Road to Reliability: High Voltage Auxiliaries on the Road

Estimated reading time: 1 minute

Thus far, this series has focused on power electronics and controls that propel the vehicle. However, EVs are not solely defined by their propulsion system. While much attention is placed on inverters, traction motors, and battery cells, an ecosystem of high-voltage (HV) auxiliary systems sustains safety, comfort, and functionality.

These systems, including compressors, heaters, coolant pumps, and the associated cabling, have evolved into critical components that ensure the vehicle functions reliably under a wide range of operating conditions. With this evolution comes a new set of challenges in terms of design, materials, reliability, and manufacturability. Failure can disable or degrade EV performance, reduce consumer trust, and inflate warranty costs. As a result, auxiliary system design and packaging are rapidly becoming focal points for innovation, integration, and reliability engineering.

Beyond the Powertrain: The Auxiliary Backbone

EV auxiliary loads initially operated at 12V or 48V, supporting lighting, infotainment, and small actuators. But to reduce energy conversion losses and support more demanding thermal management loads, many auxiliaries have now moved into the HV domain operating at 400V or even 800V supply levels for greater efficiency.

Key auxiliary HV components include compressors for cabin cooling, positive temperature coefficient (PTC) heaters or HV coolant heaters for cabin and battery thermal management, coolant and refrigerant pumps, electric brake boosters and steering actuators, and HV harnesses, contactors, and connectors. Each serves as a critical node in the functional ecosystem, ensuring driver comfort, battery safety, or chassis control, even when the traction motor is idle. These components are not merely add-ons but are vital to the system's overall efficiency, occupant safety, and comfort. Their integration, however, introduces new stresses on connectors, insulation, and the broader vehicle electrical architecture.

Packaging and Placement Challenges

Unlike propulsion components located in dedicated enclosures or drive units, auxiliaries are scattered across the vehicle, such as on the firewall, under seats, near wheel wells, or deep in the engine bay. This introduces unique challenges: environmental exposure to road spray, salt, and debris; mechanical stress from vibration or crash events; routing complexity for high-voltage cables and cooling lines; and electromagnetic interference between adjacent control units.

To continue reading this article, which originally appeared in the January 2026 edition of SMT007 Magazine, click here.