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 winding specifications for an auto switch for the U.S.A. market.
| Identifier | ExFiles\Box 59\1\ Scan307 | |
| Date | 4th April 1928 | |
| XL4008 To BY/RD. from EFC. c. RHC.{R. H. Coverley - Production Engineer} EFC7/T4.4.28. RE AUTO SWITCH FOR U.S.A. We can now give you the necessary data for the winding of this switch with a satisfactory temperature compensation. Comparing it with our own winding :- The shunt coil will consist of copper wire winding on the armature bobbin of 24 S.W.G. D.S.C. in place of our own 28 S.W.G. D.S.C. The coil is at the moment wound with 28 S.W.G. (for 6 volt working without series resistance). The pivot bobbin will contain a winding of two No. 24 S.W.G. D.C.C. Eureka wires in parallel in place of our single 24 S.W.G. D.C.C. Naturally this will be right for the half voltage if a single 24 S.W.G. D.C.C. wire is right for the full voltage, but it is largely a question of convenience and avoidance of delay in ordering another size of wire, and in any case the slight loss of space factor will give the slight advantage needed of lower resistance, for making up the required ampere turns. The field resistance will consist of 6 ft. of No. 26 S.W.G. D.C.C. Eureka. Will you please issue your instructions to RHC.{R. H. Coverley - Production Engineer} at the earliest possible moment so that we can get this switch moving and booked out to Springfield, who are urging the supply of same. EFC. | ||