L. Doublet

Break arc study for the new electrical level of 42 V in automotive applications

In order to fulfil increasing need for electric power in automobiles, satisfy environmental requirements and decrease car weight, the supply must change from 14 V to 42 V. In this work using 42 V, we studied arc parameters such as break arc duration and extinction gap for different materials, contact opening speeds and circuit loads (correlated with circuit time constant L/R). We found that these main arc parameters are greatly enhanced compared to the 14 V arc. In the case of inductive or resistive load, it was found that there are two domains: a low current domain where the material has no significant effect, and a high current domain where some materials (primarily AgSnO/sub 2/) induce high arc durations and large extinction gap. In addition, increasing opening speed reduces arc duration in all cases. The increased opening speed can however increase the extinction gap for inductive loads and decrease it for resistive circuits. We found that reducing arc duration is always beneficial with regards to erosion, but in some cases it may increase the extinction gap. At 42 V, erosion and material transfer from cathode to anode are similar to that found at low extinction gaps (<1 mm) at 14 V. At large extinction gap, however, these transfer phenomena are considerably modified by a new mechanism that induces erosion of the cathode and anode. It was found that classification of material behavior versus erosion is different at this voltage. For example AgSnO/sub 2/, which is claimed as a best compromise at 14 V for all loads, cannot be used at 42 V as it exhibits high erosion and requires a larger contact gap to ensure successful break.

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 AgSnO/sub 2/ 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.

Make arc erosion and welding tendency under 42 VDC in automotive area [electric contacts]

In this paper, we give the progress of a research program on arc phenomena and their consequences on contact materials for the next car generation power system, 42 VDC. We investigated make arc erosion, welding tendency and welding forces for the materials Ag, AgZnO, AgNi and AgSnO/sub 2/ under resistive loads and with a current range from 10 to 90 A. Using previous testing apparatus, developed for 14 VDC, we have simulated a mechanical bounce observed in relays (600 /spl mu/s duration and 80 /spl mu/m height) at make. We have found that a low material transfer from the cathode to the anode takes place at low current. However, at higher current, the transfer is in a reverse direction and the amount of material transferred is higher but this amount depends mainly on the bounce profile. In addition, a welding phenomenon appears at high current levels and can reach up to 20% of the welding tendency. However, high welding tendency does not correspond to high welding forces: this is the case of AgZnO compared to Ag.

Make arc parameters and subsequent erosion under 42 VDC in automotive area

Studies the make arc parameters and their subsequent effect on contact material erosion. Based on the typical profile of bounce in a relay (1 ms of duration and 50 /spl mu/m height) we have developed a test machine, which can simulate and evaluate erosion and material transfer. It was found that contrary to the 14 V case, the make arc takes place during the total bounce period and the extinction gap is identical to the bounce height. Arc energy is therefore greatly increased and depends mainly on the electrical current and load. The main action of this arcing is mass transfer from the cathode to the anode at low current and in the opposite direction beyond 15 A. Furthermore, the rating material performances at make arc seems to be reversed at break arc. In fact AgSnO/sub 2/ has the best performance at make, whereas it had the worst at break.