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4.2 Battery Charging Information
4-Stage Charging
The MPPT has a 4-stage battery charging algorithm for rapid, eff cient, and safe
battery charging. Figure 4-2 shows the sequence of the stages.
THGINTHGIN
BULK
CHARGE
ABSORPTION
FLOAT
EQUALIZE
VOLTAGE
TIME
Figure 4-2.
MPPT charging algorithm
Bulk Charge Stage
In Bulk charging stage, the battery is not at 100% state of charge and battery voltage has not
yet charged to the Absorption voltage setpoint. The controller will deliver 100% of available
solar power to recharge the battery.
Absorption Stage
When the battery has recharged to the Absorption voltage setpoint, constant-voltage regulation
is used to maintain battery voltage at the Absorption setpoint. This prevents heating and
excessive battery gassing. The battery is allowed to come to full state of charge at the
Absorption voltage setpoint.
The Absorption setpoint is temperature compensated if the RTS is connected.
Float Stage
After the battery is fully charged in the Absorption stage, the
MPPT
reduces the
battery voltage to the Float voltage setpoint. When the battery is fully recharged, there can be
no more chemical reactions and all the charging current is turned into heat and gassing. The
float stage provides a very low rate of maintenance charging while reducing the heating and
gassing of afully charged battery. The purpose of float is to protect the battery from long-term
The Float setpoint is temperature compensated if the RTS is connected.
overcharge.
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