Multicell battery

Fig. 2. Cutaway view of a Leclancbir flat cell used ia multicell batteries (1).

Certain problems sometimes arise with rechargeable multicell batteries which are associated with non-uniform capacities of the individual cells. In charging such batteries there must be either overcharge in some cells or undercharge in the whole system. More importantly, on deep discharge,... 

Cells are also formed into batteries with nominal OCV of 7.2 V for electric fence activators. Alternatively, banks of 11 individual cells are used to operate 10 V railway signal motors such applications require a current drain of 3 A for 5-10 s, perhaps 100 times per day. Multicell batteries are used in the US Space Shuttle programme for crew communication. Practical energy densities of up to 310 Wh/kg may be obtained. 

Another problem is that of balance between single cells in a multicell battery. Such batteries are balanced when all cells (preferably of the same type) have the same capacity and the same state of charge (SOC). In case of a mismatch between cells connected in series the battery s ampere-hour capacity is determined by the cell with the least available ampere-hour capacity. In case of cells connected in parallel, a failure (e.g., short circuit) of one of the cells can lead to the failure of the whole battery. 

A single battery cell is a low-voltage power source, so that even slight internal voltage losses (e.g., 0.1 V) produce an appreciable effect on the electrical characteristics of the whole battery. Internal voltage losses in a cell can be distributed over the whole current path from one terminal to the other. In multicell batteries with cells connected in a series, losses in the interconnections must be added to the total internal losses of all cells. 

Gaps between cells in multicell batteries for free access and circulation of air,... 

The first battery was a pile of discs alternating between silver and zinc interleafed with a separator soaked in an electrolyte. Soon Volta had improved the system with a multicell battery called couronne de tasses, whereby it was possible to draw electric current from that multicell battery at a controlled rate (. After Volta s discovery in 1800, Nicholson and Carlisle in the same year (1800) decomposed water into hydrogen and oxygen by an electric current, and Cruickshank also in 1800 deposited metals from solutions. In 1803, Hisinger and Berzelius showed that when solutions are decomposed by electric current, acids, oxygen and chlorine are deposited at the positive pole, and alkalis, metals and hydrogen at the negative pole. All this within three years of Volta s discovery. 

A rather dangerous situation arises when individual cells of a multicell battery deviate. Such nonuniformity is due most often to problems in reactant supply. Two systems of gas supply exist parallel and series. In parallel supply, the gas reaches each cell through a narrow channel coming from a common manifold. The pressure in these channels is the same for aU elements where they leave the manifold, but because of differences in gas flow resistance, the amounts of gas (or the pressure) reaching each cell may differ. In series supply, gas is fed to a first individual cell, flows through it and continues to the next cell, and so on. In each cell in series, the amount of gas needed for the reaction is consumed, leaving a lower pressure of reactant gas for the next cell. The cells thus operate at different working pressures of the gas, which constitutes a nonuniformity. 

Popular usage considers the battery and not the cell to be the product that is sold or provided to the user. In this 3rd tion, the term cell will be used when describing the cell component of the battery and its chemistry. The term battery will be used when presenting performance characteristics, etc. of the product. Most often, the electrical data is presented on the basis of a single-cell battery. The performance of a multicell battery will usually be different than the performance of the individual cells or a single-cell battery (see Section 3.2.13). 

The performance of the cells in a multicell battery will usually be different than the performance of the individual cells. The cells cannot be manufactured identically and, although cells are selected to be balanced, they each encounter a somewhat different environment in the battery pack. 

A comparison of the performance of single-cell and multicell batteries can be made by reviewing the data in Table 1.2 on single-cell batteries with the data in Table 6.5 on 24-volt multicell batteries. 

LR25-2 4 L R 25 2 A multicell battery consisting of two paraUel groups, each group having four ceUs in series of the R25 type and electrochemical system, letter L, of Table 4.2c... 

Another factor that must be considered, particularly with newly developing battery technologies, is the difficulty of scaling up laboratory data based on smaller individual batteries to multicell batteries using larger cells manufactured on a production line. 

A thermal disconnect device should be included to prevent the build-up of excessive heat. Many of the batteries now manufactured include a PTC or a mechanical disconnect, or both, within the cell. Additional protective thermal devices should be included, external to the cells, in the design of a multicell battery pack. 

Zinc-carbon batteries are made in a number of different sizes with different formulations to meet a variety of applications. The single-cell and multicell batteries are classified by electrochemical system, either Leclanche or zinc chloride, and by grade general purpose, heavy duty, extra heavy duty, photoflash, and so on. These grades are assigned accortUng to their output performance under specific discharge conditions. 

The AA-size battery is becoming the predominant one and is used in penlights, photoflash and electronic applications. The smaller AAA-size is used in remote control devices and other small electronic applications. The C and D-size batteries are used mainly in flashlight applications and the F-size is usually assembled into multicell batteries for lanterns and other applications requiring these large batteries. Hat cell are used in battery assemblies, in particular, the 9-volt battery used in smoke detectors and electronic applications. 

Multiple-cell batteries (Table 10.10) are made using either miniature or cylindrical cells. In addition, some special multicell batteries are made using flat cells of a type not used in single cell batteries. 

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