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).
Technical discussion on ignition coil design, spark plug gaps, and methods for improving insulation.
| Identifier | ExFiles\Box 164\5\ img017 | |
| Date | 15th January 1931 | |
| -2- RL/M15.1.31 contd. I believe that we strain our coils more than others, because we use too large a spark gap in the plugs for the compression ratio we now use. I think this gap setting should be between .015 and .020, not .025 and .030" as the feeler gauges would suggest, because of the unavoidable oxidising occurring. I am very definitely not in favour of increasing the number of secondary turns because it would seem that we should be increasing the voltage and the tendency for the coil to break down. It would be far better to be content in case of misfires to reduce the distance between the points. Compared with the American coils we have more strain on our insulation because they run their cars with shorter gaps and plugs are very cheap and often changed. They are not so liable to oxidation because they more often use rich mixture at some engine speeds or throttle conditions - i.e. they use more petrol because they do not run such a regular, and in many case weak, mixture as our carburetter works, and weak mixture oxidises the points, over-rich mixture deoxidises them. Every magneto has a safety gap so that the voltage cannot exceed say 10,000. One would expect that now we use non-trembler coils the voltage may on open circuit when the maximum primary current is allowed to rise to the maximum and then on breaking the circuit (primary) get a very high secondary voltage. Will EFC. find the maximum voltage that can be obtained because one would expect that the coil might often be subject to this maximum voltage by having its plug insulated with oil. In conclusion there may be many ways of improving the insulation which Mr. Brock could arrange, and naturally one feels that we ought to thoroughly dry every thing before and after putting together, then subject to a vacuum, then impregnate with bitumen, paraffin wax, insulating oil or something that should make it nearly impossible to breakdown while generating voltage up to say 15,000, which we might make an experimental coil do | ||