Equalization Recommendations; Float Charge; Renewable Energy Line; Temperature Compensation - US BATTERY US1800 XC2 User Manual

4
CHARGING AND
EQUALIZING

4.3 EQUALIZATION RECOMMENDATIONS

Some batteries within a battery bank may discharge at a higher or lower rate than
the others causing an imbalance of the states of charge. This imbalance can lead to
sulfation, loss of capacity, and premature battery failure. The process of equalizing
should be used to correct this imbalance. Equalizing is an overcharge performed after
fully charging deep-cycle lead acid batteries. An equalizing charge prevents electro-
lyte stratification and reduces sulfation, which are leading causes of premature battery
failure. US Battery recommends equalizing 2-4 hours if the following situations are
observed:
● It has been 30 days since the last equalization
● Specific gravity after charging is < 1.235 or there is >0.015 points of variance be-
tween all cells.
Many chargers today have equalizing automatically programmed into the charging al-
gorithm. However, manual equalizations can also be performed by the following steps:
● Fully charge batteries.
● Unplug charger until it completely turns off.
● Plug the charger back in. The charger should go through an entire charge cycle
again acting as an "equalization" stage.
● Measure the specific gravity. If the specific gravity is <1.235 or there is >0.015
points of variance between the cells, then repeat the equalization steps until those
two conditions are met.

4.4 FLOAT CHARGE

● A float charge is given to the batteries in order to overcome the self-discharge rate.
This should be applied to the batteries when stored and after given a full charge.
The float voltage for flooded lead acid US Batteries is 2.17 volts per cell and 2.23
volts per cell for US AGM Batteries.
24

4.5 RENEWABLE ENERGY LINE

The US Battery Renewable Energy product line is designed to withstand the common
failure modes that plague regular deep cycle lead acid batteries in renewable energy
applications. US Battery recommends a 3 stage charger for properly maintaining your
batteries. Typical "3-stage" chargers are actually two stages, bulk and absorption. The
charger manufacturers consider the float charge as the float stage. The float charge is
simply a maintenance stage to keep the batteries at 100% state of charge until needed.
True 3-stage chargers will have bulk, absorption, and a final low current high voltage
finish charge.
Since many of the charge controllers for solar applications are two stage chargers the
best way to ensure your batteries get a full charge is to increase the absorption stage
in 30 minute increments until a full charge is verified with specific gravity readings.

4.6 TEMPERATURE COMPENSATION

Temperature compensation is critical for charging and maintaining batteries in environ-
ments with ambient temperatures significantly higher or lower than 80ºF (27ºC) where
overcharging or undercharging may occur. Temperature compensation allows the
use of higher charge currents; 20% of the 20 hour rating compared to 10% when
charging FLA batteries. AGMs can accept 25% of the 20 hour rating compared to
15%. Also, temperature compensation is required for warranty claims with AGMs due
to their sensitivity to overcharging. Many chargers today come with temperature probes
making temperature compensation easy.
● The temperature compensation formula is as follows:
●Fahrenheit
●Subtract 0.0028 volts per cell per degrees F above 80ºF
●Add 0.0028 volts per cell per degrees F below 80ºF
●Celsius
●Subtract 0.005 volts per cell per degrees C above 27ºC
●Add 0.005 volts per cell per degrees C below 27ºC
●Example
●Two 6Vs wired in series for 12Vs. 100ºF sunny day in California.
●Typically the bulk charge voltage would be ~ 14.1V at 80ºF.
●At 100ºF, subtract (0.0028 * 6 cells * 20ºF) 0.336v from all voltages.
●The bulk charge voltage would then be ~13.8V.
User Manual 25