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 the failure of 20HP dynamo brush holders.
| Identifier | ExFiles\Box 50\5\ Scan215 | |
| Date | 11th September 1923 | |
| X.4333 EFC. C. Mr Davis. BY7-P11.9.23. X.4333. 20HP. DYNAMO. BRUSH HOLDERS. Referring to the instance you brought before my attention this monring, in which the brush holders on the 20HP type Dynamo which you are running on the bench failed, after dismantling the brush holders I carefully examined the fractures. My conclusions are:- 1. The failure is a fatigue failure purely and simply and has not been accentuated by "season cracking". 2. The length of time that the brush holders have been in service is not such as to justify a failure of this description. 3. The failure may have been accentuated by the following two points;- a/- The starting up of the Dynamo repeatedly on the automatic apparatus you have had for this purpose would have increased the load on the brush holders by constantly bringing into operation the static friction between the brushes and the Commutator. b/- A periodic Vibration may have been set up on the sheet metal brush holder in accordance with either the number of bars in the Commutator and the speed at which it was running, or some similar cause. 4. Although only two brushes had definitely failed, that is, the positive and the negative, the third brush shewed distinct signs of cracks starting, and would in my opinion, have followed the same course of events as the two brushes which had actually failed if running had been continued with same, but with new brush holders for the positive and negative brushes. I would like to sum up the whole position as I see it at the moment, by stating that I am somewhat alarmed by the failure, and that, in my opinion, it is of the utmost importance to urge forward the new cast type brush holders for adoption as soon as possible. In the meantime we should examine the school car and any of the Experimental cars that become available, with the object of ascertaining whether any other brush holders on different cars which have only been run on the road, are shewing signs of failure. If it should happen that you are able to contd. | ||