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).
Issues with dynamo sparking and proposing a new armature design for scheme 911.
| Identifier | ExFiles\Box 142\1\ scan0007 | |
| Date | 30th September 1937 | |
| To Dy.{F R Danby} from RM{William Robotham - Chief Engineer}/RC.{R. Childs} c. RM.{William Robotham - Chief Engineer} c. Dy{F R Danby}/RD. RE. DYNAMO TO R.R. SCHEME 911. The main features of the dynamo to this scheme are, an armature core with 36 slots, the commutator with 72 slots, and a special improved form of brush gear. The origin of this design, lies in the known tendency of the large (Phantom) dynamo to spark badly at high speeds on load, which causes rapid wear of brushes and commutator, coupled with complaints of blackening of the commutator, and brush sticking. Sparking is chiefly due to - (1) Armature reaction. (2) Bad control of the brush, by the brush gear. (3) The balance of the armature winding upset by the presence of a dummy or lap coil. Brush sticking is due to - (1) bad brush gear. (2) Oil, or oil vapour, getting on to the commutator and brush gear, together with brush dust. Evidently the troubles can only be met in the design of the armature and brush gear. Armature Reaction. Our standard machine embodies all that can be done, apart from the armature, to reduce the effect of armature reaction. The remaining thing to be done, is to reduce the number of conductors per slot; this implies less turns per coil, but a larger number of coils and slots. We thus developed an armature which compared with the standard as follows - Machine. Turns per coil. Number of coils. Total number of Conductors. Number of slots. Standard. 4 48 384 24 Expl. 2 72 288 36 | ||