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LESSON NINE

CURRENT PRODUCERS: BATTERIES, DYNAMOS AND

MAGNETOS

Q. What is the simplest method of producing electricity? A. The simplest method of producing electricity is by the use of a primary or secondary battery which generates electrical energy by the chemical combustion of one of the elements or plates of the battery.

Q. What is the cheapest method of producing electricity?

A. Electricity may be produced at lower cost by magnetic machines which change mechanical power into electricity.

Q. How many classes of batteries are used?

A. Two general classes of chemical current producers are commonly used, these being primary batteries and secondary batteries. Q. What is a primary battery?

A. A primary battery is one in which electricity is generated by the direct chemical action of the electrolyte on one of the plates composing the cell. A primary cell has positive and negative elements; that attacked by the electrolyte is usually termed the "negative" plate and is made of zinc, either in the form of a plate or a rod. The po itive element is of some substance that is not affected by the electrolyte and which serves as a collecting member for the electricity generated. In a primary battery electricity is produced at the expense of decomposition of the zinc plate and deterioration of the electrolyte. When a primary battery is exhausted or no longer capable of producing electricity, it must be practically rebuilt in order to extend its life. New electrolyte and zinc must be added to replace that used before the cell will give any more electricity.

Q. What is a secondary battery?

A. The secondary battery, commonly called the "storage battery" in America and the "accumulator" in Europe, is a form of chemical current producer in which the elements can be restored to their former condition when exhausted by passing a current of electricity through the battery in a direction opposite to that of the current flow normally given out by the battery. As a battery of this form can only produce electricity after it has been energized or charged by a current from some extraneous source, such as a primary battery or mechanical generator, it is called a "secondary" battery.

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Fig. 88.-Outlining Method of Determining Current Consumption of Induction Coil by Using Low Reading Ammeter.

Q. What is a dry battery?

A. A dry battery is the form of primary cell in which the liquid electrolyte is replaced by some form of jelly or other substance to absorb the liquid so it cannot splash out while the automobile is in operation.

Q. Describe construction of typical dry cell.

A. A part sectional view of the conventional form of dry cell is outlined at Fig. 89. The container or shell is made of zinc and

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Fig. 89.-Sectional View of Typical American Dry Cell.

serves as the negative element, while a stick of carbon placed in the center of the zinc shell and kept from contact with the metal serves as a positive element. The electrolyte or exciting material is absorbed by blotting paper, several layers of which are closely wound

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

A

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ท B

Fig. 90.-Methods of Joining Dry Cells for Ignition Service. A-Four Cells in Series Connection. B-Twelve Cells in Multiple Series Connection.

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 generally 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 are 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

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