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).
The development and modification of improved dynamos for 40/50 and 25 HP models.
| Identifier | WestWitteringFiles\W\May1931-August1931\ Scan008 | |
| Date | 6th May 1931 | |
| ORIGINAL To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/Pgt. c. Sg.{Arthur F. Sidgreaves - MD} c. Mor. E.{Mr Elliott - Chief Engineer} c. Da.{Bernard Day - Chassis Design} RV. Hs{Lord Ernest Hives - Chair}/Pgtl/AM.6.5.31. X6005/1 X6099 IMPROVED DYNAMOS 40/50 and 25 HP. It will be remembered in connection with the 40/50 dynamo that as a result of a general demand for a machine that not only had a higher output but would maintain it fairly well at high speeds, we developed a machine with a 48 coil armature. The main features of this machine were the 24 slot armature wound with a heavier gauge wire (17 gauge instead of 18) and the poles tapered to give an eccentric air gap. Although this machine proved satisfactory on experimental test, when tried out on Sg{Arthur F. Sidgreaves - MD}'s car in London it failed to keep the battery charged. This machine was used in connection with the two charge scheme but even with the extra field resistance short circuited it still failed to keep the battery charged. It was subsequently altered by doing away with the tapered poles, in which condition the cutting in speed was reduced at the sacrifice of output at high speeds. With this modification the machine was then satisfactory under traffic conditions. We have now succeeded in improving this machine so that the cutting in speed is reduced to approximately 12 m.p.h. at the same time more than retaining the high peak and degree of flatness of the high output machine. An output curve of this machine compared with the present one as fitted and being delivered on L.H. F.2. cars is attached. The improvement has been obtained by leaving off the tape of the armature coils which enables us to use four more conductors per slot. We find on examination of other makes of machines that the general practice is to dispense with tape on the armature coils and rely on the slot insulation. In our case we mill the slots and therefore we think we have a better chance of doing away with the tape compared with the usual practice of using stamped armature plates which leave a rough edge. The performance of this machine, both for cutting in and output at high speeds, is better than anything we have had before, but we still do not balance | ||