC pill (36) wire-wound resistor (28), or other electrically energizable heater or in the form of a discharge tube (60e) of a compressor, provides heat to the bimetallic element (12) causing it to deflect after the solid state starter (50) has switched to its high resistance state to switch out the solid state starter while the compressor motor remains energized.

Abstract: Electrical terminal pins (start, main and common) mounted in a glass header to provide electrical connection to a compressor motor are shown with a motor protector disposed on one of the pins in such a fashion that opposite-direction-oriented right angle female flag quick connectors are required for the start and main terminals, thereby avoiding the possibility of miswiring the terminal pins. The opening temperature of the motor protector is adjustable and the protector has a fail safe mechanism to avoid subjecting the motor to overtemperature conditions.

Abstract: A motor protector having a thermostat metal element thermally coupled to an electrical motor in a refrigerator compressor motor system has a heater responsive to motor current thermally coupled to the thermostat metal element and has an improved component arrangement to provide locked rotor and ultimate trip protection for the motor without requiring calibration of the operating temperature for the protector after assembly or after incorporation in the motor system.