Rectifier Diode / Bridge: Description and Operation

Six or more silicon diode rectifiers are used. A silicon diode acts as an electrical one-way valve. One half of the diodes have ground polarity and are pressed or screwed into a heat sink which is grounded. The other diodes (ungrounded) are pressed or screwed into and insulated from the end head. These diodes are connected to the alternator output terminal.
Since the diodes have a high resistance to the flow of current in one direction and a low resistance in the opposite direction, they may be connected in a manner which allows current to flow from the alternator to the battery in the low resistance direction. The high resistance in the opposite direction prevents the flow of current from the battery to the alternator. Because of this feature no circuit breaker is required between the alternator and battery.