Motor controllers

Motor controllers range from a simple switch to a complex system that uses solenoids, relays and timers. The basic functions of a motor controller are to control and protect the operation of an engine.

This includes starting and stopping the engine, and protecting the engine from overcurrent, low voltage and overheating conditions that could cause engine damage.

There are two basic categories of motor controllers:

  • The manual driver and
  • The magnetic controller.

Manual controller:

A hand controller is a controller whose contact assembly is operated by a mechanical link from a lever-type handle or a push-button arrangement. The controller is operated by hand.

The manual controller is provided with thermal overload and direct acting units to protect the motor from overload conditions. The manual controller is basically an “ON-OFF” switch with overload protection.

Manual controllers are normally used in small loads such as machine tools, fans, blowers, pumps and compressors. These types of controllers are simple and provide silent operation.

The contacts are closed simply by moving the handle to the “ON” position or by pressing the START button. They will remain closed until the handle is moved to the “OFF” position or the STOP button is pressed. The contacts will also open if the thermal overload trips.

Magnetic Controller :

A large percentage of controller applications require the controller to be operated from a remote location or to operate automatically in response to control signals.

The magnetic controllers allow to control the motor from remote location. The basic operations that use a magnetic controller, such as the closing of switches or contacts, are carried out by means of magnetic contactors. A magnetic controller is one that will automatically perform all operations in the correct sequence after closing a master switch.

The magnetic contactor consists of an electromagnet and a moving iron armature on which movable and stationary contacts are mounted.

When there is no current flow through the electromagnetic coil, the armature is held away by a spring. When the coil is energized, the electromagnet attracts the armature and closes the electrical contacts.

The overload devices are incorporated in the magnetic controllers. These overload devices protect the motor from overcurrent conditions that could be extremely damaging.


Instrumentation Engineer

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