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B A T T E R Y C H A R G I N G
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M O R N I N G S T A R C O R P O R A T I O N
4.0
These voltage drops will cause some undercharging of the battery. The
controller will begin PWM absorption, or limit equalization, at a lower battery
voltage because the controller measures a higher voltage at the controller’s
terminals than is the actual battery voltage. For example, if the controller is
programmed to start PWM absorption at 14.4V, when the controller “sees”
14.4V at its battery terminals, the true battery voltage would only be 14.1V
if there is a 0.3V drop between the controller and battery.
Two sense wires, sized from 1.0 to 0.25 mm
2
(16 to 24 AWG), can be used for
battery voltage sense. Because these wires carry no current, the voltage at
the TriStar will be identical to the battery voltage. A 2-position terminal is used
for the connection
Note that the battery sense wires will not power the controller, and the sense
wires will not compensate for losses in the power wires between the con troller
and the battery. The battery sense wires are used to improve the accuracy of
the battery charging.
See Section 2.3 - Step 5 for instructions how to connect the battery sense wires.
4.4 Equalization
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 sulfate crystals.
In addition to slowing or preventing lead sulfation, there are also other benefits
from equalizations of the solar system battery. These include:
Balance the individual cell voltages.
Over time, individual cell voltages can drift apart due to slight differences in
the cells. For example, in a 12 cell (24V) battery, one cell is less efficient in
recharging to a final battery voltage of 28.8 volts (2.4 V/c). Over time, that cell
only reaches 1.85 volts, while the other 11 cells charge to 2.45 volts per cell.
The overall battery voltage is 28.8V, but the individual cells are higher or lower
due to cell drift. Equalization cycles help to bring all the cells to the same
voltage.
Mix the electrolyte.
In flooded batteries, especially tall cells, the heavier acid will fall to the bottom
of the cell over time. This stratification of the electrolyte causes loss of
capacity and corrosion of the lower portion of the plates. Gasing of the
electrolyte from a controlled overcharging (equalization) will stir and remix the
acid into the battery electrolyte.
NOTE: Excessive overcharging and gasing too vigorously can damage
the battery plates and cause shedding of active material from the plates.
An equalization that is too high or for too long can be damaging. Review
the requirements for the particular battery being used in your system.
REMARQUE : Une surcharge excessive et un dégagement gazeux trop
vigoureux peuvent endommager les plaques de batteries et provoquer
l’élimination du matériau actif des plaques. Une compensation trop
élevée ou trop longue peut provoquer des dégâts. Examinez les
exigences pour la batterie particulière utilisée dans votre système.
4.4.1 Standard Equalization Programs
Both automatic and manual equalizations can be performed using either the
standard charging programs
(see 4.2)
or a custom program
(see 7.0)
.
Manual Equalization
The TriStar is shipped with the DIP switch set for manual equalization only.
This is to avoid an unexpected or unwanted automatic equalization. In the
manual mode, the push-button is used to both start or stop a manual
equalization. Hold the push-button down for 5 seconds to start or stop an
equalization (depending on whether an equalization is in progress or not).
The LEDs will confirm the transition (all 3 LEDs blink 2 times). When the
battery charging enters into equalization, the Green LED will start fast blinking
2-3 times per second.
There are no limits to how many times the push-button can be used to start
and stop equalizations. Equalizations will be terminated automatically per the
charging program selected if the push-button is not used to manually stop the
equalization.
Automatic Equalization
If the equalization DIP switch is moved to the ON position
(see 2.3 - Step 3)
,
the equalizations will begin automatically per the charging program selected.
Other than starting, the automatic and manual equalizations are the same and
follow the standard charging program selected. The push-button can be used
to start and stop equalizations in both the manual and automatic mode.
4.4.2 Typical Equalizations
The automatic equalizations will occur every 28 days (except L-16 cells at
14 days). When an equalization begins (auto or manual), the battery charging
voltage increases up to the equalization voltage (Veq). The battery will remain
at Veq for the time specified in the selected charging program
(see table in 4.2)
.
If the time to reach Veq is too long, the maximum equalization cycle time will
end the equalization. A second manual equalization cycle can be started with
the push-button if needed.
If the equalization cannot be completed in one day, it will continue the next
day or days until finished. After an equalization is completed, charging will
return to PWM absorption.
