A relay is a device that can generate jumps in one or more electrical output circuits when the input quantity (or excitation quantity) meets certain specified conditions.
As an electronic control device, relays use media (tools) such as electricity, light, magnetism, heat, etc. (ie, input), and transmit and control circuits or signals (ie, output). The input loop) and the controlled system (also known as the output loop) couple the two loops through internal mechanical or electronic devices to realize the linkage of the two loop states.
Classification of relays
Automotive-grade relays mainly include signal type and power type. At present, all German car companies use power type relays. According to the different implementation methods, it can be divided into electromagnetic relays and solid state relays, and according to different output circuit voltages, it can be divided into low-voltage relays and high-voltage relays.
Relay classification list
● The role and use of high voltage relays
● The relays used in electric vehicles are structurally electromagnetic relays.
In electric vehicles, in addition to batteries and motors, high-voltage DC relays are also the core components of electric vehicles.The high-voltage DC relay switches and protects the charging and discharging lines of the battery to prevent equipment failure or open circuit. It can automatically detect and isolate the faulty line to prevent the scope of damage to the equipment from being further expanded. life.
A high-voltage DC relay is provided between the battery system of the electric vehicle and the motor controller. When the system stops running, the relay plays the role of isolation, and when the system is running, it plays the role of connection. When the vehicle is turned off or fails, the high-voltage DC relay can separate the energy storage system from the vehicle electrical system and play the role of separating the circuit.
Electric Vehicle HVDC Relay
The main applications of high-voltage DC relays in electric vehicles are: (DC voltage control) main relays, normal charging relays, emergency charging relays, high-voltage pre-chargers and safety control high-voltage auxiliary application relays.
According to specific models and different power systems, the number of relays used in vehicles also varies. On average, an electric vehicle needs to be equipped with 5-8 HVDC relays – 2 main relays, 1 pre-charging relay, 2 emergency charging relays, 2 normal charging relays and 1 high-voltage system auxiliary relay.
Typical structure of relay
Electromagnetic relays are composed of iron cores, armatures, coils, reset reeds and contacts.
Electromagnetic relays used in low-voltage systems have small switching and breaking currents, so they are not equipped with arc extinguishing devices. High-voltage relays are equipped with arc extinguishing devices.
Reed: There are two materials: copper alloy and stainless steel. Copper alloys have good conductivity and elasticity. The conductivity of stainless steel is not strong, but the elasticity is good.
In addition to the contact force between the armature and the iron core, considering the normal wear between the contacts, a contact pressure is also required to make the reed deform flexibly. There is a pressing force.
There are many subordinate parts of the relay, and its assembly process can be divided into two types.
The iron core is the center, insert the iron core into the skeleton, after winding the enameled wire on the skeleton, assemble the yoke, armature, reed and other parts, connect the resistance in parallel to the armature, install the whole semi-finished product on the bottom plate, and install the four parts. A lead wire is inserted into the other end of the bottom plate, and finally the casing is put on. This assembly process is based on the iron core and the center, and the parts are added one by one and installed.
Another way of assembling is to assemble the components into several “semi-finished products”/”small components”, and then integrate them at the end.
The bottom plate, the limiting piece, the lead wire, and the static contact are assembled into a “small assembly A”; the skeleton, the lead wire and the enameled wire are assembled into a “small assembly B”; the yoke, the lead wire, the iron core and the resistor are assembled into a “small assembly”. “C”; the armature, the moving reed, and the moving contact are assembled into a “small assembly D”. After the four small assemblies ABCD are matched with each other, the casing is put on.
How Relays Work
Electromagnetic relays are generally composed of iron cores, armatures, coils, contact reeds and other components. As long as a certain voltage is added to both ends of the coil, a certain current will flow in the coil, thereby generating an electromagnetic effect, and the armature will overcome the pulling force of the return spring and attract to the iron core under the action of electromagnetic attraction, thereby driving the moving contact of the armature. The point and static contacts (normally open contacts) are pulled together. When the coil is powered off, the electromagnetic suction will disappear, and the armature will return to the original position with the reaction force of the spring, so that the moving contact and the original static contact (normally closed contact) are attracted, so that the pull-in and release , so as to achieve the purpose of conducting and cutting off in the circuit.
For the “normally open” and “normally closed” contacts of the relay, the following distinction can be made: the static contacts that are disconnected when the relay coil is not energized become “normally open contacts”, and the static contacts that are in the connected state when the relay coil is not energized contacts, become “normally closed contacts”.
How “Normally Open” Electromagnetic Relays Work
Relay Mechanical Characteristics
When the relay armature moves, the relationship curve F=f(δ) between the overcome mechanical reaction force Ff and the armature stroke (working air gap) δ is called the mechanical characteristics of the relay.
Relay Mechanical Characteristics：
When the input quantity X reaches a certain value, the output loop electrical parameter Y produces a jumping change.
Suction process: X<X suction, Y=Y min;
Release process: when X>X is released, Y=Ymax; when X≤X is released, Y suddenly changes to Y min
