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is important to never exceed the manufacturer’s maximum charging voltages.
Typically, a gel battery is recharged in cycling applications from 14.1V to
14.4V. The gel design is very sensitive to overcharging.
For both AGM and Gel batteries, the goal is for 100% recombination of gases
so that no water is lost from the battery. True equalizations are never done,
but a small boost charge may be needed to balance the individual
cell voltages.
Other Sealed Batteries:
Automotive and “maintenance-free” batteries are also sealed. However, these
are not discussed here because they have very poor lifetimes in solar cycling
applications.
NOTE: Consult the battery manufacturer for the recommended solar
charging settings for the battery being used.
REMARQUE : Consultez le fabricant de la batterie quant aux réglages
recommandés de charge solaire pour la batterie utilisée.
9.2 Flooded Batteries
Flooded (vented) batteries are preferred for larger cycling solar systems.
The advantages of flooded batteries include:
• ability to add water to the cells
• deep cycle capability
• vigorous recharging and equalization
• long operating life
In cycling applications, flooded batteries benefit from vigorous charging and
equalization cycles with significant gasing. Without this gasing, the heavier
electrolyte will sink to the bottom of the cell and lead to stratification. This is
especially true with tall cells. Hydrocaps can be used to limit the gasing water
loss.
Note that a 4% mixture of hydrogen in air is explosive if ignited. Make certain
the battery area is well ventilated.
Typical equalization voltages for flooded batteries are from 15.3 volts to 16
volts. However, a solar system is limited to what the solar array can provide.
If the equalization voltage is too high, the array I-V curve may go over the
“knee” and sharply reduce the charging current.
Lead-Calcium:
Calcium batteries charge at lower voltages (14.2 to 14.4 typically) and have
strong advantages in constant voltage or float applications. Water loss can be
only 1/10th of antimony cells. However, calcium plates are not as suitable for
cycling applications.
Lead-Selenium:
These batteries are similar to calcium with low internal losses and very low
water consumption throughout their life. Selenium plates also have poor
cycling life.
Lead-Antimony:
Antimony cells are rugged and provide long service life with deep discharge
capability. However, these batteries self-discharge much faster and the self-
discharging increases up to five times the initial rate as the battery ages.
Charging the antimony battery is typically from 14.4V to 15.0V, with a 120%
equalization overcharge. While the water loss is low when the battery is new,
it will increase by five times over the life of the battery.
There are also combinations of plate chemistries that offer beneficial tradeoffs.
For example, low antimony and selenium plates can offer fairly good cycling
performance, long life, and reduced watering needs.
NOTE: Consult the battery manufacturer for the recommended solar
charging settings for the battery being used.
REMARQUE : Consultez le fabricant de la batterie quant aux réglages
recommandés de charge solaire pour la batterie utilisée.
9.3 L-16 Cells
One particular type of flooded battery, the L-16 group, is often used in larger
solar systems. The L-16 offers good deep-cycle performance, long life, and
low cost.
The L-16 battery has some special charging requirements in a solar system.
A study found that nearly half of the L-16 battery capacity can be lost if the
regulation voltage is too low and the time between finish-charges is too long.
One standard charging program in the TriStar is specifically for L-16 batteries,
and it provides for higher charging voltages and more frequent equalizations.
Additional equalizations can also be done manually with the push-button.
A good reference for charging L-16 batteries is a Sandia National Labs report
(year 2000) titled “PV Hybrid Battery Tests on L-16 Batteries.” Website: www.
sandia.gov/pv.
NOTE: The best charging algorithm for flooded, deep-cycle batteries
depends on the normal depth-of-discharge, how often the battery is
cycled, and the plate chemistry. Consult the battery manufacturer for the
recommended solar charging settings for the battery being used.
REMARQUE : Le meilleur algorithme de charge pour les batteries à
électrolyte liquide à décharge poussée dépend de l’amplitude de la
décharge, de la fréquence du cycle de batterie et de la composition
chimique des plaques. Consultez le fabricant de la batterie quant aux
réglages recommandés de charge solaire pour la batterie utilisée.
