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).
Alterations to motor windings and bye-pass resistance for improved starting and reliability.
| Identifier | ExFiles\Box 64\3\ scan0022 | |
| Date | 7th November 1924 | |
| Contd. -3- EFC3/T7.11.24. been judged to be O.K. (the second by taking the flux/exciting current curve of the motor), permitted the flow of additional current through the armature and so increasing the torque in the proportion of the extra current. By starting with a relatively high value, this bye-pass resistance is being reduced until failure of the motor to start occurs in no circumstances. So far the hold-on coil has not failed to operate actually on the chassis, but it is known that under extreme conditions of temperature and low voltage, this might occur. The alterations that appear to be necessary and which are instructed for further units, which are being made up, are:- (1) To replace the actuator box and motor teaser winding at present of 18 SWG. with windings of 17 SWG. (It may even be necessary to go to 16 SWG. for reasons referred to below.) (2) To alter the hold-on coil winding, which will consist of the same No. of turns as at present but of 27 SWG. in place of 28 SWG. This will cause the winding to occupy more space. It is considered that this extra space should be allowed for this winding at the expense of reducing the cross section of the heavy current winding which at present is more than the equivalent of the main field winding on the motor; the No. of turns on this heavy winding will remain the same. Reverting to the present set of units on the chassis it is to be noted that the bye-pass put in to make the motor more certain of starting, only carries current during the interval between switching on and the main circuit being made, and therefore it might be said that the lower this resistance, the safer it is against being burnt up. We imply that it can only be on long enough to be burnt up if the motor failed to start. On the other hand, this means that a larger current has to be passed through the top relay switch contactor. | ||