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around the inside of the zinc shell. This places the electrolyte directly in contact with the metal it acts on. The carbon rod is surrounded by a depolarizing material which keeps the cell active for longer periods than if the electrolyte alone was used.
During the action of the cell, or whenever the zinc and carbon terminals are joined together to form a closed circuit, the chemical action of the electrolyte on the zinc liberates hydrogen gas which would clog or retard the action of the cell if allowed to accumulate on the carbon plate. The depolarizing medium is some chemical rich in oxygen, and its purpose is to liberate oxygen gas while the cell is in operation, which combines with the hydrogen in proper
Fig. 90.—Methods of Joining Dry Cells for Ignition Service. A–Four
Cells in Series Connection. B–Twelve Cells in Multiple Series
proportions to form water. The water thus formed is of distinct value, inasmuch as it keeps all parts of the cell moist and lowers the internal resistance. The top of the cell is sealed with a thick layer of pitch to prevent escape of the gases and to retain the elements of which the cell is composed in the zinc shell as well as to keep the elements separated.
Q. How are dry cells used?
A. Dry cells are generally employed in sets, so that batteries having different values, as regards current pressure or quantity, are produced. They may be wired together in series, in multiple, or in series-multiple connection. The latter method is that gener ally used.
Q. Describe series connection.
A. The method of connecting dry cells in series is clearly outlined at Fig. 90-A. When joined in this manner the negative terminal of one cell is always joined to the positive or opposite terminal of the neighboring one. For instance, the zinc of one cell is always connected to the carbon of the next member. When cells re joined this way, a battery is produced which has a voltage equal to that of one cell times the number of cells joined together, but the amperage of only one cell.
Q. Describe multiple connection.
A. Cells are connected together in multiple only when a current of heavy amperage and low voltage is desired. This method involves joining all the terminals of like polarity together. For instance, all the zinc terminal screws would be joined together by one wire, while all the carbon terminals would be joined by another conductor. A battery composed of cells in multiple connection would deliver a current having a voltage equal to that of one cell, but a current strength or amperage equal to that of one cell times the number of cells in the battery.
Q. Describe series multiple connection.
A. The system employed in joining dry cells in series multiple connection is clearly outlined at Fig. 90-B. Here three sets of four cells each which are coupled in series are joined together in multiple. By this method of connection, which is that generally used where the batteries are employed for ignition or lighting, one obtains the voltage of any one of the series combinations and the amperage of the three sets of cells. With a dry battery, having twelve cells coupled in the manner indicated, one will obtain a current having a pressure of six volts and a quantity of sixty amperes.
Q. What precaution is necessary when connecting dry cells together?
A. Care should be taken that the cells are well insulated from each other, and if carried in a metal box, suitable precautions should · be taken to insure against the battery containers coming in contact
with the sides of the box. The termina s on the binding posts should be screwed down tightly in order to avoid loose connections, and the cells should be packed in such a way that they cannot shake loose when in service and break or loosen the connecting wires by vibration. Care should be taken when connecting cells in series that only terminals of unlike polarity be joined together and that the terminals of the same cell are never connected together in any way.
Q. What are the advantages of the dry cell?
A. The dry cell is simple, compact, economical and easily instal.ed.
Q. What are the disadvantages of the dry cell?
A. The main disadvantages of a dry cell battery are that it is unsuitable for any except the lightest kind of intermittent service and that its capacity lessens as it is used. When the cells have deteriorated to a certain point, they must be thrown away and replaced by new ones.
Q. What is the standard size of dry cells?
A. The standard size of dry cell used for ignition purposes is. 6 inches by 27/2 inches and the cells are cylindrical in form. A larger size is sometimes used for stationary engine ignition that is about 3/4 inches in diameter and 8 inches high.
Q. What is the effect of size on battery capacity?
A. The greater the area of the plates or elements of the battery the higher its amperage or current output will be. The voltage, however, remains constant for cells composed of the same material regardless of size. For example, a dry battery no larger than a. thimble having zinc and carbon elements and the conventional alkaline excitant, will have a pressure of 1.5 volts between the terminals, which is also true of a dry cell the size of a barrel. The amperage of the larger member would be directly proportional to the amount of surface of the zinc shell acted on by the electrolyte compared with that of the smaller member.
Q. What is a storage battery?
A. A storage battery such as outlined at Fig. 91 is composed of three secondary cells joined together and carried in a common
Fig. 91.-Sectional View of Geiszler Storage Battery for Ignition Ser
container jar of hard vulcanized rubber so they form a three cell combination that will deliver a current of about 6 volts and 60 amperes. A battery of this form is capable of being recharged when exhausted, as previously described.
Q. Name the principal parts of a typical storage battery.
A. The various units of which the storage battery is composed are clearly outlined at Fig. 92. The main container is separated into three compartinents by partitions moulded integral with the jar and which divide the main container into three distinct parts. The plate assembly is composed oi either four or five plates made of lead alloy grids filled with variou; lead oxides. The plates are separated from each other by thin sheets of hard rubber, perforated with many holes for the passage of the electrolyte and a ribbed wooden separator is interposed between each pair of plates. When a five plate assembly is used, three of these are positive or collecting members, and two are negative or generating members. A five plate assembly has greater capacity than a four plate form, because both sides of the negative elements are exposed to the corresponding faces of positive plates.
The plate assembly becomes a unit because the various meml crs are joined together by a bus bar of lead burned to the lugs projecting from the plates by means of the hydrogen flame. The top of the individual compartments are then closed with hard rubber cell covers in which vents to permit of the escape of the gases without danger of losing the liquid electrolyte from splashing are screwed. The three cells are then covered by one large cover which has a soft rubber gasket interposed between the jar and cover as a packing. Other forms of storage batteries have a compound of pitch, rosin, and other elements directly over the cell covers to effectively seal the elements in their respective compartments. The disadvantage of this method is that it is difficult to remove the plate assembly for repairs or cleaning, whereas the separate cover, which is held in place by numerous small screws, can be readily removed when it is necessary to gain access to the interior of the battery.
Q. What determines the capacity of a storage battery?
A. The capacity of a storage battery depends upon the size and nature of the plates used in each cell and their number as well as the number of cells joined together to form a battery. Batteries ordinarily used for ignition purposes are either of the 6 volt, 60 ampere, or 6 volt, 80 ampere type. Those used for lighting service