Connectors play an important role in EV battery management systems

Battery management systems (BMS) are a critical component of an electric vehicle (EV), and are comprised of several subsystems that are each responsible for a specific task. They manage and monitor the battery cells and packs and provide status notification on the health of the batteries.

But that’s not all. Battery management systems support a range of functions from data acquisition to safety management systems and since they are comprised of several electronic systems, the interconnect technology becomes a critical part of the system to make connections between the battery packs and diagnostic, control, and monitoring systems.

Battery management systems are important for the electrification of vehicles, said Gijs Werner, director of distribution and marketing, FCI Basics business unit of Amphenol Communications Solutions, during his presentation at the EE Times Advanced Automotive Tech Forum.

“Advances in EV technology provide consumers with vehicles that are quieter and less expensive to operate with sophisticated advanced driver assistance systems (ADAS), enhanced safety features, and improved comfort and convenience, and a battery system needs to work in coordination with all of these features,” he added.

“However, the acceptance of these advanced EVs depends on their ability to reduce range anxiety because people fear the electric vehicle might leave them stranded and that outlines the importance of battery management systems,” said Werner. “Features like start, stop, electrical power steering, and electronic braking systems have increased the battery power load. So battery management systems play an important role in prioritizing all of these electrical loads, and do much more than control voltage, current, temperature, and cell balancing, thereby maximizing the range. They also help to protect the vehicle and its occupants from any catastrophic failures in the system.”

Werner calls the BMS  “the brains behind the battery pack” to optimize battery efficiency and maximize range, and interconnects play a big role in ensuring battery management systems work reliably and safely.

Design engineers are looking for connectors that meet the required standards and approvals such as LV214 in Europe and USCAR in the U.S., along with technical requirements such as  current capability, signal density, and vibration resistance, particularly for the harsh automotive environment. They also need to be automotive-grade and operate over higher temperatures, while housed in small and lightweight packages.

Click for a larger image. (Source: Amphenol Communications Solutions)

However, the architecture or building practices of the battery pack and BMS play a role in the selection of the connectors. Werner says there are three main types of building practices for the battery pack, which include battery cells connected to each other with a flexible printed circuit (FPC) or discrete wire, both based on a centralized module controller, as well as discrete wires using decentralized module controllers.

Click for a larger image. (Source: Amphenol Communications Solutions)

These different building practices depend on the preference of the design team but also on the application, explained Werner. However, the FPC solution offers low wiring complexity as opposed to decentralized systems with discrete wires, which have complex wiring systems for battery packs, he added.

There are also different building practices for battery management systems, which include integrated (with FPC connections) and decentralized systems. These building practices are very similar for most electric vehicles, whether it is a material handling application like a forklift or a light vehicle, said Werner.

Click for a larger image. (Source: Amphenol Communications Solutions)

Connector solutions

The module controllers and the BMS systems typically use four types of interconnects. Described as box-build systems, they use wire-to-board and FPC-to-board interconnect systems for signal solutions, which are typically automotive-grade. To connect the boards together, pin and socket connector systems or board-to-board mezzanine interconnects are the preferred solutions.

Click for a larger image. (Source: Amphenol Communications Solutions)

As examples of these four types of interconnects, Werner discusses five FCI Basics connector families that can be used for the module controllers and BMS systems. These include the MicroSpace, MicroSpace XS (including a waterproof version), WireLock, and FlexLock connectors.

Click for a larger image. (Source: Amphenol Communications Solutions)

The WireLock 1.80-mm USCAR-2 qualified wire-to-board system was specifically designed for BMS and offers a high vibration resistance design with an active primary latch and TPA (terminal position assurance) and CPA (connector position assurance) functionality. The TPA ensures that the terminals are properly locked inside the housing while the CPA ensures the connectors stay firmly together, said Werner

The current capability is 3 A with all contacts powered. Positions range from 10 to 40 positions.

Like many of these connector solutions, at the heart of the interconnect is the contact system for harsh environments, said Werner, with two contact beams to ensure good contact normal force over time.

The contact shape is designed so the terminal cannot be mis-inserted inside the housing during assembly,  and it comes with four coding types and related colors to prevent mismating and damage to the pins, he added.

For design engineers looking for compact automotive-grade systems, the MicroSpace 1.27 mm, LV214-qualified wire-to-board system is built around a crimped wire contact system that enables LV214 qualification. This connector reduces the footprint by 50% compared to 1.8-mm systems, said Werner, and it maintains a nominal current capability of 4 A per contact and all contacts are powered. It also offers high vibration resistance.

Like the WireLock, MicroSpace offers a primary latch with TPA and CPA functionality. But what’s unique is when the TPA is not in its final position, there is no electrical contact, said Werner.

This connector system also offers high flexibility with lots of options. As an example, a two-position system can be configured with three coding systems for a variety of configurations, such as side-to-side (side or top latch), staggered horizontal (side or top latch), and staggered vertical (top latch).

MicroSpace also comes in an XS version. The MicroSpace XS adds the qualification to USCAR. Again, at the heart of the system is the contact system. It offers a reinforced crimp-to-wire contact with a supported contact beam for maximum normal force that guides and aligns the mated pin so it cannot damage the contact beams inside, said Werner.

The MicroSpace XS connector system also offers TPA and CPA functionality and comes with three coding types that prevents mismating of the connector. Amphenol also recently added a waterproof version that offers the same electrical performance, and meets the IP68 rating thanks to its sealing technology. This includes two seals on the receptable and a ring and terminal seal on the header. It takes up a bit more board space but it offers the advantage of offering IP68, said Werner

The FlexLock is a 2.54-mm FPC-to-board system that offers a range of configurations and options such as a cover to protect the pins for battery management systems. Configurations include straight and right-angle receptacles and headers in surface-mount and through-hole versions.

EV battery packs and battery management systems operate in harsh environments, which means the interconnects that connect the battery cells and boards need to operate in harsh environments (including high temperature and high vibration/shock). They also need robust contact and mating systems to ensure safe and reliable operation to protect the vehicles and their occupants.