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 failures, their cause, and proposed solutions for improved winding methods.
| Identifier | ExFiles\Box 164\5\ img192 | |
| Date | 26th January 1934 | |
| 2609 E.{Mr Elliott - Chief Engineer} From Hs{Lord Ernest Hives - Chair}/Wst. c. to By.{R.W. Bailey - Chief Engineer} c. to Wor.{Arthur Wormald - General Works Manager} Hs{Lord Ernest Hives - Chair}/Wst.3/MA.26.1.34. R.R. IGNITION COIL FAILURES. The failures which are now experienced, although now only few in number, are invariably due to breakdowns occurring between the two end layers of the secondary winding. This is a trouble experienced by all manufacturers of ignition coils and high voltage induction coils, and is fundamentally due to the self-capacitance of the windings and the external circuit. The fundamental cure is therefore to reduce the self capacitance of the H.T. secondary winding layers to a minimum, and decrease the inductance of each winding layer in order that a sudden rise of voltage at the H.T. end of the winding cam be more evenly distributed through-out the winding. The correct move therefore in the direction of making our coils more immune to breakdown would appear to be in reducing the number of turns per layer on the top layers and progressively increasing the insulation between the last few end layers. A parallel built secondary winding such as we have at present is therefore wrong and we ought to arrange our winding machine so that the number of turns per layer progressively decreases as the layers increase. The amount of insulation per layer we use at present is about right but for the last five layers we should progressively increase the thickness so that between the last layer and the one beneath there is five times the normal insulation, i.e. 10 turns of wax paper .00175" thick. | ||