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).
Introductory page explaining the principles of the Smith Constant Current Dynamo.
| Identifier | ExFiles\Box 3\5\ 05-page174 | |
| Date | 8th March 1920 guessed | |
| X 275 THE SMITH CONSTANT CURRENT DYNAMO. INTRODUCTION. When a dynamo is to be used in conjunction with a storage battery or accumulator to provide electrical energy for the Lighting, Starting and Heating of Motor Cars, Aircraft, etc., where the speed at which the dynamo is driven undergoes considerable variation, it is essential that the current output from the machine should rise rapidly to a certain predetermined value as the speed increases, and then remain constant, no matter how fast the dynamo may be driven. If the ordinary shunt-wound dynamo without any special means of regulation were used, in which the armature revolves in a fairly constant magnetic field, the current supplied by the dynamo would increase as the speed of rotation increased until the heating effect of the current in the armature and field coils would cause the insulation to be destroyed, and the machine would "burn out". Another reason for limiting the current supplied by the dynamo is that the Battery should not be charged at too high a rate. The maximum charging current permissable depends on the capacity of the cells, i.e., on the area and number of positive plates in one cell, and if this current is exceeded for any considerable time the life and efficiency of the Battery are much reduced. It is evident, therefore, that a dynamo intended to work under the conditions mentioned must be provided with some method of regulating the current output. In the "Smith Patent Constant Current Variable Speed Dynamo" the desired regulation is obtained by making use of the magnetic effect of the current circulating in the armature winding of the machine to alter the strength and direction of the main magnetic field of the dynamo. The dynamo output is thus regulated by what is technically termed "armature reaction" and the dynamo is said to possess inherent electrical regulation, since no complicated external regulating devices are required. The construction of the machine is very similar to that of an ordinary two-pole shunt-wound dynamo, but it is provided with four brushes, viz.:— two main and two auxiliary brushes disposed equally round the Commutator, the main brushes being Page 1 | ||