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).
Notes on modifying 20 HP and 40/50 HP dynamos for greater output and a higher cutting-in speed.
| Identifier | ExFiles\Box 68\4\ scan0251 | |
| Date | 28th March 1928 | |
| X5663 28.3.28. 20 H.P. AND 40/50 H.P. DYNAMOS FOR GREATER OUTPUT AND HIGHER CUTTING IN SPEED. X.5663 X.8664. A 28 slot half paralleled 20 H.P. armature was tried. The cutting in speed at 80°C (14 volts) was 1280 R.P.M. (standard 715) i.e. 79% greater, and the output peak on schedule volts would have been more than double the standard 11 amperes if the commutator solder had not run when an output of 21.0 amperes (at 2100 R.P.M.) was reached. If the number of conductors were reduced to 2/3 we might expect the cutting in speed to be increased 40% and the output increased more than 50%, say 60%. If the number of conductors were reduced to 3/4 we might expect the cutting in speed to be increased 25%. and the output increased more than 33%, say 40%. On the double brush 20 H.P. dynamos we have 300/225 = 1.33 times the brush area. This would be suitable for a 40 % increase in output. We therefore suggest making 28 slot armatures for these, with three turns per coil instead of four. Since the area of C.S. of conductor is to be increased in the ratio 4/3, diameter will be increased in the ratio (4/3)½ = 1.15. Present dia. 19 S.W.G. is .040". New dia. .046", say .048" or 18 S.W.G. Contd. | ||