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 for motor field winding, including ampere turns, resistance, and cross-sectional area.
| Identifier | WestWitteringFiles\T\November1928\ Scan061 | |
| Date | 27th November 1928 guessed | |
| -5- Contd. Estimated ampere turns required = 353. This does not take into account armature reaction effect which may perhaps be considered to increase the necessary field ampere turns 50%. This would lead, at 180 amperes, to say 3¼ turns per pole. It is considered from previous experience that 4½ turns per pole will be right for this motor and that number is accordingly adopted. Approx. length of mean turn = 11½ " Total length of field strip = 4 x 4½ x 11½ + 4" = 207" + 4" = 211" Estimated resistance of field winding (p.3) = .0095 ohms (at 20°C) Resistance of strip per 1000' at 20°C = 12000/211 x .0095 = .54 ohm The cross sectional area of this strip = .00815/.54 = .0151 sq.inches Actually partly owing to reduction of teazer winding (36 turns) from 17 to 18 S.W.G., (Now no actuator box in series) we have been able to realise a C.S. area of .0185 sq.inches, bringing the field resistance down to .008 ohm. Since the armature resistance obtainable will be .010 ohm and the brushes and brush contacts about .005 ohm, we have a total motor resistance of .023 ohm which is, as desirable. | ||