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).
Field fuse failures in a 20 HP car, attributing the issue to cumulative oxidation of the fuse wire.
| Identifier | WestWitteringFiles\S\June1928-August1928\ Scan107 | |
| Date | 24th July 1928 | |
| -3- Contd. one of the shunt coil currents we think there would be difficulty with the field fuse (using present standard). I wrote another note to E.{Mr Elliott - Chief Engineer} ref. EFC2/T24.7.28 con- cerning this matter, the points in which he has probably by now taken up with you. I think that possibly the explanation of the failure of the field fuse on your 20 H.P. car is as given therein. It was a little bit difficult in the first instance to get the size of field fuse right because it could not be based on the actual fusing current of the wire as tested in the ordinary way. It was discovered that what did determine the size of the wire was the minimum current which would just not cause oxidation of the tinned surface. We had in the early stages to put up the size of field fuse twice before we got reasonably clear of failures, as you say, for no apparent reason, but which were in those cases undoubtedly due to the cumulative oxidation. Cumulative oxidation causes ultimate failure with a much smaller current than the fuse would carry originally. With the size of field fuse we had ultimately to adopt we now know that this does not (when new at any rate) provide complete protection against damage to the system in the event of a broken circuit. The breakage of the wire may be assisted by the difference of expansion in the way you suggest, but we think what is really needed is a fuse which is immune from oxidation, e.g. a sealed fuse filled with inert gas. This is merely an idea and we do not expect it is practicable. If we could have a fuse of permanent value of fusing current, we could then | ||