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 responding to an enquiry about a car's electrical system, discussing voltmeter readings, a special dynamo, and charging P.D.'s.
| Identifier | ExFiles\Box 54\1\ Scan113 | |
| Date | 30th August 1926 | |
| X4617P EFC2/T. 30th August, 1926. Mr. G.R.N. Minchin, Messrs. Peto & Radford, 50, Grosvenor Gardens, London, S.W.1. X8780 Dear Mr. Minchin, Thank you for your letter of the 23rd. inst. The reason I have not answered this before is that I had the third and last week of my holiday. I agree that the running of your car on five cells has not been long enough to notice the effect on the cutout or ignition contact points. Enclosed you will find the notes I have written on the "Utility of a Voltmeter on the Electrical system". You will see that I have specified the way this should be connected, and that contrary to your surmise it is able to give the reading of the battery on open circuit or under load, provided the car is stopped or travelling very slowly. It would have been a rather bad omission if I had not catered for that. As a matter of fact I have had a voltmeter connected in this way on the 20 HP. car I have been using this last week and it has been interesting to watch its indications. Though we know it is possible under certain circumstances to get up to or nearly to 18 volts, under actual running conditions, I did not ever get a bigger reading than 17.0. With regard to the special dynamo for you, I am afraid we have not been able to do anything yet but will get it in as soon as possible. The figures of terminal charging P.D.'s and E.M.F's which you say would be of interest to you are contained in the curves accompanying our report EFC1/T26.6.26. sent to you with our letter ref. EFC3/L. of June 26th, which we trust you received. The curves themselves support the statement that the "terminal P.D.'s at lower rates of current are considerably less than the true E.M.F.'s at high rate" (Contd) | ||