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 performance characteristics of a magneto, detailing its sparking range, electrical resistance, and milli-ampere output.
| Identifier | WestWitteringFiles\F\March1921\ Scan52 | |
| Date | 19th March 1921 | |
| Contd. -3- EFC2/T19.3.21. 14. A range of advance and retard was now arrived at as described in our EFC4/T3.2.21, but in the process of this the contact breaker lever failed receiving a permanent set indicative of too soft metal being used in its construction. The whole contact breaker lever was returned to the makers and replaced with a new one. In this case it was found that the low speed sparking was better in the makers retarded position and at a minimum speed thereabouts, so that our eworking range of 34° was selected in such a manner as to make our retarded position coincide with the makers retard, resulting in the fact that our advance position was 14.5° less advanced than that of the makers. 15. High speed sparking characteristics. Regular sparking took place at all high speeds up to 3500 R.P.M. on 7.5 mm. gaps for advance and central positions (on our range) and on 6.5 mm. gaps for retard. With lever at central and retard, shorting any one gap extinguished the spark following at speeds above 1500 R.P.M., the sparks otherwise appearing quite equal. 16. Low speed sparking characteristics. The lowest speeds for regular sparking on 5 mm. gaps in air for advanced, central and retarded positions (on our range) we found to be 430, 380 and 270 R.P.M. respectively. It will be seen as regards this magneto that there is more advantage in selecting our 34° range from the lower portion of the makers range. 18. Primary resistance .51 ohm at 18°C. 19. Secondary resistance 2400 ohms at 19°C. 20. Secondary milli-amperes Maximum 13.6 ( armature horizontal ). Minimum 8.1 ( " vertical ). This machine was reasonably quiet under all circumstances. EFC. | ||