How to choose a soft starter?

1. First, confirm whether the motor is a squirrel-cage asynchronous motor.

Asynchronous motors (also known as induction motors) are divided into squirrel-cage type and wound type according to the rotor structure. 

Soft starters are mostly suitable for induction squirrel-cage motors.

2. Understand the parameters on the motor nameplate.

For example, the model of the motor, rated current, rated power, etc. 

Generally, the capacity of the soft starter is slightly larger than the working current of the motor.

3. Load type.

For light loads, models can be selected in accordance with the standard configuration.

For some heavy loads, consider choosing a model one size larger than the standard configuration. Such as: crushers, ball mills, elevators, long belts, air compressors, Roots fans, etc., and consider heat dissipation factors and protection functions.

● Centrifugal pump load: Soft start comes with pump control function. Reduces system "water hammer" caused by fluid shock during starting and stopping. Preferably with underload protection or phase reversal protection.

● Fan load: Use the soft start function to reduce belt wear and mechanical impact, and use the braking torque function when stopping.

● Loads such as mixers, crushers, elevators, etc.: Use the soft start with double ramp start and preset low speed operation to avoid mechanical damage.

● Conveying equipment load: The soft start and preset low speed function are used to realize smooth start and stop. The soft stop eliminates the anti-inertia impact of the drag system caused by the free stop, and avoids product displacement and liquid overflow.

4. The soft starter is mostly installed in the cabinet. Know the size of the soft starter and whether the bypass is built-in.

Bypass type: When the motor reaches the rated number of revolutions, the soft starter that has completed the task is replaced by a bypass contactor, which reduces the heat loss of the thyristor and improves its working efficiency. It is also possible to use a single soft starter to start multiple motors.

No bypass type: The thyristor is in full conduction state, and the motor works in full voltage mode, ignoring voltage harmonic components, and is often used for motors that repeatedly work for a short time.

In general, when choosing a soft starter, the rated parameters and load type of the motor should be considered comprehensively.