SECTION 7 |
General Information on Lead Acid
Batteries
22
TABLE 7.4 STATE OF CHARGE VERSUS STANDING VOLTAGE
Percentage of
Full Charge
Standing Voltage of
Individual Cells
Standing Voltage of
12V Battery
Standing Voltage of
24V Battery
100%
2.105V
12.63V
25.26V
90%
2.10V
12.6V
25.20V
80%
2.08V
12.5V
25.00V
70%
2.05V
12.3V
24.60V
60%
2.03V
12.2V
24.40V
50%
2.02V
12.1V
24.20V
30%
1.97V
11.8V
23.60V
20%
1.95V
11.7V
23.40V
10%
1.93V
11.6V
23.20V
0%
= / < 1.93V
= / < 11.6V
= / < 23.20V
Check the individual cell voltages / specific gravity. If the inter cell voltage difference
is more than a 0.2V, or the specific gravity difference is 0.015 or more, the cells will
require equalization. Please note that only the non-sealed / vented / flooded / wet
cell batteries are equalized. Do not equalize sealed / VRLA type of AGM or Gel Cell
Batteries.
7.10 STATE OF DISCHARGE OF A LOADED BATTERY – LOW BATTERY
/ DC INPUT VOLTAGE ALARM AND SHUTDOWN IN INVERTERS
Most inverter hardware estimate the State of Discharge of the loaded battery by
measuring the voltage at the inverter’s DC input terminals (considering that the DC
input cables are thick enough to allow a negligible voltage drop between the battery
and the inverter).
Inverters are provided with a buzzer alarm to warn that the loaded battery has been
deeply discharged to around 80% of the rated capacity. Normally, the buzzer alarm is
triggered when the voltage at the DC input terminals of the inverter has dropped to
around 11V for a 12V battery or 22V for 24V battery at C-Rate discharge current of
C/5 Amps and electrolyte temp. of 26,7° C. The inverter is shut down if the terminal
voltage at C/5 discharge current falls further to 10.5V for 12V battery (21V for 24V
battery).
The State of Discharge of a battery is estimated based on the measured terminal
voltage of the battery. The terminal voltage of the battery is dependent upon the
following:
- Temperature of the battery electrolyte: Temperature of the electrolyte affects
the electrochemical reactions inside the battery and produces a Negative Voltage