The conveniences to be derived from the use of electricity were for many years available only by those who lived in distributing areas covered by commercial electrical generating plants. Except in towns of sufficient size to warrant the erection of expensive light and power systems or along the lines of electric power transmission, current for domestic purposes was not obtainable.
Within a comparatively few years there have been developed a number of small electric generating systems that are suitable for supplying the average household with the electric energy for all domestic conveniences. The combination of the gasoline engine, the electric dynamo and the storage battery have made possible generating apparatus that is operated with the minimum of difficulty and which supplies all of the electric appliances that were formerly served only from commercial electric circuits.
An electric generating system is commonly termed an electric plant. It consists of an engine for the development of power, a dynamo for changing the power into electricity and - to be of the greatest service - a storage battery for the accumulation of a supply of energy to be used at such times as are not convenient to keep the dynamo in active operation.
Such a combination, each part comprised of mechanism with which the average householder is unfamiliar, seems at first too great a complication to put into successful practice. Such, however, is not the case. The operation of small electric generating plants is no longer an experiment. Their general use testifies to their successful service. The working principles are in most cases those of elementary physics combined with mechanism, the management of which is not difficult to comprehend. Such plants are made to suit every condition of application and at a cost that is condusive to general employment.
In a brief space it is not possible to enter into a detailed discussion of the gasoline engine, the electric dynamo, and the storage battery with the various appliances necessary for their operation; it is, therefore, intended to give only a general description of the leading features of each. The manufacturers of such plants furnish to their customers and to others who are interested detailed information with explicit instructions for their successful management.
The first private lighting plants were made up of parts built by different manufacturers and assembled to form generating systems with little regard to their adaptability. A gasoline engine belted to a dynamo of the proper generating capacity supplied the electricity. Neither the engines nor the dynamos were particularly suited to the work to be performed, yet these combinations were sufficiently successful to command a ready sale. The energy thus generated was accumulated in a storage battery from which was taken the current for a lighting and heating device. Besides the generating and storage apparatus there is required in such a system, a switchboard, to which are attached the necessary meters and switches that are required to measure and direct the current to the various electric circuits.
Foresighted manufacturers, comprehending the probable future demand, began the construction of the various parts, suited to the work and the conditions under which they were to be employed. The manufacture of apparatus, designed for the special service and composed of the fewest possible parts, has reduced the operating difficulty to a point of relative simplicity. Experience in the use of a large number of these plants has revealed to the maker the course of many minor difficulties of operation and the means of their correction. The mechanism has been improved to prevent possible derangement and to simplify the means of control, until the private electric plant is successfully employed by those who have had no former experience with power-generating machines.
Fig. 258. - Household electric generating plant.
As an example of the private electric plant Fig. 258 shows the apparatus included in a combined engine, dynamo and switchboard, connected with a storage battery. The relative size of the machine is shown by comparison with the girl in the act of starting the motor. This plant is of capacity suitable for supplying an average home with electricity for all ordinary domestic uses. A nearer view of the generating apparatus is given in Fig. 259 in which all of the exterior parts are named. An interior view of the generating apparatus is given in Fig. 260, in which is exposed all of the working parts. The right-hand side of the picture shows all of the parts of the gasoline engine that furnishes the power for driving the generator. This is an example of an air-cooled gasoline engine in which the excess heat developed in the cylinder is carried away by a drought of air. The air draft is induced by the flywheel of the engine, which is constructed as a fan. The blades of the fan, when in motion, are so set as to draw air into the top of the engine casing and exhaust it from the rim of the wheel. The air in passing takes up the heat in excess of that necessary for the proper cylinder temperature. This form of cylinder cooling takes the place of the customary water circulation and thus eliminates its attending sources of trouble. In principle the engine is the same as is employed in automobiles and other power generation.
Fig. 259. - Combined motor, electric generator and switchboard.
On the left-hand side is seen the dynamo and switchboard.
The dynamo armature is attached to the crankshaft of the engine by which it is rotated in a magnetic field to produce the desired amount of electricity. The brushes, in contact with the commutator, conduct the electricity as it is generated in the armature, which after passing through the switchboard is made available from the two wires at the top of the board marked "light and power wires." These wires are connected with the storage battery and also to the house circuits through which the current is to be sent.
Fig. 260. - Details of motor, electric generator and switchboard.
Referring to the switchboard of Fig. 259, the three switches and the ammeter comprise the necessary accessories. The starting switch is so arranged that by pressing the lever a current of electricity from the storage battery is sent through the dynamo. The dynamo acting as a motor starts the engine. When the engine has attained its proper speed its function as a dynamo overcomes the current pressure from the battery and sends electricity into the cells to restore the expended energy, or if so desired the current may be used directly from the dynamo for any household purpose. The box enclosing the switch contains a magnetic circuit-breaker so constructed that when the battery is completely charged the switch automatically releases its contact and stops the engine.
The "stopping switch" at the right of the board and the "switch for light and circuit" on the left are used respectively for stopping the engine and for opening and closing the house circuits.
The meter performs a multiple function, in that it shows at any time the condition of charge in the storage battery, the rate at which current is entering or leaving the battery and also acts to stop the engine when the battery is charged. At any time the pointer reaches the mark indicated in the picture, the ignition circuit is automatically broken and the engine stops. The fuses on the board in this case perform the same function as those already described.