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).
The arc effect in magnetos at high speeds, its issues, and potential remedies.
| Identifier | ExFiles\Box 4\5\ 05-page088 | |
| Date | 10th April 1929 guessed | |
| -19- Contd. The arc effect might be reduced, other things remaining the same by reducing the main flux of the magneto by removing one of the permanent magnets. It would probably be found under running conditions that an engine would run as readily as before. It would appear better to retain the additional flux for starting purposes, and for ordinary running purposes at moderate speeds, the arc effect does no harm. When, however, we come to run the magneto at a high rate of speed (say above 3000 R.P.M.) the arc discharge current becomes a nuisance. Apart from mechanical contact breaker difficulties there are electrical difficulties in the way of unsatisfactory high tension distribution, unless the magneto be altered in design. The arc current is trailed out as an arc between the distributor segments and the brush at leaving, and is injurious to the distributor. There is also the difficulty that the time allowed for the arc current to subside in the secondary winding may be too short, in relation to the interval between break and the next succeeding make. This will result in the M.M.F. due to the secondary arc current being great enough during this interval to prevent the introduction of the full quantity of flux previous to the instant of make, at which instant it is required to be ready in place. This state of affairs would be improved by increasing the length of the high tension spark gaps if possible, i.e. if the safety gap would allow and if the magneto and sparking plug insulation would stand up to the increased voltage. Or it would be Contd. | ||