Fuses: The Basics

Fuses are protection devices that protect electrical circuits against undesired high currents. We can use passive fuses and pyro fuses in battery design.

Passive Fuse

Passive fuses break the circuit only as a result of high currents for a certain time. They have a weak internal structure as a melting element. During high currents above a certain limit, the internal part melts and breaks the circuit. To avoid electrical arcs, the fuse body has an internal filler element, some quartz sand, for instance [1]. Fundamental parts of passive fuses are melting element, fuse body with filler and fuse terminals.

Pyro Fuse

On the other hand, pyro fuses can actively interrupt circuits. Just like airbag systems, pyro fuses may be a part of HV systems. Electrical designers use pyro fuses in case the electrical circuit needs to be broken via an external signal. However, pyro fuses also interrupt the circuit during higher current flow than the current limit.

Boundary Conditions

Since the fuses protect the electrical system of battery as a result of a melting event, a battery designer needs to consider external parameters. These parameters are thermal and mechanical conditions as well as electrical system specifications.

Thermal conditions may accelerate or decelerate the melting event. Similarly, air pressure caused by altitude, vibration, and mechanical shocks changes the fusing behavior [2]. The most significant influencing factors are electrical system specifications:

  • Current profile
  • Failure current
  • System inductance

Besides, busbars and neighbor components make an impact on the working performance of a fuse. These components can dissipate or accumulate heat. Therefore, fusing behavior could be different.

A fuse does not protect the electrical system by itself. Contactor and fuse compatibility is essential for a safe electrical system. Therefore, contactors and fuses are sized together to give an overall system based level of protection. A poor fusing performance can cause explosion of the contactors.

References

  1. Fuse“, IDC Technologies, accessed 05 Jan. 2022.
  2. Typical fuse links applications in a Hybrid and Electric Vehicle (HEV)“, Eaton, accessed 05 Jan. 2022.

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