An AC contactor is an electrical device used to control the flow of current in a circuit. It uses its main contacts to open or close the main power circuit, while auxiliary contacts are used in the control circuit to manage the operation of the contactor itself.
The main contacts are typically normally open, meaning they only close when the contactor is activated. Auxiliary contacts, on the other hand, often include both normally open and normally closed contacts, allowing for more complex control functions. Smaller contactors can act as intermediate relays, helping to manage the main circuit by amplifying or switching signals.
The contacts of an AC contactor are usually made from silver-tungsten alloy, which provides excellent conductivity and resistance to high temperatures caused by arcing. This material ensures reliable performance even under heavy load conditions.
The operating power of the contactor comes from the magnetic field produced by the AC coil wound around a soft iron core. The core is made up of laminated silicon steel sheets shaped like a "mountain" to reduce energy loss. One of the cores is wrapped with a coil, and the voltage can be selected based on the application. To prevent vibration and instability, a short-circuit ring is added to the core’s surface. When the power is cut off, a spring mechanism helps reset the contactor.
The other part of the core is movable, designed similarly to the fixed core. It moves in response to the magnetic field, enabling the opening and closing of both the main and auxiliary contacts.
Contactors rated at 20 amps or higher come with an arc suppression cover. This component helps to quickly extinguish the arc that forms when the circuit is broken, protecting the contacts from damage and extending their lifespan.
These devices are capable of handling high-frequency operations. When used for turning power on and off, they can operate up to 1,200 times per hour without significant wear.
In terms of durability, AC contactors have a long service life—mechanically, they can last between several million to tens of millions of cycles, and electrically, they can handle hundreds of thousands to millions of operations before requiring maintenance or replacement.
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