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).
Technical memorandum discussing current density in tungsten contact points for various ignition systems.
| Identifier | ExFiles\Box 35\6\ scan 035 | |
| Date | 5th April 1921 | |
| 88304. 5.4.21. EFC. AA{D. Abbot-Anderson}53 X.2894 - TUNGSTEN CONTACT POINTS. With regard to remarks made from America to the effect that the current in tungsten contact points should not be too high, it is noteworthy that on the Liberty Delco distributor the working contacts are about .185" dia. two of them working in parallel, giving a total contact area of .0538 sq. ins. The R.M.S. current is normally 1.75 amps. so that the current density is about 32.5 amperes/sq". On the R.R. ignition the normal R.M.S. current is about 1.51 amps. so that contacts to carry this current at the same density as the Liberty would need to be about .243" dia. The Remy six cylinder distributor however which has tungsten contacts works at over 120 amps/sq.". To settle whether it is the current during contact (in view of the appreciable resistance set up) or the spark at break which causes the deterioration of tungsten on the R.R. battery ignition, an experiment might be made, in which a heavy current at low voltage is passed through a tungsten contact breaker and non-inductive resistance for a few hours, after which a small current through an inductive circuit could be made and broken without a condenser, thus causing sparking with very little current; the effects of the two cases being compared. Contd. | ||