Operation
ProStar MPPT Operator’s Manual
39
38
4.0
4.2 Battery Charging
4-Stage Charging
The ProStar MPPT has a 4-stage battery charging algorithm
for rapid, efficient, and safe battery charging. Figure 4-2
shows the sequence of stages.
NIGHT
NIGHT
BULK
CHARGE
ABSORPTION
FLOAT
EQUALIZE
VOL
TAGE
TIME
Figure 4.2. ProStar MPPT Charging Algorithm
Bulk Charge Stage
During Bulk charging, the battery is not at 100% state of
charge and battery voltage has not yet charged to the Ab-
sorption voltage set-point. The controller will deliver 100%
of available solar power to recharge the battery.
Absorption Stage
When the battery has recharged to the Absorption voltage
set-point, constant-voltage regulation is used to maintain
battery voltage at the Absorption set-point. This prevents
heating and excessive battery gasing. The battery is
allowed to come to full state of charge at the Absorption
voltage set-point. The green SOC LED will blink once per
second during Absorption charging.
The battery must remain in the Absorption charging
stage for a cumulative 150-180 minutes, depending on
battery type, before transition to the Float stage will occur.
However, Absorption time will be extended by 30 minutes
if the battery discharges below 12.50 volts (12V system) the
previous night.
The Absorption set-point is temperature compensated
through either the on-board local temperature sensor, or an
optional Remote Temperature Sensor (RTS), if connected.
Float Stage
After the battery is fully charged in the Absorption stage,
the ProStar MPPT reduces the battery voltage to the Float
voltage set-point. When the battery is fully recharged, there
can be no more chemical reactions and all the charging cur-
rent is turned into heat and gasing. The float stage provides
a very low rate of maintenance charging while reducing the
heating and gasing of a fully charged battery. The purpose
of float is to protect the battery from long-term overcharge.
The green SOC LED will blink once every two (2) seconds
during Float charging.
Once in Float stage, loads can continue to draw power from
the battery. In the event that the system load(s) exceed
the solar charge current, the controller will no longer be
able to maintain the battery at the Float set-point. Should
the battery voltage remain below the Float set-point for a
cumulative 60 minute period, the controller will exit Float
stage and return to Bulk charging.
The Float set-point is temperature compensated through
either the on-board local temperature sensor, or an optional
Remote Temperature Sensor (RTS), if connected.