Concorde SunXtender Manual

Document No. 6-0100 Rev. E
Page 19 of 41
5.4 Charging
Charging Sun Xtender® 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 Sun Xtender® 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. The battery is fully charged when the current drops below 0.5% of the battery’s rated
capacity (0.5A for a 100Ah battery). The absorption stage will typically last 2 – 4 hours before
the current reaches this level. 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. The following table provides the
recommended charge voltage settings for Sun Xtender® Batteries:
Table 5-1 Recommended Charge Voltage Settings for Sun Xtender® Batteries
Absorption Voltage at 25°C (77°F)
Float Voltage at 25°C (77°F)
Volts per Cell
2.37 - 2.40V
2.20 - 2.23V
For 12V System
14.2 - 14.4V
13.2 - 13.4V
For 24V System
28.4 - 28.8V
26.4 - 26.8V
For 48V System
56.8 – 57.6V
52.8 – 53.6V
The charging volts per cell (VPC) at other temperatures can be determined from the following
equations:
VPC (Absorption) = 0.00004T
2
- 0.006T + 2.510 (where T = °C)
VPC (Float) = 0.00004T
2
- 0.006T + 2.340 (where T = °C), but not less than 2.167 volts per cell.
See Appendix C for a chart of charging voltage versus temperature.
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, Sun Xtender® 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 20-30°C (68 to 86°F) 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.
Note that this formula is approximate and the full charge state should be verified using the
criteria given above (current drops below 0.5% of rated capacity). If the recharge does not
return 102 to 110% of the discharged capacity, the battery’s state of charge will gradually “walk
down” as it is cycled leading to premature failure. Therefore, it is important to verify that the
battery is not being undercharged.