A motor starter or controller is essentially a device providing motor protection, with which you can both stop and start your motor safely. Motor starters prevent or mitigate electrical overloading by controlling your application's electrical output when you turn it on, or when the device engages. A motor starter is similar to a relay, switching the power on and off, but it also operates as a fail-safe device to de-energise your motor if an overload occurs.
Motor starters or controllers come in various types and styles, and each type has its specific function in industrial control. They're typically activated with an inbuilt electromechanical device, known as a contactor. However, other methods of activation can also be used, including soft starts and variable speed drives (VSD). The most frequently used motor starters, however, are of the electromagnetic type, and these are also known as direct on line (DOL).
DOL starters are the most common type of single-speed starters used in industry for starting a three-phase induction motor. They have built-in protection devices to prevent overload, and sometimes also condition monitoring. They're usually activated by a selector switch, or a push-button on a PLC or digital control unit, and are used with full voltage reversing and non-reversing motor controllers.
Full voltage, non-reversing motor starters (FVNR) have three fixed line phases and a single contactor, enabling a motor to rotate only in one direction. The single contactor can only turn the motor on or off by opening or closing the power circuit. On start-up, the full line voltage goes direct to the motor, but the in-built overload protection prevents this high inrush of current from causing damage. FVNR starters are also called across the line (ATL) controllers.
Full voltage reversing motor starters (FVR), on the other hand, have two contactors that allow the device two separate actuating states. Instead of just turning the motor on or off by means of a single contactor, FVRs have both a forward and a reversing contactor. This allows a three-phase motor to operate in both directions, simply by swapping over the contactor connection.
Motors can also be started by a third method known as reduced voltage starting. This limits the inrush current when the motor first starts and gradually increases it to operating speed. This group of motor starters includes soft starters and Variable Speed Drives (VSDs). Soft starters use a simple solid-state power controller, which increases or decreases the motor voltage gradually so as to make start-up and shutting off smoother and eliminate electrical surges. A Variable Speed Drive (VSD) is very similar, but instead of just turning the motor on and off, it controls the motor speed constantly and adapts it for any change in conditions.
We have a good selection of motor starters available at Rowse Automation, mostly manufactured by Siemens. They come in a range of sizes and configurations, including power settings from 0.1A to 32A, and from 0.09kW to 15kW. We can supply both direct online starters and reversing starters, at 24V AC or DC control voltage or at 110-240V AC/DC.