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).
Experiments on coil construction, insulation, and performance to diagnose inefficiencies and ignition issues.
| Identifier | WestWitteringFiles\J\November1922\ Scan93 | |
| Date | 18th November 1922 | |
| R.R. 199 (250T) (SD676 19-7-17) MP180865 Contd. (3) EFC/1/T18.11.22. (14) Our experiments on the coils have indicated, e.g. by cutting out, or very nearly cutting out, the ballast resistance, that the provision of additional energy in the circuit does not improve matters materially. The fault can be distinctly reduced but only at the expense of a considerable loss of efficiency. It therefore appears that some more radical change in the core construction is required. On this we propose to experiment by providing a bigger and longer core and in this case to omit the hedge-hogging. (15) Regarding the material for the insulation between layers of winding, we think we should again return to the use of three layers of U.S.A. Bosch condenser paper between the layers of winding. Quite early on we thought that, owing to the high inductivity and dielectric loss we had found for this paper in connection with its use in condensers, some of the losses were taking place between the layers and we therefore put three layers of this paper instead of two. Afterwards we decided that this amount after all was inappreciable, but now we begin to think that after all this may account for some inefficiency of the coil. It is a fact that there are losses due to dielectric hysteresis because whereas the condenser will show no leak on a D.C. potential of 200 or 300 volts, it immediately begins to warm up when an A.C. potential of the same maximum value is applied. (16) It is an experimental fact that the bolts holding down the coil are in some way a source of loss, also it appears that the L.T. wires may assist, though one would anticipate that the loss mostly took place from parts of the coil in the vicinity of the last layers of secondary winding and the H.T. terminal. (17) We still do not feel that we thoroughly understand the phenomenon, because the actual results seem to be erratic. Another point we have not been able to explain is that whilst leakage is being felt by the fingers in contact with the coil, short circuiting of the ballast which some would think would make it felt all the more, practically removes the sensation. Then again we cannot give a definite answer as to why the ignition becomes defective at slow speeds. We do not think the slow break is the explanation of it, because at any speed at which the engine will run, the break is fast enough to be quite satisfactory on any other coil apparatus than ignition. On the bench at any rate with the coil cold, we find a dead slow rotation of the distributor to be just as effective. This will be tried with the coil hot. Contd. | ||