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).
Electrical test data for ballast and primary coil components.
| Identifier | ExFiles\Box 52\3\ Scan363 | |
| Date | 14th February 1924 | |
| -2- contd BALLAST. Approx. resistance (ohms) (cold).. .610 Approx. resistance (ohms). .690 (when carrying current of same heating value as working current at normal speed of timer and with primary gaps set as below under Contact Breaker). Approx. R.M.S. working current of coil at normal speed (amperes). I 2.38 Approx. average working current (D.C. value) (amperes). C 1.76 Ratio R.M.S/average current. I/C 1.355 PRIMARY & BALLAST. Approx. resistance (ohms) (ballast cold). .845 Ditto, (ballast and primary warm). R .925 Approx. time constant under working conditions (sec.) (ballast warm). tc = L/R. .00325 Final current at 12 volts, assuming working conditions (amperes) Co 6.49 Short circuit current (amperes) Ratio ballast resistance. / primary coil resistance. 2.94 Damping co-efficient. R {Sir Henry Royce} /2L 154.2 14.2.24. | ||