24 | SAMLEX AMERICA INC.
SECTION 7 |
General Information on
Lead-Acid Batteries
The discharge curves in Fig. 7.1 show the % State of Charge versus the terminal voltage
of typical battery under different charge /discharge currents, i.e. “C-Rates” and fixed
temperature of 80°F. (Please note that the X-Axis of the curves shows the % of State of
Charge. The % of State of Discharge will be 100% - % State of Charge).
7.11 LOW DC INPUT VOLTAGE ALARM IN INVERTERS
As stated earlier, the buzzer alarm is triggered when the voltage at the DC input termi-
nals of the inverter has dropped to around 10.5V for a 12V battery at C-Rate discharge
current of C/5 Amps. Please note that the terminal voltage relative to a particular of
State Discharge decreases with the rise in the value of the discharge current. For ex-
ample, terminal voltages for a State of Discharge of 80% (State of Charge of 20%) for
various discharge currents will be as given at Table 7.5 (Refer to Fig 7.1 for parameters
and values shown in Table 7.5):
TABLE 7.5 TERMINAL VOLTAGE AND SOC OF LOADED BATTERY
Discharge Current:
C-Rate
Terminal Voltage at 80% State
of Discharge (20% SOC)
Terminal Voltage When Com-
pletely Discharged (0% SOC)
12V
12V
C/3 A
10.45V
09.50V
C/5 A
10.90V
10.30V
C/10 A
11.95V
11.00V
C/20 A
11.85V
11.50V
C/100 A
12.15V
11.75V
In the example given above, the 10.5V Low Battery / DC Input Alarm would trigger at
around 80% discharged state (20% SOC) when the C-Rate discharge current is C/5 Amps.
However, for lower C-Rate discharge current of C/10 Amps and lower, the battery will be
almost completely discharged when the alarm is sounded.
Hence, if the C-Rate dis-
charge current is lower than C/5 Amps, the battery may have completely discharged by
the time the Low DC Input Alarm is sounded.
7.12 LOW DC INPUT VOLTAGE SHUT-DOWN IN INVERTERS
As explained above, at around 80% State of Discharge of the battery at C-Rate dis-
charge current of around C/5 Amps, the Low DC Input Voltage Alarm is sounded at
around 10.5V for a 12V battery to warn the user to disconnect the battery to prevent
further draining of the battery. If the load is not disconnected at this stage, the batteries
will be drained further to a lower voltage and to a completely discharged condition that
is harmful for the battery and for the inverter.
Inverters are normally provided with a protection to shut down the output of the inverter
if the DC voltage at the input terminals of the inverter drops below a threshold of around
10V for a 12V battery. Referring to the Discharge Curves given in Fig 7.1, the State of
Discharge for various C-Rate discharge currents for battery voltage of 10V is as follows:
(Please note that the X-Axis of the curves shows the % of State of Charge. The % of State
of Discharge will be 100% - % State of Charge):
Summary of Contents for PST-1000F-12
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