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 wire winding specifications, including resistance, turns, and current.
| Identifier | ExFiles\Box 72\4\ scan0004 | |
| Date | 19th March 1923 guessed | |
| -4- Contd. Square C.S. area of this wire covered (D.C.C.) = (.056)2 = .00313 inch2 Available C.S. area of winding space estimated to be .875 x .475 = .415 inch2. Hence number of turns = .415 / .00313 = 133 Length of wire in coil = 133 x 12.25 + 12 = 136 feet. Resistance at 80°C of whole field winding = 4 x 136 / 1000 x 5.58 = 3.04 ohms. Field amperes at hot cutting-in point as shunt machine = 13.6 / 3.04 = 4.47 Ampere turns = 4.47 x 133 = 595 which gives a fair margin over those estimated to be necessary. Volts lost in armature due to field current = .4 x 4.47 = 1.79 (1.6 assumed) These and ampere turns are high because we have adopted 18 S.W.G. wire where 18 1/4 S.W.G. would have been more exactly right. Contd. | ||