What role does a contactor play in a circuit?
1. Provisions of Electric Vehicle Charging Equipment [GB/T 18487.1 4.4]:
Electric vehicle power supply equipment is classified according to output voltage:
AC: single-phase 220V, three-phase 380V;
DC: 200V-500V, 350V-700V, 500V-950V.
Preferred values of DC charging current: 80A, 100A, 125A, 160A, 200A, 250A.
Note: Power supply equipment with a voltage higher than 950V is determined by negotiation between the vehicle manufacturer and the power supply equipment manufacturer.
2. Application of DC contactors in new energy vehicles and charging piles (machines)
1. Application in charging piles (machines)
Used for the DC output side of DC charging piles, charging stations, or for the output side of vehicle chargers. When the contactor is closed, it connects the charging pile and the car; when it is disconnected, it isolates the charging pile from the outside world, providing safety protection. As shown in Figure 1
Application of DC contactors in new energy vehicles and charging piles (machines)
2. Application in electric vehicles
A DC contactor is installed between the battery system and inverter in an electric vehicle. It isolates the system when it stops and connects it when it is running. When the vehicle is shut down or a fault occurs, it safely disconnects the energy storage system from the vehicle's electrical system, breaking the circuit. It also serves as a power control device in other auxiliary circuits.
Application of DC contactors in electric vehicles
Important technical indicators:
a) Isolate the power supply and load ends after the system stops running; (Important technical indicators: rated insulation voltage Ui)
b) Connects the power supply and load when the system is running (important technical indicator: agreed thermal current Ith)
c) It plays the role of breaking the circuit in case of fault. (Important technical indicators: maximum operating voltage U)
3. Product Adaptability Design
1. Environmental adaptability design:
Different from general industrial contactor products, the operating environment conditions have more stringent requirements on the adaptability of contactors for electric vehicles. They must simultaneously meet basic conditions such as a wide temperature range, a high protection level, and high vibration resistance.
1) High and low temperature design: It must meet the temperature requirements for normal use of electric vehicles and charging piles (machines) in extreme weather conditions. The product storage environment temperature is -55~+125℃, the normal operating environment temperature is -25~+40℃, and the environment temperature under extreme conditions is -40~+85℃.
2) Protection level design: It must meet the requirements of normal operation under harsh environmental conditions and normal use in rain and dust environments. The product must completely prevent dust from entering and meet the requirements of short-term immersion in water. The protection level must reach IP67.
3) Anti-vibration performance design: The product must have strong vibration and impact resistance to meet the special needs of automobiles used in various road conditions.
2. Safety and reliability design
Safety and reliability are the first and most critical factors in measuring DC contactors for electric vehicles, which are mainly reflected in arc extinguishing capability, insulation voltage and other aspects.
DC arcs have no zero crossings, making them difficult to extinguish after ignition. This is achieved by designing a dual-breakpoint, direct-acting structure. This arc-extinguishing technology, which uses compressed gas in a sealed arc-extinguishing chamber, achieves excellent arc-extinguishing performance. The principle is that arc heating creates a high-pressure gas with the gas filling. The increased gas pressure significantly reduces thermal dissipation. The pressure difference between the arc gap and the arc-extinguishing chamber accelerates gas movement, intensifying the cooling effect and rapidly extinguishing the arc.
4. Special materials and key processes
The R&D and design of any product must rely on appropriate raw material selection, advanced manufacturing measures, stable component tooling, and a complete manufacturing process before it can be fully transformed into a product. Raw materials, manufacturing processes, and production lines are all key elements of design transformation.
1) Material property requirements for key components of electric vehicle DC contactors
Material name
Material requirements characteristics
The arc extinguishing chamber material is resistant to high temperature, has high electrical strength, high mechanical strength, good insulation performance, stable chemical properties and corrosion resistance.
The terminal is high purity, high conductivity, easy to weld, corrosion resistant and has good welding performance
The yoke is corrosion-resistant, has good oxidation resistance and high magnetic permeability
The arc extinguishing medium has stable performance and good arc extinguishing ability
Magnetic blown permanent magnets have stable performance, are not easy to oxidize, have good dielectric properties, and have high magnetic permeability.
The arc extinguishing chamber welding pad has a small expansion coefficient and good welding performance
Epoxy sealing materials are resistant to high voltage, impact, aging, high shear and peel strength, and high and low temperature.
Small shrinkage, small linear expansion coefficient, high bonding strength
The guide rails are wear-resistant, flame-retardant, resistant to high and low temperatures, and have good lubricity.
2) Key process design and equipment support
As a sufficient condition to ensure reliable product quality and stable performance, the manufacturing process must rely on certain hardware facilities to be guaranteed, with tooling equipment and production lines being the first to be affected.
1. Welding process and equipment:
Laser welding is a key process to ensure product quality and reliability. The main purpose of welding is to ensure a good sealing effect, protect the coils and contacts from oxidation and contamination, and ensure the stability of their contact resistance.
Laser welding technology is used to seal the arc extinguishing chamber, so that airtight welding is achieved between the arc extinguishing cover and the magnetic yoke, and between the magnetic yoke and the sealing sleeve.
The arc extinguishing chamber is tested for airtightness after welding to ensure it is leak-free during actual use. The welded contact system and the entire machine after glue filling are evacuated and inflated. After the workpiece is evacuated to a vacuum, it is inflated according to the gas type and pressure specified in the process, and the inflation port is automatically sealed.
Essential key equipment: laser welding machine, air tightness detection device, vacuum and inflation device.
2. Packaging technology and equipment
The glue filling process is one of the key processes for epoxy glue sealed contactors. The degree of bonding between the glue and the product body after glue filling and the density of the glue are key points that need to be guaranteed.
During the glue pouring process, air inside the product, bubbles within the colloid, and bubbles generated during the pouring process can affect the glue's penetration and density, ultimately impacting the product's sealing performance. A vacuum pouring system is used to completely remove all air from the glue tank and maintain a constant vacuum. Before pouring, the air inside the product is completely evacuated to a certain negative pressure before pouring. This negative pressure allows the glue to quickly and evenly penetrate the product. Bubbles generated by the pouring impact and contact between the glue and the product are also removed, ensuring even coverage of the glue on the product's contact surface and a uniform density, ultimately achieving optimal glue pouring results.
After the glue is poured, the product needs to be placed in a drying oven for curing. During the curing process, a constant and uniform temperature field is maintained, and a reasonable curing time and heating and cooling rate are used. This minimizes the curing internal stress and temperature internal stress, ensuring good curing and bonding effects, thereby achieving a good sealing effect.
Essential key equipment: glue filling machine, vacuum workbench, glue drying device.
3. Testing technology and equipment
A reliable electrical life of the contactor is a critical performance indicator, and the load failure test is the last guarantee before the product leaves the factory.
5. Product selection for special needs
1. For some charging cabinets that need to complete battery charging and discharging functions, you can choose to use a DC contactor product with non-polarity of the main contact, breaking through the structural design limitations of the lead wire specifically for current direction.
2. Choose the right wiring method based on the limited installation space
6. Market product overview:
At present, the mainstream products of electric vehicle contactors are mainly divided into two categories: ceramic cavity sealing structure and epoxy glue sealing structure.
Rated currents include 10A, 20A, 25A, 40A, 60A, 50A, 80A, 100A, 120A, 150A, 200A, 250A, 300A, and 400A. Control voltage ranges from 9 to 36VDC. Rated insulation voltage is 1000VDC, and interrupting voltage is 900VDC.
Conclusion
The consistency of electric vehicle contactor products impacts their reliability and stability, and product consistency permeates all product development processes: design, material consistency, component tooling stability, assembly process stability, and assembly tooling stability. By leveraging extensive knowledge and concisely absorbing key insights, and accumulating substantial experience, the successful development and mass production of electric vehicle contactor products from domestically produced national brands will provide product solutions more suited to the development of new energy vehicles in my country. These products will undoubtedly be a favorite among engineers designing new energy vehicles, charging stations, and other DC electrical equipment, providing strong support for achieving their design ideals.
