Wire harnesses, sometimes called cable assemblies or cable harnesses, are used in every corner of the electronics industry, including consumer appliances, commercial equipment, robotics and industrial systems, computers and servers, telecommunications equipment, medical systems, aerospace platforms, and of course trucks and cars. However, the wiring harnesses used in electric vehicles (EVs) are the most complex and demanding.
This may come as a bit of a surprise, as drivetrain components in electric vehicles (EVs) are simpler than those in internal combustion engine (ICE) cars. Two factors that contribute to the complexity of EV cable harnesses are the use of high voltages in the drivetrain and the fact that all controls in the EV communicate via the harnesses; There are no hydraulic or mechanical linkages commonly found in ICE vehicles.
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HV cable harness
The complexity of electric vehicle harnesses begins with multiple high-voltage (HV) domains. The HV domain includes motor wiring harnesses, battery pack wiring harnesses, and separate wiring harnesses for fast charging and regenerative braking. Each of these HV wiring harnesses must be designed to handle large currents efficiently.
In addition to effectively carrying large currents and providing insulation for high voltages, these harnesses must also deal with high temperatures and high temperature rises. This requires large wire diameters, high voltage connectors, and cable protection.
Cable protection comes in many forms. Cables, especially motor drive cables, are screened to control the generation of electromagnetic interference that can interfere with the operation of other vehicle systems.
To protect people who may come into contact with the vehicle, federal safety standards require all electric vehicle manufacturers to use orange housings on any HV cables outside of a physical electrical protective barrier (Figure 1). Depending on the cable being protected, the covering can be braided tube, textile or other tape, bellows, etc.
It's not just HV
The harnesses in the HV domain are also subject to high currents to provide the high power levels needed for EV drivetrains and fast battery charging. Power levels of tens or even hundreds of kilowatts are common. Even with large diameter cables, IR losses can be large and produce a corresponding temperature rise.
The basic EV operating environment includes temperatures up to +125°C. Under some high load conditions, the surface temperature of the HV harness can reach +150°C.
Wire Diameter and Bending Radius
One way to reduce the temperature rise caused by IR losses is to use a larger diameter cable. Larger wires, with lower resistance, generally have better thermal characteristics and can emit more heat, further reducing temperature rise under high loads.
The trade-off is that larger wires have larger minimum bending radii, which makes HV harness formation and wiring more difficult. If the recommended minimum bending radius is exceeded, the insulation, shielding, or conductor may be permanently damaged. The wire diameter also directly affects the selection of HV connectors.
High voltage connector
HV connector is an important component in HV harness design. The high-voltage connectors in electric vehicle wiring harnesses must combine high electrical performance, mechanical strength, and the ability to withstand high levels of shock and vibration and exposure to harsh environments. Some considerations include:
IP68 protection class
The insulation resistance must be at least 500MΩ for 1 kVdc
High voltage interlocking mechanism
Shielded connection with HV cable to ensure high EMI performance
Chemical resistant housing material