24 | SAMLEX AMERICA INC.
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.
NOTE: The X-Axis of Curves shown in Fig 7.1 indicates the % State of Charge. % state of
Discharge should be converted to % state of Charge using formula given below:
% State of Charge = 100% - % State of Discharge
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 (21V for 24V 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 example, 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 Completely
Discharged (0% SOC)
12V
24V
48V
12V
24V
48V
C/3 A
10.45V
20.9V
41.8V
09.50V
19.0V
38.0V
C/5 A
10.90V
21.8V
43.6V
10.30V
20.6V
41.2V
C/10 A
11.95V
23.9V
47.8V
11.00V
22.0V
44.0V
C/20 A
11.85V
23.7V
47.4V
11.50V
23.0V
46.0V
C/100 A
12.15V
24.3V
48.6V
11.75V
23.5V
47.0V
In the example given above, the 10.5V / 21.0V / 42.0V 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 discharge 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 (i) 10.5V for a 12V battery, (ii) 21V for 24V battery and (iii) 42V for 48V 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.
SECTION 7 |
General Information on Lead Acid
Batteries
Содержание PST-1500-48
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