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).
Technical letter discussing the effects of current heating on ignition coil insulation and the use of ballast resistance.
| Identifier | ExFiles\Box 163\7\ img120 | |
| Date | 14th May 1930 guessed | |
| -2- contd. lately we have not been absolutely clear in the coils themselves of the effect of the current heating over long periods. It has to be remembered that the primary winding of the coil has to be well electrically insulated, i.e. for a high voltage (several hundreds). Naturally, improved electrical insulation is also improved heat insulation; therefore to some extent the two things are contradictory. Apparently we have had to find out by long experience how to make coils so that the insulation weakening effect, due to the fact of heat insulation and consequent rise of temperature, is brought down to a degree that insulation weakening will not occur over long periods of use of the coil. Our very latest proportioning of primary and ballast resistance is such, we believe, that we are just O.K. on this point for O.K. ignition in all circumstances with indefinite life of the coil. Our next move is to make an arrangement which will give a margin over this condition of being just O.K. You will understand from what I have said that it is probable that the Delco people, who had an earlier start, have already arrived at this condition. I would, however, say that it is not outside our experience to have seen the same effect occur on coils of other makes, e.g. a U.S.A. Bosch, though I do not think we have seen it on the Delco. You will probably find that the ballast resistance you will be putting on will just cure the fault without any margin, except perhaps in very exceptional circumstances in which you will appreciate that there is no margin. When you replace the coil as well, then I think you will find that you are O.K. in all circumstances for several years. But it may be possible that after, say, 30,000 to 50,000 miles running there may be no margin left though you may not realise this in ordinary running. We shall be very interested to hear what does happen, though as I have intimated, there will probably be no adverse report for some considerable time, if at all. Many thanks for the copy of your wireless catalogue which you have sent to me. You may be interested to know that we are joining the I.E.E. visit to Paris and the Pyrenees next month. Yours sincerely, | ||