The charging system consists of an generator (alternator or dynamo), rectifier, battery and regulator. The alternator generates alternating current (AC) electricity. The rectifier transforms the AC into direct current (DC). The battery accepts the charge and stores the charge until it is required.
The alternator does not produce a constant quantity of electricity. The quantity increases with engine RPM At low RPM, the battery must be called on to supply extra power. At high RPM, extra power is channeled to the battery until it is fully charged.
These systems go about their business all under the control of the regulator. The regulator controls the charging system so that the voltage and current output will not exceed predetermined specifications. The regulator senses the amount of voltage present, determines whether the battery needs charging, and directs and controls the alternator output accordingly.