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Anatomy of the Battery
Cell Arrangement:
Motive power lead-acid batteries for electric powered industrial trucks, tractors and cranes typically consist of 6, 12, 18 or 24 cells, a steel tray into which the cells are assembled, a battery terminal connector and other com ponents necessary to secure and protect the cells and provide the necessary electrical interconnections.
Battery Identification
The essential in- formation, necessary for proper care of an industrial motive power battery, appears on the battery either stamped into one of the intercell connectors or on a name plate affixed to the tray. This information usually includes the model, number of plates per cell, battery capacity, battery voltage, serial number.
Some manufacturers list, as a part of the model or type designation, the rated ampere-hour capacity of a single positive plate, such as “X75.” As an alternate means of determining rated battery capacity this number should be multiplied by the total number of positive plates in one cell. To find the number of positive plates in a cell, subtract one from the total number of plates and divide by two. To find the capacity of a battery designated “X75-19,” therefore: 19-1=18; 18÷2=9; 9 x 75=675 A.H. battery capacity.
Cell Arrangement
The individual cells, which con tain the energy generating components of the battery, may be arranged slightly differently for various types of batteries. The typical cell arrangement for 12 volt batteries (6 cells) is a single row of 6 cells; for 24 volts (12 cells) it is either two rows of 6 cells each or three rows of 4 cells each; for 32 volts (16 cells) it is four rows of 4 cells each; and for 36 volts (18 cells) it is three rows of 6 cells each.
The cells of all motive power batteries are, however, always connected in series to produce the required voltage. Cell and battery capacity, which is the available ampere-hours or watt-hours, is a function of the total number and size of plates within each cell. Voltage, though, is the same for all cells regardless of size. Each lead-acid cell yields a nominal 2 volts.
Connector Arrangement
Connections between cells are made by intercell-connectors which may be lead coated copper straps or cast of solid lead. These connections are always welded, in proper sequence, by the application of heat to the terminals of the cells.
Total energy from the battery is drawn off by terminal cables which extend beyond the steel tray wall and are in turn permanently joined to the battery terminal connector.
Cell :
This is the basic unit of any battery. A typical cell is shown in Figure 1-2. It is a galvanic cell which produces electrical energy when connected to an electrical load and, after being discharged, may be restored to its original fully charged condition. It has a nominal voltage of 2 volts and consists of an element, from which the energy is derived, and electrolyte, both of which are contained by an impact resistant, molded rubber or plastic jar. The element is prevented from contacting the bottom of the jar by means of a high impact bridge which consists of a series of support ribs. These ribs provide sediment space below the bottom of the element to accommodate particles of active material, shed by the positive plates during normal operation of the battery.
The top of each cell is fitted with a molded rubber or plastic cover sealed to the jar at the edges. A vent or filler cap is located in the center of the cover. This permits the escape of hydrogen and oxygen while the cells are gassing and, when removed, provides an opening through which water may be added to the cell. The positive and negative terminal posts, which are part of the element, fit through openings in the cover. Cells prior to being connected together are so placed that the positive terminal of one cell is adjacent to the negative terminal of the next. This permits a series connection. On some batteries the cell covers are tightened to the terminal posts by seal nuts and gaskets. On others, lead bushings are molded into the covers and welded to the terminal posts. Both methods prevent leakage of acid from the area around the terminal post.
Element
The element of the cell consists of one group each of positive and negative plates meshed together. The plates are insulated from each other by separators which are inserted between all plates. A plastic element protector is positioned on top of the separators which prevents mechanical damage to the element and aids in preventing electrical shorts which occur when particles of active material bridge the space between plates. Terminal posts are welded to each group and are used to electrically connect one cell to another. A typical element is shown in Figure 1-3.
Group
This is an assembly of plates of like polarity connected in parallel by welding to a common strap or busbar. A cell must contain one positive and one negative group. The negative group always has one more plate than the positive group. One or more terminal posts are welded to each.
Plates
The electrodes or plates are either positive or negative and consist of a cast lead alloy grid and active material. The grid provides support to the active material and becomes the primary electrical conductor. The active materials result from the addition of chemicals to lead oxides which are converted, by electro-chemical process- ing, to lead dioxide in the positive and sponge lead in the negative. Although negative plates made by all industrial lead-acid battery manufacturers are pasted and essentially similar, the positive plates in common use may be either tubular or pasted type.
Tubular type
The grid of the tubular plate consists of a series of cast lead rods connected at the top These vertical rods become the conducting cores of a like number of porous, tubular, glass or plastic retainers which contain the active material. Each tube is sealed at the top and bottom after filling to prevent the loss of active material. A typical tubular positive plate is shown in Figure 1-4
Pasted type
The grid of the pasted plate consists of horizontal and vertical or diagonal cast lead conducting members within a rectangular cast frame. A slurry of active material is pasted or squeezed into the voids and the surfaces are then covered by porous glass and plastic retainers to prevent the loss of active material. A typical pasted positive plate is shown in Figure 1-5.
Electrolyte
The element within the jar is immersed in an electrolyte, which is a solution of sulfuric acid and “pure” water. This permits the necessary chemical reac- tion to occur and provides a conducting medium in which the flow of electric current takes place. The electrolyte in a fully charged cell normally has a specific gravity of between 1.275 and 1.395 at 77 degrees F. As a cell discharges, the specific gravity decreases. Measurement of this specific gravity. by means of a hydrometer, indicates the state of charge of a cell. To save time, in determining this state of charge for the battery, a pilot cell or cells may be chosen. This is a selected cell(s) whose condition is assumed to be representative of the condition of the entire battery
Separator
Separators are made from either micro-porous rubber or plastic, both of which are resistant to heat and acid. Separators provide mechanical and electrical insulation between positive and negative plates but are porous enough to permit passage of electrolyte. The grooved or ribbed side of the separator is placed toward the positive plate to allow a free flow of electrolyte to the active material. The flat side faces the negative plate to contain the sponge lead.
Positive Plate Retainers
Tubular type plate retainers are made from porous glass or plastic which is woven or shaped into the form of a round or square tube. A plate is composed of a number of such tubes which are filled with active material in those areas surrounding the conducting cores of the grid. Pasted type plate retainers are added after pasting, typically by wrapping the plate first with fibrous type glass tape or mats and then by a perforated plastic envelope complete with bottom boot or by other suitable filtering systems. All types of retainers act to prevent the escape of positive active material during normal use. Retainers are not needed on negative plates.
DID YOU KNOW THAT ...
The individual cells, which con tain the energy generating components of the battery, may be arranged slightly differently for various types of batteries. The typical cell arrangement for 12 volt batteries (6 cells) is a single row of 6 cells; for 24 volts (12 cells) it is either two rows of 6 cells each or three rows of 4 cells each; for 32 volts (16 cells) it is four rows of 4 cells each; and for 36 volts (18 cells) it is three rows of 6 cells each.