Loss Voltage Protection For Electric Hoist

The control circuit of electric hoist consists of circuit breakers, transformer, terminal block, a control handle button, thermal relay, wire, slip lines and other electrical components. There must be loss voltage protection and undervoltage protection in the control circuit.

When the power is temporary blackout and then recovery of power supply, self locking control circuit will not switch on. Because the self-locking contact of  contactor has been disconnected. There is no current through the contact coil. The normally open contact will not be closed. So the motor will not start working by themselves. It means that it could avoid accident occur. This protection is called loss pressure protection.

When the line voltage drops, the motor torque will be reduced. At this time, the speed will be dropped, too. This has an influence on motor working. Certainly if the voltage has been dropped seriously, it may damage the motor. When the power supply voltage is reduced to a certain value and click the operation button, the flux of contactor coil will be weaken, the moving iron core will release, the normal open auxiliary contact will be disconnected and even loose self-locking function. At the same time, the main contact will be disconnected, too. So the motor has been gotten effective protection.