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).
Revised calculations for an E.A.C. starter motor under unfavourable starting conditions.
| Identifier | ExFiles\Box 64\1\ scan0129 | |
| Date | 30th May 1923 | |
| X.9620 - E.A.C. STARTER MOTOR. Revised calculations based upon LeC.1719 and RL/M16.5.23, the initial quantities being taken as relating to the assumed most unfavourable starting condition. Torque required to turn engine = 1400 lb-inches (say) Speed reduction ratio = 30 Taking 85% gearing efficiency, effective torque ratio - .85 x 30 = 25.5 Motor torque when rolling engine is therefore required to be 1400 / 25.5 = 54.9 lb-inches. Engine speed required = 40 R.P.M. Motor speed = 1200 R.P.M. Motor power is therefore .00001587 x 54.9 x 1200 = 1.045 H.P. Assuming 60% efficiency at this power electrical H.P. becomes 1.75 Motor watts - 1300 Motor volts = 9.0 Motor amperes = 145 (This allows 2.07 volts loss from 1200 volts per 100 amperes, a figure which we know from experience will be almost correct for the size of battery and cables used). Contd. | ||