Tag: dc contactor

DC reversing contactor is a switching appliance suitable for remote manipulation (closing, opening or switching) of high-power electrical appliances. The contactor is used in electric vehicles, and the coil consumes a large amount of power, which is generally used for intermittent duty. DC contactors are mainly used for making and breaking DC circuits at a long distance and frequently starting, stopping, reversing and reversing braking DC motors, and also for frequently connecting and disconnecting lifting electromagnets, solenoid valves, clutches electromagnetic coils, etc.

Iron core of the AC contactor is usually laminated by silicon steel sheet, so as to reduce the eddy current and hysteresis loss generated by alternating magnetic field in iron core, avoid the iron core overheating. However, iron core in the DC contactor's coil would not generate eddy current and there is no heating problem in DC core, so the iron core can be made of a complete cast steel or cast iron. Coil of DC circuit has no inductance, so the coil has more turns, thus leading to large resistance and copper loss. In order to keep a good heat dissipation for the coil, the coil is generally made into a thin and cylindrical shape. Coil of AC contactor has less turns and small resistance, but the coil also gives heat, so the coil is generally made into a fat and short cylindrical shape. Meanwhile, a clearance is left to facilitate heat dissipation while avoiding the coils from being burned out. In order to eliminate vibration and noise generated by electromagnet, a short circuit ring is embedded on the surface of static iron core of the AC contactor, while the DC contactor doesn't need a short circuit ring.

As equipment to disconnect load power, selection of contactor should meet requirements of controlled equipment. Except that the rated operational voltage is the same with the rated operational voltage of controlled equipment, load power, usage category, control mode, operation frequency, working life, installation method, installation dimension and economy of controlled equipment are the basis of selection. How to choose a right contactor? The principles are as follows: