26SI Series Alternator – Component Description

Illustration 1 g00862662

(1) Bearing

(2) Front frame

(3) Diode assembly

(4) Stator winding lead

(5) Bearing

(6) Spacer

(7) Ring

(8) Regulator

(9) Rectifier

(10) Rotor assembly

(11) Field winding

(12) Stator assembly

(13) Ring

(14) Rear frame (Drive end)

(15) Fan

The following items are the main parts for the N3 series alternator:


Illustration 2 g00862943


(16) Stator

(17) Rectifier

The stator (16) consists of a stator core and three independent windings. As the rotor turns, a varying magnetic field causes the stator windings to produce three-phase AC voltage. The stator is supported by the front frame and by the rear frame.


Illustration 3 g00862995


(18) Rectifier

(19) Negative diodes

(20) “D+” lead

(21) “B-” terminal

(22) Excitation diodes

(23) Positive diodes

(24) “D+” terminal

(25) “B+” terminal

The rectifier (18) is a three-phase full wave rectifier. The rectifier changes the AC voltage that is produced by the stator to DC voltage. The rectifier contains positive diodes (23) and negative diodes (19). The DC voltage from the diodes is delivered to the battery terminals.

The rectifier also contains excitation diodes (22). DC voltage from the excitation diodes energizes the field winding.

Field Winding

Illustration 4 g00863042

Field winding and leads

(26) Rear frame

(27) Two leads for the winding

(28) Field winding

The field winding (28) is the stationary coil that provides a magnetic field for the rotor.


Illustration 5 g00863050


(29) Rotor

(30) Nonmagnetic ring

The rotor (29) consists of a shaft and a magnetic core. The rotor rotates on the shaft. The rotor provides a magnetic field between the field winding and the stator.

When the current flows in the field winding, the core is magnetized. One side becomes the “N” pole. The other side becomes the “S” pole. With this form (pawl pole), both poles are magnetized by one field winding. The “N” pole and the “S” pole are separated by a nonmagnetic ring (30) .


Illustration 6 g00863056

The identification of the terminals for the regulator and alternator

(31) Regulator

(32) “DF” regulator terminal (field winding lead)

(33) “R” terminal

(34) “B-” terminal

(35) “D-” terminal

(36) “D+” regulator terminal (lead for the field winding and lead for the rectifier)

(37) Suppression capacitor

(38) “B+” terminal

(39) “D+” terminal

The regulator (31) limits the output voltage of the alternator to a preset value by controlling the current through the field winding. The regulator electronically switches the connection between the field winding and the ground. The switching occurs at variable rates. The regulator is mounted on the rear frame of the alternator. The regulator is totally enclosed, and the regulator cannot be adjusted.

Suppression Capacitor

The suppression capacitor (37) will protect the diodes in the alternator from spikes in the voltage. The suppression capacitor also suppresses radio interferences. This capacitor is mounted on the rear frame of the alternator. The lead for the capacitor is connected to the “D+” terminal (39) .

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