Electrification of automobiles has driven development of high-voltage connectors. Unlike traditional fuel vehicles operating at voltages below 14V, new energy vehicles' three-electric systems require higher-power, high-voltage systems, such as multiple voltage levels ranging from 48V to 1000V and current levels from 10A to 300A. High-voltage connectors are a significant addition to new energy electric vehicles.
When operating, high-voltage systems discharge currents of tens of amperes, or even hundreds of amperes. A problem with a high-voltage connector can lead to overheating at best, and even high temperatures or combustion at worst. To prevent combustion, it's crucial to understand key design techniques and material selection for high-voltage connectors.

 

Connector Voltage Classification
Automotive connectors can be divided into low-voltage and high-voltage connectors based on their operating voltages. Low-voltage connectors typically operate at 12V, 24V, or 48V, while high-voltage connectors operate at 60 to 800V or higher. There are significant differences between two types of connectors in terms of design and internal structure.
Differences in Design
High-voltage and low-voltage connectors differ primarily in color and size. Low-voltage connectors are typically black, while high-voltage connectors are orange. This design distinction serves to remind users of voltage level they carry. Furthermore, because high-voltage connectors must handle high voltage and high current environments, they are often larger than low-voltage connectors to ensure safety and stability.
Development of high-voltage connectors for electric vehicles has paralleled development of electric vehicles. From a connector perspective, domestic electric vehicle connectors have transitioned from metal to plastic housings. Current mainstream application types are as follows:
1.1 High-voltage connectors with plastic, shielding, and high-voltage interlocking
Representative examples of this type of connector are 800 series products in industry (these products utilize a sequence of operations to achieve a partial secondary unlocking function, rather than a direct mechanical structure), such as those from TE, Amphenol, Zhilu, and new-generation domestic products.
1.2 High-Voltage Connectors with Plastic, Shielding, High-Voltage Interlock, and Secondary Unlock
Representative products include 280 series in industry, such as TE/Smart Green and new-generation domestic products. These products utilize a mechanical structure to achieve a secondary unlocking function, providing enhanced safety.

2.1 Temperature Rise and Derating Curve
Temperature rise is one of the most critical design considerations for connectors. Abnormal temperature rise can lead to connector burnout. High-voltage connectors also have derating curves that specify corresponding values for different currents and operating temperatures. Selecting appropriate connector based on operating conditions is an effective way to avoid abnormal temperature rise.
2.2 High-Voltage Interlock (HVIL)
This connector ensures integrity of the entire high-voltage system and activates vehicle safety measures when high-voltage system circuit is disconnected or its integrity is compromised.
High-Voltage Interlock (HVIL) plastic connectors are a type of high-voltage connector designed to effectively handle high voltage and high current environments. These connectors are more complex, featuring internal and external shielding rings and interlocking features, are essential components for electric vehicles and new energy systems. Its relatively large size is designed to ensure safety and stability during use.
2.3 Secondary Unlock
Typically, system's response time to interlock terminal circuit is between 10 and 100 milliseconds. When disconnection time of connection system is shorter than system response time, hot plugging and unplugging may pose a safety risk. Secondary unlocking is designed to address this disconnection time issue. Typically, secondary unlocking can effectively control this disconnection time to over 1 second, ensuring operational safety.
2.4 Electromagnetic Shielding
Electric vehicles contain numerous electronic devices, and current generates magnetic fields. Therefore, all vehicle components must be able to resist interference.
To improve connector shielding effectiveness, two approaches are generally used. First, some plastic connectors have a metal shielding cover inside. Cable shield is connected to metal shield, forming an effective 360° shield. Second, most high-voltage, low-current connections do not have a secondary connection and instead connect to cable shield. This approach is also commonly used by existing manufacturers.
Low-voltage connectors are commonly used in voltage environments below 30VAC (60VDC). Because electromagnetic interference is relatively low in these environments, electromagnetic shielding is typically achieved through twisted wiring or external aluminum foil wrapping. Shielding layer is crucial in high-voltage connector design, ensuring all-round electromagnetic shielding and guaranteeing stability of connector and conductors.
2.5 IP Rating
IP rating consists of two numbers: the first indicates degree to which appliance is protected against dust and foreign objects, while second indicates degree of sealing against moisture and water intrusion. Higher numbers indicate higher levels of protection.
Connectors can be categorized as sealed or unsealed based on whether they require sealing. For low-voltage connectors, sealing requirements vary depending on location of use, are generally classified into three levels: S1, S2, and S3. High-voltage connectors must meet specific IP ratings, and ratings of sealed connectors vary depending on environment in which they are used.

 

Connector insulation is typically made of materials such as PA66, PBT, PA6, and PC. Contact materials are typically brass, phosphor bronze, beryllium copper, and other materials, but copper-nickel-silicon is now more commonly used abroad. Connector housings are generally made of plastic or metal.
A connector's withstand voltage is primarily affected by multiple factors, including insulation material, creepage distance, and air humidity. Common connector materials on the market include PBT, PA66, PA6T, and PA9T, each with varying performance and price. Withstand voltage of high-voltage connectors is affected by multiple factors, including insulation material, and different voltage levels require different materials.
Following are key factors to consider when selecting insulating plastic materials:
Halogen-free flame retardant, 0.75mm V0 rating; CTI > 600V; RTI-E 0.75mm > 130℃; Orange RAL2003 complies with high-voltage system regulations; A certain degree of toughness provides additional safety margin during component assembly or vibration testing; Excellent dimensional stability after humidity conditioning and aging, ensuring IP67 or higher waterproofing; Stable material performance under various operating conditions, meeting US car class 2&3 (passenger cars) and class 4 (commercial vehicles) standards; Excellent injection molding performance, low volatility, low mold deposits, and good appearance
High-voltage connectors require V0 flame retardancy. With technological advancements, low-voltage connectors are evolving towards high-speed data transmission, lightweighting, miniaturization, and integration. In contrast, high-voltage connectors must not only meet basic requirements of traditional automotive connectors for plug-in/plug-out resistance and vibration resistance, but also cope with the severe challenges posed by high voltage and high current. These requirements are particularly stringent in terms of heat dissipation, high-voltage protection, and electromagnetic interference resistance, placing even greater demands on material selection. In the future, high-voltage connectors will need to cope with even higher voltages and currents, requiring even higher standards for material selection for further development.

 

Plastic materials are diverse, and different material companies develop their own product categories. For example, one company's plastic product pyramid (which varies slightly from company to company) boasts over 50 different types. Five common types are found in electric drive systems: PA6, PA66, PPA, PPS, and PBT.

 

To provide a comprehensive reference for plastic part design, we have compiled some typical applications of plastic parts in electric drive systems, including those from Tesla, BYD, Mercedes-Benz, Nidec, and Nissan.
1.1 Tesla

 

1.2 BYD

 

 

1.3 Mercedes-Benz

 

1.4 Nidec

 

1.5 Nissan

 

Choice of connector material varies significantly depending on application scenario. Below, we introduce five common connector plastic materials, which contain important technical knowledge.
Connector plastic materials typically include LCP, Nylon, PPS, PBT, and PET.
1. LCP
LCP, or liquid crystal polymer, is a material with excellent electrical insulation properties. It can maintain its electrical properties continuously at temperatures between 200 and 300 degrees Celsius without loss of performance, and can reach temperatures of 316 degrees Celsius with intermittent use.
In addition, LCP has extremely strong corrosion resistance and is not susceptible to corrosion in environments with 90% acidity or 50% alkalinity.
LCP also has excellent thermal stability and resistance to heat and chemicals.
2. Nylon
Nylon offers excellent toughness, self-lubrication, chemical resistance, and wear resistance.
PA6T is tougher than PA9T, with a heat deflection temperature of 290℃, making it ideal for SMT connectors.
PA46 offers high strength, good toughness, and is less prone to cracking.
3. PPS
Advantages: Good rigidity, low water absorption, good dimensional stability, HDT of 260℃, and excellent flame retardancy.
Disadvantages: Slow crystallization, prone to burring, and poor toughness.
4. PBT
PBT is a crystalline engineering plastic with a distinct melting point (215-235℃). In its molten state, it has low viscosity, good fluidity, low hygroscopicity, maintaining excellent electrical stability in both humid and high-temperature conditions.
Disadvantages: Significant shrinkage after molding.
Due to its limited heat resistance, it cannot be used in SMT and can only be used in DIP connectors (such as D-SUB25P and DR-9P).
5. PET
Crystalline engineering plastic with a melting point of 245-260℃. Excellent mechanical, electrical, and solvent resistance properties.
Disadvantages: Anisotropy, significant shrinkage, slow crystallization, and more demanding drying requirements.