A charge controller connects the solar panel, the battery bank and the load. Its main function is to prevent the battery from being over charged by the solar panel as well as being over discharged by the load. Solar charge controllers can either be analogy or digital.
Most charge controllers below 10 A are analog while 10 A and above are digital. The digital charge controllers can detect the voltage connected to it. Most of the 10-30 A charge controllers are 12/24 V. Higher sized charge controller such 50A, 60 A also exist some with MPPT but are more expensive. Charge controllers are classified as either series or shunt type.