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 vehicle's dynamo and voltage regulator performance and settings.
| Identifier | ExFiles\Box 164\3\ img106 | |
| Date | 7th January 1938 | |
| -3- Rm{William Robotham - Chief Engineer}/RC.{R. Childs}10/JH.7.1.38. The values of volt drop shown, are representative of the average car, and correspond to a charging current of about ten amperes. Now the dynamo output at 13 volts, is at present limited by commutation at high speeds to about 14 amperes. Our estimated normal maximum load is about 15 amperes but may be considerably more where a radio set etc. is fitted. The estimated load then is a compromise (somewhat in favour of the dynamo) between what the dynamo can give at high speeds with reasonable safety, and what it may be called upon to give. From this, the setting of the regulator should be 15 amperes at 13 volts. Since however the characteristic of this unit varies with temperature, we must again compromise between what it will give cold and what it will give hot. Consequently the regulator is given a lower cold setting namely 14 amperes, in order that it may not be dangerously high when hot. Finally a current of 14 amperes supplied direct to a battery in such a state of charge that it would put up 13 volts would be ample, but owing to the difference in potential along the circuit, as indicated the battery does not receive this current until it has fallen in charge to 12 volts. This effect could be mitigated by :- (a) Reducing the resistance and consequently the volt-drop in the circuit. (b) Using a higher-output regulator. (c) Reducing the internal resistance of, or fitting a larger capacity battery. Work has already been done along the lines of (a) resulting in the double-contact cutout, but anything further in this direction would add to the cost without yielding much in return. The use of a higher output regulator is the most simple and convenient method. This however has the disadvantage of increasing the load on the dynamo, which is already working near the limit. In this connection arrangements have been made with the Makers for the supply of two units, specially adjusted to give a 20% increase. These will be tried out with a view to standardisation. In addition there is the feature of the divided series winding on the regulator which we are anxious to adopt and which permits a heavy boosting current to be supplied to the battery. | ||