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 starter motor relay switch designed by HPS/TT.
| Identifier | ExFiles\Box 168a\2\ img349 | |
| Date | 25th August 1937 | |
| To By o.{Mr Oldham} to RM.{William Robotham - Chief Engineer} o.{Mr Oldham} to RHC{R. H. Coverley - Production Engineer}/CMH. o.{Mr Oldham} to By/DB.{Donald Bastow - Suspensions} 6139 Re Endurance test on Starter Motor Relay Switch designed by HPS{Horace Percy Smith - Experimental Factory Mgr}/TT. The principle alteration in the design of this switch is the deletion of the carbon contacts; an endurance test has been carried out to determine the life of the copper contacts when subjected to the full inductive spark, produced on the breaking of the motor circuit. The test consisted of passing a current of 200 amperes through the main contacts, which were in series with a stalled Bentley Motor. The switch was actuated at a rate of 5 times per minute, the load being on for 3 seconds and off for 3 seconds. Under these conditions the switch completed 15,000 operations without failure. After 1600 operations the front edges of the copper contacts were given a slight radius, as beads were inclined to form on the existing sharp edge. The copper contacts were rather badly pitted at the end of the test, the wear being .003" in 13,400 operations. Readings of the contact volt drop taken during the test were as follows :- Condition of switch. | 300 amperes: 7 volt across coil. | 200 amperes. 8.67 volt across coil. | 100 amperes. 10.3 volt across coil. --- | --- | --- | --- Commencement of test. | .156 V | .105 V | .050 V.{VIENNA} 2,000 operations | .170 V | .120 V | .058 V.{VIENNA} 5,000 " | .170 V | .115 V | .062 V.{VIENNA} 10,000 " | .165 V | .120 V | .060 V.{VIENNA} 15,000 " | .220 V | .170 V | .110 V.{VIENNA} COIL AT AMBIENT TEMPERATURE. Con'd.{John DeLooze - Company Secretary} | ||