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 discussion comparing different types of trembler and chassis coils for an ignition system.
| Identifier | ExFiles\Box 34\1\ Scan028 | |
| Date | 10th December 1918 guessed | |
| -2- EFC1/AT101.21S. Contd. chassis type trembler coil made for 12 volts, but used, of course in this instance, as a plain coil. No.2 is a 6 volt type chassis coil used similarly. No.3 is the aero type A1 coil and No.4 the aero type B coil. On this table columns of coil resistance, coil inductance, corresponding necessary make ratio and platinum point gaps etc., etc., are given. We decided on trial of these four schemes that No.3 would be, on the whole, the most suitable, and this is therefore the scheme now fitted to 7 CA. It might appear that using this scheme the make ratio is rather small and the gap (.030") correspondingly wide, but we believe that the operation of the system with a small make ratio is probably better than if a coil having a higher inductance were used with a correspondingly higher make ratio. It is more on the lines of an open circuit system, and there is less probability of the current being left on. Further than this, the rate of break at slow speed is probably greater than with a higher make ratio. Trying this scheme on the bench, we find the average current consumption to be .47 ampere at 12 volts as calculated, the short circuit current is 1.95 amperes. At this short circuit current the ballast resistance, which is of nickel wire, does not begin to be red hot. The normal heating value of the current in this ballast resistance is .875 ampere. (This is the R.M.S. value of the same current whose average value is .47 ampere). There is, we think, an additional advantage in the small make ratio in connection with the distributor. We have arranged the distributor so that the spark takes place from (Contd). | ||