How to test a contactor with a multimeter?
The contactor is tested using the electrical barrier of a multimeter. The testing process is as follows:
①Detect the resistance of normally open contacts and normally closed contacts under normal conditions. Detect the resistance of the normally open contact of the AC contactor under normal conditions. Because the normally open contact is open under normal conditions, the normal resistance should be infinite. When testing, the digital multimeter will display the out-of-range symbol "1" or "OL". When testing the resistance of a normally closed contact under normal conditions, the normally measured resistance value should be close to 0Ω. For AC contactors with linkage brackets, when the linkage bracket is pressed, the internal normally open contacts will close and the normally closed contacts will open. You can use a multimeter to check whether this is normal.
②Detect the resistance of the control coil. Detect the resistance of the control coil as shown in the figure below. The resistance value of the control coil should normally be several hundred ohms. Generally speaking, the greater the power of the AC contactor, the greater the attraction force of the coil to the contacts is required (that is, the force required to flow through the coil is large current), the coil resistance is smaller. If the resistance of the coil is infinite, the coil is open circuit; if the resistance of the coil is 0, the coil is short circuit.
③ Energize the control coil to detect the resistance of the normally open and normally closed contacts. The figure below shows how to energize the control coil of the AC contactor to detect the resistance of the normally open contact. When the control coil is energized, if the AC contactor is normal, it will make a "click" sound. At the same time, the normally open contact is closed and the normally closed contact is opened. Therefore, the measured resistance of the normally open contact should be close to 0Ω and the normally closed contact should be is infinity (the digital multimeter will display the out-of-range symbol "1" or "OL" during detection). If the measured contact resistance does not change before and after the control coil is energized, it may be that the control coil is damaged or the transmission mechanism is stuck.
