What Are the Differences Between Online, Bypass, and Built-in Bypass Soft Starters?

Published: September 27, 2024

Soft starters play a critical role in controlling the starting process of AC motors by gradually applying voltage, which minimizes electrical and mechanical stress. Among the various types of soft starters, solid-state versions can be categorized into three main types: online soft starters, bypass soft starters, and built-in bypass soft starters. Each of these types has its unique characteristics, advantages, and disadvantages that cater to different applications and operational needs. In this article, we will explore the distinctions between these three types.

Online Soft Starters

Overview

Online soft starters operate without the need for a bypass contactor, allowing them to provide continuous protection from startup through operation until shutdown.

Advantages

Reduced Space Requirements:

No additional bypass contactor is needed, minimizing installation space, which can be beneficial in compact environments.

Lower Initial Costs:

The absence of a bypass contactor reduces overall cabinet costs, making online soft starters an economically attractive option.

Disadvantages

Heat Generation:

The entire operation occurs within the soft starter, leading to significant heat generation, which can affect the lifespan of internal components.

Limited Versatility:

Online soft starters may not be as adaptable in complex systems requiring more dynamic control.

Bypass Soft Starters

Overview

Bypass soft starters incorporate an external bypass contactor that engages after the motor has reached a certain speed. This design allows the motor to run directly off the supply, bypassing the soft starter during normal operation.

Advantages

Improved Heat Dissipation:

After the startup phase, the bypass allows the soft starter to handle only the detection circuits, significantly reducing heat buildup and extending service life.

Continued Protection:

Various protective functions remain active even after the motor has switched to bypass mode, ensuring that the motor is safeguarded against faults.

Disadvantages

Increased Size:

The inclusion of high-current contactors can lead to a larger overall cabinet size, which may not be ideal for all installations.

Complex Wiring:

The requirement for additional components can complicate the wiring and installation process, potentially increasing setup time and cost.

Built-in Bypass Soft Starters

Overview

Built-in bypass soft starters integrate the bypass functionality within the soft starter unit itself, eliminating the need for an external contactor. This type combines the features of both online and bypass soft starters.

Advantages

Simplified Wiring:

The built-in design streamlines the wiring process, making installations clearer and reducing the number of required components.

Compact Size:

By eliminating the need for an external bypass contactor, these units can occupy less space, allowing for more efficient use of available cabinet space.

Comprehensive Protection:

Built-in bypass soft starters offer a wide array of motor protection features, ensuring that both the motor and the soft starter are safeguarded against malfunctions.

Disadvantages

Potential Complexity in Design:

While wiring is simplified, the internal design may become complex, requiring precise engineering to ensure all functionalities work seamlessly.

Cost Considerations:

Although space and installation costs may be lower, the initial investment in built-in bypass soft starters can be higher due to the integrated technology.

Conclusion

Choosing the right type of soft starter is crucial for optimizing the performance and longevity of AC motors. Online soft starters are ideal for simple applications where space is a premium. Bypass soft starters offer versatility, although they may require more installation space. Built-in bypass soft starters strike a balance by combining the advantages of both types while simplifying wiring and offering extensive protection features.

By understanding the differences between online, bypass, and built-in bypass soft starters, you can make informed decisions tailored to your specific operational needs and ensure efficient motor control in your applications.