Why can't the output end of the frequency converter be connected to a contactor?

Today we will talk about why the output end of the frequency converter cannot be connected to a contactor? This is because when the VFD started and reaches a certain frequency, the contactor will not pull in and a large starting current will appear causing the frequency converter to trip or damage the frequency inverter device.

If a contactor must be connected to the output end of the frequency converter, one principle must be followed: start the AC contactor first and then start the frequency converter. Because the frequency converter starts from zero, the frequency is very small when starting and the current of the motor will also be very small, so there will be no impact on the frequency converter.

Pay attention when installing contactors and other switching devices at the input and output ends of the frequency converter:

1. The frequency converter does not allow frequent power outages, but it does not mean that a contactor cannot be installed at the input end.

When installing a contactor at the input end of the frequency converter, the frequency converter fault output self-locking or the host computer fault self-locking must be used. The purpose is that when the frequency converter or the host computer is working normally, the frequency converter allows output and cannot directly cut off the power after each operation. If there is a fault in the inverter or the host computer that affects the operation safety, the self-locking circuit is disconnected and the inverter is powered off and the operation output is prohibited, thereby improving safety!

2. The output of the inverter has a certain timing.

In order to prevent the motor from stalling, it often operates with a delay star closing circuit and a motor brake circuit. If there is no output contactor, it will increase the risk of output adhesion, and the motor will break when it stalls. Not opening the drive circuit is fatal. The control method in Figure 1+2 is Not allowed and are all wrong! 

                                                                  P1

It seems to be a normal circuit diagram. Press start to power on the inverter, press stop to power off the inverter, and the motor stops, but in fact it is not allowed! Explain the reason: "If a contactor is installed between the power supply and the input end of the frequency converter, it is not allowed to use this contactor to control the start and stop of the frequency converter. The contactor must be used to control the start and stop of the frequency converter, and the interval should not be Less than one hour because frequent charging and discharging can easily reduce the life of the capacitor in the inverter."

                                                         P2

When the start button is pressed, the motor and inverter are connected and the motor starts. When the stop button is pressed, the motor stops and is disconnected from the inverter! It seems like there is no problem, but in fact it is not advisable! If you are not careful, the inverter will be damaged. If you insist on using this control method, you should pay attention to "" If there are switching devices such as contactors between the output end and the motor, make sure that the inverter is on and off when there is no output. operation, otherwise it will easily cause damage to the module inside the inverter. "We can use the multi-function terminals of the inverter itself or the panel to start and stop the motor!