A charge controller or charge regulator is basically a voltage and/or current regulator to keep batteries from overcharging. It regulates the voltage and current coming from the solar panels going to the battery. Most "12 volt" panels put out about 16 to 20 volts, so if there is no regulation the batteries will be damaged from overcharging. Most batteries need around 14 to 14.5 volts to get fully charged.
The most basic type of solar charge controller is a shunt controller. This operates with a basic on/off switch: When the battery voltage is low and needs to be charged, the shunt controller will go into the “on” position and allow energy to flow from the solar panel to the battery. When the battery is fully charged, the shunt controller will switch to the “off” position and block energy flow.Shunt controllers available today are generally small and not recommended for solar panels used as a residential energy source. That’s because they are much less efficient than other options and are best used for specific purposes.
Series regulators are more advanced than shunt controllers, although they operate in much the same way. With a series regulator controller, most include multiple relays or transistors that enable multiple connection points. Series regulators are better suited for large solar arrays than shunt controllers because they do not need the same type of ventilation.
Pulse Width Modulation controllers enable multi-stage charging—including Bulk, Absorb and Flow stages—by continually regulating the energy flow. The result is a more efficient system with better charging control. At the same time, PWM controllers are also relatively cost-effective, which is why they are recommended for occasional residential applications, such as a vacation cabin.
One of the newest innovations for solar charge controllers, Maximum Power Point Tracking controllers allow solar panels to use the optimum power output voltage. MPPT controllers are also suitable for higher voltages than most other types of solar charge controller.By allowing for the best power output voltage, MPPT controllers can improve the solar panel performance by 30%. As newer options on the market, MPPT controllers also have advanced features and programming options.
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