Overload protection for capacitor split- phase motor - has induced voltage in unexcited winding compared with DC reference and microprocessor to initiate relay if threshold exceeded

摘要

The capacitor motor (start-and-run-type) has two windings, one for each direction of rotation, and a single phase voltage supply for each. A potential divider chain from the supply terminal for each winding to earth has a zener diode and suppressor capacitor across the earth-side resistor of each. The voltage across one earth-side resistor is proportional to the stator voltage of the active winding and the voltage across the other earth side resistor is proportional to the induced voltage in the respective unexcited winding, and therefore motor torque. These voltages are compared with reference DC voltages obtained by rectification from the mains and a microprocessor initiates a transistorised relay if motor torque exceeds a threshold. ADVANTAGE - Simple, inexpensive and space-saving method for motor protection against overload.