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).
Testing, comparison, and failure analysis of various ignition coils.
| Identifier | ExFiles\Box 164\5\ img314 | |
| Date | 26th October 1937 | |
| To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/RC.{R. Childs} c. By/RD. 6017. Rm{William Robotham - Chief Engineer}/RC.{R. Childs}5/MH.{M. Huckerby}26.10.37. IGNITION COILS. We have received from HPS{Horace Percy Smith - Experimental Factory Mgr}/TT three D.75673 ignition coils wound with 20,000 turns on the secondary. We have numbered these N1, N2, and N3 respectively, the 'N' indicating that the polarity of the HT lead is negative. N1 is not impregnated, N2 is impregnated with bitumen compound and N3, is impregnated and filled with same. Output curves were taken and the results show that the impregnated coils N2 and N3 have a higher output than N1, while with regard to output, the difference between impregnating and filling is negligible. We next tested an R.R. type Lucas coil and found that this gave a slightly higher output than our own coils. The output of the Lucas coil falls off with speed and at 2400 R.P.M. of the distributor is slightly less than our own coils. We have also tested a Lucas LT.1272 type coil, (enclosed in a metal case) The output of this coil is less than either the RR.D.75673 type or the R.R. type Lucas. These bench tests indicate the R.R. type Lucas coil to be slightly superior to the R.R. coil, whereas road tests indicate the R.R. coil to be slightly the better on 'pick-up'. We have received from the experimental Garage two faulty coils, one is a standard D.75673 type (15000 turn) and the other a standard D.75260 coil. The D.75673 coil was stripped and a break was found at the joint between the end of the secondary winding and the flex; the wire had been flattened out and finally broken by vibration on the insulated tube of the primary; this caused sparking across which burned through the wax paper to the next layer of winding. If this coil had been impregnated with bitumen compound this trouble could not have developed. The D.75260 standard P.III coil had broken down in the same place, only this time the wire had not broken, but had sparked through to the next layer; a thin piece of mica placed under this joint would overcome this weakness. The argument against the use of this mica is that air spaces would be formed and cause ionization to take place; however, if the coil were impregnated with bitumen compound these air spaces would be sealed, and thus prevent damage due to this action. In view of the above results we recommend that all | ||