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).
Letter responding to a query about the development of ignition coils and contact breakers, detailing the balance between current, contact point wear, and coil heating.
| Identifier | ExFiles\Box 163\7\ img119 | |
| Date | 17th May 1929 | |
| X4284. EFC1/T. 17th May, 1929. MR. G.R.N.Minchin, 50 Grosvenor Gardens. London, S.W.1. X8780 X5783 cl. X4284 Dear Mr. Minchin, I have received yours of the 16th inst. I think the answer to your query concerning "Delco" ignition, given in confidence, is merely the question of long experience, and in saying this I refer rather to the contact breaker than to the coil. To put the matter in more detail, originally we made coils with their various quantities of similar magnitude to those of the Delco. We designed and made a make and break which we thought was right. Experience showed us that the contact points did not go well. The natural thing to do was to look for ways and means of reducing the current in the system, having in mind the saving of the contact points. Accordingly we altered the quantities of the coil to lower the current in the system, which, however, resulted in a bigger heating effect on the coil. The answer to the query as to why this heating effect was not known before these finer primary coils were put on production is that the immediate heating effect does not harm the coil but that the effect is cumulative over a considerable period. Naturally in all the ignition arrangements we have put on cars these have duly passed our 10,000 mile tests and in many instances several times over. Later on we arrived at the fact that the life of the contact points was very little affected, within reason, by the magnitude of the current, but depended very much more on the exact mechanical action of the meeting and parting of the contact points, which action is now considerably improved. (Slight scrubbing action, but in a certain definite way). Having done this, we have been able to return to the coarser primary coils but until quite | ||