Some soft starters need to be configured with an external bypass AC contactor to realize the work after the normal start of the soft starter, and the motor operation is completely borne by the AC contactor. To determine whether the bypass AC contactor is good or bad, you can see whether the coil ends of the contactor have normal working voltage. Generally, the bypass AC contactor coil is 380V. There is a drawing voltage, the three-phase main contact will automatically draw, but because the soft starter controls the three-phase AC circuit, the long-term operation of the motor with large power will also cause contact oxidation or ignition resulting in poor contact.
You can choose to use a multimeter to measure whether there is three-phase line voltage at the input end of the AC contactor, and then quickly measure whether the three-phase line voltage at the output side of the AC contactor is normal in the suction state. In addition, when the high-power motor is running, do not remove the arc extinguishing cover of the contactor to run, which will cause serious accidents. After the AC contactor is removed, it can be seen whether it is drawn when it has a normal working voltage, and whether the contact point of the three-phase main contact is good to judge its quality.
Soft starters need to be equipped with another bypass contactor, and through simple wiring, so that the combination of the two, but when the transformer capacity of the working condition is small, the external bypass contactor often cannot work normally.
