Page 200 - Uninterruptible Power Supplies

Batteries
198 Chapter Seven

repeated during the life of the cell, but this treatment should not be
considered as a cycling event.
Ambient temperature has a significant effect on cell life. Published
figures from Eurobatt give 10 years life at 20°C reducing to 5 years at
an ambient temperature of 30°C. Figure 7.14 is for pure lead type cells,
which claim a slightly better performance.
Ambient temperature also has a significant effect on cell perfor-
mance manufacturers present figures based on either 20 or 25°C ambi-
ent temperature. Figure 7.15 is clearly based on 25°C. In Europe there
is a tendency to base figures on 20°C.
Increasingly, UPS manufacturers are varying the charge voltage
with ambient temperature, the basic formula being 0.003V/C per
degree C. This temperature compensation device assists in attaining
battery life, as illustrated in Fig. 7.16. For projects requiring cycling of
cells such as solar or wind energy systems, there may be a need to use
a higher constant charging rate.
Charging the cell requires a closely controlled input to achieve max-
imum results, and usually controlled rectifier systems are in common
use. Clearly any rectification will produce a ripple in the dc output and
this must be attenuated to 0.5 percent of dc float voltage and 0.5 C

CHARGING CHARACTERISTICS AT DIFFERENT TEMPERATURES

CHARGED VOLUME CHARGING CURRENT CHARGE VOLTAGE FOR 6V BATTERY CHARGE VOLTAGE FOR 12V BATTERY

(%) (xCA) (V) 0.1CA – 6.825V (13.65V) CONSTANT VOLTAGE CHARGING (V)
120
7.00 CHARGED VOLUME 14.0
CHARGE
100 VOLTAGE
6.50 13.0
80 0.1
AT 0°C (32°F)
0.08
60 6.00 AT 20°C (68°F) 12.0
0.06 AT 40°C (104°F)
40
5.50 11.0
0.04
20
0.02
CHARGING CURRENT
0 0 0
0 5 10 15 20 25 30 35 40
CHARGING TIME (HOURS)
Figure 7.13 Charging characteristics at different temperatures.

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