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of forms, some being combined with volt meters, as shown at Fig. 226. The combination instrument is the best form for the repairman to use as the volts scale can be employed for testing storage batteries while the amperemeter scale may be utilized in determining the strength of dry cells. A fully charged, fresh dry cell should show a current output of from twenty to twenty-five amperes.
If the cell indicates below six or seven amperes, it should be discarded as it is apt to be exhausted to such a point that it will not furnish current enough to insure energetic or reliable ignition. Dry cells should always be stored in a cool and dry place, so that the electrolyte will not evaporate. If moisture is given an opportunity to collect on the top of the pitch seal it will allow a gradual loss of current due to short circuiting the cells. In applying an amperemeter, care should be taken to always connect the positive terminal marked with a plus sign against the carbon terminal. In the indicating meter shown at B, it is necessary to use only one contact point which is pressed against the screw passing through the carbon rod. The case of the instrument is placed in contact with the zinc terminal to complete the circuit. A flexible wire is usually included in order to test the amperage of a group of cells should this be thought necessary. When dry cells are used for automobile ignition, they should be carefully packed in a box made of non-conducting material, such as wood, and securely covered so that there will be no chance for water to enter the container. If placed in a sheet metal case, care should be taken to line the box with insulating material and also to pack the cells tightly so they cannot shake around. The best practice is to use wedges or blocks of wood which are driven in between the cells to keep them apart. In no case should a dry cell be placed directly in a steel box, as the binding posts on the zincs might come in contact with the walls of the box and tend to short circuit the cells, producing rapid depreciation. A battery box should always be placed at a point where it is not apt to be drenched with water when the car is washed or should be watertight if exposed.
When dry cells are used for ignition there are two practical methods of connecting these up. At least four dry cells are neces
Fig. 225.-Methods of Connecting Dry Cells and Precautions to be
Observed When Wiring.
sary to secure satisfactory ignition and much more energetic explosions will be obtained if five or six are used. The common method is to join the cells together in series as shown at Fig. 225, A. When connecting in this manner the carbon terminal of one battery is always coupled to the zinc binding post of its neighbor. Connection would be made from the carbon of the first
cell to t..e zinc of the second, from the carbon of the second to the zinc of the third, and from the carbon of the third to the zinc of the fourth, this leaving the zinc terminal on the first cell and the carbon terminal on the fourth cell free to be joined to the external circuit. When dry cells are connected in series the voltage is augmented, that of one cell being multiplied by the number so joined. The amperage remains the same as that of one cell. If a dry cell has a potential of 1/4 volts, a battery composed of four cells would show 5 volts. When dry batteries are used for lighting purposes or for igniting multiple cylinder engines, in order to obtain better results, they are connected in series multiple, as shown at B. Three sets of cells joined in series are placed side by side with the free carbons at one end in line and the zincs at the other also in line. The three carbons are then joined together by one wire, the three zinc terminals by another. When joined in this manner the battery has a voltage equal to that of four cells and an amperage equal to that of three cells. If a series connected battery as at A, indicates 5 volts and 20 amperes, the series multiple connection at B will indicate 5 volts and 60 amperes. When cells are joined in multiple the drain on any one cell is reduced and it is not so likely to become exhausted as when four are used in series. The points to be watched out for when installing dry batteries are clearly outlined at the bottom of Fig. 225. It will be seen that it is not desirable for terminals to come in contact with each other or with the sides of the box nor is it conducive to good ignition to have the zinc shells in contact. A loose terminal on any one of the batteries will result in irregular ignition while a broken wire will interrupt it altogether. If the insulation is frayed where a wire passes through a hole in a metal battery box trouble may be experienced due to short circuiting of the current between the bare wire and the steel box, which may be grounded.
Storage Battery Defects. The subject of storage battery maintenance was thoroughly covered in a paper read by H. M. Beck before the S. A. E. and published in the transactions of the society. Some extracts from this are reproduced in connection with notes made by the writer and with excerpts from in
struction books of battery manufacturers in order to enable the reader to secure a thorough grasp of this important subject withont consulting a mass of literature. Endeavor has been made to simplify the technical points involved and to make the exposition as brief as possible without slighting any essential points. In view of the general adoption of motor starting and lighting systems on all modern automobiles, the repairman or motorist must
pay more attention to the electrical apparatus than formerly needed when the simple magneto ignition system was the only electrical part of the automobile. The storage battery is one of the most important parts of the modern electrical systems and all up-to-date repairmen must understand its maintenance and charging in order to care for cars of recent manufacture intelligently.
A storage battery, from an elementary standpoint, consists of two or more plates, positive and negative, insulated from each other and submerged in a jar of dilute sulphuric acid. The plates
consist of finely divided lead, known as the active material, held in grids which serve both as supports and as conductors for the active material. The active material being finely divided, offers an enormous surface to the electrolyte and thus electro-chemical action can take place easily and quickly. Two plates such as described, would have no potential difference, the active material of each being the same. If, however, current from an outside source is passed between them, one, the positive, will become oxidized, while the other remains as before, pure lead. This combination will be found to have a potential difference of about two volts, and if connected through an external circuit, current will flow.
During discharge, the oxidized plate loses its oxygen and both plates will become sulphated until, if the discharge is carried far enough, both plates will again become chemically alike, the active material consisting of lead sulphate. On again charging, the sulphate is driven out of both plates and the positive plate oxidized and this cycle can be repeated as often as desired until che plates are worn out. Thus charging and discharging simply result in a chemical change in the active material and electrolyte, and the potential difference between the plates and capacity is due to this change.
In taking care of a storage battery, there are four points which are of the first importance:
First—The battery must be charged properly.
Third-Short circuits between the plates or from sediment under them, must be prevented.
Fourth- The plates must be kept covered with electrolyte and only water of the proper purity used for replacing evaporation.
In the event of electrical trouble which may be ascribed to weak source of current, first test the battery, using a low reading voltmeter. Small pocket voltmeters can be purchased for a few dollars and will be found a great convenience. Cells may be tested individually and as a battery. The proper time to take a reading of a storage battery is immediately upon stopping or while the engine is running. A more definite determination can be made than after the battery has been idle for a few hours and