Revolutionizing Connectivity: The Rise of Vehicle Mesh Networks

Greg Zimmer from Linear Technology explains how using a wireless mesh network can boost the reliability of battery management systems in vehicles.

Lithium-ion batteries need a lot of care to stay reliable over time. They shouldn’t be pushed to their extremes when it comes to their state of charge (SoC). The capacity of these cells decreases and varies with time and use, so each cell needs to be carefully managed to stay within a safe SoC range.

To power a vehicle sufficiently, you need dozens or even hundreds of battery cells, set up in a series that can generate up to 1kV or more. The electronics involved must work at this high voltage, avoid common mode voltage effects, and measure and control each cell in these long series accurately. Plus, this equipment has to send the information from each cell back to a central point for processing.

Vehicles that use high-voltage battery stacks face tough conditions, like dealing with significant electrical noise and wide temperature ranges. The battery management electronics are expected to extend the vehicle’s range, lifespan, safety, and reliability, all while cutting down on cost, size, and weight.

Thanks to steady progress in battery cell monitoring integrated circuits (ICs), today’s car battery packs are more high-performing, last longer, and are more reliable. Wireless battery management systems (BMS) are poised to further boost the safety and reliability of these full battery systems.

Modular Battery Packs

High-power automotive batteries often consist of multiple smaller packs distributed throughout the vehicle. A typical module might contain 10 to 24 cells and can be configured in various ways to suit different vehicles. This modular design makes maintenance easier and helps with warranty issues. It also allows bigger battery stacks to be built and batteries to be spread out more efficiently in the available space.

For a distributed and modular design to work in a vehicle, especially with all the electromagnetic interference in electric and hybrid-electric vehicles, you need a solid communication system. Isolated CAN bus and isolated SPI are proven methods for connecting these modules in such challenging environments.

The CAN bus is a well-established network in automotive applications, but it requires extra components, like a CAN transceiver, a microprocessor, and an isolator, which add to the cost and take up more space.

Another option is a two-wire isolated SPI interface, which uses a simple transformer and a single twisted pair instead of the four wires needed for CAN bus. The SPI provides a robust, noise-immune connection that can work over long distances and at data rates up to 1Mbit/s.

Wireless BMS

With a wireless BMS, each module connects wirelessly instead of using CAN bus cables or isolated SPI twisted pairs. The industry’s first wireless automotive BMS was demonstrated in BMW’s i3 concept car. This system used a battery stack monitor with a wireless mesh network, eliminating the need for traditional wired connections between battery packs and the battery management system.

This fully wireless BMS demo is a significant milestone, offering the potential for better reliability, lower costs, and less wiring complexity for large multi-cell battery stacks in electric and hybrid-electric vehicles.

Car manufacturers are working hard to convince the public that electric and hybrid vehicles are both safe and reliable.