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).
Dynamo selection for future cars, comparing different sizes and their performance characteristics.
| Identifier | ExFiles\Box 168a\3\ img032 | |
| Date | 24th February 1940 | |
| Elec. 6142 IV. C. H/W. R.M/D.II.24.2.40. Dynamos for Future Cars. Some discussion has arisen over our recommendation that a five-inch dynamo continue to be fitted on the 8-cylinder car. On the one hand it is contended that if the 4.5" dynamo is large enough for cars of the Nipplet class, it is large enough for all cars, since the equipment, and therefore the load, will be the same. Our contention is that, if the equipment and load are to be the same on all cars, then all cars should have, at least, a 5" machine. But we are assuming that, on the Nipplet class of car, we can limit the equipment provided, giving the customer no more than that provided on similar cars of outside manufacture. On the other hand we regard the 8-cylinder car as our most expensive model, on which we must provide a complete system, and one, that, which will give the minimum of trouble. Based on these assumptions our arrangement are as follows:- (1) The R.R. 5" dynamo can cope with a probable load of 18 amps. at high speeds, which leave little margin for extremes of high load and speed. This we know from our tests in France, where the probable load is in the neighbourhood of 20 amps, and speeds at maximum, the result being a high life of only about 10,000 miles. (2) On the same basis of reckoning, the Lucas 4.5" machine can only cope with about 14 amps. Actually its regulator limits it to about 13 amps. (3) Our 5" machine cuts in at 14.2 m.p.h. as compared with 16.0 m.p.h. of the smaller machine. A low cutting in speed is an advantage where a car is used a lot for town work, with low speeds and frequent stopping and starting and parking. | ||