samlexsolar SCC-30AB, Owner'S Manual, Page: 19 / 48

19
3
GENERAL INFORMATION: BATTERIES
After the gassing voltage is exceeded, voltage stays approximately constant. The
whole charging current during this period results in H
2
and O
2
, which is defined
as loss.
Freezing of electrolyte
For applications with low ambient temperature, the Lead-Acid battery must also be
protected against freezing of electrolyte. The risk of freezing depends on the state of
charge. Figure 3-4 illustrates the freezing limit as a function of the state of charge.
- 80 °
- 60 °
- 40 °
- 20 °
0 °
0 20 40 60 80 100
State of charge [%]
Te
m
pe
ra
tu
re
[
°
C
]
slushy until hard
- 80 °
- 60 °
- 40 °
- 20 °
0 °
0 20 40 60 80 100
State of charge [%]
Te
m
pe
ra
tu
re
[
°
C
]
slushy until hard
Figure 3-4: Freezing limit of a Lead-Acid battery dependent on the State of Charge
Cycle life of Lead-Acid batteries
The cycle life refers to a capability of the battery to withstand a certain number of
charge/discharge cycles of given Depth of Discharge (DOD). Since the lifetime of the
battery also depends on the average depth of discharge during cycling (expressed in
percentage (%) of rated capacity), the cycling capability may be more conveniently
expressed by multiplying this average depth of discharge by the battery lifetime
expressed in number of cycles. The result is called the Nominal Cycling Capability,
which is expressed as the number of equivalent 100 % nominal capacity cycles.
The starter battery typically has a low cycling capability of less than 100 nominal
cycles, which means that it is able to withstand for example 500 cycles of maximally
20 % depth of discharge. The battery appropriate for PV application requires a good
cycling capability of at least 500 nominal cycles, which means that it should be able to
withstand for example 1000 cycles of 50 % depth of discharge (Fig. 3-5).