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 testing and development of a 20/25 Dynamo with voltage control.
| Identifier | ExFiles\Box 62\3\ scan0421 | |
| Date | 21th March 1934 | |
| Ha/Wst.2/MA.21.3.34. 20/25 DYNAMO TO R.R.SCH.481 VOLTAGE CONTROL. We have tested the first sample dynamo made to the above scheme and the results were quite satisfactory. The output for minimum safe heating at slow speeds was 13.6 amperes. At high speeds, i.e. 5000 RPM. for the same temperature rise the output dropped to 9.5 amperes. This drop in output is due to rise in temperature of the armature core due to iron losses and extra heating at the commutator due to the commutation being worse at high speeds. Actually the sparking is slightly better at high speeds than the large machine we now fit to the Bentley. It was considered that an improvement in performance could be obtained by increasing the air gap. The object in increasing the air gap was to prevent sparking at the brushes when the machine is delivering maximum output at maximum speed also to reduce the iron losses and consequence heating at maximum speed thus obtaining a larger output for the permissible temperature rise. The air gap was increased to .020" and a remarkable improvement was obtained in the performance of the machine. The output was increased to 15 amperes, at slow speeds with only 50-RPM. increase in the cutting in speed. The output at high speed was also increased to 10.5 amperes. This machine with increased air gap is considered to be quite satisfactory and further machines are being produced to be fitted to chassis for road test. In order to improve the high speed performance which is still very poor, we are carrying out further tests by chamfering the poles and by trying different grades of brushes and spring pressures. Another experiment we also wish to try is direct air cooling on the dynamo as we believe this has possibilities. We are aiming at improving this machine so that it will be possible at a later date to fit it to the Bentley in place of the large 40/50 HP. machine at present thereon. Hs{Lord Ernest Hives - Chair}/Wst. | ||