68 September/October 2023 | E-Mobility Engineering a permanent electrical contact, but the expert from the precision metal stamping and welding specialist is trying to change that with a patented ultrasonic welding process he describes as an improvement on the status quo. Sensing issues Modern BMSs monitor multiple parameters at the cell, module and pack levels, and the need for sensors and associated wiring inevitably has an impact on the main conductors. With busbars for example, voltage sensing leads are now needed to ensure battery management strategies can be realised. While these changes add cost, they help OEMs improve system performance, the electrical, industrial and power management expert notes. In a bent-metal busbar, the main requirement to support such measurement systems is to ensure that the areas from which insulation material have been stripped are as clean as possible to ensure there is an absolute minimum of resistance between the busbar and anything connected to it. In the latest battery platforms, safety requirements and lifetime management require more and more accurate monitoring of both temperature and voltage, along with other methods of detecting early-stage failure modes. “Those sensors need to be placed as close as possible to battery cells, directly integrated within a laminated busbar, for example,” says the power transfer, management and materials expert. “Also, space constraints in battery modules have required designers to investigate better integration methods, such as moving from wire harnesses to flexible printed circuit board assemblies.” Architectural impacts Busbars and interconnects will also be affected by architectural developments such as the adoption of cell-to-pack (CTP) and cell-to-chassis (CTC) battery configurations. CTP and CTC batteries are often structural, and tend to require much larger current collectors, but the basic architecture is generally the same regardless of size. They can, however, simplify the design of a battery and reduce the number of components required. Eliminating modules will naturally remove the need for module-to-module connections and therefore reduce the number of busbars. Eliminating these interconnections will also reduce the number of heat sources and improve heat dissipation. “Due to their very specific integration methods, with limited capability to change defective parts or modules, CTC or CTP solutions will increase expectations related to lifetime optimisation and monitoring,” argues the power transfer, management and materials specialist. Some of the busbars will have to be physically flexible, the expert from the electrical, industrial and power management company notes, and as competing technologies go through the process of maturing, numerous manufacturing technologies will continue to be needed. The CNC wire bending specialist notes that busbar manufacturers often operate in a ‘build-to-print’ manner, meaning they don’t always know what the final application will be. They receive orders to make parts that can be of any size and shape, and so long as they can be made from the wire stock and the designs conform to guidelines that govern factors such as the relationship between material thickness and bend radii, they will make them. Regardless of the battery type, routing of the busbars is always the last step in the design, one of the company’s experts notes. “You have your cell configuration and now it is up to the designer to connect plus to minus,” he says. Sometimes, shapes that cannot be made in a single CNC bending process can be accommodated with one or more additional steps on different machines, but occasionally, he says, they are asked to bend a bar through a radius that is just too small. For example, making a 2 mm radius bend over the ‘high’ edge of a 20 mm-wide bar would not be possible with CNC technology. “There is physically no chance of making such a sharp bend over the high edge, so we normally recommend that the bending radius standard is one times the dimension, so it would be 20 mm with the radius at 20 mm. If a customer wants such a sharp radius though, Focus | Busbars and interconnects Overmoulding is an important means of applying protective polymer coatings to busbars. Here, a copper busbar sits in the mould before the thermoplastic polymer is injected (Courtesy of Celanese)
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