Environmental Engineering Reference
In-Depth Information
Fig. 4.22
Characteristic of a conventional battery (
a
) Available capacity; (
b
) Battery voltage during
discharging
also the inception of gas secretion at 2,4 V. Hence the nominal voltages of commer-
cial accumulators are 14 V, 28 V and 42 V. The nameplate battery capacity is given
in Ah.
The available capacity depends mainly on temperature and the drawn discharge
current. A common definition is the capacity C
20
, meaning that the specified ca-
pacity is available when the battery is discharged with an output current
I
20
such
that the discharge closing voltage is reaches after 20 h. The closing voltage is nor-
mally 10,5 V, and below for larger discharge currents. Figure 4.22 illustrates the
characteristics of a standard 12 V battery. Overcharging and deep-discharge should
be avoided.
Different charging methods are known, suitable for vehicle and stationary bat-
teries, for normal or fast charge. One of the most common methods is using the
IU-characteristic; Fig. 4.23. In the first interval the current is kept constant the volt-
age reaches 2,4 V per cell and gas secretion occurs, continuing with constant voltage
until full capacity is reached.
Fig. 4.23
Charging method
using
I
/
U
control (example)
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