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).
Detailed analysis of a coil's construction, materials, and winding specifications.
| Identifier | WestWitteringFiles\V\2January1931-April1931\ Scan038 | |
| Date | 9th February 1931 | |
| -2- EFC2/ADL9.2.31. contd. "We were unable to ascertain the cause of failure owing to the black bitumen impregnation, but it was observed that the coil was not burnt out although signs of rather excessive heating were evident. The design and construction of the coil we found to be very interesting and gave evidence of being a high class coil. The case was made out of .012" (30 S.W.G.) sheet tin with a soldered seam, the top and bottom being spun over and soldered. The coil is mounted in the case on a porcelain disc 1 1/4" dia 5/16" thick in order to insulate the core, which is at H.T., from the metal case. A bakelite moulding with the top tin flange of the case apparently moulded in, holds the coil in position by a circular spigot extension which fits over the core at the top, the H.T. terminal being in the centre of the moulding externally and the two L.T. primary terminals at each side. Bent round each side of the coil were 8 iron plates (4 each side) 3" x 3 1/4" x .013" for the purpose of additional iron in the magnetic circuit and also apparently to confine the flux path within the case. This, we consider is an important feature in the design of these C.P. coils. The primary winding consisted of 404 turns of 25 SW.G. plain enamelled wire, weight 3 1/4 ozs, wound in 6 layers as follows :- Bottom layer next to secondary 82 turns 2nd layer 75 " 3rd " 71 " 4th " 65 " 5th " 57 " 6th " 54 " Each layer was insulated with a .005" thickness of varnished paper by appearance. The disposition of primary and secondary windings relative to the core was as shown in sketch. Secondary. Top Core Bottom Primary. | ||