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).
Ignition contacts, ballast resistance, and condenser effects on contact life.
| Identifier | ExFiles\Box 61b\1\ scan0152 | |
| Date | 4th June 1932 | |
| X6118 HS{Lord Ernest Hives - Chair}/WST. FROM R.{Sir Henry Royce} RL/M4.6.32. C. to SG.{Arthur F. Sidgreaves - MD} WOR.{Arthur Wormald - General Works Manager} RG.{Mr Rowledge} E.{Mr Elliott - Chief Engineer} re. IGNITION CONTACTS. It is a comparatively simple matter to make the ballast resistance unvariable with temperature by using one of the alloys having a low temperature co-efficient, such as reostine, etc. The ballast resistance was originally introduced by the Americans to non-trembler coils, and was their practice- and thought to be an advantage - of making these in iron wire that had an high temperature co-efficient, so as to reduce the current if the engine was standing or running very slowly. You now say this feature - instead of being an advantage - is a definite disadvantage, and the contacts would be better working on a circuit that does not vary materially in ohmic resistance. Regarding the contacts sent to me, we do not like them to form pips if it can be avoided, and many years ago a special feature of our design was a slight scrub on the contacts which maintained them in a flat grey white matt surface, free from pips and hollows. We seem to have lost this feature. The life of the contact seems to vary immensely with the capacity of the condenser. It may be that different coils need different condensers, but I have always thought that a large condenser ought to be favourable to the life of the points. Regarding the latest contact maker and distributor with double arms I have not seen any report on the life of the contacts. It would be very interesting to compare them under exactly the same conditions as the present standard single ones. R | ||