Analysis of the working principle of electrical relays and the phenomenon of contact rebound

In power and electronic control systems, electrical relays, as an important control element, play the role of signal amplification, isolation, conversion and protection. Its core working principle is based on the phenomenon of electromagnetic induction, that is, the closing and opening of contacts are controlled by electromagnetic force to achieve effective control of the circuit.

1. Basic working principle of electrical relays
electrical relays are mainly composed of coils, iron cores, contact mechanisms and other parts. When a certain voltage is applied to both ends of the relay coil, current will flow inside the coil. According to the law of electromagnetic induction, a magnetic field will be generated around the coil. This magnetic field will act on the iron core, causing it to be attracted toward the center of the coil. The movement of the iron core does not exist in isolation. It is usually connected to the contact mechanism, so the displacement of the iron core will drive the contact mechanism to move.

Relay contacts are divided into two types: normally open contacts and normally closed contacts. In the initial state, the normally open contact is in the open state, while the normally closed contact is in the closed state. When the iron core is attracted and moved by the magnetic field, the normally open contact will be forced to close, allowing current to pass; at the same time, the normally closed contact will be pushed open and the circuit will be cut off. This conversion mechanism enables the relay to flexibly control the on and off of the circuit, and realize functions such as remote control and automatic operation.

2. Contact bounce phenomenon and its causes
During the process of contact closing, a common problem is the contact bounce phenomenon. This is because when the moving contact and the static contact first contact, due to mechanical inertia, surface unevenness or electromagnetic force fluctuations, the contacts are uncontrolled intermittently disconnected and closed. This fast and unstable contact state will not only cause a short circuit interruption, but may also be accompanied by the generation of arcs.

The arc is a conductive channel formed by the ionization of gas in the contact gap under the action of voltage. It will generate high temperature and strong electromagnetic radiation, erode the contact material, and accelerate the wear of the contact. At the same time, the energy released when the arc is extinguished acts on the contact in the form of Joule heat, further aggravating the thermal damage of the contact.

3. The impact of contact bounce phenomenon
The contact bounce phenomenon has a significant impact on the performance and service life of the relay. Frequent contact bounce will cause an oxide layer or ablation pit to form on the contact surface, increase contact resistance, reduce conductivity, and even cause contact adhesion or failure in severe cases. In addition, the heat generated by the arc may also cause the internal temperature of the relay to rise, affecting the performance and stability of other components.

IV. Improvement measures
In order to reduce the contact bounce phenomenon and improve the reliability and life of the relay, the following measures can be taken:

Optimize contact design: Use high-quality and high-hardness contact materials, such as silver alloy, to improve wear resistance and arc resistance. At the same time, design a reasonable contact shape and contact area to ensure good contact effect and heat dissipation performance.
Add buffer mechanism: Introduce buffer springs or shock-absorbing materials in the contact mechanism to slow down the impact force when the contact is closed and reduce the possibility of bounce.
Use magnetic blow-out technology: Set a magnetic field around the contact, use the magnetic field force to lengthen the arc and extinguish it quickly, and reduce the damage of the arc to the contact.
Circuit protection design: Add components such as current limiting resistors and surge absorbers in the relay control circuit to limit the current peak and reduce the chance of arc generation.