Samlexpower PST-15S-12E Owner's manual - Section 7 |
22 | SAMLEX AMERICA INC.
SAMLEX AMERICA INC. | 23
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.
note: The X-Axis of the curves shown in fig 7.1 indicates the percentage State of
Charge. % State of Discharge should be converted to % State of Charge using the
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
12V
24V
C/3 A
10.45V
20.9V
09.50V
19.0V
C/5 A
10.90V
21.8V
10.30V
20.6V
C/10 A
11.95V
23.9V
11.00V
22.0V
C/20 A
11.85V
23.7V
11.50V
23.0V
C/100 A
12.15V
24.3V
11.75V
23.5V
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.