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).
Investigation into EAC dynamo performance concerning a change in armature and circumferential brush widths.
| Identifier | WestWitteringFiles\M\2April1925-June1925\ Scan69 | |
| Date | 19th May 1925 | |
| To R.{Sir Henry Royce} from EFC. c. CJ. c. EY. EY/ED.{J. L. Edwards} X.8660. EAC. DYNAMO. - CIRCUMFERENTIAL BRUSH WIDTHS. ------------------------------------------------- The change in the armature of the EAC. dynamo from the 29 coil, to the 57 coil type, resulted in a small (on the average), though definite, reduction in the output performance under similar conditions and for a given degree of heating, leaving us with rather less margin (to accommodate irregularities) over our specification of performance. Our careful investigations on this point are now rather pointing to the desirability of brushes of smaller circumferential width. Experimentally such brushes are easily tried by filing away brushes of ordinary width, with, however, one slight difficulty - that if the narrower working portion is made central, the full advantage of the bevelling of the top, maintaining correct bedding of the brushes, is not secured, whereas if the narrower width be put entirely on one side with this end in view, the effective average main brush position is altered. This, however, can be overcome on some of our experimental machines by shifting the main brushes bodily back. Our specification of performance of the EAC. dynamo only calls for 1 ampere more on maximum minimum peak than that for the 20 HP. dynamo. In this connection (Contd. | ||