The alternator converts mechanical energy to electrical energy. This is done by rotating a direct current electromagnetic field on the inside of a three-phase stator. The alternating current and voltage are generated by the stator. The current and the voltage are changed to direct current by a three-phase full wave rectifier. The rectifier uses six silicon rectifier diodes.
The alternator is a brushless unit. The voltage regulator is located inside the alternator. The only movable part in the assembly is the rotor. The rotor is mounted on a ball bearing at the drive end. The rotor is mounted on a roller bearing at the end with the rectifier. The conductors that carry current are stationary. These conductors are in the field winding, the stator windings, the six rectifying diodes, and the regulator circuit components.
The voltage regulator limits the voltage that is produced by the alternator at the output terminal. This is done by controlling the magnetic field that is present in the stationary field coil. The regulator allows current to flow. The current satisfies the electrical loads that are placed on the electrical system and the current charges the batteries.
An internal sense lead is used in order to control voltage. The lead is installed between the "B" terminal and the regulator.
Some of the alternators use a 6.35 mm (0.25 inch) threaded stud as a "B" terminal. This type of terminal is not insulated. When the alternator is connected to the battery, the stud will be energized.
An "R" terminal is located on the end of the alternator next to the "B" terminal. This terminal may be used by one of the following components:
- A Charge Indicator
- A Tachometer
- VIMS, CMS, EMS, etc.
- An Hourmeter
The component is provided voltage pulses at a frequency of 8 pulses for each revolution of the alternator. The current draw across the "R" terminal must not exceed 2 amperes.
The "I" terminal is located on the end of the 34SI alternator. The terminal is the second terminal from the output terminal. This terminal may be used to operate an indicator light. The terminal may also be used in order to ensure when the alternator starts. The "I" terminal is a threaded stud.
The "I" terminal is connected internally to the field circuit. An indicator light that is connected in series with the terminal will glow when there is a difference in potential between the terminal and battery voltage. When the system is charging properly, the light is off.
An isolated ground terminal is located on the end of the 34SI alternator. An isolated ground terminal is also located on the end of the isolated 30SI marine alternator. The terminal is on the opposite side from the "B" terminal. The isolated ground terminal is provided in order to connect a ground lead.
A ground terminal for the case is located on the side of the non-marine 30SI alternator housing. A screw and a lockwasher should be installed in the hole for the case ground. The screw prevents the entry of dirt and water.