SECTION 7 |
General Information on Lead
Acid Batteries
20
Table 7.2 below gives some examples of C-Rate specifications and applications:
TABLE 7.2 DISCHARGE CURRENT RATES - “C-RATES”
Hours of discharge time “T”
till the “End Point Voltage”
“C-Rate” Discharge Current in
Amps = Capacity “C” in Ah ÷
Discharge Time “T” in hrs.
Example of C-Rate Discharge
Currents for 100 Ah battery
0.5 hrs.
2C
200A
1 hrs.
1C
100A
5 hrs. (Inverter application)
C/5 or 0.2C
20A
8 hrs. (UPS application)
C/8 or 0.125C
12.5A
10 hrs. (Telecom application)
C/10 or 0.1C
10A
20 hrs. (Automotive application)
C/20 or 0.05C
5A
100 hrs.
C/100 or 0.01C
1A
NOTE:
When a battery is discharged over a shorter time, its specified “C-Rate” discharge current will be
higher. For example, the “C-Rate” discharge current at 5 hour discharge period i.e. C/5 Amps will be
4 times higher than the “C-Rate” discharge current at 20 hour discharge period i.e. C/20 Amps.
7.7 CHARGING / DISCHARGING CURVES
Fig. 7.1 shows the charging and
discharging characteristics of a
typical 12V / 24V Lead Acid
battery at electrolyte
temperature of 80°F / 26.7°C.
The curves show the % State of
Charge (X-axis) versus terminal
voltage (Y-axis) during charging
and discharging at different
C-Rates. Please note that X-axis
shows % State of Charge. State
of Discharge will be = 100% -
% State of charge. These curves
will be referred to in the
subsequent explanations.
Fig. 7.1: Charging / Discharging
Curves for 12V Lead Acid
Battery.
0 10 20 30 40 50 60 70 80 90 100 110 120 130
16.5
16.0
15.5
15.0
14.5
14.0
13.5
13.0
12.5
12.0
11.5
11.0
10.5
10.0
9.5
9.0
C/5
C/40
C/20
C/10
C/20
C/3
C/5
C/10
C/100
33.0
32.0
31.0
30.0
29.0
28.0
27.0
26.0
25.0
24.0
23.0
22.0
21.0
20.0
19.0
18.0
24V 12V
0 10 20 30 40 50 60 70 80 90 100 110 120 130
16.5
16.0
15.5
15.0
14.5
14.0
13.5
13.0
12.5
12.0
11.5
11.0
10.5
10.0
9.5
9.0
C/5
C/40
C/20
C/10
C/20
C/3
C/5
C/10
C/100
33.0
32.0
31.0
30.0
29.0
28.0
27.0
26.0
25.0
24.0
23.0
22.0
21.0
20.0
19.0
18.0
24V 12V
Lead-Acid Battery Chart - 80˚F / 26.7˚C
Battery V
oltage in VDC
Battery State of Charge in Percent (%)
DISCHARGE
CHARGE
