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).
Endurance test report on the Phantom III Starter Motor Push Button Switch.
| Identifier | ExFiles\Box 142\3\ scan0300 | |
| Date | 16th August 1937 | |
| To By.{R.W. Bailey - Chief Engineer} (crossed out) c. to By/RD. (crossed out) c. to Rm.{William Robotham - Chief Engineer} re Phantom III Starter Motor Push Button Switch. With reference to our memo. Rm{William Robotham - Chief Engineer}/Wst.2/AP.2.7.37. we have carried out an endurance test on a switch in which the carbon brush was entirely deleted, and Phosphor bronze contacts of heavier gauge fitted. The switch failed after 275 operations, the supply contacts being badly burned: this tends to prove that owing to the inductive nature of the load, a carbon contact is essential. The switch was then reassembled using the standard arrangement, but with the pig-tail of the carbon removed: by cleaning the ends of the carbon operating spring an electrical contact was obtained between the plunger and carbon contact. Arranged in this manner the switch completed 4,000 operations satisfactory, but then started sparking: on investigation it was found that the carbon operating spring had collapsed, due to overheating. If this method were used a phosphor bronze spring of heavier gauge would be necessary. We then carried out a further endurance test on a standard switch in order to determine the life of the pigtail. The switch completed 12,000 operations without sparking, after which slight intermittent sparking was noted: 15,000 operations were completed under these conditions. On dismantling, the pig-tail was found to be broken. Satisfactory operation in this condition presumably due to the broken ends of the pig-tail making before the main contact. Further tests will be carried out using a carbon contact with its pig-tail coiled within the spring. By/RD. is obtaining some contacts with longer pigtails to enable this to be done. We understand that production is now cleaning the ends of the carbon operating spring, which will add considerably to the life of the pigtail. Rm{William Robotham - Chief Engineer}/RC.{R. Childs} | ||