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).
Issues with ignition coils for the Wraith model, specifically internal overheating and the risks of not using a ballast resistor.
| Identifier | ExFiles\Box 164\5\ img347 | |
| Date | 18th May 1938 | |
| Noted [Signature] EX Rm.{William Robotham - Chief Engineer} 6017. BY.18/G.18.5.38. WRAITH - IGNITION COILS. In considering the various reports, which have been produced recently in regard to the internal temperatures of the various coils, I think it is fairly clear that we are running a risk in fitting coils without an internal ballast resistance, that is where the whole of the resistance in the circuit is produced as a part of the coil winding internal to the casing. With the present coil, which we have been running up to now, it is agreed that we may have some complaints of misfiring under certain extreme conditions. This, however, is not to be compared with what would happen from a customer's point of view if a coil burnt out, and I am satisfied that neither our own high voltage coil nor the Delco has done sufficient running on our cars to make it certain that we are on safe ground, particularly when we bear in mind we have been through this once before in EFC's time, and the trouble was only clear when I insisted that each coil was unwound, as EFC. said it was too laborious a job to be done, and was not likely to give the evidence as to the cause of failure. By unwinding the failed coils, we quickly established the fact that it was internal overheating, and upon this basis we have since produced a coil which is practically trouble-free, so far as failure of coils is concerned. I think the point of view I am expressing is a rational one, and in the interests of the customer and ourselves I therefore propose that for the first 100 Wraiths we use our standard coils, but in the meantime continue to experiment extensively with both the Delco and our own special coils with higher voltages resulting from a greater number of turns incorporated in the coil. BY.{R.W. Bailey - Chief Engineer} [Signature] | ||