The importance of Soft start on motor control


“Soft Start” is a function allowing one to gradually turn on an electronic device’s output until it reaches 100% output. This is commonly used in motor applications, in which a starting current value is suppressed to allow a smooth startup.

The above time chart example shows Omron’s G3J-T series Solid State Contactor in 3-phase motor applications. You may find that

  1. When the devices receives the signal from “Operation Indicator lit Monitor Output”, the load current will start to ramp up.

  2. Due to the device’s soft start characteristics, the load current will be controlled to ensure that the output remains within the rated current value according to the application.

  3. For some advanced controllers, the soft start time depends on the load characteristics (e.g. inertia and friction factor) in addition to the starting torque, ramp-up time and ramp down time. Therefore the soft start will not excessively extend due to the ramp up time being increased.