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).
Ignition coil temperature tests and the charring effect on the primary winding.
| Identifier | ExFiles\Box 69\1\ scan0239 | |
| Date | 16th October 1929 | |
| By.{R.W. Bailey - Chief Engineer} from EFC. c. HS.{Lord Ernest Hives - Chair} c. HS{Lord Ernest Hives - Chair}/AJL. c. EY/RD. X8710. EFC1/AM.16.10.29. X.8710. IGNITION COIL TEMPERATURES AND CHARRING EFFECT ON PRIMARY WINDING. Further to our EFC1/AM.10.10.29, you will probably be interested to have the details of a very conclusive test which we recently made on an up-to-date S.S. standard 22 SWG. primary coil. The first portion of the test consisted in running the coil electrically connected in the normal manner but with the coil in an oven in which the ambient temperature was maintained at 100°C. In addition to this high ambient temperature other circumstances were rendered extreme as follows :- Supply voltage 18.0 Distributor make ratio .75 (normal ratio .50) Ballast resistance 1/2 value instead of the normal 1/4. Eight hours of continuous running in these circumstances constituted the first portion of the test. The second portion of the test followed the first portion immediately and consisted in leaving the primary circuit on contact, the voltage of supply being reduced to 15 and the heating current of the oven being taken off so that the oven could cool down. It will be seen that the first portion of the test represents, in an exaggerated manner, the very worst possible condition of normal running of the coil under the bonnet of a car, whilst the second portion represents the error of leaving the circuit switched on while the bonnet temperature is otherwise cooling down. Between the first and second portion of the test and also after the second portion, suitable resistance measurements of the windings were made by which the temperature of the primary was estimated to be 190°C. in the first case, and to have fallen to 136°C. in the second case. | ||