Friday, May 6, 2011

A how to guide for the Control Circuit of a Direct On Line DOL Electric Motor Controller

As mentioned in the previous article, the Direct On Line (DOL) control circuit is an electrical control system which is intended for controlling the DOL power circuit. The electrical schematic diagram below illustrates the operational system of the DOL control circuit used in every electrical industry involving industrial process automation control technology.

Wiring Diagram DOL Motor Control Circuit
DOL Motor Control Circuit
The DOL control circuit consists of a combination of switches and auxiliary contacts where the operational behavior of the main contactor coil relies from.

When the RUN push button switch is pressed down, the control circuit is complete which causes the electricity to proceed down to the coil of the main contactor, this activates all contact points of the main contactor including the three pole open contacts previously shown on the power circuit which  when closed would result in a current flow going directly to the motor terminals to run the motor.

The drawing above shows the open auxiliary contact from the main contactor connected across the RUN push button switch which provides a holding contact to maintain the main contactor coil energized even after the release of the RUN push button switch, thereby allowing the motor to run uninterrupted without having to keep the RUN button pressed down continuously.

The control circuit provides two interrupting contacts, one is the OFF push button switch which is manually pressed by a human operator to stop the motor when necessary, and another one is the thermal overload contact which automatically opens the control circuit upon detection of motor overload current.

The DOL motor control circuit discussed above controls the DOL power circuit presented in the previous article.

To facilitate for a further understanding about the concept of the DOL electric motor control circuit, a flowchart diagram is provided to serve as a schematic representation of the sequence of operation of the DOL electric motor control circuit.

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