Capacity traction batteries

Typical dimensions for the /5-alumina electrolyte tube are 380 mm long, with an outer diameter of 28 mm, and a wall thickness of 1.5 mm. A typical battery for automotive power might contain 980 of such cells (20 modules each of 49 cells) and have an open-circuit voltage of lOOV. Capacity exceeds. 50 kWh. The cells operate at an optimum temperature of 300-350°C (to ensure that the sodium polysulfides remain molten and that the /5-alumina solid electrolyte has an adequate Na" " ion conductivity). This means that the cells must be thermally insulated to reduce wasteful loss of heat atjd to maintain the electrodes molten even when not in operation. Such a system is about one-fifth of the weight of an equivalent lead-acid traction battery and has a similar life ( 1000 cycles). 

Work at Harwell has concentrated on scaling up the lithium polymer battery technology for use in electric vehicle traction batteries. The project, supported by the Commission of the European Communities, has systematically scaled up the cell active area. The various cell sizes are shown in Figure 6.33. The larger cells were used to construct two 80 A h units which are shown in Figure 6.34. The results of the project have highlighted the need for capacity balance and excellent cell-to-cell reproducibility. 

The degradation and aging mechanism depend on several factors [36,37]. At present the guaranteed calendar lifetime of a lithium battery ranges from 2 years (e.g. Sam) to 8 years (e.g. Ampera, Volt) depending on the car s manufacturer. An average lifetime for traction batteries of 10 years is still a development target, which have not been reached and demonstrated at a practical level. But of course, a battery can also be used below 80% of its nominal capacity. A second use phase of batteries, e.g. for stationary applications, has not been considered. 

Nominal capacity after 10 discharges electrolyte density 1.28 + 0.01 kg/L electrolyte temperature 25 °C. Table 2.7 Lead-acid traction batteries in plastic trays with single cells and positive tubular plates (DIN 43 598 part 2). ... 

Figure 2.6 shows the specific drawable energy of lead-acid traction batteries of different designs. The lower graph represents the capacity of the common PzS cells. Further development of this cell type for application in electric road vehicles of the PzF type yields accordingly higher values. 

Development on the forklift truck sector for higher transport performance naturally leads to greater stress on the battery. This could lead to shorter charging intervals of the vehicles. In connection with the limited space inside forklift trucks energy density of traction batteries will have to be improved. Most of the German battery manufacturers introduced a new generation of batteries averaging 15% more capacity than with the presently standardized types. 

Capacity indicators for traction batteries are on the market in many variants, of different reliability, and adapted to different battery types. This is understandable since the useful capacity of a lead-acid battery is dependent on several parameters, such as physical and chemical impacts, design and type of the battery, aging, temperature, and load. The user s demand in any case is to have a capacity indicator, comparable with a fuel indicator in a motorcar. 

Another way to calculate the residual capacity of a traction battery is based on the evaluation of voltage and current. Both parameters have to be measured continuously, and the typical performance characteristics of a battery type have to be inserted in the calculation process. Often this type of capacity indication is part of the electronic control of a vehicle. 

The capacity test of a traction battery is performed not only for quality assurance, but also to evaluate the endurance of the battery during operation. The capacity test is the only way to get a view of the electrical power of a battery. The test is described in EN 60 451, Part 1, as a discharge with a constant current I5 (A), compensation of the temperature by 0.6% per degree if the electrolyte temperature differs from 30 °C. To execute a test qualified testing equipment and educated staff are needed. 

DIN 43 537 Lead-acid accumulators traction batteries for road-bound electric vehicles, cells of low maintenance type Nominal capacities, main dimensions. 

The cycle life characteristics of traction batteries are presented in Figure 1.28. This figure shows the relationship of cycle life to DOD at the 6-h discharge rate, cycle life being defined as the number of cycles at 80% of rated capacity. It is quite... 

Traction or motive power batteries are made in many different sizes, limited only by the battery compartment size and the required electrical service. The basic rating unit is the positive-plate capacity, given in amp-hours at the 5- or 6-h rate. The 2-V cell in the traction batteries is grouped with 2 to 16 positive plates, or 5 to 33 positive and negative plates. Traction batteries are often assembled to have battery voltage in... 

FIGURE 23.29 Effect of discharge rate on capacity of traction batteries at 25°C. Comparison of performance of flat-pasted-plate vs. tubular-plate batteries. 

FIGURE 23.30 Capacity available on intermittent discharge of traction batteries at 25°C. 

FIGURE 23.31 Effect of temperature on capacity of traction batteries, typical flat-plate design. From Ref. 23.)... 

Traction or motive-power batteries are made in many different sizes, limited only by the battery compartment size and the required electrical service. The basic rating unit is the positive-plate capacity, given in Ampere-hours at the 5- or 6-h rate. Table 23.14a lists the typical U.S. traction plate sizes using flat-pasted plates between 5 and 33 plates are used to assemble traction cells, as also shown in the table. Ratings of the cell are the product of the capacity of a single positive plate multiplied by the number of positive plates. The cells, in turn, are assembled in a variety of battery layouts, with typical voltage in 6-V increments (e.g., 6, 12, 18 to 96 V) resulting in almost 1000 battery sizes. Popular traction battery sizes are the 6-cell, 11-plates-per-cell, 75-Ah positive-plate (375-Ah cell) and the 6-cell, 13 plates-per-cell, 85-Ah positive-plate (510-Ah cell) batteries. Table 23.146 presents similar information on the tubular positive-plate batteries. 

The stationary battery is designed with excess electrolyte (highly flooded) to minimize maintenance and the watering interval and is generally positive-plate-limited in capacity (compared with traction batteries, for example, which are electrolyte- or acid-limited). The stationary batteries are capable of being floated and moderately overcharged. 

Stationary batteries, like traction batteries, are available in a variety of plate and cell sizes. Stationary battery systems are assembled on insulated metal racks with groups of cells in series, having nominal system voltages of between 12 and 160 V. Some battery installations are made with several such series cell strings connected in parallel for greater storage capacity. Most stationary batteries in the United States are made with pasted positive plates. In Europe, Plantd and tubular positives are more popular. 

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