EVER since the invention of the incandescent lamp, and its resulting widespread adoption for the lighting of dwellings, many persons living outside the zones supplied with current by central stations have desired to possess small lighting plants of their own. Heretofore, however, this has not been practical for the man of moderate means, because of the large amount of power consumed by the carbon-filament lamp and the necessarily large outlay for equipment and running expenses. Recent progress in the lampmakers art has resulted in giving us the tungsten filament, which is three times as economical in the consumption of power as the old carbon lamp, so that now an ordinary sized dwelling can be brilliantly lighted by so simple and inexpensive an outfit as would seem to place this within the reach of a great many who cannot get electricity from central stations. The following description will give first a good idea of a suitable plant for the practical lighting of a house wired for a total of about eighteen sixteen-candle-power lamps. As all the lamps located in the various parts of a house are not required to be lighted at the same time, it is assumed that ordinarily not over seven lamps will be used, and that the maximum demand, on special occasions such as receptions or parties, will be for twelve lamps to burn all night. In cases where a plant is to be installed principally for lighting, and it is not intended to operate electric heating devices or motors, except in small sizes and only occasionally, then thirty-two volts is probably the best selection that can be made for the system. This has been adopted as a standard voltage for the lighting of railroad cars, and tungsten lampmakers are prepared to furnish lamps for it in candle-power of 8, 12 and 16. The necessary equipment of a plant consists of four parts; the engine, the generator, the switchboard and the storage battery. In general it is best to buy these from manufacturers who make a specialty of such apparatus, but the Handy Man who can spare the time can no doubt derive much pleasure from making a large part of the apparatus himself, as hereinafter more particularly described. An electric lighting outfit takes up but little room, and may be installed in one corner of the tool-house, garage or other outbuilding if one does not wish to erect a separate house for it. In the photograph in Fig. 1, is shown a neat power-house of field stone, built over a live spring at the foot of a hill. The same engine that runs the dynamo also drives a lathe and grindstone, as well as running a pump supplying the house-tank with water from the spring. The simplest and most economical form of storage battery to buy is known as the two-plate, or couple, type, which consists of two plates in each jar, supported by bent connecting straps resting across the edges of the adjacent jars. Sixteen cells are required for a thirty-two-volt system, and these, having a capacity of thirty-six ampere-hours, can be purchased for about fifty-five dollars. Sometimes a bargain can be found in the way of a battery, suitable for a very small plant, in the secondhand or discarded electric vehicle battery of the lead type. Cells of this kind, when new, have a capacity of about 120 ampere-hours, but this is' soon reduced by the severe conditions of service, and when the point is reached where the vehicle will no longer run a sufficient number of miles on a charge the battery plates have to be replaced by new ones. The old plates, which go back to the melting pot, usually can be purchased for very little money, and, when properly cleaned and assembled in suitable glass jars, will give many months of useful service. For those who prefer to make their own batteries, however, some good hints were given in this department of the Scientific American of March 11th, 1911. A simpler form of construction has been devised by the author, embodying the modifications shown in the upper left-hand corner of Fig. 2, where the positive and negative elements are separated . by a porous earthen flower-pot instead of by strips of wood. This construction has the advantage of a considerable saving in labor, as the lead cylinders do not have to be nicely made or riveted, and of an increase. in useful life as short-circuits cannot be formed by active material falling to the bottom of the jar between the plates. As the capacity of a cell of this kind is not directly proportional to its weight, it is more desirable to make thirty-two small cells than sixteen larger ones. The small cells can be connected in two series of sixteen each, thus becoming equivalent to sixteen cells of double the size. For those who have had little or no previous experience in this kind of work it is recommended that only one-half of the batteries be made to start with, and that the second half be attempted only after the first series have been put in service long enough to show up possible defects. For a cell of suitable capacity, the containing vessel may be a glass jar or a glazed earthen crock having inside dimensions not less than 5Y2 inches diameter by 5Y2 inches high. The flower-pot may be 4Y2 inches outside diameter at the top by 414 inches high. Plug up- the hole in the bottom by standing the pot on a sheet of paper and pouring in just enough melted sealing wax to fill the hole, but not to cover the bottom. In assembling, put a thin layer of the granulated lead in the bottom of the crock J, and pack it down well. Stand the flower-pot P in the middle, and bend one strip of 1/16 inch sheet lead E to fit inside the pot and one to fit outside. These “cylinders” may be Fig. 2.—Details of storage cell and diagram of connections. the same height as the pot, and the terminal straps L may be formed by bending up strips one inch wide partly cut from the metal, thus doing away with riveted connectors. Pack the remaining spaces in the crock and the pot with granulated lead G, up to within a quarter of an inch of the rim of the pot. It is very important to arrange the connecting straps L so that they may be bent to pass out at diametrically' opposite points close to the rim of the crock, so as to leave room between them to lay a square of glass 0 to serve as a cover. These covers are necessary to catch the fine spray of acid that would otherwise fly out during charging. A cell of the dimensions given requires a total of about seven pounds of lead, of which about 4% pounds are granulated. Granulated lead is prepared by heating melted lead red hot in the ladle and then pouring It from a height of about five feet into a pail of water. In storage battery work success depends largely on the use of pure materials. In selecting the. lead for granulating reject anything suspected of containing solder, zinc or other impurities. Never use the cheap, or “commercial” sulphuric acid, or water that is “hard.” Use a good quality of acid and either distilled or rain water. The proper electrolyte to use in the cells is dilute sulphuric acid of a specific gravity of 1.2. This can be purchased already' prepared, or it can be made by slowly adding one part of concentrated acid to each five parts of water. 'When the cells are filled to a point one-quarter of an inch above the flower-pots, the level of the liquid should be nearly an inch below the tops of the crocks. The completed cells should be arranged in shallow wooden trays, the bottoms of which are covered with a layer of clean sand about half an inch deep. Not more than eight cells should be grouped in a single tray, on account of leakage of current over the surface of the jars and through the sand. After the jars are in place, the surface of the sand all around them may be liberally dusted with dry sodium bicarbonate (baking soda) which not only neutralizes any acid that slops over on the sand, but tends . to keep the last dry, as the sodium sulphate formed is an efflorescent salt. It is well to remember that a solution of bicarbonate of soda in water is the best wash for use in the event of any acid getting spattered in one's eyes, and the author recommends that a bottle of this be kept in a handy place for use in such an emergency. Thirty-two of the cells made as described will cost less than twenty-five dollars for the materials alone. but to this must be added the cost of current used in the forming process, which takes considerable time. To form the cells properly a current of three or four amperes should be passed through each series of them, either continuously or intermittently for a total of about fifty hours. Then they should be completely discharged and reversed, or given a similar charge in the opposite direction.; About ten such reversals are required to develop sufficient capacity for practical purposes. When this has been accomplished always ch.._ ge the cells in the direction that makes the central plate positive. .For charging the battery a shunt-wound generator, or dynamo, is required. For those who may care to build this part of the apparatus, the design given in Scientific American Supplement, No. 600, is to be commended on account of its very complete description. A machine built in accordance with those instructions may be made to serve a useful purpose, especially if it be provided with more modern ring-oiling bearings and carbon brushes, to insure against the need of shut-ing down for hot boxes and commutator troubles. A more modern and dependable generator, however, can be purchased for about twenty-five dollars. In ordering a machine it should be required to meet the following specifications: Volts, 42; amperes, 5; speed, 1,800 to 2,000 revolutions per minute; type, shunt generator. The most satisfactory' kind of power to use for driving the generator is the small gasoline engine. One-half horse-power would be ample for this purpose, but as yet few engine makers have developed anything in so small a size; so that good, reliable engines are to be had only in sizes beginning with about one horsepower, and costing from thirty dollars upward. Where there is water power available even less than one-half horse-power will give good results, since the water-wheel requires no attention and may be allowed to charge the battery slowly and for long periods of time. Where one already has any kind of power at hand it may not be necessary to buy an engine to run the generator. For wherever there is a steam engine, gasoline engine or a water-wheel already installed for doing other work, a suitable pulley and belt may be arranged to drive the generator, and the power thus absorbed will be so small that in many cases it never will be missed. A simple and convenient arrangement of the switchboard connections is also shown in Fig. 2. It is necessary' to have an ammeter A to measure the current passing through the battery. The most desirable scale is one having the zero in the middle and reading up to ten amperes on each side, showing charge or discharge. A. voltmeter V is also a great convenience, but is not essential, as the working of the generator can be indicated by a 4 candle-power 55-volt lamp. In order to charge the storage battery, the dynamo must impress upon the battery's terminals a voltage considerably higher than thirty-two. This means that if any lamps are lighted while the charging is being done they will take so much current at the increased pressure as to be quickly burned out. To guard against this mishap there are shown in the diagram three extra cells of battery in addition to those previously mentioned. These extra cells are called c. e. m. f. (counter electro-motive force) cells, and their purpose is to oppose or neutralize about six volts of the pressure that would otherwise be applied to the lamp. The c. e. m, f. cells may be more easily made than the (Continued on page 378.)
This article was originally published with the title "Small Isolated Electric Power Plants"