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).
Comparison between Lucas E.575 dynamos and the company's own make, focusing on winding schemes, switching, and output curves.
| Identifier | ExFiles\Box 182\M19\ img011 | |
| Date | 1st February 1931 | |
| -2- EFC3/ATG.2.31 contd. It will be remembered that the Lucas E.575 dynamos which used to be standard on the Silver Ghost before we adopted our own make of machine for the Phantom, were arranged in this way. It must also be remembered that, for the sake of simplicity not only in the dynamo itself but in the switching, we did not adopt a similar scheme and that we should reasonably be able to over-come or minimise the difficulties by the use of single third brush control. A Lucas dynamo constructed in this manner has four terminals instead of three and though the dynamo has advantages (in some cases) in the shape of its output curve, the charge switching becomes more complicated. It will be remembered that in the case of the E.575 dynamos we had a number of difficulties arising out of the complication of the windings and the switching, which difficulties were very fully gone into at that time. It was also considered, and reasonably so at the time, that some degree of falling away of the output characteristic with speed was an advantage. The principle of the winding is that instead of having a single field winding spanning from one main brush to the control brush as we do, there is a plain (finer) shunt winding spanning the main brushes together with a coarse winding spanning between one main brush and a control brush but with a much smaller span than in the ordinary single winding. This means that there has to be provision on the switch for the coupling up of both windings for charging purposes and there are also difficulties concerning which it may vaguely be remembered that, in the case of the E.575 machines, we spent a considerable amount of time and thought. All along therefore, we have had the advantage of simplicity and there can be little doubt that we have avoided a good many other troubles by utilising the simpler form of machine. We think you have always agreed that this extra complication should be avoided and urged that other methods should be found of keeping up the output at speed, as later became necessary, particularly with the advent of the two-rate charge scheme. It is certainly agreed that the shape of the output curve obtainable from the Lucas machine is definitely more suitable for our present circumstances, though we should not say that it has always been so. The shape of the Lucas curve has been more nearly approached on our own machines by the introduction of reluctance into the magnetic circuit, which introduction has so far had no other beneficial effect, but in all cases has had the bad effect of increasing the speed of cutting in. Therefore, although the modified output curves thus produced have been more suitable in some cases, the application of the @ fusing. | ||