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Basics: Charge Controllers
The charge controller (or regulator) connects between the panel and the battery. The charge controller functions a) to protect the batteries from overcharging; b) to protect the panel from power going back into it from the batteries at night (assuming no blocking diode fitted); and c) helps maintain battery condition by keeping the battery voltage high.
CHOOSING A CONTROLLER: Charge controllers are rated for a certain solar input in Amps. This should always be lower than the rated Amps of the solar panel. If you only know the panel wattage then multiply the Amps x 12 to give you a conservative wattage equivalent.
WHEN TO USE A CONTROLLER: As a rule of thumb, use a controller when the rated Amps of the panel is more than 1% of the battery capacity.
TYPES OF CONTROLLER: There are two basic types of controller: on/off and shunt (also known as Pulse Width Modulated). On/off as its name suggests, switches of the power from the panel to the battery when the voltage reaches a certain level, and switches back on when it drops. This means that there are periods of time when there is no power going from the panel to the battery. Shunt controllers allow the battery voltage to increase, and then maintain it at a steady but high level.
SELF-CONSUMPTION: Beware, all controllers use up some of the power produced by the solar panel. This is normally a tiny amount, but adds up over time and can be important if there isn’t much slack in your system.
DISPLAYS: Some controllers display battery state and input from the solar panel, either as LED lights or on an LCD display.
MOUNTING: Charge controllers should be mounted somewhere dry. Some are more watertight than others.
MULTIPLE BATTERIES: The easy method of charing multiple batteries is to use a Charge Controller specifically designed for charging multiple batteries. However, there are two other methods, firstly using diodes and a resistor with one charge controller /uploads/asset_file/MorningStar_charging_two_batteries.pdf, or using two charge controllers and diodes /uploads/asset_file/MorningStar_using_two_charge_controllers.pdf.