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).
Analysis of vehicle starting performance, comparing different batteries and cables.
| Identifier | ExFiles\Box 168b\2\ img047 | |
| Date | 11th August 1930 | |
| -3- Contd. The line is an S.A.E. standard and is 12 volts at zero amps, 10 volts at 200 amps, and 8 volts at 400 amps, (straight line characteristic). If the terminal volts at the motor depart from this line, the speed curve, brake horsepower and efficiency curve will be altered, but the torque curve will remain unaltered. The ordinate of the speed curve at any current value will be reduced in proportion to the ordinate of the voltage curve. On the chart of terminal volts I have shown the voltage at starting motor which we obtain at present and the voltage that we should obtain with the 90 ampere hour Willard or the new Exide battery, using thicker cable. You will see that if we take the 200 amperes line as representing severe winter starting conditions, with our present battery and starter cable we only obtain 7-3/4 volts at the motor, whereas with batteries of greater capacity and thicker cable we could obtain about 10 volts. This would make a difference of between 28 and 22 R.P.M. of the engine with the existing starter motor, and of 45 and 35 R.P.M. with the new Bijur starting motor. It is therefore well worth while to consider fitting the greater ampere hour battery and thicker starter cable. BATTERIES: The particulars of the Willard battery are as follows :- SJEN-28. Length in inches Width in inches Height in Inches Weight in Pounds Ampere Inter-mittent Hour Capacity 5 7-1/2 At 20 Minute Rate. 17 7/8 7 1/8 9-13/16 100 104 90 82 104 Voltage drop approximately 1 volt per 100 amps. (Ther makers claim somewhat better results than this, but this figure corresponds closely to our tests). Contd. | ||