Soft Starters

Soft starters are motor starting devices that use thyristors to ramp up the voltage applied to an asynchronous motor, limiting the inrush current and mechanical shock. They are used on constant-speed loads such as pumps, fans, compressors and conveyors to reduce the voltage drop at start-up and the stress on belts and gears, and on pumps to reduce water hammer with a soft stop. This category includes Schneider Electric's Altistart and Altivar Soft Starter families; models from the ATS01, ATS22, ATS130, ATS430, ATS480 and ATS490 series are listed in rated currents such as 47 A, 140 A, 320 A and 590 A. Choose the device according to the motor's rated current and power, the mains voltage (for example 208-690 V), whether the start is normal or heavy duty, and the need for communication. For applications with long or frequent starts, the next current rating up may be required, so the manufacturer's selection table should be used. A soft starter does not adjust the motor's speed; it does not replace a frequency inverter in applications that need speed changes during operation.

Products

How to choose Soft Starters

Soft starters are motor starting devices that use thyristors to ramp up the voltage applied to an asynchronous motor, limiting the inrush current and mechanical shock. They are used on constant-speed loads such as pumps, fans, compressors and conveyors to reduce the voltage drop at start-up and the stress on belts and gears, and on pumps to reduce water hammer with a soft stop.

  • Separate sensing, motion control, logic processing and operator interface requirements.
  • Select signal type, supply voltage, communication protocol and I/O count for the machine network.
  • Verify housing size, sensing distance and PNP/NPN output polarity against the PLC input card.

Frequently asked questions

What is Soft Starters and where is it used?

Soft starters are motor starting devices that use thyristors to ramp up the voltage applied to an asynchronous motor, limiting the inrush current and mechanical shock. They are used on constant-speed loads such as pumps, fans, compressors and conveyors to reduce the voltage drop at start-up and the stress on belts and gears, and on pumps to reduce water hammer with a soft stop.

What should I compare when choosing Soft Starters?

Choose the device according to the motor's rated current and power, the mains voltage (for example 208-690 V), whether the start is normal or heavy duty, and the need for communication.

Where can I find technical details for Soft Starters products?

A soft starter does not adjust the motor's speed; it does not replace a frequency inverter in applications that need speed changes during operation.

Soft Starters Selection Guide: Technical Criteria and Engineering Practice