Battery cell bypass with frangible actuator

Abstract

A frangible actuator and switch isolates a defective cell in a battery by switching an electrical circuit when the current through a fusible link exceeds a predetermined value. The high impedance of the defective cell causes most of the battery's current to flow through the fusible link. The actuator releases a spring-loaded plunger when the high current causes tensile failure of a fusible link. Electrical contacts coupled to the pre-loaded plunger are displaced by a predetermined distance, causing the contacts to move into or out of contact with electrical terminals. The actuator includes two mating parts held together by a restrainig wire, which is in turn held in place by the fusible link. When the fuse melts, fails in tension or otherwise triggers due to excessive current, the restraining wire loosens and allows the two actuator parts to separate. This separation in turn permits the spring loaded plunger to advance, triggering the switching action. The actuator contains the fusible link on an insulator portion rather than on one of the mating parts, so that the connecting wires will not mechanically interfere with the separation of the mating parts. Pins are used between the mating parts to prevent unwanted rotation of the parts and to prevent the resulting false activation of that could thereby occur. The switching contacts use toroidal springs as contact elements to maximize contact area and thereby increase current capacity of the switch.