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 explanation of magneto ignition timing, focusing on current at break and spark intensity.
| Identifier | ExFiles\Box 4\5\ 05-page077 | |
| Date | 11th April 1923 | |
| -8- Contd. break will be so arranged that, for the fully advanced position the primary current is arrested before it reaches its peak value, and that, for the fully retarded position it is arrested some time after reaching its peak value. In this case the mid-position of the contact breaker lever will correspond to a larger current being arrested at break than for either the fully advanced or fully retarded position. Leaving the points of break in both positions the same, and making the point of make later for both advanced and retarded positions, by the same amount, will slightly lower the peak value and therefore the current at break in each case, but this may have an advantage in another respect which will be pointed out later when dealing with the phenomena which occur between the instants of break and make. If now the speed be considered reduced say to 100 r.p.m. the peak value of the current in either the advanced or retarded position will be considerably smaller and will also occur earlier so that, whereas for the advanced position the break may occur at or about the peak, in the retarded position the break will occur some little time after the peak of current is passed. Hence, in a magneto running at a slow speed the stronger spark is obtained in the fully advanced position, it being always understood that it is the value of the primary current at break upon which depends the intensity of the secondary spark produced. The spark in the fully retarded position is weak and may be strengthened | ||