Relay News

A subminiature power relay is an electrical switch that is designed to control high power circuits in a compact and lightweight package. The subminiature designation refers to the relatively small size of the relay, which allows it to be used in applications where space is limited.

Everyone may have used electromagnetic appliances or other electromagnets in production practice. For comrades who often use these electrical components, they will definitely have such experience: when the voltage applied to the coil is constant, the farther the armature is from the core column, that is, the larger the air gap, the smaller the force it receives, The smaller the air gap, the greater the suction: if you want to increase the suction at a certain air gap, you must increase the voltage across the coil (if allowed).

In the power control relay the return spring and the contact spring are made of circular or sheet-like elastic materials (such as spring steel wire, tin bronze, phosphor bronze, brass, German silver, silver magnesium nickel, etc.). When it is mechanically deformed, it has a certain elasticity. We all have this feeling in practice, the greater the deformation of these springs, the greater the elastic force it produces: the smaller the deformation, the smaller the elastic force; no deformation, that is, the spring is in a free state, and no elastic force is generated. Further experiments and theoretical analysis show that: within a certain range, the size of the elastic force (F) is proportional to the size of the deformation (X). Mathematically expressed as: F=CX

We know that in a power control relay with contacts, the main task of the contacts is to "open" and "close" the circuit, so there are only two forms of movement: "divide" and "close". This "opening and closing" movement of the contact system is mainly based on the combined action of the force generated by the return spring (or reed) and the mechanical force transformed by the external input signal (this is the force in two opposite directions). Completed. That is to say, only when the input signal is small enough that the mechanical force converted by it is smaller than the force of the return spring,

Above, we start from the different working states of the power relay contacts, and focus on analyzing its contradictory essence in each working stage. However, the power relay contact itself is a whole, and the tasks specified in each stage are completed by the same power relay contact. Moreover, the characteristics of the different stages of work in the same whole are interconnected, influenced and contradicted each other. For example, the welding that may occur when the power relay contacts are working in the closed state will cause it to fail to achieve the disconnection process, so it is not possible to break the circuit; and the arc or spark that occurs when the power relay contacts open and close the circuit. The destructive effect will cause it to fail to conduct the circuit normally and reliably in the closed state.

In addition to ensuring reliable arc extinguishing, the distance between the dc power relay contacts when the dc power relay is disconnected should also be able to withstand sufficient circuit voltage without being broken down, that is, the dc power relay contacts must have sufficient dielectric strength, which is necessary for the dc power relay contacts to be disconnected.

Closing the power relay contacts is not an easy task. Because when the dynamic and static power relay contacts collide, there will be no mechanical wear, and the power relay contacts will bounce or bounce back. When it bounces, a series of short electric or sparks will be generated, which will make the circuit unable to be connected accurately and cause high-frequency interference. In severe cases, the power relay contacts will be burned or even a fusion welding accident will occur. There will be a bounce, which will drive the power relay contact to bounce back, and the distance will increase, and the impact will be more serious.

​Experiments have shown that when the current disconnected by the relay contacts is small, there will not be a large amount of gas decomposition and arcing between the relay contacts. However, if the inductance in the circuit is large (usually there is always a certain inductance in the circuit), a high overvoltage will appear on the inductance when it is disconnected, and it will be added to the relay contact gap together with the power supply voltage. If this voltage is large enough (greater than 270~300 volts), it will cause the relay contact gap just separated by a little distance to break down and discharge. Due to the small energy of the power supply, this discharge cannot develop into an arc and disappear immediately, which is called "spark discharge", as shown in Figure 2-4.

In production or daily life, we often use certain electrical appliances such as knife switch power relays, contactors, etc. to disconnect the circuit, and we often observe such a phenomenon when disconnecting the circuit: a dazzling spark appears between the contacts, Sometimes it is fleeting, sometimes it lasts for a certain period of time. This is what we usually call a "spark" or "arc". Its appearance will seriously affect the normal breaking of contacts, reduce its service life, and even cause more serious accidents. Therefore, we must carefully analyze the characteristics and laws of its production and development in order to try to eliminate it.

When the latching relay contacts work in the closed state, in addition to some faults caused by the above-mentioned contact resistance, an accident called "cold welding" often occurs in miniature latching relays, especially reed latching relays. can't be togetherfreed. The cause of this cold welding is generally considered to be that the contact surface of the contact is under the action of pressure or slip, the surface film is destroyed, the direct metal contact area increases, and the total affinity between metal molecules increases.

The contact resistance of power relay is an objective phenomenon, which can not be avoided at any contact. However, when we understand its essence and grasp its characteristics, we can further analyze its influencing factors and take corresponding measures to reduce or eliminate its impact.

Are these hazards of contact resistance manifested in any case? no, it isn't. Because the occurrence of this hazard is closely related to the circuit parameters closed by the contact. Different circuit parameters lead to different properties and hazards of contact resistance. For example, when the contact is used to close the circuit with high voltage and current (such as high-power power relay, contactor, etc.)