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Posted on 2nd Feb 2024

The pros and cons of soft starters

Lenze Drive

According to CM Industry Supply Automation Lenze Drive & Keb Drive Supplier, Soft starters are devices used to gradually ramp up the voltage and current supplied to an AC motor during startup, rather than applying full voltage immediately. They offer several advantages and disadvantages:


Reduced Mechanical Stress: Soft starters help reduce mechanical stress on motors and connected equipment by gradually ramping up the voltage and current during startup. This can extend the lifespan of the motor and decrease maintenance costs.

Smooth Startup: By gradually increasing the voltage and current, soft starters provide a smooth and controlled startup process, minimizing torque and current peaks. This reduces the risk of equipment damage and mechanical wear.

Elimination of Inrush Current: Soft starters effectively eliminate inrush current, which occurs when a motor is started at full voltage. Inrush current can cause voltage drops, electrical disturbances, and nuisance tripping of protective devices.

Energy Efficiency: Soft starters can improve energy efficiency by reducing the power demand during motor startup. By avoiding sudden voltage surges and current spikes, they help prevent unnecessary energy consumption and reduce electricity costs.

Controlled Acceleration and Deceleration: Soft starters offer adjustable acceleration and deceleration times, allowing precise control over the motor's speed changes. This enables smoother operation and better control over conveyor systems, pumps, and other motor-driven equipment.

Compatibility with Various Loads: Soft starters can be used with a wide range of AC motor types and loads, including induction motors, synchronous motors, and variable torque loads. They are suitable for applications in industries such as manufacturing, HVAC (heating, ventilation, and air conditioning), and water treatment.


Limited Control: Soft starters provide basic control over motor acceleration and deceleration but may not offer the same level of functionality as variable frequency drives (VFDs). They do not allow for continuous speed control or dynamic adjustments during operation.

Higher Initial Cost: Soft starters typically have a higher initial cost compared to traditional direct-on-line (DOL) starters. However, the potential savings in energy consumption, maintenance, and equipment longevity may offset this initial investment over time.

Reduced Starting Torque: Soft starters may result in a slight reduction in starting torque compared to full-voltage starting methods. While this may not be a significant issue for many applications, it's essential to ensure that the motor can provide adequate torque to meet the load requirements.

Limited Diagnostic Capabilities: Soft starters may have limited diagnostic features compared to VFDs. They may not provide detailed monitoring or fault detection capabilities, making it more challenging to diagnose issues and troubleshoot problems.

Not Suitable for Constant Speed Applications: Soft starters are primarily designed for applications that require controlled acceleration and deceleration. They may not be suitable for applications where the motor needs to operate at a constant speed or requires precise speed regulation.

Heat Dissipation: Soft starters dissipate heat during operation, which may require additional cooling measures, such as ventilation or heat sinks, especially in high-power applications.

Overall, soft starters offer significant advantages in terms of reducing mechanical stress, minimizing inrush current, and improving energy efficiency during motor startup. However, they may have limitations in terms of control flexibility and diagnostic capabilities compared to VFDs. According to CM Industry Supply Automation Lenze Drive & Keb Drive Supplier, The choice between soft starters and other motor control methods depends on factors such as the application requirements, budget constraints, and desired level of control and monitoring.