"Electrical arc phenomena and its interaction on contact material at 42 volts DC for automotive applications"

In order to fulfill the increasing needs of electrical power in automobiles, the electrical network, currently at 14 VDC, must be changed to 42 VDC. This involves that switching DC devices have to be improved to insure reliability and electrical safety. Therewith, for improve comprehension of arc phenomena and its interactions with contact materials under 42 VDC, the authors undertook a study on this subject. This work summarizes the whole of work and tackles the arc phenomena at break and make, the contact material transfer and the problems of welding at make. Thus, we studied break arc duration, arc length (gap) and material transfer versus the effect of material, opening speed and loads. We have established that the arc duration and its length are extremely extended by a few millimeters compared to the arc in 14 VDC. At 42 VDC and low current, erosion and transfer direction is similar to the previous one obtained at low arcing length in 14 VDC. However at large gap, with 42 VDC inductive loads or high current, new mechanism erosion mode takes place which induce the cathode and the anode loss. Erosion and arc length of AgSnO₂ contacts is higher than other material: for this particular behavior, some complementary investigations, using X chemical analysis, have been undertaken. It seems that electrical arc enriches in tin element the contacts surfaces leading to this behavior. In other way, we have investigated make arc erosion, welding tendency and welding forces for all materials. It was found that contrary to the 14 VDC case, the make arc takes place during the total bounce period. The rating material performances at make seem to be reversed than at break. This study enables to understand the material effect at this higher voltage and thus should allow the improvement of the material itself. Anyway, the commutation devices of 42 VDC should employ improved materials and also additional systems of arc reduction.