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 problems of ignition screening for a 20/25 engine in a light tank, comparing battery and magneto systems.
| Identifier | ExFiles\Box 163\2\ img003 | |
| Date | 4th August 1932 | |
| To P. from Hs{Lord Ernest Hives - Chair}/Wst. c. E.{Mr Elliott - Chief Engineer} c. Wor.{Arthur Wormald - General Works Manager} Bv. X6008 Hs{Lord Ernest Hives - Chair}/Wst.2/AD4.8.32. IGNITION SCREENING OF 20/25 ENGINE IN LIGHT TANK The screening of the battery ignition on this engine presents rather a formidable problem. With the magneto the screening problem is much easier owing to the fact that the magneto is a complete high tension generator and can therefore be easily screened complete with its wires. With a battery ignition system, however, it not only becomes necessary to screen the high tension wires, coil and ignition distributor but also the whole of the electric wiring on the tank. This extra screening is necessary owing to the fact that the ignition coil primary is linked through the switch to the battery to which the generator and all the wiring on the tank is also connected. This means that the whole of the electric system virtually broadcasts the high frequency impulses sent to the battery from the coil primary and unless the electric system is metal screened throughout, these disturbances will occur. This problem cropped up quite recently in connection with the proposal to fit a battery ignition distributor to a Kestrel engine. It would be possible, however, to provide a system of chokes and filters on the general electrical service side of the accumulator in order to obviate screening the whole of the wires, but as weight is of very much less consequence in this instance than in an aeroplane it would be more effective to use metal braided wires for the whole of the electric wiring. It will also be necessary not only to screen the wires but also such items as switchbox and distribution board, in fact any electrical unit which is in any way connected to the battery from which the ignition coil is tapped. There is also the question as to whether our ignition coil will be able to cope with the extra capacity represented by the metal braided high tension cables and the screen over the distributor. Battery ignition systems always inherently have less spark energy than a magneto and consequently any additional load in the form of either resistance leak or capacity leak will reduce the final voltage available at the sparking plugs. | ||