Contact erosion in automotive DC relays

Contact degradation of automotive relays was studied to understand the relationships between switching operations (make, break, and make-and-break) and loads (resistor, lamp, and motor). This information is essential in proper relay design, specification, and application in an automotive electrical system. Contact resistance was measured and the eroded surfaces were analyzed to explain the degradation process. Significant dependence of degraded contact resistance on types of load and switching operation was found. Prominent pips and craters that can cause premature relay failures were formed during the make operation by anode-to-cathode transfer. Break arcs transferred material from cathode to anode and formed a porous layer to increase contact resistance. The amount of material transferred decreased with shorter arcing time, which also decreased with load inductance. The degradation process is explained as an interaction among switching mechanics, load current characteristics, and arc phenomena