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 relationship between the current and the voltage during the 3 phases of the charge cycle can be shown visually by the graph below.
