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).
Dynamo output, field resistance, battery charging, and potential overheating issues.
| Identifier | ExFiles\Box 163\6\ img086 | |
| Date | 9th December 1930 | |
| EFC2/AD9.12.30 contd. -2- that with only one resistance (compromise) some trouble is almost sure to occur in both extreme cases, so that two or even three standard values of the resistance become, it may be said, a necessity. The lowest value of resistance will be approximately such as will enable the high output dynamo to continue to deliver current to a fully charged battery with a reasonable margin against overheating. To explain this statement we should say that the output of the dynamo without field resistance to a fully charged battery is such that if continued indefinitely in hot weather, there would be little margin of safety against the running of the commutator solder. For the purpose of getting sufficient output to balance the heavy head lamp current, the output setting of the dynamo can be, and is, deliberately arranged to be so in view of the fact that it is not intended to be run without a field resistance. The value of the lowest experimental resistance referred to is represented approximately by the low resistance now left on Sg{Arthur F. Sidgreaves - MD}'s car 58-GN. It is to be seen by running this car in London in winter circumstances, whether the battery charge is maintained with this rearrangement, the reduced output being only about one ampere less on the peak than the unreduced output (which unreduced output nearly balances the head lamps). There is plenty of current available for this purpose provided the average speed is high enough, and to some extent the fact that the reduced output is considerable at speeds above about 17 miles per hour at which it becomes available, may compensate for the fact that no output is available at the lower speeds owing to the lateness of the cutting in. The cutting in point of a high output machine even unreduced by the insertion of field resistance is later than we wish for — it has been explained that with the present size and weight of machine available we cannot have the early cutting in simultaneously with the high output. We wish it to be realised that this is particularly the case when we have to guard against the possibility of the machine being run on nearly full or full output with no load on the system, and with the battery P.D. having risen to a high value due to completion of charge. This may, for instance, happen if the client deliberately, for the purpose of getting the full output to charge the battery, removed the lamp fuses and switches on to head lamps. | ||