Forklift Battery Cell Arrangement
Motive power lead-acid forklift batteries for electric powered industrial Cranes, Tractors, trucks and forklifts consist of 6, 12, 18 or 24 cells, a steel tray with which the cells are assembled, a forklift battery terminal connector and many other components that are required to secure and protect the cells and provide the necessary electrical interconnections.
Fotklift Battery Identification
The essential information which is necessary for proper care of an industrial motive power forklift battery appears on the forklift battery, either stamped into one of the intercell connectors or onto a name plate affixed to the tray. This information generally includes the model, number of plates per cell, forklift battery capacity, forklift battery voltage and serial number.
Some manufacturers list, as 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 forklift battery capacity this number should be multiplied by the total number of positive plates in one cell. In order to find the number of positive plates in a cell, subtract one from the total number of plates and divide by two. If you want to find the capacity of a forklift battery designated “X75-19,” therefore: 19-1=18; 18÷2=9; 9 x 75=675 A.H. forklift battery capacity.
The individual cells, which contain the energy generating components of the forklift battery, can be arranged slightly differently for various kinds of forklift batteries. The normal cell arrangement for 12 volt forklift 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.
All motive power forklift battery cells are, however, always connected in series in order to produce the required voltage. Cell and forklift 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, however, is the same for all cells regardless of size. Each lead-acid cell yields a nominal 2 volts.
Connections between cells are made by intercell-connectors which can be lead coated copper straps or cast of solid lead. These connections are always welded, in the correct sequence, by the application of heat to the terminals of the cells.
The total energy from the forklift battery is drawn off by terminal cables which extend beyond the steel tray wall and are in turn permanently fixed to the forklift battery terminal connector.
The basic unit of any forklift battery. A galvanic cell which produces electrical energy when connected to an electrical load 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 forklift 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.
The element of the cell is made up of one group each of positive and negative plates which are meshed together. The plates are then insulated from each other by separators which are inserted between all of the plates. A plastic element protector is positioned on top of each of the separators which prevents mechanical damage to the element and aids in preventing electrical shorts which can occur when particles of active material bridge the space between plates. Terminal posts are then welded to each group and are used to electrically connect one cell to another.
This is an assembly of plates of like polarity connected in parallel by welding to a common strap or bus-bar. A cell must contain one negative and one positive group. The negative group always has one more plate than the positive group. One or more terminal posts are welded to each.
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 processing, 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.
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.
The grid of the pasted plate consists of horizontal and Diagonal or Vertical 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.
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 reaction 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 whose condition is assumed to be representative of the condition of the entire forklift battery
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.