Saturday, May 7, 2011

A how to guide for the Control Circuit of a Forward Reverse Electric Motor Controller

Controlling the AC induction motor's rotation either in the forward or reverse direction with the push of a button is made possible by the forward reverse control circuit. The electrical diagram below illustrates the operational sequence of the forward reverse control system specific for the command of the forward reverse power circuit used in every electrical industry involving industrial process automation control technology.


Forward Reverse Motor Control Circuit
Forward Reverse Motor Control Circuit
The forward reverse motor control circuit consists of two DOL motor controller circuit which are connected side by side to accommodate the required forward and reverse function of the system.

Note that the control circuit incorporates an interlocking contact inserted between the push button and the contactor coils of each circuit to prevent the simultaneous activation of both forward and reverse contactor coils at the same time.

Pressing the forward push button will activate the forward contactor coil which will close a corresponding contact connected across the forward push button switch which is intended to latch the circuit to allow the operator to release his finger from the switch while maintaining the forward contactor circuit locked, with the motor continuously running uninterrupted in the forward rotation.

Consequently, the activation of the forward contactor coil would also open the interlock contact connected before the reverse contactor coil, which provides a safety measure that prevents electricity to pass through to the reverse contactor coil in case of an unintentional switching of the reverse push button switch while the forward contactor is energized.

In a similar manner, when the reverse contactor coil is energized in the first place with the pressing of the reverse push button switch, its associated contact placed as an interlock before the coil of the forward contactor will also be opened, hence preventing any incidental power flow to reach the forward contactor coil, thus, avoiding any simultaneous activation of both forward and reverse coil at the same time.

Changing the rotation of the motor regardless of whether it is actively running in the forward or the reverse direction is made possible by firstly pushing the the STOP push button switch to release the locked status of any energized coil, the OFF push button refreshes both forward and reverse circuit to OFF state which would return all contacts to their initial ready state, awaiting command from the forward or reverse push button switch.

The thermal overload contact serves as a safety disconnect switch that disengages any energized coil in order to shut down the motor upon detection of overload current driven by the motor.

The forward reverse motor control circuit presented above controls the forward reverse power circuit presented in the previous article.

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