Using inverters in electric motors

In electric motors, inverters can play a crucial role in regulating performance and efficiency. An inverter, also known as a variable frequency drive (VFD), is a device that converts alternating current (AC) to direct current (DC) and then back to AC at a desired frequency and voltage.

This conversion process allows for precise control of motor speed and torque, making inverters essential for applications requiring variable speed operation.


What is the difference between inverters and soft starters?

Soft starters and inverters are key components in electric motor control, each serving distinct functions.

Inverters offer comprehensive control over the motor’s speed and torque by adjusting the frequency and voltage of the AC supply. The inverter can provide a smooth start and stop of the motor, as well as providing speed control. This capability not only enhances energy efficiency but also allows for more precise and adaptable motor performance.

In contrast, a soft starter is designed to reduce the inrush current and gradually increase the voltage supplied to the motor, enabling a smooth start and stop only. This helps in minimizing mechanical stress and extending the lifespan of the motor.

Both devices are critical for motor protection and control, ensuring optimal operation across various industrial applications, and your options will depend on your industrial needs. While the inverter, or VFD, is the more expensive solution for stopping and starting the motor, its energy efficiency and speed control provide benefits in many applications.

Differences between inverters and soft starters

Feature Inverters Soft starters


Converts AC to DC and back to AC for precise speed control           Gradually increases voltage to reduce inrush current and ensure smooth start

Speed control

Provides variable speed control Does not offer speed control

Energy efficiency

High, due to precise control Moderate, primarily reduces starting current
Applications Suitable for applications needing variable speed and torque Ideal for applications requiring a gradual start
Cost Higher Lower
Complexity More complex installation and operation Simple installation and operation

How do inverters work?

Inverters operate by converting the incoming AC power to DC and then inverting it back to AC at a controlled frequency and voltage. This process allows for precise control over the motor’s speed and torque, enabling it to adapt to varying load conditions.

Inverters are particularly useful in applications where energy efficiency and variable speed are paramount, such as in HVAC systems, conveyor belts, and pump operations.

How do soft starters work?

Soft starters function by gradually ramping up the voltage supplied to the motor, which limits the inrush current and reduces mechanical stress during startup, thus the name “soft start”. This gentle increase in voltage helps in avoiding abrupt starts that can damage the motor and connected equipment.

Soft starters are typically used in applications that require a smooth start but do not need variable speed control, such as in compressors, fans, and mixers.

Soft starter vs inverter: which is better for your application?

Choosing between a soft starter and an inverter depends on your specific industrial needs and applications.

Here are some considerations to help you decide:


  • Precise speed control
  • Higher energy efficiency
  • Suitable for applications needing variable speed and torque

Soft starters:

  • Cost-effective
  • Simple to install and operate
  • Ideal for applications requiring a gradual start

If your application demands precise speed control and energy efficiency, inverters are the better choice. However, if you require a cost-effective solution for a smooth start without the need for speed control, soft starters are the ideal option.

At Hoyer, we provide both soft starters and inverters to cater to diverse industrial needs, ensuring optimal motor performance and protection.