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 4½ inch diameter starter motor (Sequence J.3).
| Identifier | ExFiles\Box 61b\3\ scan0262 | |
| Date | 17th December 1931 | |
| Y6091 To R.{Sir Henry Royce} E.{Mr Elliott - Chief Engineer} From Hs{Lord Ernest Hives - Chair}/Wst. Hs{Lord Ernest Hives - Chair}/Wst.2/MA.17.12.31. J.3. STARTER MOTOR (SEQUENCE). We give below preliminary calculations for this 4½" dia, motor which are being tried out by Ry. to see if the same are practicable. These calculations are based on the assumption that at a maximum cold engine turning torque of 600 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 = 218 x 10³ 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 = .0053 sq/ins Slot area. = .0300 sq/ins Suggest use copper strip .130 x .056". Estimated ampere turns required = 320. Assume 50% increase due to armature reaction effects. = 640. With current of 127 amperes this gives approx 4½ turns per pole. Resistance of main field. = .0175" C.S. area. = .0063" Suggest 12 S.W.G. D.S.C. wire to be used. Teazer winding estimated for the same ampere turns. = 30 turns of 18S.W.G. D.S.C. wire. Hs{Lord Ernest Hives - Chair}/Wst. | ||