# Popular Mechanics/Volume 49/Issue 1/Five Dollars Builds A-Battery and Charger

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Five Dollars Builds A-Battery and Charger
By LAWRENCE B. ROBBINS
Building an efficient A-battery and charger is not only an easy but an interesting task that many radio fans would have undertaken before except for the lack of definite details. The low cost, five dollars, appeals to those with limited pocketbooks, and the interest of the work to the experimenter who likes to do these things for himself. Ordinary quart fruit jars and auto storage-battery plates, easily obtained from the grocery and nearest battery station, respectively, are the main elements in the construction of both units. One, two or three cells can be made up to suit the needs of the builder, depending on the type of tubes he is using in his set. For instance, if the set employs tubes of the 199 type, two cells only will be required. The fruit jars cost about 10 cents each, and the plates from 15 to 20 cents apiece. Fifteen plates in all will be required for a 6-volt three-cell battery, five plates to each cell.
Select three 1-qt. fruit jars and discard the tops, clean them thoroughly and inspect them for cracks or flaws. Build a wooden case to contain the three jars comprising the A-battery, provided a 6-volt type is required, reducing the dimensions given so as to take two jars if a 4-volt type is to be built. The dimensions for the case will be found in sketches below and on page 122; 1-in. wood stock is used for the case and the outside measurements are 14 in. long, 6 in, high and 5 in. wide. The inside partitions are made of the same wood stock, are fitted across the inside at equal distances and reach from top to bottom. The three compartments thus formed are 4 in. square and 5$^1$⁄$_2$ in. deep, inside measurement, permitting the fruit jars to fit snugly, with the tops projecting about 1$^1$⁄$_{2]}$ in. above the top of the case. The completed case should then be painted inside and out with two coats of asphaltum; when thoroughly dry, screw the handles in position at each end, as shown in the illustration. These handles may be ordinary drawer pulls from the local 5 and 10-cent store, and rubber-headed tacks for feet ​may also be obtained from the same place. The plates should measure 5$^1$⁄$_2$ in. from top to bottom, disregarding the lug at top, and should be 2 in. wide. Saw out these sections, including the lug, as shown on this page; by following down one of the individual lines separating the columns of paste inserts, a straight cut is assured. To further reduce the cost, a second plate. 2 in. wide, can be cut from the remaining section and a lug soldered to the top, but this is not advised. Three negative plates and two positive plates are required for each cell, therefore, when buying the plates for the three-cell job ask for nine negative and six positive plates. The negative plates come pasted with pure, spongy lead and will have a gray color, the positive plates are a chocolate-brown color, the paste filler used being peroxide of lead. Wood or rubber separators can also be obtained from the battery-service station or garage; these are cut down from standard sizes to 7 in. long by 2 in. wide and four are required for each cell, as shown on page 121.
The plates are now assembled, first a negative, then a separator, then a positive plate with the lug on the opposite side, then the separator and so on, until three negative and two positive plates are assembled. All positive lugs should be on one side and all negative lugs on the other; snap two large rubber bands around the unit at top and bottom to hold them together. The plate bars, or lug connectors, are made from heavy sheet lead, cut and bent in the manner shown in the illustration above. The plate lugs are soldered in the slots shown; this operation is simplified by clamping the units in a vise and using a large, hot soldering iron and plenty of solder. Care should be taken not to connect positive to negative plates in any way by dropping solder between them. The upright strip of the plate bar is drilled for bolting to the connecting strap as shown in the sketch; these connecting straps of heavy sheet lead being 1 in. wide and long enough to reach from one jar to the other. The plate bars soldered to the lugs extend across the edge of the jars and support the assembly in each cell; the top view on page 121, at lower right, shows all three units in position, with the connection straps across the partitions connecting the cells in series. When the cells are assembled in the case, the negative plate of one cell should face the positive plate of its neighbor; the connecting straps, drilled at each end, are then bolted to the plate bars with brass bolts and nuts, ​well smeared with vaseline after tightening. Bolt a spring terminal clip to each end lug and mark the positive and negative ends for identification; a daub of red paint on the positive terminal is the usual method. The cut-away illustration of the completed storage battery, on page 122, shows the plates clearing the bottom of the jars; this is necessary to provide sediment space. The electrolyte for filling the cells is made by mixing chemically pure concentrated sulphuric acid with chemically pure water. The full-strength acid is mixed with the water to obtain the suitable specific gravity necessary for the battery; the usual proportion is 20% acid by volume. When mixing the acid, never add the water to the acid; pour the correct amount of water in a bottle, pitcher or jar and then add the acid to the water very slowly. Ready-prepared electrolyte can be obtained from the local battery-service station, saving much time and trouble, and the maker is advised to buy his electrolyte rather than make it. Fill each cell so that the electrolyte will come about 14 in. above the tops of the plates; any space between the jars and the case should be filled with corrugated board or similar material, to hold the jars rigid.
The storage battery completed, we are now ready for the rectifier, or charger as it is commonly known; this is made from a single quart-size fruit jar. An electrode support is made for the top of this jar from a strip of hardwood, ½ in. wide, boiled in paraffin; the aluminum electrode is cut from a sheet of heavy aluminum, the thickness of which is not important, but the heavier the better, and it should be as pure as possible to obtain. The lead electrode is cut from heavy sheet lead; both electrodes are 7 in. long by 14 in. wide; drill three holes in one end of each electrode and fasten to the wood top as shown in the insert on this page, with brass wood screws, the center screw holding a spring-clip connector. Fill the jar with either a saturated solution of borax; a rather dilute solution of sodium bicarbonate, or, better still, a solution of monobasic ammonium phosphate in the proportion of one pound to the gallon of distilled water. In either case, distilled water must be used in making the solution; fill the jar to within about one inch of the top and pour a thin layer of transformer oil or other heat-resisting oil to prevent evaporation or creeping. Set the rectifier jar in a small tub of water that is provided with an inlet and an outlet to keep the water level below the top of the jar by at least 2 in. This is easily done by means of two short lengths of rubber tubing connected to a faucet and drain, the outfit, of course, being placed near the water supply. This cooling tub need not be equipped for water circulation, but this method is advised for best results. The hookup shown in sketch above is self-explanatory and needs little ​comment; the 500-watt resistance may be taken from an electric heater or the heating element from a flatiron may be used. The aluminum electrode is always positive; see that this is connected through the switch so that it goes to the positive terminal of the storage battery. To charge the battery, throw the switch arm over to the connections to the rectifier and turn on the 110-volt a.c. lighting circuit; the charging rate will be about 2 amp. an hour. When the charge is completed, throw the switch arm over to the opposite side, connecting the battery with the receiving set, and turn off the current. Ten to twelve hours will be sufficient to charge the battery even from a low hydrometer reading. Keep the rectifier as cool as possible and occasionally scrape off the white coating that forms on the aluminum electrode if a solution of borax is used. We have prepared a large blueprint showing the various steps in the construction of both units and suggested hookups. This may be obtained from Popular Mechanics radio department, 200 E. Ontario st., Chicago, for 25 cents, to cover cost and mailing. Specify blueprint No. 126.
Homemade Fuses on Battery Cable
Any Radio Owner Can Provide Protective Fuses in the Battery Cable
When a set of radio tubes are accidentally burned out or the batteries are short circuited and discharged, the radio owner begins to think of safety-first methods and ways of preventing these expensive accidents. In the drawing is shown a fused battery cable. This will give protection to the tubes and it is easily and quickly made. About 1 ft. from the end of an ordinary battery cable, the braided covering is removed, leaving the insulated battery wires exposed for about 2 in. In the center of each of two large bottle corks, a hole is drilled to permit the corks to slide over the cable. They are then fastened on the cable with glue at the place where the braided covering was removed, the exposed battery wires being between the two corks. For the fuse base, a small piece of bakelite is cut and drilled as shown in the drawing. Small brass clips, to hold the fuses, are fastened to the base with screws. These clips make it easy to renew the burned-out fuses. The B-negative and A-positive leads are cut and connected to the fuse clips. Fuses are made from the tinfoil that comes wrapped around candy and chewing gum. It is cut in strips, $^1$⁄$_{16}$ in. wide, for the A-battery fuse, and about $^1$⁄$_{32}$ in. wide for the B-battery fuse. A bakelite cardboard tube is used for a cover; this slides over the corks and protects the fuses from accidental breakage or from being short-circuited. The cover is held in place by small wood screws.—R. J. Williams, Chicago.
Ball-Antenna Kit
It is claimed that radio reception can be improved considerably by using a ball antenna of the kind shown in the illustration. This outfit comes in a kit and can readily be assembled and installed by anyone. It consists of a bracket, glass insulator and a hollow aluminum ball, 10 in. in diameter. Being non-directional, several of these can be installed on an apartment roof without interference. Selectivity is another advantage claimed for this type of aerial.
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