How to detect contactors with a multimeter? Contactor detection method
① Measure the resistance of normally open and normally closed contacts under normal conditions. The following figure shows the resistance of the normally open contact of an AC contactor under normal conditions. Since the normally open contact is in an open circuit state, the normal resistance should be infinite. The digital multimeter will display the symbol "1" or "OL" for exceeding the range during detection. When detecting the resistance of the normally closed contact under normal conditions, the normal measured resistance value should be close to 0 Ω. For AC contactors with linkage frames, pressing the linkage frame will close the normally open contacts inside and open the normally closed contacts. A multimeter can be used to check if this is normal.
② Detect the resistance of the control coil. The resistance of the control coil is shown in the following figure. The normal resistance value of the control coil should be several hundred ohms. Generally speaking, the higher the power of the AC contactor, the greater the suction force of the coil on the contact (i.e., the greater the current flowing through the coil), and the smaller the coil resistance. If the resistance of the coil is infinite, the coil is open circuited, and if the resistance of the coil is 0, the coil is short circuited.
③ Apply power to the control coil to detect the resistance of normally open and normally closed contacts. The following diagram is used to test the resistance of the normally open contact by energizing the control coil of the AC contactor. When the control coil is powered on, if the AC contactor is normal, it will make a "click" sound, and the normally open contacts will close and the normally closed contacts will open. Therefore, the measured resistance of the normally open contacts should be close to 0 Ω, and the normally closed contacts should be infinite (the digital multimeter will display the symbol "1" or "OL" when detecting). If there is no change in the measured contact resistance before and after the control coil is powered on, it may be due to damage to the control coil or jamming of the transmission mechanism.
