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 the electrical resistance in a standard starter motor system, focusing on battery and cable performance.
| Identifier | ExFiles\Box 168b\2\ img059 | |
| Date | 8th September 1921 | |
| x802 Extract from EFC5/T8.9.21. X.4399 - R.R. STANDARD STARTER MOTOR WITH FIELD COILS TWO SERIES TWO PARALLEL. X.802. X.664. Our point is that in order to fully appreciate the advantage of the two series two parallel winding, it would be necessary to see that the battery and cable resistances were brought to an absolute minimum. Our standard cable resistance, for instance 27' of 84/25's is .0083 ohm reckoned at 20°C. We consider that the absolute minimum of cable resistance should be .005 ohm., and of virtual battery resistance, worst condition, .015 ohm, giving a total of .02 ohm corresponding to a loss of volts, due to 100 amperes, of 2; thus agreeing with our assumed characteristic. The effective or virtual resistance of our standard battery reckoned on the loss of volts from 12 volts due to a current of the ordinary magnitude of 100 amperes, is satisfactorily less than the figure .015 when the battery is fully charged, or after a considerable rest, but on a discharge of this magnitude being allowed to take place, this figure is increased rather sooner than perhaps is desirable. (This feature was O.K. before the introduction of the recent modifications). The batteries which we have tested on high rate discharge and have shown up best in this respect, namely, maintaining their virtual internal conductance (reckoned in this way) for the longest periods have been :- | ||