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 operation regarding current, E.M.F., and spark intensity at different speeds and timings.
| Identifier | ExFiles\Box 4\5\ 05-page078 | |
| Date | 13th June 1920 | |
| -9- Contd. progressively by advancing the contact breaker. On the other hand, if the speed of the magneto be considerably increased, say to 3000 r.p.m. the peak of current in both cases advance and retard is now considerably later than before, and although the peak value is still less for retarded position than for advanced, the current at break in the advanced position is smaller than for the retard position, because break for the advanced position now occurs earlier relatively to the peak. For the retard position it comes at or about the peak. Hence in a magneto running at a high speed the stronger spark is obtained with the lever fully retarded. It will be instructive to further consider how, given the points of make and break, the primary current at the instant of break, and therefore secondary spark intensity, depends upon the speed of the magneto. We have seen that in order to maintain the necessary current in the primary winding, which current maintains the existing core flux, an E.M.F. must be produced in the winding by the slipping back of the core flux. This E.M.F. is proportional to the rate of change or slipping back of the core flux and can be maintained with a smaller loss of flux if the time is shorter. When the magneto speed is dead slow there is no appreciable E.M.F. or current produced in the primary winding and the core flux slips back or readjusts itself to the distribution it would have if the armature were stationary, as fast as the armature Contd. | ||