IEEE 485:2010 pdf free download – IEEE ecommended Practice for Sizing Lead-Acid Batteries for Stationary Applications
6.2.1 Temperature correction factor
The available capacity of a cell is affected by its operating temperature. The standard U.S. temperature forrating cell capacity is 25 C (77 °F).If the lowest expected electrolyte temperature is below this standardtemperature, select a cell large enough to have the required capacity available at the lowest expectedtemperature. If the lowest expected electrolyte temperature is above 25 C (77 °F), it is a conservativepractice to select a cell size to match the required capacity at the standard temperature and to recognize theresulting increase in available capacity as part of the overall design margin. Table l lists cell size correctionfactors for various temperatures for lead-acid cells with nominal 1.215 specific gravity. For unlistedtemperatures within the range of Table 1, interpolate between adjacent values and round off to two decimalplaces.
Table 1 shows typical temperature factors for lead-acid nominal 1.215 specific gravity cells. Consult themanufacturer to see whether specific temperature factors are available for the battery being evaluated.
6.2.2 Design margin
lt is prudent to provide a capacity margin to allow for unforeseen additions to the dc system and less-than-optimum operating conditions of the battery due to improper maintenance,recent discharge, or ambienttemperatures lower than anticipated, or a combination of these factors. A method of providing this designmargin is to add 10% to 15% to the cell size determined by calculations. If the various loads are expected togrow at different rates, it may be more accurate to apply the expected growth rate to each load for a giventime and to develop a duty cycle from the results.
The cell size calculated for a specific application will seldom match a commercially available cell exactly,and it is normal procedure to select the next higher capacity cell. The additional capacity obtained can beconsidered part of the design margin.
Note that the“margins” described by 6.3.1.5 and 6.3.3 of IEEE Std 3231″-2003 [B3] are to be appliedduring “qualification” and are not related to “design margin.”
6.3 Cell size
This subclause describes and explains a proven method of calculating the cell capacity necessary forsatisfactory performance on a given duty cycle.The application of this method to a specific duty cycle,using an optional preprinted worksheet to simplify the calculations， is demonstrated in A.2 of Annex A.Instructions for the proper use of the worksheet are given in 6.4.
6.3.1 Initial calculation
Equation (1) (see 6.3.2) requires the use of a capacity rating factor C, (see 6.3.3) that is based on thedischarge characteristics of a particular plate type and size. Thus, the initial calculation must be based on atrial selection of positive plate type and capacity. Depending on the results of this initial calculation, it maybe desirable to repeat the calculation for other types or sizes of plates to obtain the optimum cell type andsize for the particular application. In addition,it may be desirable to repeat the calculation to take intoaccount any differences in performance per plate within a given series of cells. Use the capacity from thefirst calculation as a guide for selecting additional types to size.
6.3.2 Sizing methodology
The cell selected for a specific duty cycle must have enough capacity to carry the combined loads duringthe duty cycle.To determine the required cell size, it is necessary to calculate,from an analysis of eachsection of the duty cycle (see Figure 2), the maximum capacity required by the combined load demands(current versus time) of the various sections.The first section analyzed is the first period of the duty cycle.Using the capacity rating factor (see 6.3.3) for the given cell type, a cell size is calculated that will supplythe required current for the duration of the first period. For the second section, the capacity is calculatedassuming that the current A，required for the first period,continued through the second period;thiscapacity is then adjusted for the change in current(A-A ) during the second period. In the same manner,the capacity is calculated for each subsequent section of the duty cycle. This iterative process is continueduntil all sections of the duty cycle have been considered. The calculation of the capacity Fs required byeach section S, where S can be any integer from 1 to N, is expressed mathematically in Equation (1).Fs willbe expressed as watt-hours, ampere-hours, or number of positive plates, depending upon which C, is used(see 6.3.3).