SunXtender Technical Manual

Document No. 6-0100 Rev. H
Page 20 of 43
The charging current during the Bulk stage should be set as high as practical; higher current
levels mean faster recharge time and less time for the plates to become sulfated. 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:
Charge Time = [(DOD/100) x Rated Capacity (Ah) ÷ Output of Charger (Amps)] + Absorb Time.
For example, charging a 100Ah battery at 40% DOD with a 25A charger would take:
[(40/100) x 100 ÷ 25] + 3 = 4.6 hours to reach full charge.
If a 10A charger is used, it would take:
[(40/100) x 100 ÷ 10] + 3 = 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.
For repetitive deep cycling applications (deeper than 50% DOD), chargers should have an
output current of at least 0.2C (20 Amps for a 100 Ah battery). If the output current is less than
this value, the cycle life of the battery may be negatively affected. If a charger with at least 0.2C
output is not practical, an alternative charge profile using a low rate constant current stage at
the end of the absorption stage will normally improve the cycle life. The constant current stage
should be at 0.02C (2 Amps for a 100Ah battery) for no more than one hour.
Some types of battery chargers allow the user to input the Peukert constant to obtain an
optimum charging profile. For Sun Xtender® batteries, the recommended value of the Peukert
constant is n = 1.12.
5.5 Conditioning
Conditioning should be done when the battery is showing symptoms of capacity loss or when
the float voltages of series-connected batteries show excessive variation. These conditions can
be caused by letting the battery dwell too long in a low state of charge condition, or by repetitive
undercharging.
NOTE: Some chargers use the term Equalizing Charge instead of Conditioning Charge. An
Equalizing Charge is generally applied to flooded lead acid batteries that are susceptible to acid
stratification. However, an Equalizing Charge may be used to provide a Conditioning Charge for
Sun Xtender® batteries as described below.
To apply a Conditioning Charge, first go through the normal charge cycle to bring the battery to
full charge. The Conditioning Charge should then be applied by charging for 8 hours using the
volts per cell (VPC) given in the following equation:
VPC (Conditioning) = 0.00004T
2
- 0.006T + 2.705 (where T = °C).
At 25°C, the conditioning voltage is 2.58 VPC (15.5 volts for a 12-volt battery). By using the
temperature-compensated voltage, calculated from the above equation, batteries that are not in
controlled temperature environments may be conditioned without bringing them to room
temperature. If temperature compensation is not available, it is best to bring the battery to room
temperature before applying the conditioning charge.