Protective circuit for control of capacitor motor - has monitoring relay which drops out, independently from mains voltage fluctuation, when speed drops and/or on excessive torque

摘要

The protective control is speed and/or load dependent, and the motor concerned has several phase windings, and can be connected to the mains through a switch monitored by a relay. The motor (M) or its capacitors (9) is in a secondary circuit (17) with a rectifier (G12) controlling the mains switch relay (18) with a control resistor (R5) and a Zener diode (ZD3). In order to compensate for mains voltage fluctuations, a stabilising circuit (12) - with a voltage divider (14) - is provided, so that the relay (18) drops out, when the motor (M) is connected to the mains - independently from mains voltage fluctuations - and relay holding voltage value is not reached owing to drop in motor speed and/or excessive torque.