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 report on observed weaknesses and proposed modifications to electrical contacts, including a dynamo circuit sparking test.
| Identifier | ExFiles\Box 166\3\ img025 | |
| Date | 31th July 1934 | |
| -2- Hs{Lord Ernest Hives - Chair}/Wst.3/MA.31.7.34. Cont'd.{John DeLooze - Company Secretary} It is noticed also that the copper link has a steel spring between it and the terminal post. It should be therefore arranged for this copper link if possible to make direct contact to the terminal post and not through a steel spring. The next weakest part noticed was the main contact, which appears to have insufficient contact area. A plain copper contact with a good area of contact surface and backed up by a steel spring might be an improvement in this respect. The most satisfactory part of the main contact circuit was the copper block to the main finger contact rubbing on the brass drum. This however, could be still further improved by bedding the block to the drum for a minimum distance of say .050". Also the spring pressure on this contact (at present about 14 ozs.) might be with advantage increased to 20 or 24 ozs. Modifications such as indicated above would reduce both the heating and the volt drop at the various parts of the contacts and therefore might very well be applied to all the other contacts in a lesser degree. (4) In order to ascertain the extent of sparking likely to take place when breaking the main dynamo circuit, the main finger contact was made to break a dynamo circuit with a current of 15 amperes at 14 volts. The spark observed was quite appreciable but the capabilities of such a spark to cause burning can only be estimated from a long endurance test. We consider however that the rubbing action of these contacts will help to keep them clean. As soon as an opportunity arises we intend to carry out a bench endurance test on this or another switch to ascertain this effect. | ||