Variable Frequency Drive VS Soft Starter

Overview

A large inrush current is usually required when an AC motor is accelerated to full speed while using a full voltage connection. In addition, the torque of the AC motor is pretty much uncontrolled and may shock the equipment that is connected, hence causing damage. Viable frequency drives and soft starters are equipment designed to reduce limit torque and inrush currents, protecting expensive equipment and extending the life of the motor as well as coupling devices.

Whether you need to buy a soft starter or a variable frequency driver will mostly depend on the type of your application. Also on your mechanical system requirements and cost.

Soft Starters

These devices help protect the motor and connected equipment from damage by keeping the terminal voltage at control. This restricts the initial inrush of current and minimizes the mechanical shock related with motor startup, providing a more gradual ramp up to full speed. These starters can also benefit electrical systems with limited current capacity by limiting the inrush current. Since a soft starter gradually increases the motor terminal voltage, a more regulated motor acceleration is also produced. Soft starters have also capabilities to provide a gradual ramp to stop where sudden stopping may result problems in the connected equipment.

Benefits of choosing a soft starter

Soft starters are generally a more economical choice for applications that only need torque and speed control during motor startup. Moreover, they are in most cases, the perfect solution for applications where space is a concern, as they usually take less space than other variable frequency drives.

Variable Frequency Drives

These drives are motor control devices designed to protect and control the speed of an AC induction motor. Also referred to as adjustable frequency drive a variable frequency drive can keep the speed of the motor at control during the start and stop cycle, as well as during the run cycle.

Benefits of choosing a variable frequency drive

These drives feature a fully adjustable speed; controlled starting, stopping, and acceleration; provides smooth motion for applications like escalators and elevators; offer dynamic torque control and maintain speed of the equipment. Plus they offer the versatility of been self-diagnostics and communications, having a PLC- like functionality and software programming, advanced overload protection, digital and analog input/outputs and relay outputs.

Variable frequency drives also offer the best energy savings for pumps and fans. Their adjustable flow method changes the flow curve and extremely reduces power requirements.

Selecting the right motor control equipment for your needs

Variable frequency drives are bigger and more expensive than soft starters, especially in large horsepower applications. Moreover, variable frequency drives also take up more space. As mentioned above choosing between a variable frequency drive or a soft starter well depend on your application.