Whether you’ve already purchased an electric motor or are still in the planning stage, familiarizing yourself with the different electric motor controls can help you maximize the productivity and efficiency of your operation while extending the service life of your motor, electronics, and all the mechanical assets connected to your motor.

Motor control is any switch or device used to start, stop, or control the speed of an electric motor. Because each application has unique objectives and operating parameters, it is often necessary to control the motor's speed and protect it from a variety of risks specific to your usage. To select the right control for your application, the first step is to take a look at what you need the motor to do, and then select the motor control that gives you the capabilities you require.

Soft Starters
If your motor will be started under substantial load, especially if it occurs frequently, there is a high risk of damage from the electrical and mechanical shock that occurs when full power is applied to a motor at standstill. Depending on the load, a motor may experience a current surge up to five times the rated level at start-up, which can damage sensitive electronics and overheat the motor windings, drastically reducing its service life. This current surge also makes the motor accelerate suddenly, causing mechanical shock that can damage the motor bearings, gearbox and driven load. Over time, this will greatly increase maintenance, operational downtime, and parts replacement costs.

It is highly recommended to install a soft starter to safely manage your motor's start-up process if your motor is started under a substantial load. The soft starter ramps up the power to the motor slowly, alleviating current surges and preventing overheating in the windings. This means that your motor will accelerate slowly and smoothly, protecting the motor, gearbox and load. You can also customize the soft starter's start-up parameters, including the time it takes to reach full speed, to suit your project needs.

When your electric motor is required to run at full speed all the time, a soft starter may be sufficient. However, to precisely control and manage your motor's speed during all phases of operation and respond to changes in operational conditions, speed control is necessary.

Speed Controls
Speed controls enable your electric motor's speed to be continuously adjusted to meet the requirements of your operation, giving you the ability to maximize efficiency and performance at all times. Speed controls can replace soft starters to safely bring an electric motor up to speed, maintain a specific speed or adjust to changing circumstances. They are often capable of providing dynamic braking, which is useful for quickly and smoothly bringing a heavy load to a stop. AC and DC speed controls operate on different principles, but they are designed to achieve the same result.

AC motor speed controls are commonly divided into two categories: Variable Frequency Drives (VFDs), and Vector Controls, also known as Field Oriented Controls (FOC). VFDs manage the speed of the motor by modifying the frequency of the power supply and are the most common and cost-effective way to control the speed of an AC motor. However, they lose precision at lower speeds and are unable to create holding torque in a motor.

Vector Control drives enable the speed of an AC motor to be precisely controlled over the entire speed range, even giving a motor capability to provide full torque at zero speed (holding torque). They achieve this by managing the motor's speed and torque separately, using a sophisticated control algorithm to produce the desired output. This enables servo-like control of an AC motor, a capability that was previously only available with DC motors. Vector Control drives are generally more expensive than VFDs, but their precise speed-control capability is essential for many finely-tuned, responsive electric motor applications. A special Vector Duty or Servo motor is needed for this type of drive.

DC motor speed control is much simpler, as it only requires management of the input voltage, which is usually achieved using a PWM voltage regulator. DC speed controls also provide good precision over the entire speed range of the motor.

Magnetic Starters
A magnetic starter is a device that enables an electric motor to be started and stopped safely, especially when operating a heavy load. Magnetic starters offer controls for the operator and safety protections to prevent damage to the motor in case of overload.

Magnetic starters consist of an electromagnetic contactor or switch and a thermal overload relay. The relay is usually closed manually by the operator pushing the start button. It is then held in a closed position by an electromagnetic force that can be automatically cut off when a hazardous situation is detected. The relay opens when excessive current passes through or overheating occurs, opening the switch and cutting off power to the motor to protect it from damage.

If you start your motor with a heavy load, or it experiences intermittent high load during operation, it is recommended to use a magnetic starter to protect your motor from damaging surge currents.

Summary
Selecting the right motor controls gives you the capability to fine-tune the productivity of your application and protect valuable assets from electrical and mechanical damage.

Here at eMotors Direct, we offer a comprehensive range of electric motors, gearboxes, and motor controls, giving you the components you need to build a complete package that meets all your performance objectives.