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).
Test results for a modified 20/25 dynamo with increased field resistance and reduced pole core width.
| Identifier | ExFiles\Box 168a\3\ img178 | |
| Date | 26th March 1935 | |
| (603) E.{Mr Elliott - Chief Engineer} From Ha/Wst. c. to Ty. c. to Vor. Ha/Wst.9/MA.26.3.35. 20/25 DYNAMOS. With reference to E.G/HP.22.3.35., item (2) we have now carried out a test on a standard 20/25 dynamo with the pole cores reduced in width .176" and the space filled up with extra turns on the field winding. The results of our tests were satisfactory in that we have increased the field resistance to a safe value without appreciably affecting the performance of the dynamo. Two extra layers of field winding per pole were accommodated and this increased the total resistance of the field winding to 6.5 ohms as compared with 5.8 ohms on the standard machine. This should now effectively prevent overloading of the regulator contacts. The reduction in the pole core section has increased the "cutting in" speed from 12 M.P.H. to 12.5 M.P.H. approximately. This is not considered serious in view of the benefit gained in other directions and especially as we anticipate that we shall regain this loss of speed later with poles having a larger polar arc. Ha/Wst. | ||