High-Voltage Cables for Electric Vehicles (EVs) – Everything You Need to Know
(Last Updated On: 06/07/2023)
High-Voltage Cables for Electric Vehicles (EVs) – Everything You Need to Know
High-voltage cables are integral to automotive engineering, facilitating vital electrical connections and maintaining safety and efficiency. The evolution of high-voltage cable technology in automotive engineering has paved the way for cost and weight reduction, while still ensuring reliable performance. With the shift to aluminum core wires or copper clad aluminum core wires, electric vehicles can benefit from lighter and more efficient cabling. At Bonnen Battery, we are committed to providing high-quality lithium batteries to battery project managers. In this blog post, we explore the development of high-voltage cables, discuss their design and production process, and reveal the latest trends for a more efficient future.
Figure 1 shows the layout diagram of high-voltage components in an electric vehicle.
The layout position of high-voltage components in electric vehicles is used to arrange the high-voltage connection harness between various high-voltage components such as batteries to PDUs, motor controllers to motors, AC/DC charging and so on.
Ⅰ Incorporating the high-voltage wiring harness in your vehicle: A quick guide.
Figure 1 shows the layout of high-voltage components for pure electric vehicles. Reasonably arrange the high-voltage connection harnesses between various high-voltage components such as battery to PDU, motor controller to motor, AC/DC charging, etc. through the layout position of high-voltage components in BEVs.
Design protective measures for high-voltage cables when passing through sharp edges or holes during vehicle development. Ensure safe placement by avoiding heat or vibration sources and maintaining ample distance.
The high-voltage cable has a large outer diameter and weight. To avoid stress concentration, the minimum bending radius of the cable is generally greater than five times its diameter. Proper load distribution requires additional support fixtures. The fixed point spacing for linearly arranged bundles should be ≤300mm with fixed points at both ends for curved arrangements. The distance between fixed points and connectors must be ≤150mm to withstand weight and vibration loads. Fixtures must use automotive-grade zip ties and insulation brackets etc.
The drive motor cable needs to consider the impact of component movement and vibration, and the size of the cable should be reasonably designed to meet the stress distribution of the length, and also to avoid the accumulation of the cable caused by excessive length. For the movement of the cable, it is necessary to add a fixed structure with rubber ring buffer and guide groove to avoid scratching the cable with other components, which may cause damage to the cable.
During the cable layout process, EMC electromagnetic interference factors should be considered, and shielded high-voltage cables should be used to avoid high-frequency noise emission. High and low voltage cables must be arranged separately to avoid mutual interference caused by cross overlapping of cables.
To ensure a sleek and professional cable layout, keep the direction consistent with the attachment’s guidance and avoid diagonal placement. When routing cables in the engine compartment, prioritize running them beneath or within structural components. Additionally, protect the exposed high-voltage cables underneath the vehicle with sturdy protective tubes and plates for added safety.
Considering installation and maintenance, different specifications and positioning methods should be used for connectors in the same part to prevent incorrect insertion. A certain gap should be left at the end of the connector for easy insertion and removal.
Since high voltage has exceeded the safety voltage of the human body, and the vehicle body cannot be grounded in the same way as the low-voltage system, so that a dual track system must be adopted.
Ⅱ How to select the HV cable types?
1. Cable diameter
Accurately identify the main circuit and branch circuit based on the layout diagram of each high-voltage electrical component of the vehicle, and determine the characteristics of the high-voltage components connected to the high-voltage cables. Characteristics include working voltage, rated power, peak power, rated current, peak current, duration, etc.
The working temperature and environmental temperature also have an impact on the cable diameter, as high current transmission can lead to high power consumption and increased temperature rise of related components. Therefore, the design of high-voltage cables must be able to withstand higher temperatures. If the layout environment of the cable exceeds the allowable working temperature of the cable, a cable with a larger cross-sectional area must be selected. For instance, when Tmax reaches 180 ℃, the cross-sectional area of the conductor needs to be raised by one level for use, and when Tmax reaches 250 ℃, the cross-sectional area of the conductor needs to be raised by two levels for use.
2. Cable structure
The cross-section of high voltage cables is circular, and the sheath color is orange. High voltage cables can be divided into single core cables and multi-core cables in terms of type. A multi-core cable is composed of multiple single core wires, which must simultaneously meet the relevant technical parameters of the single core cable. If there is any signal transmission in the multi-core cable, please use separate shielding to ensure that the signal is not lost. The wire mainly adopts multi-core soft copper stranded wire to meet the technical requirements of internal resistance and soft bending of the wire. The insulation layer must be resistant to high and low temperatures, flame retardancy, and is mostly a composite structure. For EMC protection, high-voltage cables with shielding layers are braided with bare copper or copper plated wires on the inner sheath layer, with a weaving density of ≥ 90%.
Ⅲ How to select high-voltage connectors.
1. High voltage connector
Electrical performance: it is necessary to consider relevant electrical performance parameters such as rated working voltage, rated working current, insulation resistance, withstand voltage level, shielding and interlocking.
Environmental performance: it is necessary to consider the requirements of working temperature, environmental temperature, salt spray level, flame retardant level, solution resistant reagents, and prohibited substances. There may be other requirements based on different design requirements.
Mechanical performance: Test the vibration resistance and corresponding mechanical life according to different working conditions.
Safety performance: High voltage interlocking is adopted, which is divided into built-in and external types. Due to the compact layout and small volume of the built-in type, electric vehicles all use built-in type and detect the high-voltage interlocking through controllers such as VMS or BMS. It is required that after the high-voltage connector is disconnected, the live part can be reduced to below 60Vd. c and 30Va. c within 1 second. In order to ensure personal safety.
MSD, namely manual maintenance switch, is a key component to ensure the high voltage Electrical safety of pure electric vehicles. It is an executive component that can realize the electrical isolation of the high voltage system at a critical moment. It can highly integrate both the breaking device and the fuse. It can also protect the circuit from overcurrent and short circuit while configuring appropriate fuses inside, Reasonable design and operation of maintenance switches play a vital role in the Electrical safety of electric vehicles.
3. Charging interface
There are currently two types of charging interfaces, AC charging interface and DC charging interface. The rated voltage of the AC interface is 250V AC or 440V AC, and the rated current does not exceed 63A. The rated voltage of the DC interface is 750V DC or 1000V DC, and the rated current does not exceed 250A. The rated voltage and current value of the charging interface must be determined according to the vehicle layout requirements.
Ⅳ Cable fixing and protection.
1. Cable fixing
There are various ways to fix the cable, and based on the layout of various high-voltage components in the vehicle, the fixing method of the cable or connector should be reasonably selected. Currently, the commonly used fastening methods include: integrated fixed tie with wedge shaped fixing head, integrated fixed tie with fir tree shaped fixing head, etc., which are suitable for circular hole fixing; Integrated welding stud fixing straps, isolation type double clamp head straps with welding stud fixing components, etc. are suitable for welding stud fixing; Fixed straps and clip components such as pipe clamps are suitable for fixing to pipes, hoses, and wiring harnesses; Plate edge buckles are suitable for fixing metal or plastic edges with a thickness not exceeding 3mm; Heavy duty fixing device is suitable for wire diameter ≥ 35mm2; The cable conduit support is suitable for lifting the cable from the frame track to separate the cable from the protruding parts of the vehicle body and prevent cable wear; The connector buckle is suitable for fixing high-voltage connectors; The corrugated pipe buckle is suitable for quickly fixing corrugated pipes.
2. Cable protection
Corrugated pipe protection: The use of closed type corrugated pipe has characteristics such as friction resistance, flame retardancy, and heat resistance. The temperature resistance range of the bellows is -40~150 ℃, and it can also reach 200 ℃ in a short time. Common materials on the market include PA (nylon), PE (polyethylene), and PP (polypropylene), which have advantages in flame retardancy, friction resistance, and bending fatigue resistance. The color of the bellows must be orange, used to distinguish the low-voltage wiring harness of the entire vehicle, And use rubber sheath plastic sealing or PVC tape winding to fix and seal the cable.
Protective tube protection: For cables arranged in narrow spaces or special areas, special cable protective tubes need to be used for shielding and protection. General protective pipes have characteristics such as stable chemical properties, non-aging, and strong corrosion resistance.
Shield protection: For the high-voltage wiring harness (total positive and total negative of the battery) arranged in the chassis, the design of the shield should consider factors such as waterproofing, anti sediment splashing, and anti scratching. The majority of protective panels use ABS+PC, which has high impact resistance, high heat resistance, and high impact strength and flame resistance at low temperatures.
Sheath protection: Self-rolling sheaths can be used for parts that are vulnerable to damage and impact, and are characterized by high temperature resistance, impact resistance, cut resistance, light weight and easy installation.
Tape protection: Tape is widely used for cables, and is often used for protection, bundling, insulation, flame retardant, marking, etc. High-voltage cables are made of PVC tape with good flame retardancy, and the temperature resistance can reach 80°C.
Ⅴ Shielded EMC design.
When the electric vehicle is running, the repeated changes in electrical loads and the frequency conversion technology widely used in the system cause severe fluctuations in cable voltage and current, and generate large EMC electromagnetic interference, which affects the electric vehicle itself and the electronic and electrical products and equipment in the surrounding environment. Therefore, the shielding design for electromagnetic interference protection should be considered in the design and selection of the harness to meet the requirements of the whole vehicle for electromagnetic compatibility.
Pure electric vehicles include both high-voltage and low-voltage cables in the entire vehicle cables. From the perspective of EMC shielding design and development, when selecting shielded cables, it is not only necessary to consider their shielding performance, shielding mesh density, but also mechanical strength, environmental impact, and other characteristics. When the entire cable is affected by excessive mechanical, weather, and humidity, the shielding at the connection will be most severely affected. High voltage connectors should also choose metal connectors or plastic connectors with shielding function.
Each interface of the high-voltage cables adopts shielding treatment, and the front and rear motor interfaces are crimped with shielding snap rings and electrical box rails. The controller and battery box connectors use structural components with shielding function. At present, and most manufacturers add magnetic rings to relevant high-voltage components, including equipment and cables.
A magnetic ring is a ring-shaped magnetic conductor, which is a commonly used anti-interference component in electronic circuits and has a good suppression effect on high-frequency noise. The magnetic ring has different impedance characteristics at different frequencies. Generally, the impedance is very small at low frequencies. When the signal frequency increases, the impedance of the magnetic ring increases sharply. So under the action of the magnetic ring, for the high-voltage cables of the high-voltage system, the magnetic ring should be as close as possible to the inlet and outlet of the high-voltage cables of the motor and controller. It can effectively suppress the passage of high-frequency interference signals.
Ⅵ High voltage safety HVIL.
High Voltage Interlock Loop or HVIL (High Voltage Interlock Loop) uses low-voltage electrical signals to check the electrical integrity of the entire high-voltage module, cables and connectors.
When the interlock fails, it must be ensured that the high-voltage system of the vehicle is powered off and the high-voltage system cannot be powered on before the fault is eliminated, and the corresponding warning signal is triggered at the same time.
When the module with high voltage is disconnected from the high-voltage circuit, it can prevent electric shock accidents caused by people touching live parts due to the presence of capacitive loads in the high-voltage circuit (specific discharge procedures must be performed to release the high voltage to a safe voltage range), ensuring personal safety .
When the module with high voltage is disconnected from the high-voltage circuit, it can prevent electric shock accidents caused by people touching live parts due to electrification of high-voltage cables and accidental power-on of the whole vehicle, so as to ensure personal safety.
During the use of the vehicle, prevent the sharp decline in product performance and fire accidents caused by local heating and arcing caused by improper human operation, vehicle bumps, product aging, line wear, etc., and ensure vehicle and personal safety.
Ⅶ Production process of HV cables control.
Production process requirements: According to the requirements of the drawing, the cutting line requires neat cuts without burrs, and tolerances should be considered in dimensions——insulation sheath (corrugated pipe, protective pipe, double-wall heat shrinkable pipe)——peeling appearance is neat, the size is strictly in accordance with the requirements of the connector pins – the quality of the crimping and crimping of the terminals is evenly stressed, and there is no phenomenon of crushing and leakage of copper – the assembly is based on the interface definition required by the drawing – the conduction test is carried out with a multimeter – the size inspection – appearance inspection – packing into storage.
Ⅷ Development Trends.
1. Technological progress
The development of high-voltage cables technology is also reflected in the cables processing technology. The cables that involves battery pack voltage collection and temperature collection has high requirements on the crimping process. Due to the limitation of terminal materials in the large-diameter part of the high-voltage cables, hydraulic equipment must be used, and traditional stamping process cannot be used. New equipment must be used when processing parts with waterproof requirements.
For future higher voltage and current platform models, due to the high current, the heat of the cable will increase rapidly, and increasing the cable diameter will make the installation, use and layout very difficult, so the future technical development of cable thermal management must be considered, and whether to adopt the cooling method of the high-voltage wire harness still needs to be solved by actual data or prototype vehicle verification.
In order to reduce fuel consumption and reduce the weight of the vehicle, the large number of cables on the vehicle has become the key goal of the lightweight. At present, the materials used in automobile cables are mainly copper. In order to save the amount of copper used in high-voltage cables of pure electric vehicles, the future trend is to use aluminum core wires that are 40% lighter than copper core wires or copper-clad aluminum core wires. A large reduction in cost can also reduce weight and improve cost performance. Although the space occupied by the aluminum core wire is larger than that of the copper core wire, it can be solved by adjusting the layout space in the process of vehicle design and development, while the copper-clad aluminum core wire should be made of hard copper wire or copper alloy wire, so The tensile strength is greater than that of pure copper core wire.
High-voltage cables technology is continuously evolving and improving. With advances in materials, production processes, and development trends of lightweighting, it’s clear that the future of high voltage cables will be much safer and more efficient than ever before. By employing cutting edge technologies such as aluminum core wires or copper clad aluminum core wires for electric vehicles, manufacturers can reduce weight while still providing reliable performance over time. As we move into a new era of automotive engineering where safety and efficiency are paramount concerns, high-voltage cables will become increasingly important components to ensure both personal safety and fuel economy.
Designing a high-voltage cable system involves selecting the right components for reliable performance and safety. At Bonnen Battery, we understand the importance of choosing the right lithium battery for your battery project. Our blog post explores the different factors to consider when selecting HV cable types, high-voltage connectors, cable fixing, protection, and shielded EMC design. We also discuss the significance of high voltage safety (HVIL) design and the latest development trends in high-voltage cable technology. If you require lithium batteries or have any questions, please contact us, and we will be happy to assist you.
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