User manual

Document No. 6-0101 Rev. D Page 19 of 38
5.4 Charging
Charging Lifeline® AGM batteries is a matter of replacing the energy removed during discharge
plus a little extra to make up for charging inefficiency. The amount of energy necessary for
complete recharge depends on the depth of discharge, rate of recharge, and temperature.
Typically, between 102% and 110% of the discharged ampere-hours must be returned for full
recharge.
The most efficient method of charging Lifeline® AGM batteries is to use a 3 stage charging
profile. In the first stage, a constant current is applied until the voltage reaches a pre-set limit.
The first stage is often called the Bulk charging stage. In the second stage, the voltage is held
constant at the same pre-set limit until the charging current tapers to a very low value, at which
point the battery is fully charged. The second stage is often called the Absorption charging
stage. A voltage limit of 14.3 volts ± 0.1 volts (7.15 ± 0.05 volt for a 6 volt battery) should be
used when the battery temperature is 77°F (25°C). The battery is fully charged when the
current drops below 0.5% of the battery’s rated capacity (0.5A for a 100Ah battery). In the third
stage, the charging voltage is reduced to a lower value that minimizes the amount of
overcharge, while maintaining the battery at 100% state of charge. This third stage is often
called the Float charging stage. A float voltage of 13.3 ± 0.1 volts (6.65 ± 0.05 volts for a 6 volt
battery) should be used when the battery temperature is 77°F (25°C). The charging voltages at
other temperatures can be determined from the following table:
Table 5-1. Charging Voltage at Different Temperatures for a 12 Volt Battery*
Temp °F
Absorption
Voltage
Float
Voltage
Temp °F
Absorption
Voltage
Float
Voltage
-40
16.88
15.86
70
14.41
13.39
-30
16.58
15.56
77
14.30
13.30
-20
16.30
15.28
80
14.27
13.25
-10
16.03
15.01
90
14.15
13.13
0
15.78
14.76
100
14.04
13.02
10
15.54
14.52
110
13.95
13.00
20
15.31
14.29
120
13.87
13.00
30
15.10
14.08
130
13.81
13.00
40
14.90
13.88
140
13.76
13.00
50
14.72
13.70
150
13.73
13.00
60
14.56
13.54
160
13.71
13.00
* For a 6 volt battery, divide the voltage by 2. For a 2 volt battery, divide the voltage by 6.
The charging current during the Bulk stage should be set as high as practical; higher current
levels mean faster recharge time. Due to the low impedance design, Lifeline® batteries can
tolerate in-rush current levels as high as 5C (500A for a 100Ah battery). The time to reach full
charge at temperatures in the range of 68 to 86°F (20-30°C) can be estimated from the following
equation:
Time to Reach Full Charge = [(DOD/100) x Rated Capacity (Ah) ÷ Rated Output of Charger
(Amp)] + 2 hours.
For example, charging a 100Ah battery at 50% DOD with a 25A charger would take:
[(50/100) x 100 ÷ 25] + 2 = 4 hours to reach full charge.
If a 10A charger is used, it would take:
[(50/100) x 100 ÷ 10] + 2 = 7 hours to reach full charge.