Saturday, May 7, 2011

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

There are certain applications that requires forward and reverse direction of motor rotation, such as a conveyor system, or perhaps the opening and closing of valves. Another example is with overhead cranes which would also require a hoist up and down function, traverse forward and backward, and a left and right traveling function. Such application would most certainly make use of a forward and reverse motor control which is intended to achieve clockwise and counter clockwise motor rotational direction.

power circuit of a forward reverse motor controller
Forward Reverse Power Circuit
The electrical schematic diagram on the right which features a CAD drawing provides an illustration of the power circuit of a forward reverse motor controller used in every electrical industry involving industrial process automation control technology. The diagram appears similar to the DOL motor controller except for an additional reverse contactor connected in parallel across the forward contactor.

The main circuit breaker is the main power supply switch that provides power to the line side terminals L1, L2, L3 of the two contactors, awaiting for any of these two contactors to close to deliver the voltage to the terminal of the motor U1, V1, W1 in order to run the motor.

The forward contactor is configured in such a way as to run the motor to its normal forward rotation with L1 connected to U1, L2 to V1, and L3 to W1. Whereas the configuration of the reverse contactor is wired in contrast to the configuration of the forward contactor so as to provide a reverse rotation of the motor, with L1 to W1 instead U1, then L3 to U1 instead of W1, while maintaining L2 connected to V1.

The thermal overload relay provides motor overload protection which detects motor overload current to shut down the control system of the forward reverse motor controller. The forward reverse motor control circuit controls the forward reverse power circuit which is presented and discussed in the next article.

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