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).
Letter to a Mr. Sidney regarding ignition tests, battery voltage, and sparking on a Phantom model.
| Identifier | ExFiles\Box 70\3\ scan0156 | |
| Date | 28th March 1926 | |
| X4783 PN{Mr Northey}17/DN28526. X8780 May. 28th March, 1926. Dear Mr. Sidney, Very many thanks for the trouble you and your son have taken in the notes sent to me regarding the tests you made with the ignition of your Phantom. The view you express is, I quite agree, one which the ordinary reasonable man might be expected to give, but I fear that the whole question is to under what conditions harmful sparking may take place at the make and break, is rather more complex than you might think. In the first place, every accumulator having lead plates will, when fully charged, rise to a voltage of at least 2.5 volts per cell, that is, when your battery is fully charged and therefore should not require charging any further, a short dose of current from the dynamo, even at [strikethrough] as low a rate as 4 or 5 amps., will bring the voltage per cell up to 2.5, or 15 volts for six cells. Now in the design of the ignition throughout, the condition has undoubtedly been taken into account that the voltage of the battery will rise at times to 15 volts and that the current therefore will rise in direct proportion as 12 volts is to 15 volts, or, as you have put it, from 2 amps. to 2.75 amps., without causing any undue deterioration of the make and break points. You would find by experiment that to break a current of, say, 3 amps. between two platinum points in a circuit where the voltage was not greater than 15 volts, there would be practically no destructive spark, but in the case we have to consider, the matter is complicated by the fact that there are certain induced currents and certain very high voltages arising by induction, that may tend to cause damage to the make and break points if certain other conditions were not entirely O.K. Contd. | ||