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 failure analysis, testing results with paraffin wax insulation, and proposing rubber sheathing as a solution.
| Identifier | WestWitteringFiles\J\November1922\ Scan65 | |
| Date | 9th November 1922 | |
| Contd. -7- EFCL/T9.11.22. a considerable drop of electrostatic potential between the outer layers of the secondary and the bakelite case itself, so that the bakelite case would not be subjected to the full potential, it being understood that this potential is applied to the bakelite on account of the ionised air space acting as a conductor. This idea is, we think, now confirmed by the latest result just to hand on the 16000 turn coil in a mouldensite case, in which the space referred to is filled with a mixture of paraffin wax and resin. This coil has run the engine under worst condition (already described) for 2 1/2 hours without failure, using the standard 25* ballast resistance. Failure occurred after 2 3/4 hours apparently due to the fact that the insulating wax had melted and run out, but we think it is sufficient evidence that the presence of this insulating medium is a cure for the defect. The temperature inside the bonnet had attained 90°C. An alternative which we intend to try is the use of a rubber sheath between the secondary and the case and in the first instance we are using a cycle inner tube for this purpose, having already satisfied ourselves that rubber is unaffected at this temperature. We are not sure whether the 16000 turn secondary is right for other conditions as a number of experiments which have been previously made on the number of secondary turns on 40/50 coils have rather indicated that it would be Contd. | ||