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).
Use and performance of fusible sentinels on 20 HP and 40/50 HP dynamos.
| Identifier | ExFiles\Box 165\6\ img162 | |
| Date | 10th November 1927 | |
| X5660 To R.{Sir Henry Royce} from EFC. E.{Mr Elliott - Chief Engineer} RJ. E.{Mr Elliott - Chief Engineer} C. Wor.{Arthur Wormald - General Works Manager} Ev.{Ivan Evernden - coachwork} EFCl/T10.11.27. 20 HP. & 40/50 HP. DYNAMO SENTINELS. X.5660 X.8671 Fusible sentinels, placed on the carcases of dynamos on cars and in good metallic contact with them, and melting at a temperature of 97ºC, which temp. we have arrived at as being the safe limit for the carcase, have been used. Bench tests have shown that unless there is bad commutation leading to local commutator heating, there is a margin of 5º between the melting of these sentinels and the running of the commutator solder. * These sentinels have only melted and then only just melted - on our up-to-date machines, i.e the 20 HP. with 57 commutator segments and the recently standardised N.B. type of 40/50 machine, under exceptional circumstances of running. Normally they do not reach melting point. We have not had a case of commutator solder running with either - (a) The up-to-date 20 HP. 57 comm. segment machine, or (b) The N.B. type 40/50 dynamo recently standardised, which has been due to the intrinsic heating of the dynamo itself with correct circumstances in the rest of the system. Isolated cases (about two 20 HP. machines) which we have had have been traceable to faults in the circuit quite apart from the generator The use of these sentinels on the machines which have been fitted with auto switch charge reducers have shown that these early experimental auto switches prevent the dynamo from attaining such a high temperature. EFC. | ||