Wiring Harness Cognition for New Energy Vehicles
Common Specifications
Commonly used specifications for wires in automotive wiring harnesses include wires with nominal cross-sectional areas of 0.5, 0.75, 1.0, 1.5, 2.5, 4.0, 6.0, and other square millimeters. Each wire has an allowable load current value and is used for electrical equipment of different power requirements. Taking the example of a vehicle wiring harness, the table below shows the use classification of wiring harnesses with different specifications:
Specification Application Classification
Wire Harness Function
If modern cars are compared to the human body, the ECU (Electronic Control Unit) is equivalent to the human brain, the engine is equivalent to the human heart, the chassis is equivalent to the human legs, the engine oil is equivalent to the human blood, the sensors are equivalent to the sensory organs, and the actuators are equivalent to the motor functions.
The wiring harness is equivalent to the human nervous system. It serves as the main network of the vehicle’s electrical circuit, connecting various electronic and electrical components inside the vehicle. Regardless of whether it is a high-end luxury car or an economical ordinary car, the composition of the wiring harness is essentially the same. It consists of wires, connectors, and wrapping tape.
The wiring harness not only ensures the transmission of electrical signals but also guarantees the reliability of the connecting circuit. It supplies specified current values to electronic and electrical components and prevents electromagnetic interference to surrounding circuits.
High-Voltage Electrical Design Principles
①Two-Wire Design:
High-voltage components in electric vehicles typically include power batteries, air conditioning compressors, electric heaters, drive motors, chargers, and DC/DC converters. Since most high-voltage components are high-power devices, a two-wire system is employed to ensure proper operation, safety, and prevent leakage in the high-voltage electrical system.
A two-wire circuit forms a complete loop for current flow, starting from the positive pole of the power supply, passing through the wire to the electrical equipment, and returning through the wire to the negative pole of the power supply.This requires two wires between the power supply and the electrical equipment. On the other hand, a single-wire circuit uses only one wire to connect the power supply to the electrical equipment, while the other wire is replaced by metal parts such as the engine chassis and vehicle frame to form a circuit (commonly known as ground). Cars often employ single-wire circuits.
②Separate Design of High and Low-Pressure Systems:
To avoid introducing electromagnetic interference generated by the high-voltage system into the low-voltage system and to ensure that communication and control signals of the low-voltage system are not interfered with, the high-voltage and low-voltage wiring harnesses are kept separate.
High-Voltage Wiring Harness Distribution
The high-voltage wiring harness in a vehicle is divided into five sections:
Power battery high-voltage cable: Connects the power battery to the high-voltage box.
Motor controller cable: Connects the high-voltage box to the motor controller.
Fast charging harness: Connects the fast charging port to the high-voltage box.
Slow charging harness: Connects the slow charging port to the car charger.
High-voltage accessory wiring harness (high-voltage wiring harness assembly): Connects the high-voltage box to the DC/DC converter, on-board charger, air conditioning compressor, and air conditioning PTC (Positive Temperature Coefficient) heater.
High voltage electrical physical diagram
Insulation Testing of High-Voltage Wire Harnesses
Insulation Resistance Requirements:
Under the maximum operating voltage (700V), the minimum insulation resistance value for the DC circuit should exceed 100Ω/V, and for the AC circuit, it should exceed 500Ω/V. To meet these requirements, each component in the circuit should have higher insulation resistance depending on the circuit’s structure and the number of components.
High-Voltage Wire Harness Insulation Performance Testing Method:
Using the motor controller cable as an example, the insulation performance of the high-voltage wire harness is tested.
