Electronic motor protection system

Abstract

An electronic motor protection system which protects electric motors against various fault conditions such as over-temperature (,) of the individual windings of the motor and low voltage (,). 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 (T,) while the combination of a zener follower (Z,, Z,, Q,) and series regulator (U,, Q,, Q,) provide independent DC voltage supply levels or voltage rails (VR,, VR,) for control circuitry over a wide range of input voltages. A dead-band voltage range is provided by a circuit section (,) which works in conjunction with a 240 volt, low voltage cut-out circuit section (,) to prevent the possibility of chatter in 240V motors and excessive voltage from being applied to 120 volt motors. The motor is protected by means of an output relay (K) being de-energized upon detection of a fault condition which energizes an adjustment circuit (,) to stabilize the load seen by the power supply transformer. According to a second embodiment input voltage level is detected by comparator circuitry (U,A) in the secondary side of a transformer (T,) which switches contacts of a double pole, double throw relay K,to switch first and second primary transformer windings (TP,, TP,) from a parallel configuration when exposed to 120 VAC to a series configuration when exposed to 240 VAC.