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TriStar MPPT 600V Operator’s Manual
46
Operation
Certain battery types benefit from a periodic boost charge to stir the electrolyte, level the cell volt
-
ages, and complete the chemical reactions. Equalize charging raises the battery voltage above
the standard absorption voltage so that the electrolyte gasses. 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 equalize
set-point. If there is insufficient charge current to reach the equalization voltage, the equalization
will terminate after an additional 60 minutes to avoid over gassing or heating the battery. If the
battery requires more time in equalization, an equalize can be requested using the TriStar Meter
or pushbutton to continue for one or more additional equalization cycles.
The Equalize set-point is temperature compensated if the RTS is connected.
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.
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 crys-
tals 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 bat-
tery 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.
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 67.00 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 equaliza-
tion. 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 Settings
table (see table 4-1 in this section) shows one sealed battery set-
ting with an Equalization cycle. This is only a 0.4 Volt boost cycle to level individual cells. This is
not an equalization, and will not vent gas from sealed batteries that require up to 57.60 V charg-
ing (48 V battery). Many VRLA batteries, including AGM and gel, have charging requirements up
to 57.6 V (48 V battery). This “boost” charge for sealed cells can be disabled by setting the equal-
ize setting switch to manual if required.
