Do you know the relay contact protection and contact matters?

Release time：

2022-10-31 09:47

We know that the contact protection of relay is more cruel than Mosfet, and the load of ordinary relay is much larger than Mosfet. Typical DC large capacity DC motor, DC clutch and DC solenoid valve. When these inductive load switches are closed, surges caused by hundreds or thousands of volts of reverse electromotive force may shorten or completely damage the contact life.
Of course, if the current is small (for example, near 1A), the back EMF will produce arc discharge, which will pollute the contact with metal oxides, thus causing damage to the contact and increasing the contact resistance. It is pointed out here that the relay will fail sooner or later. We mainly protect the contact to prolong the service time of the relay, because the contact will always deposit carbon and age, and its surface is not as clean as it was.
When the service life of the relay approaches the later period, the contact resistance increases rapidly. Under normal room temperature and pressure, the core dielectric breakdown voltage of air is 200~300V. Therefore, our goal is usually to control the voltage below 200V.
We generally have the following centralized methods to suppress:
1. Relay contact protection circuit - relay series RC circuit
2. Relay contact protection circuit - relay parallel RC circuit
3. Relay contact protection circuit - relay parallel diode circuit
The standard diode greatly extends the return time, and the connection of ordinary diode and zener diode has little effect on the return time. For inductive load, when the contact is separated, the arc generation time will be prolonged and the contact life will be shortened. For example, a relay with a diode connected to a coil takes 9.8 milliseconds to release the contacts. If the Zener diode is combined with the small signal diode, the time will be shortened to 1.9 milliseconds. The return time of the relay with no diode connected to the coil is 1.5 ms.
Electrical relay contact protection circuit - relay series RC circuit: electrical contact protection

relay,contact

Switching capacity of electric contact

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Type of contact

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Disconnectable contacts are an indispensable part of switching appliances. According to their different structures, they can be divided into the following types: (1) Knife contact: it has a simple structure and can be divided into surface contact and line contact, which are widely used in low-voltage switches and high-voltage disconnectors. (2) Butt joint contact: It has the characteristics of simple structure and fast action, but the contact surface is unstable and varies greatly with the pressure. It is easy to rebound during operation, without self-cleaning effect, and the contact is easy to be burned by electric arc. This contact is usually used for distribution circuit breakers with rated currents below 1000 A and below 500 A

Contact of nanomaterials

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