MPPTāFour Charging Stages
Sunbee MPPT Controllers have a 4-stage battery charging algorithm for rapid, efficient, and safe battery
charging.
U(V)
Equalize
Charge
14.8V
14.5V
13.7V
MPPT Charge
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In this stage, the battery voltage has not yet reached boost voltage and 100% of available solar power is
used to recharge the battery.
Boost Charge
When the battery has recharged to the Boost voltage setpoint, constant-voltage regulation is used to
prevent overheating and excessive battery gassing. The Boost stage remains 120 minutes and then goes to
Float Charge. Every time the controller is powered on, if it detects neither over discharged nor overvoltage,
the charging will enter into boost charging stage.
Float Charge
After the Boost voltage stage, the controller will reduce the battery voltage to the Float voltage setpoint.
When the battery is fully recharged, there will be no more chemical reactions and all the charge current
transmits into heat and gas at this time. Then the controller reduces the voltage to the floating stage,
charging with a smaller voltage and current. It will reduce the temperature of battery and prevent gassing,
also charging the battery slightly at the same time. The purpose of Float stage is to offset the power
consumption caused by self-consumption and small loads in the whole system, while maintaining full
battery storage capacity.
In Float stage, loads can continue to draw power from the battery. If the system load(s) exceed the solar
charge current, the controller will no longer be able to maintain the battery at the Float setpoint. Should
the battery voltage remain below the boost reconnect charging voltage, the controller will exit Float stage
and return to Bulk charging.
Equalize Charge
Certain types of batteries benefit from periodic equalizing charge, which can stir the electrolyte, balance
battery voltage and complete the chemical reaction. Equalizing charge increases the battery voltage, higher
than the standard complement voltage, which gasifies the battery electrolyte. If it detects that the battery
is being over discharged, the solar controller will automatically turn the battery to equalization charging
stage, and the equalization charging will be 120mins. Equalizing charge and boost charge are not carried
out constantly in a full charge process to avoid too much gas precipitation or overheating of battery.
WARNING: Risk of explosion!
Equalizing flooded battery can produce explosive gases, so well ventilation of battery box is
necessary.
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