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 a 20 HP starter motor.
| Identifier | ExFiles\Box 35\4\ scan 156 | |
| Date | 4th July 1928 | |
| X.4384 4.7.28 X.4384. NEW ASPECT OF CALCULATIONS FOR 20 H.P. STARTER MOTOR, DATED 1.7.21. Engine 500 lb-inches. 96.5 r.p.m. On conductors:- 610 lb-inches at 96.5 r.p.m. or at 8.4 : 1 ratio 72.7 lb-inches at 810 r.p.m. Power .935 H.P. = 697 watts Elec. eff. assumed .55 Power supplied = 1266 watts. 137 a at 9.26 volts. Back E.M.F. = 5.10 volts. Volts = 5.1 Speed = 810 r.p.m. Torque = 72.7 lb-inches. Resis = 4.16 / 137 = .0304 ohm ØZ = (60x10^8 x 2 x 5.10) / (810 x 4) = 18.9 x 10^6 ØZ = (10^8 x 2 x 72.7) / (1.41 x 4 x 137) = 18.9 x 10^6 Ø = 161,000. Z = 116 EFC. | ||