5.0
Operation
48
GenStar MPPT
49
Certain batteries benefit from a periodic boost charge to stir the electrolyte, level the cell voltages,
and complete the chemical reactions. Equalization (EQ) charging raises the battery voltage above
the standard absorption voltage so that the electrolyte gases. The green SOC LED will blink
rapidly two (2) times per second during equalization charging. The duration of the equalize charge
is determined by the selected battery type. See table 4-1 in this section for more details. The
Equalization Time
is defined as time spent at the equalization set-point. If there is insufficient charge
current to reach the equalization voltage, the EQ will terminate after an additional 60 minutes to
avoid over gasing or heating of the battery. The GenStar MPPT meter, or LiveView, can also be used
to set EQ voltage and duration.
The Equalization set-point is temperature compensated with use of the included Remote
Temperature Sensor (RTS), if connected.
Why Equalize?
Routine equalization cycles are often vital to the performance and life of a battery - particularly in a
solar system. During battery discharge, sulfuric acid is consumed and soft lead sulfate crystals form
on the plates. If the battery remains in a partially discharged condition, the soft crystals will turn
into hard crystals over time. This process, called, “lead sulfation”, causes the crystals to become
harder over time and more difficult to convert back to soft active materials. Sulfation from chronic
undercharging of the battery is the leading cause of battery failures in solar systems. In addition to
reducing the battery capacity, sulfate build-up is the most common cause of buckling plates and
cracked grids. Deep cycle batteries are particularly susceptible to lead sulfation.
Normal charging of the battery can convert the sulfate back to the soft active material if the battery
is fully recharged. However, a solar battery is seldom completely recharged, so the soft lead sulfate
crystals harden over a period of time. Only a long controlled overcharge, or equalization, at a higher
voltage can reverse the hardening of sulfate crystals.
When to Equalize?
The ideal frequency of equalizations depends on the battery type (lead-calcium, lead-antimony, etc.),
the depth of discharging, battery age, temperature, and other factors. One very broad guide is to
equalize flooded batteries every 1 to 3 months or every 5 to 10 deep discharges. Some batteries,
such as the L-16 group, will need more frequent equalizations.
The difference between the highest cell and lowest cell in a battery can also indicate the need
for an equalization. Either the specific gravity or the cell voltage can be measured. The battery
manufacturer can recommend the specific gravity or voltage values for your particular battery.
Preparation for Equalization
First, confirm that all of the system loads are rated for the equalization voltage. Consider that at 0°C
(32°F) the equalization voltage will reach 16.75 volts for L-16 batteries with a temperature sensor
installed. Disconnect any loads at risk of damage due to the high input voltage.
If Hydrocaps are used, be sure to remove them before starting an equalization. Replace the
Hydrocaps with standard battery cell caps. The Hydrocaps can get very hot during an equalization.
Also, if Hydrocaps are used, the equalization should be set for manual only (DIP switch #7 is Off).
After the equalization is finished, add distilled water to each cell to replace gasing losses. Check that
the battery plates are covered.
Equalize a Sealed Battery?
The
Battery charging profile
table (see table 4-1 in this section) shows two sealed battery charging
profiles with Equalization cycles. These are minimal “boost” cycles to level individual cells. This is not
an equalization, and will not vent gas from sealed batteries that require up to 14.4V charging (12V
battery).
Many VRLA batteries, including AGM and gel, have charging requirements up to 14.4V (12V battery).
Depending on the battery manufacturer’s recommendation, the “boost” cycle for sealed cells can be
disabled by setting the equalize setting switch to manual, if required.
5.2.7 Charging Variables
Each charging variables in this section is graphically illustrated with examples below:
Absorption Extension Threshold
Figure 5-3. Absorption Extension Charging Profile
If battery voltage discharges below the Absorption Extension Threshold the previous night,
Absorption charging will be extended on the next charge cycle as shown in the example in Figure
5-3 above.
The voltage threshold and extension time depend on the chosen standard profile or custom settings.
1:00
2:00
3:00
4:00
5:00
6:00
12.50 V
Bulk
Extended
Absorption
Float
Absorption
Absorption Extension Voltage
time (hrs)
