Fig. 1,046.—One plate or "grid" of a type of storage cell constructed by inserting buttons or ribbons of the proper chemical substances in perforations. Some such cells use crimped ribbons of metallic lead for inserting in the perforations, others pure red lead or other suitable material.
As to the theory at this time, it may be stated that Clerk Maxwell, although the leading electrician of his time, speaks of the storage battery as storing up a quantity of energy in a manner somewhat analogous to the ordinary condenser; hence the use of the word "accumulator" for storage battery.
In 1879, R. L. Metzer did away with the tedious forming process, by mechanically applying the active material. This important discovery was not, however, generally known, until 1881, when Camille Faure obtained important patents concerning the method of shortening the time of formation.
Charles F. Brush, working independently of either Faure or Metzer, arrived at the same result, and the United States courts have decided, after long litigation, that to him belongs the priority of invention in this country.
Figs. 1,047 to 1,050.—Electric Storage Battery Co. plates. Fig. 1,047, "Manchester" positive plate; fig. 1,048, box negative plate; fig. 1,049, "Tudor" positive plate; fig 1,050, pasted negative plate.
Ques. To what use is the storage battery sometimes put in electric lighting or power stations?
Ans. To carry the "peak" of the load; that excessive portion of the load which, for instance, in electric lighting stations has to be carried only for two or three hours a day. To carry the entire load at minimum hours. To act as equalizer or reservoir. Also for equipment of annex or substations.
Fig. 1,051.—"Unformed" plate of one pattern of Gould storage cell. The particular plate shown has total outside dimensions of 6×6 inches. The clear outline of the grooves indicates absence of oxides, due to action of "forming" solutions, or charging current.
Theory of the Storage Battery.—The action of the storage battery is practically the same as that of the primary battery and it is subject to the same general laws. The cells of a storage battery are connected in the same way as primary cells, and when charged is capable of generating a current of electricity in a manner similar to that of a primary battery. It differs, however, from the primary battery in that it is capable of being recharged after exhaustion by passing an electric current through it in a direction opposite to that of the current on discharge. This difference constitutes the principal advantage of the storage battery over the primary battery.
Figs. 1,052 and 1,053.—Electric Storage Battery Co., type H "exide" plates. This form of plate is used for large "stand by" batteries. Fig. 1,052, positive plate; fig. 1,053, negative plate.
Ques. Describe a storage cell.
Ans. A storage cell consists of plates or of grids in an electrolyte, of such a character that the electrical energy supplied to it is converted into chemical energy (a process called charging). The chemical energy can be reconverted into electrical energy (a process called discharging).
Ques. Describe the electrolyte generally used.
Ans. It consists of a weak solution of sulphuric acid which permits ready conduction of the current from the primary battery, the greater the proportion of acid within certain limits, the smaller the resistance offered.
Fig. 1,054.—Elements of 6 volt 40 ampere hour "Aplco" portable (3 cell) storage battery. The grids are made from an alloy of lead and antimony; hard lead straps which are burned together, are used for joining the plates. Specially treated separators are used.
Ques. What is the effect of the current passing through the electrolyte?
Ans. It decomposes the water into oxygen and hydrogen; this is indicated by the formation of bubbles upon the exposed surfaces of both plates, these bubbles being formed by oxygen gas on the plate connected to the positive pole of the primary battery, and hydrogen on the plate connected to the negative pole.
Because, however, the oxygen is unable to attack either platinum or silver under such conditions, the capacity of such a device to act as an electrical accumulator is practically limited to the point at which both plates are covered with bubbles. After this point the gases will begin to escape into the atmosphere.
Ques. What is the prime condition for operation of a storage battery?
Ans. The resistance of the electrolyte should be as low as possible in order that the current may pass freely and with full effect between the electrodes. If the resistance of the electrolyte be too small, the intensity of the current will cause the water to boil rather than to occasion the electrolytic effects noted above.
Ques. What happens when the charging current is discontinued, and the two electrodes joined by an outside wire?
Ans. A small current will flow through the outside circuit, being due to the recomposition of the acid and water solution. The process is in a very definite sense a reversal of that by which the current is generated in a primary cell.
Hydrogen collected upon the negative plate, which was the cathode, so long as the primary battery was in circuit, is given off to the liquid immediately surrounding it, uniting with its particles of oxygen and causing the hydrogen, in combination with them, to unite with the particles of oxygen next adjacent. The process is continued until the opposite positive plate is reached, when the oxygen collected there is finally combined with the surplus hydrogen, going to it from the surrounding solution.
This chemical process causes the current to emerge from the positive plate, which was the anode, so long as the primary battery was in circuit. The current thus produced will continue until the recomposition of the gases is complete; then ceasing because these gases, as before stated, do not combine with the metal of the electrodes.
Types of Storage Battery.—There are three classes of storage cell which are commercially important:
1. Plante cells;
2. Faure cells;
3. Alkaline cells.
According to construction secondary cells may be classified as follows:
1. Lead sulphuric acid cells;
2. Lead copper cells;
3. Lead zinc cells;
4. Alkaline zincate cells.
The lead sulphuric acid type includes all those cells belonging to the Plante and Faure groups.
Lead copper cells consist of sheets of metal coated with lead oxide, serving as the positive electrode, and copper plates for the negative electrodes. These plates are immersed in a solution of copper sulphate. Cells belonging to this class are not employed in commercial practice, being useful only for laboratory experiments.
Lead zinc cells are similar to the preceding type, but differ by having zinc for the negative electrode, and zinc sulphate for the electrolyte. The voltage of these cells is slightly higher than that of the ordinary cell, and their capacity per unit of total weight is high, but they are apt to lose their charge on open circuit, besides they possess most of the disadvantages of the Plante cells.
Alkaline zincate cells have copper for the positive, and iron for the negative electrode. The electrolyte is composed of sodium, or potassium, zincate. Cells of this type are used to some extent for traction purposes.
In addition to the above there are some special forms of cell which do not belong to the four preceding types.
Ques. Describe the Plante type.
Ans. In the Plante type the lead is chemically attacked and finally converted into lead peroxide, probably after it has gone through several intermediate changes. The plates are all formed as positive plates first and then all that are intended for negative plates are reversed, the peroxide being changed into sponge lead.
Figs. 1,055 and 1,056.—Willard plates; fig. 1,055, negative plates; fig. 1,056, positive plates. Both positive and negative plates are of the Planté type, made from one integral piece of rolled lead. These are grooved plates. The projections are tapered, that is, they are wider at the base than at the surface, for strength. The center web of each positive plate is tapered from the top of the plate downward to secure uniform distribution of the current all over the surface of the plate.
Fig. 1,057.—Wood separator for spacing the plates, as used in the Willard storage cells.
Fig. 1,058.—Positive plate.
Fig. 1,059.—Perforated rubber separator.
Fig. 1,060.—Wood separator.
Fig. 1,061.—Negative plate.
Fig. 1,062.—Hard rubber cover.
Fig. 1,063.—Vent plug.
Fig. 1,064.—Pillar connecting strap.
Fig. 1,065.—Hard rubber jar.
Fig. 1,066.—Complete element.
Figs. 1,058 to 1,066.—Parts of the Willard "Autex" automobile cells.
Ques. What is done to make the Plante plate more efficient?
Ans. The surfaces are finely subdivided, the following methods being those common: scoring, grooving, casting, laminating, pressing, and by the use of lead wool.
Ques. Describe the Faure or pasted type.
Ans. This form of plate is constructed by attaching the active material by some mechanical means to a grid proper. The active material first used for this purpose was red lead, which was reduced in a short time to lead peroxide when connected as the positive or anode, or to spongy metallic lead when connected as the cathode or negative, thus forming plates of the same chemical compound as in the Plante type.
The materials used at the present time by the manufacturers for making this paste are largely a secret with them, but in general they consist of pulverized lead or lead oxide mixed with some liquid to make a paste.
Ques. How do Faure plates compare with those of the Plante type?
Ans. They are usually lighter and have a higher capacity, but have a tendency to shed the material from the grid, thus making the battery useless.
Many ways have been tried for mechanically holding the active material on the grid, the general method involving a special design in the shape of the grid. Some of these designs are: 1, solid perforated sheets of lattice work; 2, corrugated and solid recess plates not perforated; 3, ribbed plates with projecting portions; 4, grid cast around active material; 5, lead envelopes, and 6, triangular troughs as horizontal ribs.
The Electrolyte.—Sulphuric acid is generally used as electrolyte; the acid should be made from sulphur and not from pyrites, as the latter is liable to contain injurious substances.
Ques. How is the electrolyte prepared?
Ans. One part of chemically pure concentrated sulphuric acid is mixed with several parts of water. The proportion of water differs with several types of cell from three to eight parts, as specified in the directions accompanying the cells.
Figs. 1,067 to 1,079.—Willard connecting straps and connectors.
Ques. What test is necessary in preparing the electrolyte?
Ans. In mixing the water and acid, the hydrometer should be used to test the specific gravity6 of both the acid and the solution. The most suitable acid should show a specific gravity of about 1.760 or 66° Baumé.
Ques. In preparing the electrolyte, how should the water and acid be mixed?
Ans. The mixture should be made by pouring the acid slowly into the water, never the reverse. As cannot be too strongly stated, in mixing, the liquid should be stirred with a clean wooden stick, the acid being added to the water slowly; the latter is corrosive and will painfully burn the flesh.
Distilled or rain water should be used in preparing the electrolyte. When made, the solution should be allowed to cool for several hours or until its temperature is approximately that of the atmosphere (60 being the average). At this point it should have a specific gravity of about 1.200 or 25° Baumé. If the hydrometer show a higher reading, water may be added until the correct reading is obtained; if a lower reading, dilute acid may be added with similar intent.
The electrolyte should never be mixed in jars containing the battery plates, but preferably in stone vessels, specially prepared for the purpose. Furthermore, it should never be placed in the cell until perfectly cool.
Ques. What is the effect of mixing the acid and the water?
Ans. The mixture becomes hot.
Before using, the mixture should be allowed to cool.
Ques. What kind of a vessel should be used?
Ans. The vessel should be of glass, glazed earthenware, or lead.
Ques. At what density is the resistance of dilute sulfuric acid at a minimum?
Ans. At 1.260.
The percentage of concentrated sulphuric acid and of water per 100 parts of the electrolyte for various specific gravities is given by the following table:
| Sulphuric acid (Per cent.). |
Water (Per cent.). |
Specific gravity of Mixture. |
|---|---|---|
| 50 | 50 | 1.398 |
| 47 | 53 | 1.370 |
| 44 | 56 | 1.342 |
| 41 | 59 | 1.315 |
| 38 | 62 | 1.289 |
| 35 | 65 | 1.264 |
| 32 | 68 | 1.239 |
| 29 | 71 | 1.215 |
| 26 | 74 | 1.190 |
| 23 | 77 | 1.167 |
| 20 | 80 | 1.144 |
| 17 | 83 | 1.121 |
| 14 | 86 | 1.098 |
| 10 | 90 | 1.068 |
The electrolyte of the desired specific gravity may be purchased ready for use, but in cases where it is desirable to save freight, the acid may be diluted at the point of installation.
Ques. What is the effect of a deep containing vessel?
Ans. Parts of the plate surface may do more than their share of the work due to the difference in the density of the electrolyte at the top and bottom. The containing vessel should, therefore, never be deeper than about 20 inches unless some artificial means of acid circulation be used.
Ques. What is the effect of changes in temperature on the electrolyte?
Ans. The resistance of the electrolyte is changed, being less for increase of temperature.
Figs. 1,080 to 1,084—Acid hydrometers for liquids heavier than water. Fig. 1,080, standard storage battery hydrometer with guiding points designed for "hydrometer syringe," shot bulb, with red line at 25 Baumé, 5 inches long, double scale 10 to 40 Baumé, 1.050 to 1.400 specific gravity. Fig. 1,081, plain hydrometer with shot bulb, 5 inches long, double scale 10 to 40 Baumé, 1.050 to 1.400 specific gravity. Figs. 1,082 and 1,083, hydrometer with small flat bulb, used in car lighting batteries, shot bulb, 4½ inches long, single scale, reading from 1.100 to 1.250 specific gravity. Fig. 1,084 jar for hydrometers.
Ques. How should the cells be filled?
Ans. Enough of the electrolyte should be poured into the jars to completely cover the plates, or to within about a half inch of the top edge of the jar. Large cells should be filled by means of an acid proof pump and rubber hose.
Ques. What change takes place after filling the jars?
Ans. The specific gravity of the electrolyte will fall considerably, but will rise again when the battery is charged.
Ques. What may be said with respect to the density of the electrolyte?
Ans. It should never exceed 1.200 when the battery is fully charged.
Ques. How much electrolyte is used per 100 ampere hours battery capacity, on an 8 hour rating?
Ans. About ten pounds; in automobile batteries, about four pounds is sufficient.
Fig. 1,085.—The hydrometer syringe; a convenient device for testing electric vehicle cells. By slightly compressing the bulb and inserting the slender tube through the vent hole in the cover of the cell sufficient acid may be drawn up to float the hydrometer within the large glass tube, and the reading can be made at once. The acid is returned to the cell by again compressing the bulb, and the reading of the next cell taken. The laborious and uncleanly method of drawing out sufficient acid by a syringe is thus avoided.
Ques. What may be said with respect to impurities in the electrolyte?
Ans. The electrolyte should be free from chlorine, nitrates, acetates, iron, copper, arsenic, mercury, and the slightest trace of platinum.
Mercury alone has no injurious effect unless it be present in sufficient quantity to amalgamate the plates, but in combination with any other metal, may cause local action.
Figs. 1,086 to 1,089.—The "Champion" Accumulator; views showing parts and assembly. Fig. 1,086, empty plate; fig. 1,087, filled plate; fig. 1,088, complete element, small type; fig 1,089, cell assembled. The plates are of the envelope type and are made thick. The active material is held firmly in place by a covering of lead. A few thick plates are used instead of many thin ones.
The following tests should be made for impurities before the electrolyte is poured in the cells:
Chlorine.—To a small sample of the electrolyte add a few drops of silver solution (20 grains of silver dissolved in 1,000 cu. cm. of water). A white precipitate indicates chlorine.
Nitrates.—Place some of the electrolyte in a test tube, and add 10 grains of strong ferrous sulphate solution. Carefully pour down the side of the test tube a small amount of chemically pure concentrated sulphuric acid. A brown stratum between the electrolyte and the concentrated acid indicates the presence of nitric acid.
Acetic acid.—Neutralize the electrolyte with ammonia, then add ferric chloride. If the solution turns red, and is afterwards bleached by the addition of hydrochloric acid, acetic acid is present.
Iron.—Neutralize a sample of the electrolyte with ammonia; boil a small portion with hydrogen peroxide, and add ammonia or caustic potash solution until the mixture becomes alkaline. If a brownish red precipitate forms, it indicates iron.
Copper.—If copper be present, a bluish white precipitate will be formed when ammonia solution is added to the electrolyte.
Fig. 1,090.—One cell of the Gould storage battery for electric vehicle use. According to the data given by the manufacturers, this cell, containing four negative and three positive plates, has a normal charging rate of 27 amperes; a distance rate of 22 amperes for four hours; a capacity of 81 ampere hours at 3 hours discharge, and of 90 ampere hours at 4 hours discharge. Forty such cells are generally used for an average light vehicle battery.
Mercury.—This is indicated by an olive green precipitate when a solution of potassium iodide is added to the electrolyte, or by a black precipitate when lime water is added.
Platinum.—A rough test for traces of platinum is made by pouring the electrolyte into a cell in which the battery plates are immersed. If gassing take place for some time on open circuit, it is an indication of the presence of platinum.
Ques. What should be done with old electrolyte?
Ans. When a battery is taken down the electrolyte may be saved and used when re-assembling the battery, providing great care be exercised when pouring it out of the jar, so as not to draw off with it any of the sediment. It should be stored in convenient receptacles, preferably carboys, which have been thoroughly washed and never used for any other purpose.
Fig. 1,091.—Phantom view of an "Exide" sparking or ignition battery. It contains three cells. In this type, the terminal lug has been designed to obviate the creeping of the electrolyte with its accompanying corrosion. The positive and negative terminals are for identification.
The electrolyte saved in this manner will not, however, be sufficient to refill the battery, and as some new electrolyte will be required, in general it is recommended that the old supply be thrown away and all new electrolyte (1.200 specific gravity) be used when re-assembling.
Voltage of a Secondary Cell.—This depends on the density of the electrolyte, the character of the electrodes and condition of the cell; it is independent of the size of the cell.
The voltage of a lead sulphuric acid cell when being charged is from 2 to 2.5 volts. While the cell is being discharged, it decreases from 2 to 1.7 volts. The voltage due to the density of the electrolyte may be calculated from the following formula:
V = 1.85 + .917 (S - s)
in which
V = voltage;
S = specific gravity of the electrotype;
s = specific gravity of water at the temperature of observation.
Fig. 1,092.—The Exide storage cell. The positive and negative plates are separated by thin sheets of perforated hard rubber, placed on both sides of each positive plate. The electrolyte and plates are contained in a hard rubber jar.
Fig. 1,093.—An Exide battery of five cells. The box which holds the cells is usually made of oak, properly reinforced, with the wood treated to render it acid proof. The terminals as shown, consist of metal castings attached to the side of the box and plainly marked.
Connection for Charging.—The dynamo cable connections may be made either before or after filling the cells. In making these connections great care should be taken to be sure that the positive terminal of the battery is connected to the positive lead of the dynamo, and that the negative terminal of the battery is connected to the negative lead of the dynamo. In order to insure that the reverse connections are not made accidentally, the dynamo leads should be tested by a pole tester, and the positive and negative poles marked red and black respectively.
Figs. 1,094 to 1,109.—Parts of the "Exide" sparking battery. A, positive plate; B, negative plate; C, wood separator; D, positive strap; E, negative strap; F, terminal lug; H, connector; I, terminal bolt connector, stud, thumb nut and hexagonal nut; J, copper washer for bolt connector; L, hard rubber jar; M, hard rubber cover; N, hard rubber cylinder vent; O, vent plug for cylinder vent; R, wood case; S, strap handle; T, fitting for strap handle. The "Exide" sparking battery is also adapted for electric lighting of automobiles, for head lights, tail lights, side and interior lights.
The polarity of the dynamo wires being determined, they may be joined to the proper terminals by means of suitable clamps or by solder.
Wherever possible the dynamo should be of the direct current, shunt wound, or special compound type, but in cases where only alternating current can be obtained, suitable rectifiers or converters should be used for changing it to direct current.
Charging.—Before beginning to charge a storage battery, it should be gone over carefully, and any cell that is not up to the standard should be disconnected and put in working order before being replaced. In general, if the current used in charging be too large, it will waste energy by evolving an excess of heat and gas; if too small, an insulating deposit of white lead sulphate will be formed on the positive plate, thereby preventing the formation of the proper amount of lead peroxide.
Figs. 1,110 and 1,111.—Switchboard and motor dynamo circuit connections for charging a battery from direct current mains.
Ques. How should a battery be charged for the first time?
Ans. It is essential that the current be allowed to enter at the positive pole at about one-half the usual charging rate prescribed, but after making sure that all necessary conditions have been fulfilled, it is possible to raise the rate to that prescribed by the manufacturers of the battery.
Ques. What is the usual period for charging a new battery?
Ans. With several of the best known makes of storage battery the prescribed period for the first charge varies between twenty and thirty hours.
Figs. 1,112 and 1,113.—Switchboard and motor generator circuit connections for charging a battery from alternating current mains. The connections of a third wire are shown, for use in case a three phase circuit is available.
Ques. How is the electrolyte affected by the first charge?
Ans. A change of specific gravity occurs. The specific gravity should be about 1.200 when the solution is poured into the cells.
At the completion of the first charge, it should, on the same scale be about 1.225. If it be higher than this, water should be added to the solution until the proper figure is reached, if it be lower, dilute sulphuric acid should be added until the hydrometer registers 1.225.
At the first charging of a cell, when the pressure has reached the required limit, the cell should be discharged until the voltage has fallen to about two-thirds normal pressure, when the cell should again be recharged to the normal voltage (2.5 or 2.6 volts).
The manufacturers of a well known cell of the Plante genus prescribe for the first charge, half rate for four hours, after which the current may be increased to the normal power and continued for twenty hours successively.
Fig. 1,114.—Plates of Edison storage battery. The positive or nickel plate consists of one or more perforated steel tubes, heavily nickel plated, filled with alternate layers of nickel hydroxide and pure metallic nickel in excessively thin flakes. The tube is drawn from a perforated ribbon of steel, nickel plated, and reinforced with eight steel bands, equidistant apart, which prevent the tube expanding away from and breaking contact with its contents. The tubes are flanged at both ends and held in perfect contact with a steel supporting frame or grid made of cold rolled steel, nickel plated. The negative or iron plate consists of a grid of cold rolled steel, nickel plated, holding a number of rectangular pockets filled with powdered iron oxide. These pockets are made up of very finely perforated steel, nickel plated. After the pockets are filled they are inserted in the grid and subjected to great pressure between dies which corrugate the surface of pockets and force them into good contact with the grid.
Ques. What strength of current should be used in charging a cell?
Ans. It should be in proportion to the ampere hour capacity of the cell.
Thus, as given by several manufacturers, the normal charging rate for a cell of 40 ampere hours should be five amperes, or one-eighth of its ampere hour rating in amperes of charging current.
Ques. What should be the voltage of the charging current before closing the charging circuit?
Ans. The voltage should be at least ten per cent. higher than the normal voltage of the battery when charged.
Fig. 1,115.—Complete element of Edison storage battery with insulators. After the plates are assembled into a complete element, narrow strips of treated hard rubber are inserted between the plates, thereby separating and insulating them from each other. The side insulator is provided with grooves that take the edges of the plates, thereby performing the dual function of separating the plates and insulating the complete elements from the steel container. At the ends of the element, that is between the outside negative plates and container, are inserted smooth sheets of hard rubber. At the bottom, the element rests upon a hard rubber rack or bridge, insulating the plates from the bottom of container.
Fig. 1,116.—Four Edison cells (type A-4) in wooden tray.
Ques. What indicates the completion of a charge?
Ans. When a cell is fully charged the electrolyte apparently boils and gives off gas freely. The completion of a charge may be determined by the voltmeter, which will show whether the normal pressure has been attained.
Ques. How should the voltage be regulated during the first charge?
Ans. It should be allowed to rise somewhat above the point of normal pressure.
|
Fig. 1,117.—Cell of Edison storage battery. The jar or container is of nickel plated sheet steel with welded seams; the walls are corrugated to give strength. The cell cover, of sheet steel, has four mountings, two being pockets to contain stuffing boxes about the terminal posts. One of the other two is a separator which separates spray from the escaping gas while the battery is charging. The fourth mounting is for filling with electrolyte. The electrolyte consists of a 21% solution of potash in distilled water with a small per cent. of lithia. The density of the electrolyte does not change on charge or discharge.
Ques. How often should a battery be charged?
Ans. At least once in two weeks, even if the use be only slight in proportion to the output capacity.
In charging a storage battery, it is essential to remember the fact that the normal charging rate is in proportion to the voltage of the battery.
Thus, a 100 ampere hour battery, charged from a 110 volt circuit at the rate of ten amperes per hour, would require ten hours to charge, and would consume in that time an amount of electrical energy represented by the product of 110 (voltage) by 10 (amperes) which would give 1,100 watts, or 11/10 kw.
Fig. 1,118.—Diagram illustrating method of charging storage battery of stationary gas engine ignition system; the system is simple to install and will give satisfactory results. Two storage batteries are used, one being charged while the other is operating the sparking coil. Where charging current is available at the point where the batteries are used, the following diagram shows the system of connections, which can be easily followed, A represents the source of charging current and B the bank of lamps (or other resistance, such as an ordinary rheostat) sufficient to cut down the charging voltage to that required by the battery. C and D are two double pole double throw knife switches connected at their hinges to two batteries, E and F, each consisting of a group of cells. G represents the leads to the sparking coil terminals. From the diagram, it will readily be seen that by throwing the switches in opposite directions one battery will be charging while the other battery is discharging to the engine, thus giving a constant source of supply, and insuring that the spare battery will be full and ready for service by the time the other is discharged. The method of determining the necessary resistance for cutting down the line voltage for charging the battery is illustrated by the following example: If a battery require about 3 amperes for charging, how is this current obtained from a 110 volt circuit? Each 16 candle power carbon filament lamp in the lamp bank would give approximately 1/3 ampere with the cells in series in the lamp circuit. Therefore, 3 x 3 or 9 lamps should be used in parallel to give 3 amperes.
Ques. If in charging a battery, one or more of the cells do not boil at the completion of the charge, or fail to show the proper voltage, what should be done?
Ans. The charging must be continued until the cadmium test shows the required voltage, but if the prolonging of the charge be liable to damage the plates in the other cells, the defective cell or cells should be cut out of circuit when the battery discharges and then placed in circuit again when the battery is recharged. If the desired result cannot be attained by this method, the plates which require additional charging may be charged in a separate cell.
Figs. 1,119 and 1,120.—Emergency connections for weak ignition battery. It sometimes occurs through carelessness or neglect, that the storage battery is discharged so low that the engine explosion will not take place, and it is necessary to run somehow or other for a short time. In such cases the following suggestion may be followed: If there be two storage batteries, connect them in series. If there be one storage battery and a set of dry cells, connect the positive terminal of the storage battery to the negative or outside terminal of the dry cell; set and connect to the coil leads as if they were one battery. The above suggestions should only be followed in emergency, for it may injure the coils, and is harmful to the battery.
Ques. How is the cadmium test made?
Ans. A plate of cadmium is mounted in a hard rubber frame and immersed in the electrolyte. The test consists in taking voltage readings between the cadmium plate and the positive or negative plates of the cell. During charge the cadmium plate reads negative to the negative plate, until the cell is about full, when the reading should be zero; the charge should be continued until the cadmium reads 0.2 volt positive to the negative while charging at the normal rate.
Ques. Name some portable instruments that should be provided for testing batteries.
Ans. 1, a hydrometer syringe (specific gravity tester); 2, an acid testing set (can be used instead of the syringe); 3, a low reading voltmeter; 4, suitable prods, and 5, a thermometer.
Ques. What precaution should be taken in charging a battery?
Ans. Care should be taken not to have a naked flame anywhere in its vicinity.
To either charge or discharge a battery at too rapid a rate involves the generation of heat. Thus, while this is not liable to result in a flame under usual conditions, the battery may take fire, if it be improperly connected or improperly used.
Ques. What is the effect of varying the charging current?
Ans. In charging a storage cell, particularly for the first time, a weaker current than that specified may be used with the same result, provided the prescribed duration of the charge be proportionally lengthened. The battery may also be occasionally charged beyond the prescribed voltage, ten or twenty per cent. overcharge effecting no injury, although if frequently repeated, it shortens the life of the battery.
Ques. What are the charge indications?
Ans. The state of the charge is not only indicated by the density of the electrolyte and the voltage of the cell, but also by the color of the plates, which is considered by many authorities as one of the best tests for ascertaining the condition of a battery.