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).
Page of calculations for armature and field coil specifications, including resistance and length.
| Identifier | ExFiles\Box 72\4\ scan0002 | |
| Date | 19th March 1923 guessed | |
| -2- Contd. Total number of armature turns = 232 Armature resistance is that of 58 turns in series. Length of mean armature turn (approx) = 13.5" Total length for armature resistance = 58 x 13.5 / 12 = 65 ft. Armature temperature considered to be 100°C under continuous working conditions. Resistance per 1000' for 18 S.W.G. at 100°C = 5.9 ohms. Armature resistance (hot) = .065 x 5.9 = .384 ohm. Allow .016 ohm for brushes and contacts giving .40 ohm as taken (Here see table Page 3). Ampere turns required per pole = 456 Resistance of mean turn of field coil = volts per coil / ampere turns per coil = 3.4 / 456 = .00745 Length of mean turn of field coil = 12.25" Ohms per 1000' at 80°C (say) = 12000 x .00745 / 12.25 = 6.70 18 S.W.G. is 5.58 19 S.W.G. is 8.01 Owing to the relative low armature resistance it is considered that 18 S.W.G. is the more suitable wire to use. Contd. | ||