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4. PV Charge Control Mode
The SBC-7200 Series PV Charge Controller can operate in the several modes. This includes the
3-stage Charge Control, Equalization Charging Mode, DC Load Control Mode, NIGHT-LIGHT
mode, Temperature Sensing and Over Temperature Protection features.
4.1 3-Stage Charge Control
The main function of charge controller is to regulate the flow of electricity from the photovoltaic
panels to the batteries. In PV systems with batteries, the batteries must be protected from
overcharging and be maintained at fully charged state.
The PV Charge Controller uses the Micro-Processor and PWM ( Pulse Width Modulation ) to
give optimal and safe charging .
It makes varying On-Off pulses of electrical energy from the photovoltaic(PV) panel in charging
the battery according to the battery state. It has 3 stages of charging, as follows:
a. BULK CHARGE – At this mode, a preset maximum constant amount of current (amps) is
fed into the battery as the no PWM is present. As the battery is being charged up , the voltage of
the battery increases gradually.
b. ABSORPTION CHARGE – After the preset voltage is reached (approximately 28.6 volts
for a 24 volt system) the voltage is then held constant. As the battery continues to be charged at
constant voltage, the charging current decreases. The charging voltage is held at the Bulk
Voltage Setting for one full hour with various rapid On-Off pulses (PWM). It then switches to
Float Charge Mode.
c. FLOAT CHARGE –The controller will maintain the battery voltage at the float voltage
setting by giving shorter On-pulse charge to make up for any detected self discharge of the
battery. When the battery voltage drops below the Float Voltage Setting for a total period of 5
minutes, a new charging cycle is activated in Bulk Charge.
The three stages charging method works well with the chemical reaction that occurs as a battery
is being charged. When a battery is more discharged, a regulated maximum current can be
applied, since there is a lot of material available for the reactions to occur.
As the battery refills, less and less chemical material is available for the reaction. By using PWM
to slowly reducing the charge current, while maintaining a preset high voltage, the battery is
more closely refilled at the reaction rate of the chemicals. Finally, the Float voltage keeps the
battery fully charged at all times taking care of the self discharge .
Remarks:
1. When the Battery is charged up to Bulk Charge Voltage setting, the LCD will only show the
Bulk charge voltage one or two times quickly, then the PV controller switches to Absorption
charge
2. The "Batt Volt" display during Absorption charge is less than Bulk Voltage Setting. The
difference will decrease as the Absorption time increase.
3. The "Batt Volt" display during Float Charge is less than the Float Charge Voltage Setting.
P.7
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