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).
Responding to a query on the electrical system's capacity and dynamo output for a 20 HP car, GLK-46.
| Identifier | ExFiles\Box 37\1\ scan 152 | |
| Date | 28th June 1927 | |
| W/S. To HO. from EFC. X3199 EFC3/T28.6.27. 20 HP. CAR GLK-46 (LORD DAWSON OF BENN) X5783 X5780 X3199 Your HO6/EBN27.6.27 has been handed to the undersigned. Answering your query in regard to the amount of current required for standard head lamps, side or wing lamps and tail lamp, these lamps, together with the ignition, require 9 amperes of current. The remaining items mentioned by you are only an intermittent load and need not be counted. The peak output of the dynamo in these circumstances of running would be about 10½ amperes, but that would occur at road speed of about 24 m.p.h. At higher speeds the generated current will fall and will balance the load mentioned at a speed of about 33 m.p.h. Above that speed, the requirements, not including body lights, will be in excess of the output, and the battery will discharge. The curve of dynamo output is purposely arranged like this so as to avoid too high a rate of charge at high speeds in daylight running, and naturally the whole things is a compromise. In regard to your question as to what additional load can be put on this system, this cannot be answered without knowing the conditions of daytime running. If the night running you describe was repeated night after night, then owing to the speed being somewhat lower sometimes, it is probable that the system would just keep going. Naturally, however, the system will not keep going with only night running such as you describe if an additional load is added. If, however a considerable amount of daytime running is done, during which the charge of the battery is replenished, and if we suppose for the sake of argument that equal running time under daylight conditions is achieved, we are of the opinion that it would be possible to have an additional load of 3 to 4 amperes for body lighting during the night running. According to the varying proportions of day and night running, the amount of the additional load possible would be less or more than this. That is to say, if the night running was a good deal less than the amount of daytime running, the load could be in excess of this amount, and vice versa. You will see, therefore, that we cannot give any definite answer but that it must be decided with the help of the above hints in accordance with the duty which the car has to perform. In a general way it may be said that the system is arranged so that it will just keep itself going, without additional load, under the largest nighttime conditions of ordinary load which may be met with. EFC. Note returned. | ||