An investigation of fretting wear behaviour of nickel coatings for electrical contacts application in dry and lubricated conditions

International audienceFretting remains a major cause of connector failure and can impair reliability of complex system. Much work is devoted to minimise the effects of cyclic displacements in the contact interface. One of the options is to choose proper materials for the final layer and eventually select an underlayer. Another option is to apply a lubricant compatible with the electrical function of the connecting device. Its effect must be the reduction of friction with the preservation of conduction. In this work we have investigated the properties of nickel electrodeposited on cuprous coupons submitted to an imposed sine displacement fretting test (1 Hz, 25 μm, 2.5 N). The contacts are of the sphere on plane type. The plating conditions are shown to have a large effect on the microstructure, roughness and composition of the nickel coatings. Consequently the fretting behaviours of the compared coating are different. Fretting degradation is evaluated for our application as the number of cycles for which the build-up of oxidised debris gives a value of electrical resistance superior to a threshold. During the fretting test the rough nickel with large grains is observed to be prone to very high friction and partial slip. Fretting of the smoother coating with small grains is characterised by gross slip. Contacts were lubricated with solutions of perfluorinated polyether (PFPE). It is shown that a strong friction reduction takes place and that the fretting degradation is postponed. Surface analysis shows that fluorine is grafted in the interface and protects the interface. The electrodeposition process and the properties of the nickel coating are shown to have an effect on the lubricant behaviour in the contact interface. These results show the strong potential of lubricated nickel for applications in the field of electrical devices

An investigation of fretting wear behaviour of lubricated nickel coatings for electrical contacts application

LGEP 2013 ID = 1454International audienc

Experimental Evaluation of the True Remaining Capacity of Legacy Lead-Acid Batteries

International audienceOne of the common challenges in remote microgrid installations is inexpensive, reliable, and less laborintensive battery tests to measure the capacity of used batteries and link it to their remaining life. These capacity tests are usually misinterpreted, which results in a healthy battery being junked or may arise economic issues due to oversized battery banks in microgrids. In this work, we conducted several discharge experiments on 12V 100Ah lead-acid batteries in a controlled manner using an electronic load. The battery is subsequently discharged to 10.5V at C2.5, C3, C5, C10, C20, and C40 rates. When summed up using altered Crate discharge sequences, the individual capacities resulted in 100.71Ah, 100.23Ah and 78.96Ah, 89.43Ah for the fresh and weak batteries, respectively. Irrespective of the discharge sequence, the cumulative net capacities are found quite close to the battery's actual capacity for fresh but much different for weak batteries. Results show that the remaining battery's true capacity does not disappear at a high rate and may further be utilized at lower discharge rates. The outcome of these experiments provides the basis to identify fresh and weak batteries and to size the battery banks for the low-cost rural microgrids more efficiently and economically

Plateforme de caractérisation de modules photovoltaïques en extérieur

National audienc

Comportement électrique et tribologique des contacts glissants or/or d’uncollecteur tournant type cil/bague

International audienc

Nouveau dispositif pour l'étude des propriétés électriques et tribologiques des contacts glissants cil/bague

International audienceMany industrial systems require the transmission of electrical current from a static part to a rotating one. This is achieved by a sliding contact within a slip-ring device. According to the applications various designs can be used as well as various materials for the brush ring contacts. These devices usually have to be fully operative for many years. Understanding the wear mechanisms and the electrical behaviours are of major interest.This work presents a set-up for the investigation of electrical and tribological behaviour of sliding contacts of the wire/ring type. Fitted with a special wire holder, a rotating pin-on-disc tribometer (Anton Paar TRB3) was used to allow the friction of a wire on a disc. The gold wire is the same as in a real slip ring device and the brass discs have the same gold coatings as in the real slip rings. Voltage drop through the interface is measured with the 4-point probes method. Data such as friction coefficient, rotational speed and voltage drop are measured via the tribometer software. A second acquisition system is synchronized to the tribometer and allows the measurement of the voltage drop and rotational speed with high acquisition rates. This set-up allows the investigation of various parameters such as rotating speed, current value, normal force, roughness and lubrication conditions. It is an essential tool to identify degradation mechanisms in a simplified geometry with the aim of helping the analysis of results of tests performed on the real slip ring systems

Revisiting the theory and usage of capacitance techniques: application of high efficiency amorphous/crystalline heterojunction solar cells

International audienc

Electrical and tribological behaviour of gold/gold sliding contacts of the wire/ring type for slip ring applications

International audienceMany industrial systems require the transmission of electrical current from a static part to a rotating one. This is achieved by a sliding contact within a slip ring device. These devices usually have to be fully operative for many years. Understanding the wear mechanism and the electrical behaviour are of major interest. In order to study the triboelectrical behaviour of sliding contacts of the wire/ring type, a rotating ball-on-disc tribometer (Anton Paar TRB 3) has been used. The friction of a wire on a ring is reproduced by the friction of a wire on a disc thanks to a special wire holder. The gold alloy wire is the same as in the real slip ring device and the brass disc has the same gold alloy plating as in real slip rings. Voltage drop through the interface is measured with the 4probes method. This setup allows to study the influence of various parameters such as rotating speed, current value, normal force, lubrication conditions, and more. In this paper, the new experimental setup, and the first results obtained during its implementation are presented

Analysis of Fretting Behavior of Silver and Gold Flashed Palladium-nickel Dissimilar Coatings for Connectors

International audienceIt is well known that good wear performance can be obtained with Au-flashed palladium-nickel sphere on flat contacts simulating various connector applications. It has also been shown that these good wear properties could be recorded for asymmetrical coatings such as a noble metal sphere on Au-flashed palladium-nickel. In this paper we investigate the fretting properties of such asymmetrical coatings particularly of Ag versus Au flashed PdNi. The contacts are submitted to severe fretting wear by applying imposed sine displacements of amplitude similar to the Hertz contact radius. The contact resistance, the friction force and wear evolutions were analyzed and correlated to 3D profilometry measurements allowing wear volumes quantification and EDS elemental identification of the wear tracks.Very different behaviors are observed whether the silver coating is on the sphere or on the plane though in both case the embedding of the oxidized wear debris by silver improves the fretting behavior. The transfer of silver from the sphere contact onto the palladium nickel flat is seen to be beneficial to the electrical stability of the interface for a long time, leading to more stable results than even silver/silver contacts. Nevertheless an unusual phenomenon of the galling type is observed for which more investigations are needed