Discharging battery performance, evaluation

Many consortia and publications have proposed a number of standard drives to evaluate battery performance. Schedules such as the Federal Urban Drive Schedule (FUDS), the Highway Fuel Economy Test (HWFET), and the Dynamic Stress Test (DST) are used as yardsticks of performance on a comparative basis. As metrics for fuel economy or other corporate standards, they may be appropriate but these should not generally be used as the real-world test of battery performance. Where performance is to be measured, it is recommended here that a Kochis Stress Test (KST) be used, which is a test philosophy that states that the maximum loads (charge and discharge) that will be used in the vehicle should be used to establish performance traits. This implies two points (i) the test should be demonstrated and calibrated in a vehicle that is the intended application (ii) if vehicle calibrations are changed, the effect on battery performance must be re-evaluated. 

Example of Evaluation of Battery Performance Under Different Modes of Discharge... 

Both the Leclanche and zine-ehloride batteries have performance eharaeteristies that show advantages in specific applications, but poor performance in others. A variety of faetors influence battery performance (see Chap. 3). It is necessary to evaluate speeifies about the application (discharge conditions, cost, weight, etc.) in order to make a proper selection of a battery. Many manufacturers provide data for this purpose. 

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. 

The alloys recently investigated in the fabrication of Ni-MH batteries include the AB5 (LaNij) type and ABj (zirconium vanadium [ZrVj]) type. During the evaluation of these alloys, the material scientists failed to explore critical performance characteristics of the alloys other than the discharge capacity and progressive... 

The mode of discharge of a battery, among other factors, can have a significant effect on the performance of the battery. For this reason, it is advisable that the mode of discharge used in a test or evaluation program be the same as the one used in the application for which it is being tested. 

Thus, in evaluating or comparing the performance of batteries, because of the potential difference in jrerformance (service hours) due to the mode of discharge, the mode of discharge used in the evaluation or test should be the same as that in the application. This is illustrated further in Fig. 3.7. 

Note. As discussed in Chap. 3, when evaluating batteries for a specific application, it is important to use the equipment loads and discharge conditions as inaccurate results will be obtained in these conditions are not correctly simulated. Further, the results could also be significantly different from the rated capacity or generalized performance data and characteristics of a particular battery. 

The Jet Propulsion Laboratory (Pasadena, CA) has evaluated several types of lithium primary batteries to determine their ability to operate planetary probes at temperatures of -80°C and below. Individual cells were evaluated by discharge tests and Electrochemical Impedance Spectroscopy. Of the five types considered (Li/SOCl2, Li/S02, Li/Mn02, Li-BCX and Li-CFn), lithium-thionyl chloride and lithium-sulfur dioxide were found to provide the best performance at -SOT. Lowering the electrolyte salt to ca. 0.5 molar was found to improve performance with these systems at very low temperatures. In the case of D-size Li/ SOCI2 batteries, lowering the LiAlCl4 concentration from 1.5 to 0.5 molar led to a 60% increase in capacity on a baseline load of 118 ohms with periodic one-minute pulses at 5.1 ohms at -85 C. 

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