The most basic function of the solar charge and discharge controller is to control the battery voltage and turn on the circuit, and when the battery voltage rises to a certain level, stop the battery charging. The older version of the controller mechanically completed the opening or closing of the control circuit, stopping or starting the power delivered to the battery.

Controllers are used in most photovoltaic systems to protect batteries from overcharging or overdischarging. Overcharging can vaporize the electrolyte in the battery, causing failure, while overdischarging the battery can cause the battery to fail prematurely. Overcharging and overdischarging may damage the load. Therefore, the controller is one of the core components of the photovoltaic power generation system and the main part of the BOS (Balance of System).
The role of solar controller:

(1) Protect the battery from overcharging and overdischarging, and prolong the service life of the battery.

(2) Prevent the solar cell array and the battery polarity from being reversed.

(3) Prevent the internal short circuit of the load and the controller and other equipment.

(4) Display of the working status of the photovoltaic system: display of the state of charge of the battery and display of the terminal voltage of the battery.

(5) Load status display: charging voltage, charging current, charging capacity, etc.

(6) Auxiliary power supply working status display: solar radiation energy, temperature, wind speed, etc.