Why a Charge Controller is necessary
Since the brighter the sunlight, the more voltage the solar cells produce, the excessive voltage could damage the batteries. A charge controller is used to maintain the proper charging voltage on the batteries. As the input voltage from the solar array rises, the charge controller regulates the charge to the batteries preventing any over
Modern multi-stage charge controllers
Most quality charge controller units have what is known as a 3 stage charge cycle that goes like this :
1) BULK :
During the Bulk phase of the charge cycle, the voltage gradually rises to the Bulk level (usually 14.4 to 14.6 volts) while the batteries draw maximum current. When Bulk level voltage is reached the absorption stage begins.
2) ABSORPTION :
During this phase the voltage is maintained at Bulk voltage level for a specified time (usually an hour) while the current gradually tapers off as the batteries charge up.
3) FLOAT :
After the absorption time passes the voltage is lowered to float level (usually 13.4 to 13.7 volts) and the batteries draw a small maintenance current until the next cycle.
The Charge Controller is installed between the Solar Panel array and the batteries where it automatically maintains the charge on the batteries using the 3 stage charge cycle.