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).
Test report on the fuse in the resistance unit circuit of a C.A.V. regulator, detailing failure modes and proposed improvements.
| Identifier | ExFiles\Box 166\2\ img133 | |
| Date | 18th November 1937 | |
| 6092. To By, from Rm{William Robotham - Chief Engineer}/RC.{R. Childs} c. By/RD. Rm{William Robotham - Chief Engineer}/RC.{R. Childs}7/MH.{M. Huckerby}18.11.37. FUSE IN RESISTANCE UNIT CIRCUIT OF C.A.V. REGULATOR. In testing this unit, it was assumed that the regulator had already failed to operate on the second-stage contacts; which is the first necessary condition to the burning out of the field resistance unit, and the consequent possibility of fire. The second condition is, that the main dynamo circuit be broken; due to the armature fuse "blowing" on overload, as the result of the first-stage contacts sticking, or the fuse being faulty etc. To satisfy the first condition, the fixed second-stage contact was removed from the regulator used in connection with the test. The second condition was obtained by removing the armature fuse from the circuit. With the resistance safety fuse provided, which has a nominal fusing value of 2 amperes, the actual fusing current was found to range from 2.4 to 2.7 amperes, with a corresponding dynamo terminal voltage of from 57 to 65 volts. These values were reached at a dynamo speed of about 3,000 r.p.m. or a road speed, on the Bentley car, of about 43 m.p.h. This is a big improvement on our present arrangement, wherein we rely on the field fuse "blowing" which requires a current of at least 4 amperes, with a corresponding terminal voltage of about 95 volts. Even with this reduced current, however, the resistance unit was found to get very hot; the cotton covering of the wire becoming charred, and giving off a great deal of smoke. In view of this, we would like to try fuses made up with one gaugesmaller wire, some of which we are proceeding to obtain. We would like to point out that, as received, the resistance unit was wound with 56 turns of 23 S.W.G. D.C.C "Glowray" wire. This had a resistance value much in excess of the 15 ohms required. It was found that 40 turns gave, nearly the necessary 15 ohms. Rm{William Robotham - Chief Engineer}/RC.{R. Childs} | ||