Developer Blog

22/03/2024 by Bryan Hennessy

Bryan Hennessy’s Q1/2024 SAE J3271 update

Blue electric truck connected to charger on blue background with

There are applications for CAN that are considered non-traditional; not the fixed layout control system found in most CAN applications. Two ‘new’ areas where CAN is being considered fall within this category: megawatt vehicle chargers and tractor/trailer connections.

Electrifying trucks

While electric car chargers are common throughout much of the world, they will not be adequate for charging the heavy-duty electric powered vehicles under development. The heavy duty trucks, electric ferries, and electric aircraft now in development will require much more powerful charging stations because their battery banks are much larger, and the industries they serve require much faster recharge times. 

The standard under development to meet these needs is the Megawatt Charging Standard (MCS), labelled SAE J3271 by the Society of Automotive Engineers. This is a DC charging standard that increases the amount of charge that can be delivered to vehicles that fall under its remit. There are several aspects of this application that differentiate it from the charging stations being used today. Very high reliability is one of these. Connections must consider an environment with moving parts (cables and connectors), outside temperature and moisture extremes, rough handling, and dirty conditions to name just a few. To make things more difficult, the higher power ranges of this standard require liquid cooling in the cable and connector. This will necessitate different expertise in the design of the components, and therefore different standards committees and task forces working in parallel.

Hitching trucks to trailers

In a distinctly different application that I have written about before, truck/trailer connections of the near future have many of the same challenges, except for liquid cooling. Unlike most uses for CAN CC and CAN FD, these applications require connecting two parts on a network together every time the connection is made, and there will most likely be one ECU on each of the parts. If you study the Acknowledge bit in CAN CC and CAN FD, you understand why these networks are not valid networks until this connection is made. And then there is the question of termination. CAN requires a terminator on or close to each end of the trunk cable. With the cable disconnected somewhere in the middle, the termination requirements make it so neither half is a valid network on its own. 

Both megawatt chargers and truck/trailer connections must consider upgradeability and longevity in relation to protocol detection and adaptation. When one ECU is plugged into another, you must know either exactly how it is configured to communicate, or be able to detect and adapt to a common communications protocol. CAN CC, CAN FD, CAN XL (a little further out), Ethernet 10Base-T1S, 1000Base-T1, and ISO 11992 with 12 or 24 volts signalling are being considered for one or both applications.

The ISO 11992 standards, used for tractor/trailer connections mostly in the European markets, have given developers experience with a few of the issues being considered in MCS and future truck/trailer interfaces. The areas of overlap are related to the requirement for high reliability, and the need for a split network with termination on each side. ISO 11992 is a proven standard that also allows for communications in fault conditions, such as single wire connections where CAN_H or CAN_L are shorted or open. The experience gained from ISO 11992 with termination on each side of the network gives us some confidence going forward, but the additional selections between networks, speeds, and protocols are requiring developers to produce novel solutions, then to prove that these solutions meet the high reliability needs of these applications.

Kvaser is an industry leader in digital control technology and will continue to monitor and contribute to these standardization processes while providing high-quality interfaces and data loggers to meet the needs of this industry.

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Bryan Hennessy

Bryan Hennessy is the Technical Partner Manager for Kvaser AB, with a background in J1939, CAN diagnostics, marine electronics, and semiconductors.