Alternator - Delco W/integral Regulator GMC Cab & Chassis R2500

IDENTIFICATION

Alternators in production include 12SI, and 17SI series and CS-130 series, with integral regulators. Rated ampere output is stamped on housing. Alternators for Chevrolet and GMC are available in 66, 78, 94 and 120-ampere ratings for SI series. CS series alternators are available in 85, 100 and 105-ampere ratings. Jeep models are rated at 42, 56, 66, 78 and 80 amperes.

OPERATION

Two brushes carry current through slip rings to and from field coil mounted on rotor. Stator windings are assembled on a laminated core that forms part of the alternator frame.

A rectifier bridge, connected to stator windings, contains 6 diodes (3 positive and 3 negative) molded into an assembly. This rectifier bridge changes stator AC voltage into DC voltage, which appears at output terminal.

The blocking action of the diodes prevents battery discharge back through alternator. Because of the blocking action, the need for a cut-out relay is eliminated. Alternator field current is supplied through a diode trio which is also connected to stator windings.

A capacitor is mounted to end frame, protecting rectifier bridge and diodes from high voltage and suppressing radio interference noise. Some vehicles are equipped with ammeters, others with voltmeters.

DESCRIPTION

There are 2 types of alternators used on these vehicles. The SI series integral regulator alternators features an external 2-terminal connector on alternator.

The CS series integral regulator features an external 4-terminal connector on alternator. The SI and CS use a solid state regulator mounted inside alternator housing. These alternators are available with different outputs at idle and maximum capacity.

SI and CS series alternators consist of 2 end frame assemblies (housing), rotor, stator, brushes, slip rings and diodes. Rotor is supported in drive end frames by ball bearings and in slip ring end frame by roller bearings. Bearings contain enough lubrication to eliminate need for periodic lubrication.

Scheme 1

ADJUSTMENT

No periodic adjustments or maintenance of any kind is required on alternator assembly. Regulator voltage is preset, and no adjustment is possible.

DO NOT attempt to polarize alternator. DO NOT short or ground any terminals except as instructed. Avoid operating alternator with battery out of circuit or output terminal open. Alternator and battery must share the same ground polarity.

TROUBLE SHOOTING

Note. See the TROUBLE SHOOTING - BASIC PROCEDURES article in the GENERAL TROUBLE SHOOTING section.

TESTING

Note. Before making electrical checks, visually inspect all terminals for clean, tight connections. Check alternator mounting bolts and drive belt tension. Battery must be in good condition to test charging system.

UNDERCHARGED BATTERY

1. With ignition on, connect a voltmeter from alternator "BAT" terminal to ground, then from No. 1 terminal to ground, and last, No. 2 terminal to ground.
2. A zero reading indicates an open between connection and battery. Opens in the No. 2 lead may be between terminals at the crimp between harness wire and terminal, or in wire. (Scheme 2) NOTE: If preceding test is satisfactory, continue to next step.
3. Disconnect battery ground cable. Connect an ammeter in circuit at "BAT" terminal of alternator. Reconnect battery ground cable. Turn on all available accessories.
4. Connect a carbon pile across battery. Operate engine at 2000 RPM and adjust carbon pile as required to obtain maximum current output.
5. Ampere output must be within 10 amps of rated output. If output is not within 10 amps of rated output, ground field winding by inserting a screwdriver into test hole. (Scheme 2) Repeat step 4).
6. If output is increases to within 10 amps of rated output with field grounded, regulator is defective. If output remains below 10 amps of rated output, check field winding, diode trio, rectifier bridge, and stator.

Scheme 2

OVERCHARGED BATTERY

Attach voltmeter between alternator terminal No. 2 and ground. If reading is zero, No. 2 lead circuit is open. If battery and No. 2 lead circuit check out good, alternator will have to be disassembled for further checks or replaced. Proceed to OVERHAUL procedure.

DISASSEMBLY

1. Scribe marks on housings for reassembly reference. Remove through bolts connecting housings. Separate front and rear housings by prying apart with screwdriver.
2. Place a piece of tape over slip ring end frame bearing to prevent entry of dirt. At this point brushes may drop onto rotor shaft and become contaminated with bearing lubricant. Clean brushes as soon as possible with a cleaner (acetone) to keep them from becoming grease soaked.
3. Place rotor in vise and tighten vise only enough to permit removal of shaft nut. Remove shaft nut, washer, pulley, fan and collar. Separate front housing from rotor shaft. Remove 3 stator lead attaching nuts and remove stator leads from bridge terminal.
4. Separate stator from rear housing. Remove diode trio lead clip attaching screw, and remove diode trio. Remove capacitor attaching screw and remove capacitor lead from bridge rectifier.
5. Remove bridge rectifier and battery terminal attaching screws and remove bridge rectifier. Remove 2 brush holder screws and one diode trio lead strap screw. Remove brush holder and brushes. Note location of brushes for reassembly.
6. Remove voltage regulator. Remove front bearing retaining plate screws. Press front bearing out of housing with collar. Press out rear bearing from housing by inserting collar inside housing and pressing bearing toward the outside.

INSPECTION

Wash all metal parts except bearings, stator and rotor. Inspect rotor slip rings. They may be cleaned with 400 grit or finer polishing cloth, while rotor is being rotated. Slip rings may be lathe turned to .002" (.05 mm) maximum indicator reading.

Slip rings are not replaceable. Excessive damage will require rotor replacement. Inspect brushes for wear, replacing them if more than 50% worn.

ROTOR FIELD WINDING TEST

1. To check for grounds, attach ohmmeter leads to shaft and slip ring (each ring in turn). If reading is not infinity, replace rotor.
2. To test for open field, attach ohmmeter leads to each slip ring. Resistance should measure about 2.4-3.5 ohms. If not, replace rotor.

Scheme 3

Note. Delco 17SI alternator has delta stator windings and cannot be checked for open circuit.

STATOR TEST

1. For 12SI series alternator, measure resistance between stator leads. (Scheme 4) If reading is not infinity, replace stator.
2. On all models, connect ohmmeter leads to any stator lead and to stator frame. Ohmmeter reading should be infinity. (Scheme 4)

Scheme 4

DIODE TRIO TEST

1. Remove diode trio from end frame. Connect an ohmmeter to single connector and to one of the 3 connectors. (Scheme 5) Note reading and reverse leads. If readings are the same, replace diode trio.
2. A good diode trio will give a high and low reading. Repeat tests between single connector and each of the 3 connectors. Connect ohmmeter to each of the 3 connectors. If any readings are zero, replace diode trio.

Note. Before replacing diode trio, also check rectifier bridge. Do not use high voltage, such as 110-volt test lamp, when testing diode trio.

Scheme 5

RECTIFIER BRIDGE TEST

1. Position ohmmeter with one lead touching grounded heat sink and the other lead touching flat metal on one of the 3 terminals or threaded studs. Observe reading and reverse test lead connections. (Scheme 6)
2. If both readings are the same, replace rectifier bridge. A good bridge will give a high and low reading. Retest all terminals (6 tests with insulated heat sink).
3. Connect test leads to insulated heat sink and one edge of the 3 terminals. Observe reading and reverse connections. Repeat test on all terminals (6 tests with insulated heat sink).
4. When all 12 tests have been made, testing is complete. DO NOT use high voltage lamp to check bridge. DO NOT replace diode trio or rectifier bridge unless at least one pair of readings is the same (with leads reversed).

Scheme 6

Scheme 7

REASSEMBLY

1. Assemble bearing and slinger (flat washer on some models) in front housing. Press bearing in with fitted collar over outer race. If bearing retainer plate felt seal is hardened, replace retainer plate.
2. Install retainer plate and screws. Press rotor into end frame. Assemble collar, fan, pulley, washer and nut. Tighten nut to 40-60 ft. lbs. (54-82 N.m).
3. If rear bearing was removed, support inside of rear housing with hollow cylinder. Place flat plate over bearing. Press bearing into housing from outside, until bearing is flush with end frame.
4. Install springs and brushes in brush holder. Install wooden toothpick in hole at bottom of holder to retain brushes. Install voltage regulator. Attach brush holder into rear housing, noting stack-up of parts. Allow toothpick to protrude through hole in rear housing
5. Install diode trio lead strap attaching screw and washer. Tighten brush holder screws. Position bridge rectifier on rear housing with insulator between heat sink and rear housing.
6. Install bridge rectifier and battery terminal screws. Connect capacitor lead to bridge rectifier. Position diode trio on end housing. Install diode trio lead clip screw, making sure insulating washer is over top of diode trio connector.
7. Install stator on rear housing. Attach stator leads to bridge rectifier terminals. Remove tape covering bearing and join front and rear housings with scribe marks aligned. Install through bolts and tighten. Remove toothpick from brush holder assembly.

SPECIFICATIONS

ALTERNATOR OUTPUT SPECIFICATIONS FOR SI SERIES

ALTERNATOR OUTPUT SPECIFICATIONS FOR CS SERIES

See also:
• TROUBLE SHOOTING - BASIC PROCEDURES