1993-03-01

The Use of Polymeric PTC Devices in Automotive Wiring Systems 930012

Designers are faced with conflicting needs to provide reliable protection against short circuits and overload conditions in a vehicle's electrical system and to reduce vehicle cost and weight. Traditional approaches rely on a limited number of large fuses to protect multiple circuits. However, a consequence of this approach is the need for large, heavy, complex wiring assemblies. The availability of conductive polymer, positive temperature coefficient resistors, which latch when tripped and automatically reset when the fault is cleared, presents designers with an opportunity to rethink wiring assembly design. Significant savings in wiring assembly size, weight, and cost can be achieved by replacing centralized fusing with strategically located PTC resistors. Of equal importance, use of PTC resistors can eliminate the need for the vehicle's operator to locate and replace blown fuses.Automobile manufacturers are under constant pressure from prospective customers to provide higher quality and better reliability. Customers are also demanding more interior room and more built-in features in new family vehicles. Since most of the desired features are electrically powered, their inclusion requires more complex wiring assemblies. However, the need for larger electrical systems creates a dilemma for designers who are also faced with the need to meet ever-increasing fuel economy requirements, in part by reducing overall vehicle weight.A typical modern vehicle may contain hundreds of electrical circuits and a kilometer of wire. The sheer complexity of the wiring system can make conventional circuit design techniques difficult to use and may lead to unnecessary overdesign. As a result, designers are turning to new and emerging technologies to replace traditional and accepted design techniques.

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