A Study of Arc Duration on Supple Carbon Contacts in the Automotive Field

Membrane switching technology is commonly used to operate electrical apparatus such as remote controls, automotive switches, mobile phones, etc. This technology is based on a movable contact, mounted in a supple elastomer frame which allows the contact to be pressed against a stationary contact, mounted on a Printed Circuit Board (PCB). The material of the movable contact is typically a carbon-loaded polymer or a metal whereas the PCB electrode structure is copper, coated with a layer of gold. The current trend is to use this technology for power applications such as operating a coil or a direct actuator control. As reported in the literature, for such currents <1A and inductive loads, microarcs occur between rigid, metallic contacts, during break and make. Their duration and subsequent damage depend highly on the material and the mechanical separation. On the other hand, the high contact resistance of a flexible carbon-loaded polymer and the progressive separation due to its flexibility are expected to modify arc ignition and persistence characteristics. In this paper, we present experimental measurements of the electrical characteristics of such contacts and the consequences of arcing on contact reliability. Long contact rise times of the voltage are found compared to common metallic contacts. These complex voltage characteristics have been analyzed to extract arc voltage and duration. It was found that this supple and resistive contact allows an inductive load to be switched with a minor over-voltage and self-protection against arcing compared to common rigid metallic contacts.