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).
20 HP dynamo with coarser gauge armature for higher output.
| Identifier | WestWitteringFiles\S\June1928-August1928\ Scan079 | |
| Date | 11th July 1928 | |
| To R.{Sir Henry Royce} from EFC. c. BJ. E.{Mr Elliott - Chief Engineer} c. Ev.{Ivan Evernden - coachwork} ORIGINAL EFC5/T11.7.28. 20 H.P. DYNAMO WITH COARSER GAUGE ARMATURE FOR HIGHER OUTPUT. We have now experimentally tested and handed over for fitting to the 20 H.P. 'India' chassis the first 20 H.P. dynamo with coarser gauge armature winding, viz. three turns per coil of 18 S.W.G., instead of four turns per coil of 19 S.W.G. as in the case of the standard machine. The main brushes are 7º retarded from the no load neutral position. A suitable setting of the machine was found to result in a control brush angle of i.e. main positive brush to control brush) of 126º (present standard 121º). This corresponds to a smaller field span than the standard. In the normally hot condition the balancing speed for 14.0 volts was found to be 945 r.p.m. as against 710 r.p.m. for the standard machine. The peak ampere output on the approved setting was 15.5 amperes (at the schedule voltage of 18.4) at 2150 r.p.m., as against the present standard peak output of 11.0 amperes (at 17.5 schedule volts) at 1725 r.p.m. At 13000 r.p.m. the output falls to 14.0 amperes (at 18.1 volts). A curve of output of the machine in comparison with the representative standard output is attached. In the cold condition the balancing speed for 12.4 volts was 840 r.p.m. Owing to the increased output of the machine and the utilisation of the same system of commutator and brushes it is not possible to allow the same rise of temperature on | ||