An E-Vehicle (i.e. electrified vehicle such as EV and HEV) is often equipped with a traction battery with voltage of as high as 200 to 600 Volt dc. It is critical that such voltage shall not be put in circuiting contact with any person at any point – workshop, crash or post-crash rescue. NHTSA have defined testing procedures in FMVSS 305 so as to assure that a basic level of safe guard systems shall be utilized by conventional EVehicles. The paragraph S5.3 (b) demands that the traction battery shall present an external voltage <60 Volt dc after crash. This is commonly solved with relays and melting fuses which have their Pros and Cons. Relays/contactors have the benefit of being a reversible active component but are limited to operative currents and are prone to switching bounces and they are relatively heavy, large and expensive. A melting fuse is a passive component that can operate at extreme currents but is irreversible and their cutting speed is dependent on the magnitude of the fault-current.

In this paper Autoliv will present a methodology on how to disconnect a faulty battery unit rapidly (in milliseconds) regardless of the magnitude of the fault-current. This methodology can also be used to divide a traction battery down to minor units of <60 Volt dc or even bypass and disconnect a faulty battery module with maintained power electronics in order to retain mobility as well as adding the option of discharge the disconnected module so as to prevent stranded energy.

Autoliv has investigated how to use pyrotechnic switches for disruption of over-currents in a traction system with battery packs of about 300-400 Volt dc. Those tests, aiming at safe disconnection without lasting arcs, included static faulty-current tests and tests simulating an E-Vehicle traveling 50-70 km/h on a horizontal surface. Autoliv’s Pyro Safety Switch (PSS) arrangement proved capable to safely disconnect both a complete battery pack (ranging from 300 to 400 Volt dc) and the intended battery module (30-60 Volt dc) in less than 0.5 milliseconds.