9-1. General.

a. The main generator is a brushless type consisting of a stationary three-phase armature and a rotating salient pole wound field. The exciter, mounted integrally with the main generator, consists of a three-phase rotating armature mounted on the shaft with the generator field and a stationary salient pole field. The exciter has ten poles.

b. A full wave bridge rectifier containing six diodes is mounted on the shaft. Access to test or replace the rectifiers is through the access hole on the end of the endbell assembly. Access to the exciter stator and rotor, and inspection of the main generator armature and field, require disassembly of the generator.

c. The generator shaft is directly driven by the engine shaft through flexible metal disk coupling. The flexible coupling compensates for misalignment between the two shafts to eliminate injurious stress on the connecting components.

d. The main generator stator is installed in the stafor frame and is fastened to and spaced by longitudinal ribs which are part of the frame. An eye bolt on the stator frame provides a means of lifting the unit. The exciter stator is mounted in an endbell which positions on the stator frame rabbit.

e. The rotor is supported at one end by a single bearing in an endbell bolted to the stator frame. The opposite end of the rotor is provided with a blower assembly and coupling disk which bolts directly to the engine flywheel. The rotor is skewed to improve generator output voltage waveform.

f. The bearing is a double-seal type ball bearing, packed with grease conforming to Specification MILG-23827. It provides a minimum of 5000 hours of service at continuous loads.

9-2. Generator Removal and Disassembly.

a. Insulation Resistance. To test insulation resistance, use a megohmmeter to measure the resistance between a winding and ground. The insulation resistance of each of the windings should be at least 1 megohm at 75°F. If this value is not met, clean or dry out the winding and repeat the test. Replace if defective.

NOTE

Low insulation resistance may be caused by dirt or excessive moisture. Insulation failure may be caused by wrong voltages, induced voltages caused by opening field circuits too quickly, oil and grease, high temperatures or excessive vibration.

(4) If the dc ammeter indicates incorrect input exciter current to obtain rated voltage in steps (2) or (3) above, the generator has failed. Proceed with the following steps. If the output is as specified, the excitation system assembly has failed (refer to paragraph 8-1). The following steps are presented to enable isolation of the fault within the generator. Only steps (5), (6) and (7) would normally be done without some disassembly of the generator.

(5) Remove six bolts securing air intake grille and remove grille. Remove screws, cover plate, and gasket from generator endbell. See figure 9-1. Remove bolts from the six diodes on the exciter rotor frame, one at a time, replacing each diode after testing. Test diodes per paragraph 14-12b.

then remove bearing retainer.

(4) Pull the bearing (33) with a suitable bearing puller and replace with new bearing.

(5) To remove the rotating diode assembly, bend up the lock tab on lockwasher and unscrew the locknut.

(6) Unscrew the generator field leads from the plate (8), (fig. 9-2) and unsolder the six exciter leads from the diodes. These leads should be tagged to maintain the polarity of the diodes when reassembled.

CAUTION

Use a soldering iron no larger than 100 watts and as little time and force as possible to unsolder the leads. The diodes can be damaged by excess heat or force sufficient to bend the stem or break the glass seal.

(7) The surge protector may be removed from the rotating diode assembly.

(8) After the leads are dis connected, the rectifier assembly (fig. 9-2), key and spring washer will slide off the shaft.

(9) To remove the rotor assembly from the stator proceed as follows: Slide the rotor through the stator toward the drive end far enough so that a sling may be placed under the generator field core. Hoist the rotor slightly to free it. Pull the rotor axially while applying leverage at the drive end to balance the rotor on the sling. It may take one or two repositionings of the sling to get the sling near the center of the rotor core for proper balancing of the assembly. (10) The exciter rotor may be removed from the shaft by using a bearing puller near the outside diameter. Be careful not to bear on windings if exciter rotor is to be reused.

(11) Balance plates are shrunk on the shaft and may be removed with heat. Apply heat with a torch to the hub of the balance plate. Move the torch around the periphery of the hub using care not to apply the torch to the shaft. The balance plate bore will expand and the balance plate may be removed manually.

(12) The coupling hub is shrunk fit on the shaft. To remove, use a cutting torch to cut through the hub at the keyway to prevent shaft damage. After cutting through, use a chisel in the cut to open the bore and remove the hub.

(13) The generator stator core is not to be removed from the stator frame because the concentricity between bore and rabbit fits would be disturbed and cause voltage modulation problems. When removing the rotor stack from the shaft, remove in the direction, that the stack was pressed on.

(2) Inspect rotor and stator of generator and exciter for loose, frayed, or burned windings.

(3) Inspect coupling disks and fan for distortion and excessive wear.

(4) Inspect for missing or defective hardware. (5) Inspect rotating diode assembly for broken diode cases. Test diodes per paragraph 14-10. 9-4. Generator Repair and Rebuild.

a. Generator Repair. Proceed as follows:

(1) Replace or rebuild all defective parts (refer to paragraph 9-2d for disassembly information.)

5. (Deleted)

6. Washer

7. Surge protector 8. Plate

ME 6115-545-34/9-2 C1

To remove coils from an iron core, it is recommended that the part be heated in a moderate oven temperature (1500 C) to facilitate removal. Single coils should not be replaced as adjacent parts of the winding may be damaged during coil removal. (2) Apply varnish to any damaged areas of insulation.

(3) Replace damaged exciter rotor or stator. b. Generator Rebuilding (50/60 Hz). Proceed as follows:

(1) Stator winding procedures.

(a) Single wires may be spliced by brazing. The splice is to be insulated by sliding sleeving over the wire prior to brazing and relocating the sleeving over the splice after completion. The sleeving is to extend a minimum of 1/2-inch beyond the bare uninsulated portion of wire. The sleeving material is to be the same as that used for cross-overs on the connection end. Splices shall be made in the end turn of the coil only and shall not be made in the straight leg. Where more than one splice is required, the second splice must not occur on the same coil end and must not occur in adjacent coils. Where more than one splice is necessary in the same coil or an adjacent coil, the splice may be made in the connection end of the coil.