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 comparative testing of various ignition coils against a standard and a new modified coil.
| Identifier | ExFiles\Box 181\M13\M13.2\ img079 | |
| Date | 13th August 1931 | |
| Hs{Lord Ernest Hives - Chair}/HEM2/AD13.8.31 contd. -2- manufactured by Telco-Remy, De Jon, Marelli and Lucas respectively these being representative of U.S.A. Continental and British practice. As these coils, owing to the relatively high inductance of their primary winding, are designed to run with a fairly high contact breaker make ratio, we set the contact points to .010" instead of .020" in order to give them a fair comparative test with our standard coil which is designed to run with a 50/50 make ratio. Throughout the test the plug gaps were set to .030". The coils were heated up on the engine by running with the cooling water temperature at 95°C. before testing, as we have found that the coil voltage is reduced slightly when hot, presumably due to increase of insulation dielectric leakage effects with temperature throughout the coil windings and in the case. It was found that all the coils misfired at 10 m.p.h. and up to 20 m.p.h. on full load top gear pick up, the Springfield De Jon and the Lucas being very bad, the Telco-Remy being the best giving about the same performance as our present standard coil. We then tried a modified standard coil which we have produced experimentally with a larger secondary voltage output and this coil never misfired at all under the same test conditions over an extended road test, showing it to be definitely superior to all the others. This coil has a secondary well insulated throughout with the best quality waxed paper insulation we can obtain and is wound with 21,000 turns of 44 SWG. wire instead of 18000 turns of 42 SWG. Using the finer gauge wire enables us to get the winding in the same space as the standard. We have carried out severe breakdown tests on this coil on our H.T. transformer test rig without failure and tests are continuing in order that we shall be satisfied there is no likelihood of this coil being less reliable in service than our present standard. We consider that this coil run with .020" plug gaps will not allow any possibility of misfiring at low speeds under full load on the 20/25 as it has an ample reserve of voltage when required. With regard to the design of our coil, we still feel that there are advantages to be gained by the use of an outside primary for the following reasons :- | ||