26SI Series Alternator – General Information

The alternator is an electronic component that is belt driven. The alternator is used to charge the storage battery during engine operation. The alternators that are covered by this manual are inside cooled. Air is drawn through baffles. The baffles are located in the rear cover. The air exits from the drive end frame behind the fan.

The alternator converts a combination of mechanical energy and magnetic energy to alternating current and voltage. 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 26-SI is a self-rectifying alternator. The 26-SI is also a brushless unit. The voltage regulator is built in 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 regulator and diodes are enclosed in a sealed compartment.

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. The voltage allows current to flow in order to satisfy the electrical loads that are placed on the system.

An internal sense lead is used in order to control voltage. The lead is installed between the diode trio and the regulator.

Some of the 26-SI alternators use a .25 inch threaded stud as an output terminal. With this type of terminal, the exposed metal parts are not insulated. The exposed metal parts will have battery voltage when the parts are connected to the battery.

An “R” terminal is located on the side of the alternator. The “R” terminal is on the opposite side from the output terminal. This terminal may be used to operate the one of the following components:

  • A Charge Indicator

  • A Tachometer

  • An Hour Meter

  • A Similar Device

The component is provided voltage pulses at a frequency of 8 pulses for each revolution of the alternator. The “R” terminal’s components must not draw more than 4 amperes.

The alternator’s case is grounded. However, do not operate the unit without an external path to ground. A screw and a lockwasher are installed in a .25 inch threaded hole. The hole is located in the housing by the rectifier. The hole is between the output terminal and the “R” terminal. The “R” terminal is provided in order to connect a ground lead if a ground lead is used. Otherwise, the ground path is through the mounting hardware and brackets to the engine. A paper tag is located on a replacement. The tag identifies the “GROUND SCREW”. Remove the tag and discard the tag. The screw and the lockwasher should be installed in the housing. This is done in order to prevent the entry of dirt and water.

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