Eaton Debuts All-In-One Power Distribution for EVs

September 19, 2022

Kami Buchholz

Destruction avoidance is one of the chief duties of Eaton’s battery disconnect unit (BDU) for light-duty passenger EVs. “A short circuit event in a typical battery electric vehicle is capable of producing as high as 25,000A of current for a short duration, and the BDU can sense this and shut down the circuit before electrical or thermal damage can occur,” Kevin Calzada, global product strategy manager for Eaton’s eMobility business, told SAE Media at the 2022 Detroit auto show.

Eaton recently beefed up its BDU by adding upgraded Breaktor circuit-protection technology for an all-in-one, multi-functional device. The Breaktor performs the switching and protection functionality with the BDU and helps to reduce complexity of the overall BDU system, Calzada explained. Fuses, contactors, and pyro switches are replaced via the Breaktor – as are busbars, fasteners and other connection components. Eaton has approximately 20 patent filings for its Breaktor and BDU relating to circuit-protection components and controller functions, such as pre-charge, isolation detection and current/voltage sensing.

Current production passenger EVs rely on one of three traditional BDU configurations: fuse and contactor; pyro fuse and contactor; or fuse, pyro fuse and contactor. All three conventional configurations provide switching and circuit protection, but system complexity, serviceability and other issues are common.

At its highest functional level, Eaton's BDU acts as an overall on/off switch for the entire battery pack. It also can switch between different modes of operation, such as driving and charging. When driving, the BDU is on. When the vehicle is parked, the BDU shuts off and electronically isolates the stored battery energy from other vehicle systems.

“The BDU with Breaktor also has the ability to sense an electrical fault/overcurrent event and shut down the circuit within a few milliseconds,” Calzada noted. That same detect and shut down activity applies to a short-circuit event. “The built-in protection function that the BDU offers can be done using either Breaktor or EV fuses,” he said.

When the BDU is paired with Breaktor technology, ‘contactor welding’ is avoided. Contactor welding is the unwanted outcome of a high-current event, such as a short-circuit or system overload, in which high current flows through the system until a circuit-protection device actuates and stops the current. During this brief energy burst, the contactors in a typical BDU design can bounce, due to the Lorenz forces in the device. Arcing then occurs between the contacts, as does extensive heating within the device. When arcing and extensive heating happens, a common failure-mode outcome for a typical contactor: the contacts weld together.

“After the contacts weld together in a contactor, there is then no way to isolate electrically or turn-off the battery pack and the vehicle system is permanently energized,” Calzada explained. The issue also can create risk to vehicle occupants and first responders after a vehicle crash if the battery cannot be disconnected. “The Breaktor ensures that even after a fault event, the battery can still be switched off and safely isolated from the rest of the vehicle,” he said.

Eaton’s Breaktor enables up to 350 kW DC fast charging when used to protect and switch the DC fast-charge circuit, allowing a passenger EV to charge in 15 minutes or less. The circuit-protection technology can carry 500A continuously and up to 750A of continuous current when an active or passive cooling system is engaged. According to Calzada, Eaton’s Breaktor achieves best-in-class current ratings. The BDU’s Breaktor can be reset after a high-energy fault through software, bypassing the need to open the battery pack.