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).
Comparison of ignition coil insulation with American counterparts, discussing potential improvements through methods like vacuum impregnation and oil filling.
| Identifier | WestWitteringFiles\V\October1930-February1931\ Scan208 | |
| Date | 15th January 1931 guessed | |
| (2) 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 cases weak, mixture as our carburetter works, and weak mixture oxidises the points, over-rich mixture deoxidises them. Every magneto has a safety spark 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 than 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 everything 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 by putting it on an alternating current circuit - i.e. test it to destruction and then make it still better insulated. And also, provide on the coil some limit to the voltage such as a 10 m/m spark gap with reliable points to limit the voltage to say 8,000 or 10,000. After learning all we can from Ferranti and the American coil, or any other source, I shall look out for a further report from EFC. One might expect that something could be done by impregnating firstly by a vacuum, then a pressure of say 100 lbs. per sq. in. Also the coil case might be arranged to be filled with insulating oil as is used on transformers for power lines. My experience with Remy coils was that American coils failed in England because they absorbed damp and were made in a dry climate for a dry climate. The same as 30/40 yrs. ago we suffered in England by moisture getting into our dynamo and electro motor work. At WW. we generally have trouble with magneto fibre absorbing moisture and the contact makers failing. The troubles were never so bad on the European continent, and in USA. R.{Sir Henry Royce} | ||