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).
Magneto performance, spark gaps, and a comparison of dynamo systems.
| Identifier | ExFiles\Box 49\5\ Scan073 | |
| Date | 19th May 1921 | |
| OY. from Hs. {Lord Ernest Hives - Chair} x4276 Hs {Lord Ernest Hives - Chair} 4/LG19.5.21. RE. MAGNETOS. You will have undoubtedly read my report on the requirements of Magnetos for 40/50 chassis. The real object of that report was to prove that the Bench Tests which have been made on different magnetos do not represent the conditions of working in he engine and are not reliable as a guide in showing the relative values of different magnetos. If you get any trouble with missing fire on magnetos, I think the first thing you should do is to see whether it is jumping the safety spark gap. I think you should ask the Bosch people why they fix their safety gap at 9 m {Mr Moon / Mr Moore} /m instead of 10 m {Mr Moon / Mr Moore} /m as on the German Bosch machine. We have been enquiring why it is that all tests on magnetos are taken with 5 m {Mr Moon / Mr Moore} /m gaps; why have they chosen 5 m {Mr Moon / Mr Moore} /m? The Watford people do not know any reason except that it is the gap used by other Magneto people. R, EFC {E. Fowler Clarke - Electrical Engineer} and myself had an interview with the Watford people the other day. We shall, very shortly, adopt their sleeve type magnetos and later on a larger type machine. In your memo OY11/G4.5.21., you show that you obtain a 5 m {Mr Moon / Mr Moore} /m spark at 36 R.P.M. of the Magneto. This is very difficult to believe. I have tried turning the magneto at 36 R.P.M. and it is absolutely creeping over. We are quite convinced now, however, that the quality of a magneto for good slow running does not entirely depend on the length of spark at slow speeds. I see by your letter that you are fitting a Bijur set to 4.EX Car before it is returned. R. {Sir Henry Royce} is now definitely of the opinion that the 3rd. brush control for the dynamo is the most practicable. It is not the ideal but it is the most simple and the most reliable. For instance, the Delco Dynamo fitted to the Marmon car appears to be very satisfactory. We have not had the least trouble with the electrical equipment on that car. It has now completed about 5000 miles. The dynamo is very good as regards silence. What surprises us as regards the Marmon, is the fact that the output from the Dynamo is only 10 or 11 amps. with a 6-volt machine. This output just balances the lamps, which means that the bulbs must be gas-filled and low candle power. We have never had the least difficulty with the Battery being run down and I, personally, should feel very pleased if the electrical equipment on our own chassis behaved as well. I cannot see what advantage would be gained if we fitted a Bijur or a voltage control regulator to the Marmon car. contd:- | ||