DC contactor
DC contactor refers to a contactor used in DC circuit, which is mainly used to control DC circuit (main circuit, control circuit, excitation circuit, etc.). The iron core of DC contactor is different from that of AC contactor. It has no eddy current, so it is generally made of mild steel or industrial pure iron. Since the suction coil of the DC contactor is connected with DC, there is no impulse starting current and no violent impact of the iron core. Therefore, it has a long life and is suitable for frequent starting and stopping. The selection of AC and DC contactors can refer to the electrical product catalogue according to the working voltage and current of the line. Selection mode of DC contactor. 1. Select the type of DC contactor The type of DC contactor shall be selected according to the type of load current and the weight of load, that is, AC load or DC load, light load, general load or heavy load. 2. Rated current of main contact of DC contactor The rated current of main contact of DC contactor can be calculated according to empirical formula IN main contact ≥ PN motor/(1~1.4) If the motor controlled by the DC contactor starts, brakes or reverses frequently, the rated current of the main contact of the contactor is generally reduced to one level for use. 3. Rated voltage of the main contact The voltage marked on the nameplate of the contactor refers to the rated voltage that the main contact can withstand, not the voltage of the suction coil, When in use, the rated voltage of the main contact of the contactor shall not be less than the rated voltage of the load. 4. The selection of operating frequency refers to the number of times the contactor makes and breaks every hour. When the making and breaking current is large and the making and breaking frequency is too high, it will cause serious overheating of the contact, even fusion welding. If the operating frequency exceeds the specified value, DC contactor with one higher rated current shall be selected. 5. Selection of coil rated voltage The rated voltage of the coil is not necessarily equal to the rated voltage of the main contact. When the circuit is simple and there are few electrical appliances used, 380V or 220V voltage can be directly selected. If the circuit is complex and the electrical appliances are used for more than 5h, 24V, 48V or 110V voltage can be used (36V, 110V, or 127V according to the international regulations in 1964) Working principle of coil and DC contactor: when the contactor coil is energized, the coil current generates a magnetic field, which makes the static iron core generate electromagnetic attraction to attract the moving iron core and drive the contact action: the normally closed contact is disconnected, and the normally open contact is closed. The two are linked. When the coil is powered off, the electromagnetic force disappears, and the armature is released under the action of the release spring to restore the contact: the normally open contact is disconnected, and the normally closed contact is closed.