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).
Most efficient winding arrangements for an ignition coil.
| Identifier | ExFiles\Box 164\5\ img432 | |
| Date | 13th December 1939 | |
| To Ev.{Ivan Evernden - coachwork} c. to Jnr.{Charles L. Jenner} RM{William Robotham - Chief Engineer}/RC.{R. Childs}8/JH.13.12.39. re Ignition. The most efficient arrangement for the windings of an ignition coil is obtained when the auto-transformer system is employed. In this the turns and therefore the voltage of the primary and secondary are additive. It is also known that the most economical results are obtained when the centre electrode of the sparking plug is made negative with regard to the coil. It is impossible to provide for both the above conditions unless the positive terminal of the battery is earthed. We at present, earth the negative terminal of the battery and in order to make the central electrode of the sparking plug negative, arrange for the primary and secondary to be wound in opposite directions. When the windings are so arranged, the end of the secondary adjacent to the primary should be connected to the battery side of the primary, or a further loss is incurred due to the windings acting in opposition. Figs. A.{Mr Adams} B. C. and D.{John DeLooze - Company Secretary} show diagrammatically four possible arrangements for the windings of an ignition coil. The arrows show the direction of induced voltage at break). (a) Winding cumulative: centre electrode of the sparking plug positive. Battery negative earthed. (b) Windings in opposition centre electrode of the sparking plug negative, battery negative earthede. (Std. R.R. arrangement). (c) Windings non-cumulative but not in opposition: centre electrode of sparking plug negative: battery negative earthed. (d) Windings cumulative: centre electrode of sparking plug negative: battery positive earthed. Thus the most efficient arrangement is shown in (d) and for this, it is essential that the battery positive is earthed. | ||