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).
Analysis of excitation curves and performance of a Pre-War Bosch Dynamo.
| Identifier | WestWitteringFiles\E\November1920\ Scan45 | |
| Date | 10th November 1920 | |
| To R.{Sir Henry Royce} from EFC. c. to CJ. c. to E.{Mr Elliott - Chief Engineer} c. to PN.{Mr Northey} c. to Da.{Bernard Day - Chassis Design} c. to EWT. for Oy. c. B.Y. ORIGINAL EFC1/T10.11.20. X. 796 - PRE-WAR BOSCH DYNAMO. In our EFC1/T5.10.20 it was remarked that the hot and cold open circuit volt-speed curves (10 to 17 volts) of the Bosch dynamo were very nearly coincident. This at first suggested that within certain limits the armature flux was approximately constant for variation of field current. We therefore took field excitation curves of this dynamo with entirely separate excitation and obtained the curves marked I and II on attached photostat, corresponding to speeds between 375 and 475 R.P.M., from which curves it will be seen that the field excitation curve follows more nearly a magnetisation curve of iron without an air gap than in the majority of machines, this being due no doubt to the smallness of air gap of the Bosch dynamo. The curves show, however, that the armature flux does rise with excitation, therefore one is led to assume that the gain in E.M.F. due to increased flux was counter-balanced by the loss of terminal P.D. due to the increased field current in the armature. In order, therefore, to thrash out this point, a second pair of curves III and IV were taken, labelled "Self-excitation". An imaginary variable temperature condition of the field winding in which it can have any resistance between certain limits was imitated by inserting additional resistance in the field circuit to correspond to higher resistance than normal, and inserting Contd. | ||