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 engine starting performance, comparing two series two parallel winding schemes and the impact of battery and cable resistance.
| Identifier | WestWitteringFiles\G\September1921\ Scan43 | |
| Date | 1st September 1921 | |
| Contd. -2- a very bad characteristic the high resistance motor might even turn the engine faster. It has been confirmed by tests on the car that the advantage of the two series two parallel scheme is not so great as would appear from our figures. There is an increase in the rate at which the engine is turned of about 9 R.P.M. on 42 R.P.M. (nearly worst condition of cold engine), but to appreciate this difference it is necessary to make sure that the battery is in a similar condition in the two cases, otherwise the variations in the battery itself may completely mask the effect and perhaps lead one to assume that there is no advantage in the modified arrangement of field coils. 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, | ||