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 a Phantom III starter motor push button switch.
| Identifier | ExFiles\Box 168a\2\ img358 | |
| Date | 21th September 1937 | |
| To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/RC.{R. Childs} c. By/RD. c. HA. 6139. Rm{William Robotham - Chief Engineer}/RC.{R. Childs}3/AP.21.9.37 Re. Phantom III. Starter Motor Push Button Switch. (Further to our memo Rm{William Robotham - Chief Engineer}/RC.{R. Childs}1/JH.16.8.37) We have now completed an endurance test on a pushbutton switch, in which the spring loaded carbon contact to D.74948 was fitted with a longer pigtail to enable the flex to be coiled within the spring (D.74007). This modification was introduced to avoid the snatching action produced by the spring on the flex and so avoid the breaking of same. The switch was operated at a rate of 10 times per minute, 3 seconds 'on', 3 seconds 'off', the electrical load approximating that obtained in actual service i.e. 13 amps in the motor circuit and 5.5 amps in the main switch coil circuit. The switch had completed 22,800 operations when the plunger jammed in the 'on' position, this seizure was due to heat acting on, and shrinking the bakelite mounting (D.74944). In normal use this heat would not be developed, and was only caused by the severe test to which the switch was subjected. In all, this switch had completed 42,700 operations using this particular bakelite piece. On examination the spring loaded carbon contact pigtail was found to be in good condition with no strands broken; although both this and the spring showed signs of overheating. In dismantling, the pigtail became detached from the carbon, and so ended the life test. This test proves that the longer pigtail, coiled within the spring, is a decided improvement and should eliminate further trouble; care must be taken that the flex be coiled round a small enough wire, in order to avoid any risk of trapping by the spring. We formed our coil by winding round a .035" diam. wire. Rm{William Robotham - Chief Engineer}/RC.{R. Childs} | ||