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).
Defining the limit for a battery's virtual internal resistance required for operating the starter motor.
| Identifier | ExFiles\Box 168b\2\ img062 | |
| Date | 13th September 1921 | |
| H.R. MSka. 100 T/S H 13-9-21 MMc. EFC1/T13.9.21. -2- Contd. that the E.M.F. remains at the figure 12.00 and that the difference between actual terminal voltage and this figure is due to an apparent internal ohmic resistance which we will call the virtual resistance of the battery. We can then fix a limit for this virtual internal battery resistance so that if it is above this figure in any battery or in a given battery at any time, the battery is not suitable, or in a suitable condition respectively, for operating the starter motor on the car. In the case of our own chassis system using the R-R starter motor (including the case in which the fields are arranged two series two parallel) we have, as already stated in our EFC5/T8.9.21, fixed this figure at .015 ohm (for the battery and .005 ohm for the cable, giving a total of .020 ohm). Up to the present our high rate discharge test of a battery has consisted in discharging the battery, after a full charge, through an invariable resistance of .0763 ohm. If we add to this resistance figure a figure for the limit of the virtual internal resistance of the battery, we obtain .0913 ohm, a resistance through which an E.M.F. of 12.0 volts will drive a current of 131.4 amperes. Thus, to comply with our limit of battery resistance, a battery should be capable of discharging at least 130 amperes through this resistance. Certain of the batteries tried, as instanced in our previous report, have been capable of doing this | ||