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).
Description of the Smith Constant Current Dynamo's operation, connections, current curves and regulation.
| Identifier | ExFiles\Box 3\5\ 05-page176 | |
| Date | 8th March 1920 guessed | |
| THE SMITH CONSTANT CURRENT DYNAMO. connected to the auxiliary brushes half a pole pitch in advance through suitable resistances. Fig. 1. shows diagrammatically the general arrangement and connections of the machine. It will be noticed that the field magnet windings S.S'. are connected direct to the main brushes A.B. The main brush A is connected through the resistance R to the auxiliary brush A', and the main brush B is similarly connected to the auxiliary brush B' through the resistance R'. It is by the particular disposition and interconnection of the brushes that the required distribution of current in the armature winding at different speeds is obtained. Not only does the distribution of current in the armature provide the armature reaction for regulating the machine but it also greatly reduces the heating which occurs in the armature conductors. CURRENT CURVES OF THE DYNAMO. In Fig. 2. are shown test curves relating to a 12 volt 10 ampere machine when charging a 12 volt battery. Curve A shows the current output to the battery at various speeds, and it will be noted that the current rises very rapidly from the point C, where the dynamo commences to charge the battery, until the full output of 10 amperes is attained. The current then remains constant no matter how high the speed becomes. Curve B shows the current flowing in each of the resistances R.R' in Fig. 1. It will be seen that at speeds from 0 to 550 revolutions per minute, before the dynamo is connected to the battery, the current gradually rises. The dynamo is then connected to the battery and commences to charge it, the current in the resistances then falling off until at the point E it is zero. A further increase in speed results in the current through the resistances reversing and gradually increasing until, when the dynamo reaches its full output of 10 amperes, the current in the resistances is half of this value, i.e., 5 amperes. REGULATION OF THE DYNAMO. The magnetising forces produced by the armature currents, known as “armature reaction,” on which the dynamo depends for its regulation, may be divided into two classes:- (1). The magnetising force which acts at right angles to the main magnetic field from the poles of the machine. Page 3 | ||