Welding tendency, contact resistance and erosion of contact materials in motor vehicle relays

After a brief discussion of the problems of switching contacts in motor vehicles, the test and measurement installations used for investigation are described. The installation is supplied by a 12-V battery, which is permanently connected to a charging unit. A hybrid switch, in which the switching operations are performed by thyristors and the current is carried by mechanical contacts, makes it possible to make and break the test current at any time. The test current flows through one of the two test devices and can be set by changing the connected load. The load may consist, apart from the groups of lamps used here, of different motors or other loads. The electronic controller controls and monitors the test. Ag/Ni with nickel content from 10 to 30% is shown to be optimum for smaller current loads, while sintered, extruded Ag/SnO₂ 88/12%-SPW (sintered and highly compressed by extrusion, with additives) is shown to have distinct advantages over Ag/Ni, Ag/CdO, and internally oxidized Ag/SnO₂ in the higher range of current