Understanding the role of current limit in soft starters

An essential feature within some soft starters is the 'current limit.' This functionality enhances operational efficiency and ensures the safety of electric motors by regulating the power surge typical at startup.

What is a current limit in soft starters?

The 'current limit' in a soft starter is a crucial control feature that helps regulate the motor's initial voltage upon startup. The current limit works by gradually increasing the voltage to a predefined level and maintaining it throughout the start phase.

It essentially sets a maximum current level that the motor can draw. If this threshold is reached, the soft starter temporarily suspends the voltage increase until the current falls below the set limit, then resumes ramping up to full voltage.

This controlled approach significantly reduces mechanical stress on the electric motor and other connected components, thereby extending the equipment's overall life.

Soft starter with and without current limit

When equipped with a current limit, a soft starter carefully manages the motor's start-up phase. It begins by applying a low initial voltage and gradually increases this voltage, closely monitoring the current. If the current reaches the predefined limit, it stabilises the voltage supply before safely ramping up, ensuring a balanced start without undue stress on the motor.

In contrast, a soft starter without a current limit feature applies a constant or step increase in voltage without regulating based on the current drawn. This can lead to spikes in current that may cause excessive mechanical stress and early wear on the motor and electrical components, potentially leading to higher maintenance costs and downtime.

Read more about soft starters in electric motors.

Why choose a soft starter with current limit?

• Smooth start and stop operations: Ensures that the motor ramps up to speed gently, minimizing mechanical shocks.
• Extended motor lifespan: Reduces wear and tear on motor components, ensuring longer service life.
• Reduced energy consumption: Optimizes power use during start and stop phases, lowering operational costs. Read more about optimising energy usage with electric motors here.
• Improved safety and reliability: Enhances overall system safety, preventing damage and reducing downtime.

Soft starter or VFD?

When deciding between a soft starter and a Variable Frequency Drive (VFD) for your motor applications, it's important to understand the key differences and benefits of each solution.

Soft Starter:

A soft starter is designed primarily to manage the startup and shutdown phases of an electric motor. By gradually increasing the voltage, a soft starter reduces mechanical stress and peak current draw. This is particularly beneficial in applications where a gentle ramp-up is needed, reducing wear and tear on both the motor and connected equipment. Soft starters are typically more cost-effective than VFDs and simpler to install and maintain.

VFD:

A Variable Frequency Drive, on the other hand, offers more advanced control over motor speed and torque. VFDs can vary the motor's speed continuously by adjusting the frequency and voltage supplied to the motor, making them ideal for applications requiring precise speed control and high energy efficiency throughout the operation. This makes VFDs suitable for variable load applications, such as conveyors, pumps, and fans, where the ability to adjust motor speed can lead to significant energy savings.

You can read more about the differences between VFDs and soft starters here.

Do you need a current limit in your soft starter?

Are you consistently facing issues with high start-up currents or mechanical stresses in your motor applications? Implementing a soft starter with a current limit might be your solution.

This feature is particularly advantageous in scenarios where:

• Motors are frequently started and stopped.
• There is a need to minimize electrical and mechanical stress to extend the equipment's life.
• Operations are in environments where consistent and reliable performance is critical.

To determine whether a current limit is necessary for your specific application, consider the operational demands of your machinery, the nature of the load, and the consequences of current spikes. Consulting with experts like us at Hoyer can provide you with tailored advice, ensuring that you select the most appropriate motor control solution for your needs.

By understanding the benefits and functionalities of current limits in soft starters, businesses can make informed decisions that enhance efficiency, safety, and reliability in their industrial operations.