In advanced battery systems, the quality of power electronics plays a crucial role in determining the final product’s performance, functionality, and reliability.
This is especially true in the latest battery management and charging systems, which incorporate wide-bandgap semiconductors and optimized power topologies. In these advanced designs, safety mechanisms must operate quickly and reliably—any failure in these systems could lead to severe battery malfunctions, posing risks to both the product and the user.
Need for Improved Stored-Energy Systems
Nearly every advanced application currently in development necessitates next-generation battery systems. Smart grid-level energy systems require enhanced power storage just as much as advanced electric vehicles (EVs) do, and these needs are intrinsically linked, as illustrated in Figure 1.
While each application has distinct requirements, the fundamental need for safe, reliable, and cost-effective energy storage remains constant.
In life-critical applications such as automotive safety, the significance of fail-safe subsystems cannot be overstated. The battery system in an EV is analogous to the fuel tank in a conventional vehicle, as the stored energy must be managed safely.
Modern batteries contain substantial energy, and catastrophic failures can lead to thermal runaway, posing fire risks. The increasing media coverage of EV fires has heightened awareness of this issue, underscoring the necessity of addressing safety concerns to avoid hindering public adoption of electric vehicles.
The elevated cell densities in advanced battery systems necessitate stringent safety protocols and devices as the associated power levels present considerable challenges in managing short circuits.
To develop a robust and safe system that ensures reliability throughout a vehicle’s lifespan, manufacturers must incorporate high-performance components into their designs.
Fuses and Contactors
Fuses, or equivalent devices, are essential circuit-protection components that safeguard the system in the event of a short circuit by interrupting the line under specific conditions.
Various types of fuses exist, but each features an engineered conductor, typically metallic, designed to fail (melt) in a controlled manner when exposed to elevated temperatures resulting from a short circuit. This destructive protection mechanism ensures circuit safety by completely severing the power source.
However, this burn-out response has certain limitations, particularly concerning the inconsistency of current flow in a power circuit under load.
In designs requiring high-power pulses, the wide operating range of current necessitates the use of higher-rated fuses to prevent nuisance tripping, thereby increasing the system's vulnerability to overheating and thermal issues.
Additionally, the non-reversible nature of fuses has led to a growing preference for electromechanical safety devices such as circuit breakers, which can be reset and do not rely on destructive mechanisms for operation.
A contactor is another type of electromechanical protection device, differing from a circuit breaker in its intended function; it is not designed to interrupt a short circuit. Instead, contactors connect directly to high-current loads and serve as high-power switching devices operated by an external control mechanism.
Power contactors are favored in demanding applications where circuit resetting is necessary, and high current levels are present. Although similar in operation to relays, contactors are distinguished by their robustness and additional features that facilitate arc control and suppression during switching.
When discussing battery systems, high-voltage contactors play a crucial role in ensuring safe circuit continuity in hybrid and electric vehicles, as well as in charging systems and high-powered industrial applications.
These contactors are designed to rapidly and securely connect and disconnect circuits, effectively managing arcing and inrush scenarios. For instance, in EVs, normally, open contactors safely link the battery pack to the system and disconnect when the vehicle is not in operation.
Solution
Various circuit protection solutions exist that can interrupt a circuit more quickly than traditional fuses, operating closer to normal conditions without nuisance tripping, thereby minimizing potential damage compared to thermal fuses.
One such solution is the GigaFuse from Sensata Technologies’ GIGAVAC brand, shown in Figure 2.
This fast-acting, hermetically-sealed electromechanical device generates low heat and allows for precise circuit tripping at specified currents. Its design significantly reduces resistance, eliminates thermal aging and enhances system efficiency.
Figure 2. The GigaFuse from GIGAVAC is a fast-acting device that trips circuits at exact, specified currents. Image Credit: Sensata Technologies, Inc.
Available in both passive and passive/active configurations, the GigaFuse utilizes the magnetic field of the current, specifically the Lorentz force, to trigger the device's opening mechanism.
Figure 3 illustrates the operational characteristics of the GigaFuse, with the blue line indicating the triggering threshold. This demonstrates that the device can open the circuit more rapidly than a fuse and closer to the desired operating conditions. The path of the triggering threshold can be adjusted based on the construction of the circuit-tripping device.
Due to its minimal heat generation during operation, the GigaFuse is immune to thermal aging and related nuisance tripping caused by temperature fluctuations in the circuit.
Over time, such thermal cycles can render the conductor metal in traditional fuses brittle, compromising the physical integrity of the connection and reducing operational lifespan. In contrast, the GigaFuse maintains fast and consistent clearing times regardless of ambient temperature variations.
These characteristics enable the end user to design a safe circuit while simultaneously reducing the performance requirements of the contactor.
Figure 3. This diagram demonstrates how circuit protection solutions such as GIGAVAC’s GigaFuse operates, with the blue line representing the triggering threshold, showing that the device can open the circuit faster than a fuse and closer to the desired operating conditions. Image Credit: Sensata Technologies, Inc.
The GigaFuse can also enhance the performance of the contactor within the circuit. When a contactor is incorrectly paired with a fuse, it can interfere with the fuse’s ability to function properly.
As the contactor levitates, it dissipates energy that should be available to trigger the fuse, instead diverting the current onto itself. This overload can prevent the fuse from detecting a short circuit, potentially leading to catastrophic failure.
For example, in a scenario involving a 500 amp contactor and a 500 amp fuse, it could take several seconds at 1000 amps to trip the fuse, while a GigaFuse set at 1000 amps can trip within 3 milliseconds.
Traditional thermal fuses often experience a gray zone where current levels may exceed the contactor's interrupting capacity before reaching the thermal threshold for a fuse to activate. This delay is effectively eliminated with the GigaFuse.
Additional advantages of the GigaFuse include an extremely low contact resistance (less than 0.15 mΩ), which results in reduced power loss and improved efficiency of the electrical system.
Moving Forward
Electrical protection devices like the GigaFuse play a critical role in circuit safety across high-power systems—and their benefits extend beyond advanced batteries.
Applications ranging from motion control to alternative energy generation can take advantage of this component’s efficiency, thermal performance, and rapid response.
As a fast-acting, hermetically sealed electromechanical device, it is particularly useful in environments where thermal aging or nuisance tripping poses challenges. Additionally, GIGAVAC’s GigaFuse is well-suited for coordinating with contactors and providing protection in short-circuit conditions.
Advanced battery systems require sophisticated circuit protection solutions to enhance battery safety and performance and to promote greater market acceptance of EVs. The elevated current levels and power densities in next-generation battery systems necessitate high-performance safety components.
Circuit protection solutions such as the GigaFuse empower designers to deliver the essential protection needed for today's advanced battery systems and tomorrow's battery systems.
Acknowledgments
Produced from materials originally authored by Markus Beck from Sensata Technologies.
This information has been sourced, reviewed and adapted from materials provided by Sensata Technologies, Inc.
For more information on this source, please visit Sensata Technologies, Inc.