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).
Analysis of current behaviour in a dynamo's brushes and armature at various rotational speeds, comparing different dynamo types.
| Identifier | WestWitteringFiles\C\May1919\ Scan46 | |
| Date | 7th May 1919 | |
| R.R. 235A (500 T) (S.D. 408. 26-4-17.) Bm. 2/156/13. Contd. -3- EFCl/T7.5.19. attains a zero value (when the voltage between the control and negative brushes is zero) and then reverses with further increase of speed. The control current is thus assisting the main field while the speed is low, and opposing it while the speed is high. On still further increase of speed, the control current (now reverse) becomes at some speed equal in value to the sum of the main and main field currents. This occurs on this particular dynamo when warm, at about 2200 R.P.M., and is clearly illustrated on the curves on photostat sheet E by the intersection of two of these at the point marked X. Further reference, however, will be made to this point. At this point the main negative brush is inoperative and can be removed without affecting the currents in the system; it is however, already slightly positive to the control brush owing to the ohmic drop in the control winding. On still further increase of speed the current in the negative brush reverses so that the current is coming out from this brush and adding to the main current to constitute the control current. These points are well illustrated by the curves herewith to which further reference will be made. We are attaching a table of currents at different speeds (with the dynamo correctly connected) in order to show the variation in the currents carried by the various brushes. We have also drawn a diagram to show what portions of the armature these various currents have to traverse. We are sending separately also a similar table for the C. A.{Mr Adams} V.{VIENNA} N. G.{Mr Griffiths - Chief Accountant / Mr Gnapp} R.{Sir Henry Royce} R.{Sir Henry Royce} type dynamo. The object of these is to make a comparison between the relative heating of the two armatures. It would appear that in the Lucas case the large currents has to traverse a smaller section of the armature Contd. | ||