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).
Investigation into a 20 HP dynamo failure caused by an incorrectly fitted negative brush.
| Identifier | ExFiles\Box 47\4\ Scan118 | |
| Date | 27th September 1923 | |
| To EP.{G. Eric Platford - Chief Quality Engineer} from EFC. c. BY.{R.W. Bailey - Chief Engineer} c. Mr. Brock. X4FF8 EFC3/T27.9.23. X.4383 - 20 H.P. DYNAMO FAILURE - 40 G.I. Y4373 Examination of this dynamo showed that it had considerably overheated and melted out the solder from the commutator connections. The cause of the failure was almost certainly due to a new negative brush having been incorrectly fitted outside. We do not know why a new negative brush should have been necessary, but from the condition of the dynamo, it is clear that this new brush was jammed in the holder and had not, we think, at any time made contact with the commutator. Such a condition is, of course, as serious (in fact it is the same thing) as the battery being disconnected, and the dynamo would be excited when running with no opportunity of cutting in. Thus the overheating has occurred. Admittedly this is a weakness of the third brush system of control, which perhaps up to the present has not been fully realised, i.e. if the contact of the negative brush with the commutator is not satisfactory, overheating may occur. We are now making experiments to prove that with any combination of incorrect bedding of three brushes in the machine, so long as these are definite in making contact, subject to the full pressure of the spring between Contd. | ||