Читать книгу Harper's Electricity Book for Boys - Joseph H. Adams - Страница 10

When more current is desired than the simple batteries will give, a storage-battery should be employed as an accumulator. This result can be secured by coupling primary cells in series, so that they will be constantly generating and feeding the battery. Storage-batteries are too heavy to be shifted about, like single cells or small plunge-batteries; they should be placed in a cellar, where the charging or primary cells can be located close by, and, unless positively necessary, the battery of cells and the accumulator should not be moved.

With sufficiently large insulated wires (Nos. 12, 14, or 16 copper), the current may be carried to any part of the house for use in various ways—such as running a light motor or a fan, lighting a lamp-circuit, or fusing metals and chemicals for experimental purposes. While the battery to be described is not a light one in weight, nor as economical as the improved new Edison storage-battery, it is a good and constant one, and, if not overcharged or abused, will last for several years.

The component parts of a storage-battery are lead in metallic and chemical form, the electrolyte, or fluid, in which the plates are immersed, and the water-tight and chemical-proof cell or container. From a plumber, a supply-house, or a lead-works, obtain a quantity of three-eighth by one-quarter-inch strip-lead of the kind called chemical, or desilverized; also a larger quantity of lead-tape, one-sixty-fourth of an inch thick and three-eighths of an inch wide. This last is also known as torpedo-lead, and is kept by electrical supply-houses.

If the three-eighths by quarter-inch strip-lead cannot be had, then purchase eight or ten pounds of heavy sheet-lead, and, with a tin-shears, divide it into strips three-eighths of an inch wide and twenty-nine inches long, taking care to cut it of uniform width and with true edges. From hard-wood three-eighths or half an inch thick, cut a block six by seven inches and make four countersunk holes in it, so that it may be screwed fast to a table or bench, as shown in Fig. 11 A. Around this the lead strips should be shaped and beaten at the corners to make the angles sharp.

From the three-eighths by quarter-inch, or sheet-lead strips, make seven frames as shown in Fig. 12. This is done by binding a strip of the lead around the block, as shown at Fig. 11 B. Where the ends come together insert a short piece of lead, three-eighths or half-inch, as shown at Fig. 12 A, and solder it fast. A soldering-iron may be heated with a Bunsen-burner gas-flame or in a charcoal fire. However, if gas is available, it would be better to use the blue flame from a Bunsen burner and direct the hot blast directly on the work with a blow-pipe, and so fuse the lead points together. After a little practice with the blow-pipe it will be used for many pieces of work in preference to the soldering-iron. If the sheet-lead is used for the frames in place of the three-eighths by quarter-inch strips, two or three strips will have to be taken, so as to build up the band of the frame to about a quarter of an inch in thickness. When soldered together, or fused at the edges, these built-up frames will be as rigid as the solid metal.

Now cut a number of strips of the thin lead-tape six inches and a half long, and others that will necessarily be somewhat longer, for each frame is to be filled with straight and crimped pieces, as shown in Fig. 13. If there is a fluting-iron in the house, the crimping may be done in the brass gears at one end of the machine. Or two wheels may be cut from hard-wood with a fret-saw, and made fast to a block with screws, as shown in Fig. 14. A handle, attached to one wheel, will make it possible to turn the gears; and they should be placed just far enough apart to allow the tape to pass through without tearing or squeezing. Put a washer between the wheel and the block to prevent friction.

When a frame is in the position shown in Fig. 13, and lying on a piece of slate or flat stone, you will first put in a crimped piece of tape, as shown at Fig. 13 A, and under this arrange a straight piece (Fig. 13 B); then, with the blow-pipe and flame, fuse fast to the frame and catch the flutes of the crimped piece to the straight one every inch or two. Add alternate crimped and straight strips until the frame is filled and presents the appearance of Fig. 13. When the seven frames are ready, lay three of them aside for the positives and four for the negatives. Note that the positives are red and the negatives a dark yellow when they are filled with the active material.

There are several methods of depositing the active material in the mesh or net-work of the plates, but some of them are too technical, others too complicated, and still others require charging machinery. The following plan will be the simplest and easiest for the amateur:

At a paint-store, or from a wholesale druggist, obtain several pounds of oxide of lead (red-lead) and a similar quantity of litharge (yellow-lead). In an earthen vessel, or large jar, make a solution composed of water, twenty ounces, and commercial sulphuric acid, two ounces. This is the mixture commonly known as “one to ten.” Place some red-lead (dry) in an old saucepan or soup-plate, and add a little of the acid solution: then, with an old table-knife or small trowel, mix the lead into a stiff paste, like soft putty. Do not get it too thin or it will run; nor too thick, as then it will not properly adhere to the lead-mesh of the frames. With the frame lying on its side, plaster in the red composition between the flutes and fill up the frame solid with it. Treat all three of the positive frames in the same manner, taking care that the exposed surfaces of the composition-filling is smooth and flush with the edges of the lead frame and mesh. Do not disturb these plates for a while, but let them remain in position, so as to set and partially dry. Add acid solution to the yellow-lead in a similar manner, and fill the four negative plates. When partially dry, the plates will be ready to combine in a pile.

At a supply-house obtain some sheets of cellulous fibre, three-sixteenths of an inch thick, or some asbestos cloth. If neither can be had, then soak some pieces of ordinary brown card-board in a solution of silicate of soda and let them dry. Lay a negative (yellow) plate on the table with the lug at the left (Fig. 13 C). On this place a square of the fibre, asbestos, or card-board; and on top of it lay a positive (red) plate with the lug at the right side. Continue in this manner until the seven plates are stacked, the four negative lugs being at the left and the three positives at the right. Tie the plates securely together with cotton string bound about them in both directions; then stand the pile up so that the lugs are at the top, as shown at Fig. 15, with every alternate lug in an opposite direction. Obtain two lead bars three-eighths of an inch square, or cut strips from the sheet-lead and solder them together, turning the ends as shown at Fig. 13 D. Drop one of these bars into the lugs of the positive plates, as shown in Fig. 15 H, and solder it fast at the three unions. Repeat this with the other bar in the lugs of the negative plates, and the pile will then be ready for immersion in the electrolyte. To both ends of each plate-bar solder binding-posts, so that the conductor-wires can be attached at one end and the feed-wires at the other. If a hard rubber or glass cell can be had for the battery so much the better; if not, a stout box may be made from pine, white-wood, or cypress, and thoroughly coated with asphaltum varnish or asphaltick. At an electrical supply-house you can purchase some “P and B” compound, which is acid and water proof. This is excellent for the inside coating as well as for the outside of the box.

The box should be made of wood not less than three-quarters of an inch thick, and the sides, ends, and bottom should be in one piece, free from knots, sappy places, or cracks. Brass screws should be used to hold the boards together, and before the joints are made the butt-ends of wood and the sides, against which they impinge, must be thoroughly coated with the asphaltum or compound. Put together the four sides first and then make the bottom fast, placing the screws two inches apart and countersinking the wood, so that the screw-heads will lie flush, as shown in Fig. 16. The box should be large enough to allow about one inch of space all around the pile, and deep enough for the solution to cover the plates and two inches of space above it to the top edge of the cell. The complete storage-battery will then appear as shown in Fig. 17.

The electrolyte is composed of sulphuric acid and water in the proportion of one ounce of acid to four of water, making a five-part solution. This should be mixed in an earthen or glass jar, and the acid poured slowly into the water, the latter being stirred while the acid is added. When the solution cools (for adding acid to water creates heat), add about two ounces of bicarbonate of soda, and mix the solution thoroughly.

When the pile is in place within the box (having first removed the string which bound the plates together) pour the electrolyte slowly into the cell, taking care that none of it spatters, for it will eat clothing or anything else that it touches. Before placing the pile, or electrolyte, in the box, it should be thoroughly tested for leaks by allowing water to stand in it for several days. Indeed, you should be very generous with the asphaltum, or compound, when coating the angles and points inside the box; for if the acid solution gets at the screws it will corrode them and the box will soon leak and fall apart. As a precaution against the acid working over the top of the box, the upper edge, for an inch or two, should be coated with paraffine over the asphaltum or acid-proof coating.

A cell constructed in this way should accumulate about two volts and one hundred ampere-hours, and will run a one-sixteenth horse-power motor. The expense of making these plates is about twenty-five cents each, and, including the cell and coating materials, each storage-battery will cost approximately two dollars. The lasting qualities of the battery depend on the use or abuse it is put to; but with ordinary care it should last from three to five years.

When the battery ceases to accumulate properly the pile should be removed, and, after washing it thoroughly, the bars should be cut away and new positive plates made and installed. The positive plates are the ones that deteriorate and need replacing; the negatives are almost everlasting, and with proper usage will live for fifteen or twenty years.

Directly the electrolyte is in the cell, connect the poles of your primary cells so as to begin the accumulation of current. Never exhaust the charge of electricity from your storage-cell, and never leave it uncharged when the electrolyte is in, or the plates will be ruined. A battery consisting of from five to twenty bluestone cells will be the best with which to charge this accumulator; and if more than one cell is desired, any number of them can be made and coupled up in series. Take care, when connecting the wires from the primary cells, to see that the positive wire is connected with the positive plates and the negative with the lead bar joining the yellow plates. If by accident you should make a misconnection, bubbles will rise from the electrolyte. This is not right, so reverse the wires and the accumulation of current will then take place without agitation in the cell.