Page 52 - Battery Reference Book

Effect of cell layout in batteries on battery characteristics 1/37
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1 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 4648 Number in series, m
482412 8 6 4 3 2 1 Number of strings, n
Figure 1.15 Various configurations of 48 two-volt cells. Effect of configuration on e.m.f., current and electrical resistance

Table 1.12 Characteristics of series-parallel multi-cell batteries (48-cell)

Number of Cells in m Internal ETOT ITQT CTOT Duration oj Joule heating Power
-
strings of series in
cells in e8ach string RTOT
parallel (n) (m) (a) (Ah) (cays)
1 48 48 4.8 96 20 3 840 4 459 1920
2 24 12 1.2 48 40 3840 4 459 1920
3 16 5.33 0.533 32 60 3840 4 459 1920
4 12 3.00 0.300 24 80 3840 4 459 1920
6 8 1.33 0.133 16 120 3840 4 459 1920
8 6 0.75 0.075 12 160 3 840 4 459 1920
12 4 0.33 0.033 8 240 3 840 4 459 1920
16 3 0.19 0.019 6 320 3840 4 459 1920
24 2 0.083 0.0083 4 480 3840 4 459 1920
48 1 0.021 0.0021 2 960 3840 4 459 1920
“h = 4 h discharge per cell

For a maximiam value of ITOT (Le. I,,), forming the but
expression: dlToT/dn and equating to zero, we find that
(1.104)
&TOT - (NR, + Rextn2 where RTOT is the total internal resistance of the group
-
dn dn
of n x m cells. Hence
= NR, - R,,trz2 = 0 (1.103)
RTOT = Rat (1 .l05)
Hence
Thus, to obtain the maximum current (Im,) from a
NR, = Rextn2
group of m x n cells, the external resistance. R,,,, for
and the group of cells should be equal to the combined
internal resistance (RTOT = (rn/n)R,) of the group of
N cells.