Reliability of Thermal Relays in Automotive Applications

Abstract: Despite the vast increase of relays in automotive applications, little is known of how to perform reliability tests on them. Reliability of relays is defined as the probability of a relay to function without failure, when operated correctly, for a given period of time, under stated conditions.Accordingly, there is a need for improving life-expectancy test methods for relays. The immediate objective of this research project is to develop a guideline of how to check reliability of relays.Identifying the main parameters that affect reliability, perform an endurance test and material analyses of the tested relays were the main areas of interest in this work. In addition, common failure modes during the relays performance were identified.The results show that supplied voltage, breaking current and load type are parameters that affect arc duration and, thus, the contact damage. Most common failure modes were contact welding and increase in contact resistance due to arc erosion and oxide formation. Moreover, contact resistance stability has been proved to be a factor capable to determine the quality of contacts and to predict early failures in relays.