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).
Preliminary calculations for a 4 1/4 inch diameter J.3. starter motor (Semience).
| Identifier | ExFiles\Box 179\2\ img067 | |
| Date | 17th December 1931 | |
| To R.{Sir Henry Royce} E.{Mr Elliott - Chief Engineer} From Hs{Lord Ernest Hives - Chair}/Wst. ORIGINAL Hs{Lord Ernest Hives - Chair}/Wst.3/MA.17.12.31. J.3. STARTER MOTOR (SEMIENCE) X5620 We give below preliminary calculations for this 4 1/4" dia. motor which are being tried out by W. to see if the same are practicable. These calculations are based on the assumption that at a maximum cold engine turning torque of 80 lb/ins the motor will turn the engine at 60 R.P.M. Electrical power = 1200 watts represented by a current of 127 amperes at 9.46 volts. Maximum useful flux per pole = 216 x 10^3 No of armature conductors = 78 i.e. 39 slots one coil per slot. Back E.M.F. when rolling engine. 4.33 volts. Total resistance of motor. .0403 ohms. Field resistance. .0175 ohms. Armature. " .0175 ohms. Brush resistance. .0053 ohms. Resistance of one armature turn = .00180 ohms Cross sectional area of conductor = .0033 sq/ins Slot area. = .0300 sq/ins Suggest use copper strip .130 x .036". Estimated ampere turns required = 320. Assume 50% increase due to armature reaction effects. = 640. With current of 137 amperes this gives approx 4 1/2 turns per pole. Resistance of main field. = .0173" C.S. area. = .0068" Suggest 12 S.W.G. D.S.C. wire to be used. Teazer winding estimated for the same ampere turns. = 30 turns of 18 S.W.G. D.S.C. wire. Hs{Lord Ernest Hives - Chair}/Wst. | ||