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).
Calculations and specifications for an E.A.C. Starter Motor.
| Identifier | WestWitteringFiles\K\June1923\ Scan71 | |
| Date | 19th June 1923 | |
| ORIGINAL SECRET E.{Mr Elliott - Chief Engineer} A.{Mr Adams} C. To R.{Sir Henry Royce} from EFC. c. CJ. EY. EFC4/T19.6.23. X.9620 - RE E.A.C. STARTER MOTOR. Answering your R4/M4.6.23, herewith please receive further calculations revised to suit as nearly as possible the conditions therein stated. It was not possible to assume an engine torque of 2200 lb-inches at a speed of 33 r.p.m., as the electrical power represented by this product, making due and suitable allowances for efficiencies, is greater than the maximum power available at the motor terminals on the characteristic usually assumed, namely, 1 volt drop from 12 volts per 50 amperes. On this characteristic the maximum power would occur at 6 volts 300 amps. and therefore 1800 watts. We have, however, by assuming the overload engine torque to be 1900 lb-inches, the engine speed as 30 r.p.m. in place of 33, and an efficiency of 53%, made out a consistent set of calculations which are given herewith, and which by assuming a wolsr flux density of 6400 lines per cm. result in a number of conductors, namely 82, which you suggest. The calculations further result in requiring at the 178 amperes, 4 3/4 turns per field pole, and this we find can be got in quite nicely. As an alternative we feel that you would like a larger number of turns, say 6 1/4, to be tried and accordingly | ||