From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The causes and investigation of failures in Entex ignition coils.
| Identifier | WestWitteringFiles\V\December1930-February1931\ Scan188 | |
| Date | 28th January 1931 | |
| To-R.{Sir Henry Royce} from EPC. [STAMP: RECEIVED 29 MAY 1931] ORIGINAL EPCl/AD28.1.31. ENTEX IGNITION COILS. Your EL/415.1.31. Coil failures of the type that have principally occurred recently are not, we consider, to be ascribed to the presence of moisture either contained originally or subsequently absorbed from the atmosphere. They are also not concerned with the utilisation of bakelite cases. It should be made clear that the majority of coil failures have taken place across the insulations of the innermost layers of the secondary (either first to second or third to fourth or both) at points where the potential gradients are greatest. It should perhaps here be stated that such failures do appear to have been minimised by the introduction of the latest type of coil to D.72503 which is built with paxolin tubes constituting rigid smooth bases for the primary and secondary windings. The difficulty with regard to arriving at the reasons for such failures has been the surprising lack of consistency in the results of various experimental trials which have been made. It has not, for instance, always appeared that increased thickness of insulation has improved matters particularly where this increase of thickness leads to a more irregular bedding of the wires and thus possibly to a shearing action on the insulation. We have been able to measure the maximum voltages of successive layers both severally and additively and by doing so have found a distinct lack of proportionality to the number of turns. The conclusion from this is that the happenings in the secondary windings of ignition coils are a good deal more complicated, due probably to the presence of localised capacity and varying self-inductance as the layers get larger, than would be supposed from the ordinary mathematical treatment of the case. Particularly does this seem to be the case in the first few layers owing probably to the existence of parasitic oscillations. With regard to the question of the degree to which the magnetic circuit should be closed, the fact that in the case of ignition coils a certain amount of | ||