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).
The selection and testing of fuse wire sizes for a dynamo's field circuit, including test data under cold and hot conditions.
| Identifier | WestWitteringFiles\K\October1923\ Scan12 | |
| Date | 1st October 1923 | |
| Contd. -7- EFC1/T1.10.23. carrying capacity to act as a protection against such over-excitation ? Although it is a complication to have a second size of fuse wire (three sizes of fuse) and a second supply of wire to be carried, nevertheless this may be better by reducing the possibility of damage to the dynamo. As the fuses stand at present, there would still, of course, be the danger of the wrong fuse being put in the field circuit and it might be considered necessary to have a different kind of fuse for this particular circuit. The right size of fuse wire would be 40 S.W.G. (.0048" dia.) fusing at 6.4 amperes when put in our present fuse holders. With the machine normally cold and normally hot respectively, the quantities to cause this fuse to go, with the dynamo on open circuit, would be as follows :- COLD. HOT. Dynamo speed 920 1225 Main dynamo volts. 26.0 33.5 Field volts. 17.5 23.0 Field amperes. 6.4 6.4 Road speed. 12.45 16.6 m.p.h. In normal running, the greatest field current ever obtainable is 3.5 amperes. Thus we should allow a margin of safety of 83% on the fusing current. A further test has been made on a heat insulated machine with this fuse in the field circuit, running the dynamo always at its maximum speed consistent with just not blowing the fuse, and it is considered that this test Contd. | ||