A soft starter is an electronic device used to control the starting and stopping of electric motors, particularly those with high power ratings. It reduces the initial current surge, also known as inrush current, that occurs when a motor is started directly across the line. Soft starters help to minimize mechanical stress on the motor and the connected load, as well as prevent voltage sags in the power supply.

The primary function of a soft starter is to gradually ramp up the voltage applied to the motor during the starting process, rather than applying the full voltage instantaneously. By doing so, it limits the starting current to a preset level, typically around 30-60% of the motor's full load current.

Here's how a soft starter works:

1. Start Ramp-U : When the motor is energized, the soft starter gradually increases the voltage applied to the motor. This ramp-up process typically takes a few seconds.

2. Current Limiting : During the ramp-up, the soft starter ensures that the motor current stays within the predefined limit, preventing excessive current draw.

3. Full Voltage : After the ramp-up period, the soft starter reaches full voltage, allowing the motor to run at its rated speed.

4. Bypassing : Some soft starters have bypassing mechanisms that engage once the motor reaches its full speed. In bypass mode, the soft starter is essentially bypassed, and the motor is directly connected to the power supply for more efficient operation.

Soft starters offer several advantages, including:

1. Reduced Mechanical Stress : By gradually ramping up the voltage, soft starters reduce the mechanical stress on the motor and mechanical components, extending their lifespan.

2. Minimized Inrush Current : Soft starters help prevent voltage drops and disturbances in the power supply by limiting the inrush current during motor starting.

3. Smooth Motor Start : The gradual voltage ramp-up results in a smoother and controlled motor start, avoiding sudden jerks or torque spikes.

4. Energy Savings : Limiting the starting current can lead to energy savings, especially in applications where frequent starts and stops occur.

Soft starters are commonly used in various industrial applications, such as pumps, fans, conveyors, compressors, and other heavy-load equipment. They are especially beneficial in applications with high starting torque requirements, where reducing the inrush current is essential for smooth and controlled motor operation.