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).
Contact breaker timing and performance test results for a magneto.
| Identifier | WestWitteringFiles\R\2October1927-November-1927\ 74 | |
| Date | 2nd November 1921 | |
| Contd. -2- EFC3/T2.11.21. Contact breaker timing. Referring to the position of maximum flux of the armature (dead slow) i.e. the position in which the armature is naturally held by the magnet, as the datum position, we find that in the advanced position of the contact breaker, the make occurs 20° before this datum position. The range of the magneto is 54.5° (N.B. Our General Specification asks for not less than 58°, whereas you have, in one of your notes to Mr. North, mentioned a figure 55°). The advance break occurs at 113°, the period of make being 133°, corresponding to a make ratio of .74. (6) In an endurance test carried out on the magneto in which it was run for 7 hours at a speed of 2000 r.p.m. with timing lever fully advanced, sparking being caused to take place on a sequence of H.T. 3rd. point spark gaps in air set to 5.5 mm., the observed results were quite O.K. (7) On our routine short circuit test in which the magneto is run at 1500 r.p.m. for half an hour with timing lever central and with the primary and secondary windings short-circuited to the framework of the magneto, the performance of the machine was O.K. (9) & (10) The open circuit volt-speed curve and the short circuit ampere-speed curve made on this machine showed a satisfactory result, and showed that the volt-ampere capacity at 2000 r.p.m. is 33.9, as against 29 for one of the latest EW6 Watford sleeveless machines. (11) Utility test. For the purpose of this test a 3.0 mm. annular spark gap (dia. of central electrode .087", inside dia. of earthed electrode .325") in air, shunted by a non-inductive chemical leak of value 3 microhmos (we have since altered this figure to 2.5 as being more suitably representative of the leak which might occur on the H.T. circuit) is arranged to replace one of the six test gaps sparked by the magneto, the remaining five gaps set as before to 5.5 mm. The speed range over which the magneto was capable, for all positions of the hand range lever, of firing this special test gap with shunted leak regularly, was found to be 500 to 4500 r.p.m. Our Specification calls for a speed range of from 700 r.p.m. to 2100 r.p.m. corresponding to 3 microhmos leak (we have since altered this to 700 to 2500 corresponding to 2.5 microhmos leak). | ||