Зображення сторінки
PDF
ePub
[blocks in formation]

Fig. 4.-Methods of Connecting Dry Cells and Precautions to be Observed

When Wiring.

neighbor. Connection would be made from the carbon of the first cell to the 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 en. gines, 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. 4. 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 or 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.

One of the disadvantages of primary cells, as those types which utilize zinc as a negative element are called, is that the chemical action produces deterioration and waste of material by oxidization. Dry cells are usually proportioned so that the electrolyte and depolarizing materials become weaker as the zinc is used and when a dry cell is exhausted it is not profitable to attempt to recharge it because new ones can be obtained at a lower cost than the expense of renewing the worn elements would be.

The number of dry cells necessary will vary with the system of ignition employed and the size of the motor. While two or three

cells will ignite small engines such as used in motorcycles, five or six will be needed on automobile engines employing high-tension ignition. When the make-and-break system, or low-tension method, is used eight or ten cells are necessary. If the engine is a multiple cylinder one, it will draw more current than a single cylinder type because of the greater frequency of sparks. On four-cylinder cars dry cells should be joined in multiple series, which is the most economical arrangement. Cells used in multiple connection are more enduring than if the same number were used independently in single-series connection. A disadvantage of a dry cell battery is that it is suited only for intermittent service and it will soon become exhausted if used where the current demands are severe. For this reason most automobiles in which batteries are used for ignition employ storage or secondary batteries to furnish the current regularly used and a set of dry cells is provided for use only in cases of emergency when the storage battery becomes exhausted.

Principles of Storage Battery Construction.-Some voltaic couples are reversible, i. e., they may be recharged when they have become exhausted by passing a current of electricity through them in a direction opposite to that in which the current flows on discharge. Such batteries are known as “accumulators” or “storage batteries.” A storage battery belies its name as it does not store current and its action is somewhat similar to that of the simpler chemical cell previously described. In its simplest form a storage cell would consist of two elements and an electrolyte, as outlined at Fig. 5, A. The storage battery differs from the primary cell in that the elements are composed of the same metal before charging takes place, usually lead instead of being zinc or carbon. One of the plates is termed the “positive” and may be distinguished from the other because it is brown, or chocolate in color after charging, while the negative plate is usually a light gray of leaden color. The active material of a charged storage battery is not metallic lead but oxides of that material.

The simple form shown at A consists of two plates of lead which are rolled together separated by insulating bands of rubber at the top and bottom to keep them from touching. This roll is immersed in an electrolyte composed of a weak solution of sul

phuric acid in water. Before such a cell can be used it must be charged, which consists of passing a current of electricity through it until the lead plates have changed their nature. After the charging process is complete the lead plates have become so changed in nature that they may be considered as different substances and a chemical action results between the negative plate and the electrolyte and produces current just as in the simple cell

[graphic][subsumed][subsumed][merged small][merged small][subsumed][merged small][merged small][merged small][ocr errors][merged small]

Fig. 5.-Types of Accumulators or Storage Batteries. A-Simple Form

of Cell. B~Battery Composed of Three Cells Such as commonly Used for Ignition Purposes.

shown at Fig. 3, A. When the cell is exhausted the plates return to their metallic condition and are practically the same, and as there is but little difference in electrical condition existing between them, they do not deliver any current until electricity has been passed through the cell so as to change the lead plates to oxides of lead instead of metallic lead.

When storage cells are to be used in automobile work they are combined in a single containing member, as shown at Fig. 5, B,

which is a part sectional view of a Geiszler storage battery. The main containing member, a jar of hard rubber, is divided into three parts. Each of these compartments serves to hold the elements comprising one cell. The positive and negative plates are spaced apart by wood and hard rubber separators which prevent short circuiting between the plates. After the elements have been put in place in the compartments forming the individual cells of the battery, the top of the jar is sealed by pouring a compound of pitch and rosin, or asphaltum, over plates of hard rubber, which keeps the sealing material from running into the cells and on the plates. Vents are provided over each cell through which gases produced by charging or discharging are allowed to escape. These are so formed that while free passage of gas is provided for, it is not possible for the electrolyte to splash out when the vehicle is in motion.

It will be evident that this method of sealing would not be practical on a cell where the members attacked by the acid had to be replaced from time to time, but in a storage battery only the electrolyte need be renewed. When the plates are discharged they are regenerated by passing a current of electricity through them. New electrolyte or distilled water can be easily inserted through holes in which the vents are screwed. The cells of which a storage battery is composed are joined together at the factory with bars of lead which are burned in place and only two free terminals are provided by which the battery is coupled to the outer circuit.

The capacity of a storage battery depends upon the size and the number of plates per cell, while the potential or voltage is determined by the number of cells joined in series to form the battery. Each cell has a difference of potential of two and two tenths volts when fully charged, therefore a two-cell battery will deliver a current of four and four tenths volts and a three-cell type, as shown in part section at Fig. 6, will give about six and six tenths volts between the terminals. In the form shown each cell is composed of a number of plates and their separators. One group of the plates is positive, the remaining negative members. The size of storage battery to be used depends upon the number of cylinders of the engine and also if battery is to be used for

« НазадПродовжити »