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).
Modifying dynamo brush dimensions to improve output at slower speeds.
| Identifier | WestWitteringFiles\M\2April1925-June1925\ Scan68 | |
| Date | 19th May 1925 guessed | |
| EFC4/T9.S.25. -2- Contd. we do not regard the dynamo as being one whose main function is to give more output, but one which is capable of giving the output at a slower speed If it is agreed that the output is not intended to be materially larger, then there is no reason why the brushes should be of greater circumferential width. They might be of greater circumferential width in proportion to the larger commutator diameter, so as to subtend the same angle and this addition would about allow the same current density with the slightly larger output. In any case, however, comparing the EAC. with the present standard 20 HP., we have 33% more total axial length in the brushes, so that taking all things into consideration, it would not seem unreasonable to reduce the main brushes down to 3/4 or 2/3 of their present circumferential width. We have already made two independent experiments with an exaggerated reduction (down to 1/3), and in each case the output has been definitely more for the same degree of heating. It is not suggested that this amount would be suitable for standardisation, but it is often a very useful thing to do to make an experiment on an exaggerated case in the first instance to get a better idea of the magnitude of the effect that such a change would have. In connection with our further experiments, we are enquiring whether it would be possible to use EAC. control | ||