Alternator - Chrysler Dodge Caravan I

DESCRIPTION

Alternator main components include stator, rotor, rectifiers, capacitor, brushes, bearings, end shields (alternator housing) and drive pulley. The built-in silicon rectifiers convert AC (alternating current) into DC (direct current) output. The 114-amp model has 12 silicon rectifiers while all other models have 6 rectifiers.

OPERATION

The alternator brushes relay current between slip rings and field coil. A rectifier bridge, connected to stator windings, contains diodes 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 this blocking action, the need for a cut-out relay is eliminated. Alternator field current is supplied through a diode arrangement that is also connected to the stator windings.

TROUBLE SHOOTING

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

CHARGING CIRCUIT RESISTANCE

Note. Before making test connections, disconnect negative battery cable at battery.

1. Disconnect "BAT" lead at alternator. Connect a 0-100 ampere scale DC ammeter in series between alternator "BAT" terminal and disconnected "BAT" lead wire. Connect positive lead of voltmeter to disconnected "BAT" lead wire. Connect negative lead of voltmeter to positive post on battery.
2. Disconnect regulator harness connector. Connect a jumper lead from connector Green wire to ground. Connect a tachometer, and reattach battery ground cable. Connect a variable Carbon Pile Rheostat (C3950) to battery terminals (set in open or off position). (Scheme 1)
3. Start engine, and immediately reduce engine speed to idle. Adjust engine speed and set variable carbon pile rheostat to obtain 20 amps flowing in circuit. Voltmeter reading should not exceed.5 volts. If a high voltage drop is indicated, inspect, clean and tighten all connections in charging circuit.

Note. If necessary, test voltage drop at each connection to locate connection with excessive resistance.

Scheme 1

Scheme 2

CURRENT OUTPUT

1. Disconnect "BAT" lead at alternator. Connect a 0-100 ampere scale DC ammeter in series between alternator "BAT" terminal and disconnected "BAT" lead wire. Connect positive lead of voltmeter to "BAT" terminal. Connect negative lead of voltmeter to ground. (Scheme 2)
2. Disconnect regulator harness connector. Connect a jumper lead from connector Green wire to ground. Connect a tachometer to engine and reconnect negative battery cable. Connect a variable carbon pile rheostat between battery terminals (open or off position). (Scheme 2) Start engine.
3. Adjust engine speed and variable carbon pile rheostat until a speed of 900 RPM (114-amp) or 1250 RPM (all others) and a voltmeter reading of 13 volts (114-amp) or 15 volts (all others) is obtained. DO NOT allow voltage to exceed 16 volts. Observe ammeter. If current output is not within specification, remove alternator and proceed to BENCH TESTING.

FIELD COIL CURRENT DRAW

1. Connect a jumper wire between one field terminal of alternator and negative terminal of a fully-charged battery. Connect ammeter positive lead to the other field terminal of alternator. Connect ammeter negative lead to battery positive terminal.
2. Connect a jumper wire from negative terminal of battery to alternator end shield. (Scheme 3) Slowly rotate alternator by hand. Observe ammeter reading. Field coil draw should be 2.5-5.0 amps at 12 volts.
3. A low coil draw is an indication of high resistance in field coil (brushes, slip rings or rotor coil). A high coil draw indicates possible shorted rotor coil or grounded rotor. No reading indicates an open rotor or defective brushes.

Scheme 3

RECTIFIER (DIODE) TESTS

Note. DO NOT break protective plastic diode cases. Always touch test probe to metal strap nearest diode. Rectifier diodes may be tested with a test light or tester C-3829A. Test Light Method

1. With rectifier end shield and stator assembly separated, test rectifiers with a 12-volt battery and test light (No. 67 bulb). Connect test light to battery positive terminal and one test probe. Touch other test probe to negative battery terminal. Measure rectifier continuity with probes touching heat sink and rectifier top strap.
2. Reverse probes. If light glows with current flow in one direction, rectifier is okay. If light glows with probes either way, rectifier is shorted. If light does not glow at all, rectifier is open. Test each rectifier in same manner. Replace defective rectifier and heat sink assemblies.

Scheme 4

Tester C-3829A Method (Positive Rectifiers)

1. Remove alternator brushes and through bolts. Separate rectifier end housing and stator from drive end housing and rotor. With alternator on insulated surface, connect test lead to alternator "BAT" output terminal. Plug tool into 110-volt AC power supply.
2. Touch metal strap of each positive rectifier with test probe. Reading for satisfactory rectifiers will be 1 3/4 amperes or more and should be approximately the same for each rectifier. When 2 rectifiers are good and one is shorted, reading taken at good rectifiers will be low and reading at shorted rectifier will be zero.
3. Disconnect lead to rectifier reading zero and retest. Reading of good rectifiers will now be within satisfactory range. When one rectifier is open, it will read approximately one ampere, while the 2 good rectifiers will read within satisfactory range.

Tester C-3829A Method (Negative Rectifiers)

1. Remove alternator brushes and through bolts. Separate rectifier end housing and stator from drive end housing and rotor. Connect test lead to rectifier end housing. Touch metal strap of each negative rectifier with test probe.
2. Test specifications and results will be approximately the same as for positive rectifiers, except meter will read on opposite side of scale. If a negative rectifier shows shorted condition, remove stator from rectifier end shield and retest. Stator winding could be grounded to stator laminations or rectifier end shield, indicating a shorted negative rectifier.

STATOR TEST

Note. On 114-amp alternators, stator windings are "Delta" wound, and cannot be checked with common shop equipment. If stator is not grounded, and all other components check correctly, suspect an open or a short in stator.

1. Separate stator from both end shields. Press ohmmeter lead firmly onto any bare spot on frame. Press ohmmeter lead firmly to each of the 3 phase lead terminals, one at a time. (Scheme 5) If zero or low resistance is measured, stator lead is grounded.
2. Press ohmmeter lead firmly on one phase lead, and contact each of the other 2 stator leads. If no continuity exists, stator is open. Install a new stator if it is open or grounded.

Scheme 5

ROTOR TEST

1. Test rotor for grounded, open or shorted field coils, using an ohmmeter. (Scheme 6)and (Scheme 7). Touch ohmmeter probes to shaft and each slip ring. Test for grounds between each slip ring and rotor shaft. No continuity should exist.
2. Check for open field by connecting ohmmeter leads across slip rings. Normal resistance reading with rotor at room temperature is 1.7-2.1 ohms for 114-amp alternator and 1.5-2.0 ohms for all other models.
3. Readings between 2.5 and 3.0 ohms would result from rotors operating at high engine compartment temperatures. Readings above 3.5 ohms indicate high resistance, possibly requiring rotor replacement. If reading is below 1.7 ohms (114-amp alternator) or 1.5 ohms (all other models), the field coil is shorted.

Scheme 6

Scheme 7

DISASSEMBLY

1. Remove brush screws and insulating washers. Lift brush assemblies from end shield. Remove through bolts. Pry between stator and drive end shield with blade of screwdriver, using slot provided.
2. Carefully separate drive end shield, pulley and rotor assembly away from stator and rectifier end shield assembly. If negative heat sink diode straps are on top of positive heat sink straps, remove 4 hex head screws on negative rectifier and heat sink assembly. Remove heat sink assembly.
3. On all except 114-amp alternators, remove nut, washer and insulator from output ("BAT") terminal on outside of end shield. Turn end shield over to remove capacitor, insulated washer and positive heat sink assembly. Remove insulator from "BAT" terminal hole.
4. On 114-amp alternators, reach inside end shield. Remove nut and insulator attaching positive heat sink to end shield. Remove capacitor screw, capacitor and insulator.
5. Remove screws attaching negative heat sink to end shield. Remove positive and negative heat sink assemblies, noting location of insulators. Remove terminal block attaching screws and terminal block.
6. On all except 114-amp alternators, remove mica insulator from end shield and loosen 4 hex head screws on negative rectifier and heat sink assembly. Remove 2 outer screws and remove heat sink assembly.
7. Using a Puller (C-4068 or C-4333 on 114-amp models), remove drive pulley from shaft. Remove screws attaching bearing retainer to drive end shield on 114-amp alternators. Separate bearing retainer from end shield. Support end shield and tap rotor shaft with plastic hammer to separate rotor from end shield.
8. Using puller, remove drive end ball bearing. If needle roller bearing in rectifier end shield must be replaced, it can be pressed out of end shield using an End Shield Support (C-3925) and Press Adapter (C-3770A).

SLIP RING REPLACEMENT

Slip rings are not serviced as individual units. If slip rings are worn or damaged, rotor assembly will have to be replaced.

REASSEMBLY - ALL EXCEPT 114-AMP ALTERNATOR

1. Position grease retainer on rotor shaft and press onto shaft with Installer (C-3921). Press until grease retainer bottoms on rotor shaft. Position rectifier end shield bearing on base of Needle Bearing Installer (C-4201-1). Place end shield on top of bearing so it is aligned. With top part of Bearing Press (C-4201-2) placed on end shield, press assembly until bottomed. NOTE: New bearings are pre-lubricated and should require no additional lubrication.
2. Insert drive end bearing in drive end shield. Install retainer plate to hold bearing in place. A metal spacer supplied with replacement rotors and ball bearings is not a part of original alternator assembly. Place spacer on pulley end of rotor shaft. Position bearing and drive end shield on rotor shaft. Support base of rotor shaft. Press bearing end shield into position on rotor shaft with an arbor press and Adapter (C-3858). CAUTION: Ensure bearing is installed squarely to avoid damage to bearing and rotor shaft.
3. Install pulley on rotor shaft. Shaft of rotor must be supported, so all pressing force is on pulley hub and rotor shaft, (not on bearings). DO NOT hammer pulley on or apply more than 6800 lbs. (3084 kg). If removed, install output terminal stud and insulator through end shield.
4. Be sure mica insulators are in place and undamaged. Install positive heat sink assembly over studs. Guide rectifier straps over studs on terminal block. Install capacitor. Slide negative rectifier and heat sink assembly into place. Position straps and install screws.
5. Position stator over rectifier end shield and install winding terminals on terminal block. Press stator pins into each end shield. Route leads so they cannot contact rotor or sharp edge of negative heat sink. Position rotor and drive end shield over stator and rectifier end shield. Install through bolts. Compress both ends, and tighten through bolts evenly.
6. Install field brushes in insulated holders. Position vertical and horizontal field brushes properly in rectifier end shield. Place an insulating washer on each field brush terminal. Install lock washers. Be sure brushes are not grounded. Rotate pulley slowly by hand to ensure rotor blades do not contact stator leads.

REASSEMBLY - 114-AMP ALTERNATOR ONLY

1. Position rectifier end shield bearing on base of Support Tool (C-4330-1-3). Place end shield on top of bearing, so that it is properly aligned. With Bearing Installer (C-4330-2) placed on end shield, press into place until end shield touches base of press.
2. Insert drive end bearing in end shield. Position retainer and tighten mounting screws with rotor spacer in position. Place bearing and drive end shield on rotor shaft. Press end shield into position with arbor press and Adapter (C-3858).
3. Install pulley on rotor shaft. Support shaft so that pressing force is on pulley hub and rotor shaft. Press pulley on shaft until it contacts inner race of drive end bearing. DO NOT hammer pulley or exceed 6800 lbs. (3084 kg) of force. Position insulator and capacitor on positive heat sink mounting stub, and tighten attaching screw.
4. Position terminal block in rectifier end shield and tighten screws. Position negative heat sink in end shield with metal straps in place over studs on terminal block. Install mounting screws and tighten.
5. Install insulator on positive heat sink stud and place assembly into end shield. Verify metal straps are properly positioned over studs on terminal block. From inside end shield, install insulator on positive heat sink stud and tighten nut.
6. From outside of end shield, install insulator on stud, and tighten mounting bolt. Position stator over end shield and install terminals on terminal block. Route leads so they cannot contact rotor or sharp edges of negative heat sink.
7. Position rotor and drive end shield over stator and end shield assembly and align through bolts. Compress stator and both end shields manually. Install and tighten through bolts. Install field brushes in brush holder with long terminal on bottom and short terminal on top. Install insulators and mounting screw.
8. Position brush holder assembly to end shield, making sure it is properly seated, and tighten mounting screw. Rotate pulley by hand to ensure rotor poles do not contact stator winding leads.

Exploded View of Typical Chrysler Motors Alternator. Scheme 8

ALTERNATOR OUTPUT SPECIFICATIONS

OUTPUT SPECIFICATIONS

Rotation

Clockwise at drive end.

2.5-5.0 amps at 12 volts while rotating by hand.

Capacitor Capacity

Capicity is .50 mfd. plus or minus 20%.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• TROUBLE SHOOTING - BASIC PROCEDURES