112 Chapter 9 Figure 11 SAE Level 3 combined connector. Today these systems still have relatively low efficiency, meaning that a good portion of the energy that is trying to get transmitted is getting “lost” in the process. However, major improvements are being made in this technology, which may make it mass-market-ready in the very near future. Design Guidelines and Best Practices The second half of the control electronics system is the high- and low-voltage electronics. This includes the contactors, HVIL, fuses, MSD, and the high- and low-voltage wiring harnesses.
Contactors and precharge contactors or relays are electromechanical switches, or relays, that will close in order to make the connection and to allow current to flow, or open to stop the flow of current and voltage. The HVIL is a system of components and systems that creates a closed circuit when the battery pack is sealed; if one part of the pack is “opened,” the circuit is broken and the contactors are opened in order to prevent current from flowing. MSDs are included in most automotive high-voltage batteries. The MSD is a fuse that is usually placed at or near the “middle” of the pack.
The battery disconnect unit is the combination of the BMS, contactors and relays, fuses, and electronics components integrated into a single unit. Several suppliers offer “off-the-shelf” HV electronics power distribution units.