SamplexPower PST-1500-12 Mode D'emploi page 22

SECTION 7 |
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. The % State
of Charge can be converted to % State of Discharge using formula given below:
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
C/3 A
C/5 A
C/10 A
C/20 A
C/100 A
In the example given above, the 10.5V / 21.0V Low Battery / DC Input Alarm would trig-
ger 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 10.5V for a 12V battery (at around 21V for 24V battery) to warn the user to
disconnect the battery to prevent further draining of the battery. If the load is not dis-
connected 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 (20V for 24V 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
22 | SAMLEX AMERICA INC.
General Information on Lead Acid
Batteries
% State of Discharge = 100% - % State of Charge
Terminal Voltage at 80% State
of Discharge (20% SOC)
12V
10.45V
10.90V
11.95V
11.85V
12.15V
Terminal Voltage When Completely
Discharged (0% SOC)
24V 12V
20.9V 09.50V
21.8V 10.30V
23.9V 11.00V
23.7V 11.50V
24.3V 11.75V
24V
19.0V
20.6V
22.0V
23.0V
23.5V