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 testing of a coil and the charring temperature of its cotton insulation.
| Identifier | ExFiles\Box 69\1\ scan0240 | |
| Date | 6th October 1929 guessed | |
| -2- After being subject to this treatment, the coil was first normally tested and was found to be quite normal in operation, and afterwards it was opened up and unwound for examination. The condition of the cotton insulation of the primary wire was found to be that a very slight discolouration only i.e. the very beginning of the charring condition. In this connection some tests we have made to ascertain the charring temperature of cotton insulation will be of interest. Both by electric heating and electrical resistance of a wire, and also by direct observations given in an oven, we have arrived at the following temperatures :- Very slight discolouration is produced at 200°C. (Note the agreement between this and the estimated temperature of the primary winding of the coil in the first portion of the test). Light brown colouration is produced at 240°C. Dark * * * 280°C. Insulation turns black at about 320°C. We consider that the above test satisfactorily demonstrated, that any case of charred 22 SWG. primary winding of a coil on a car, could only be explained by the existance of some abnormally high voltage on the system, and therefore by the result of a fault not properly belonging to the ignition system. EFC. | ||