- Fiat 850 (1970-73)
- Fiat 124 (1968-73)
CHANGES, CAUTIONS, CORRECTIONS
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| INTERNAL WIRING DIAGRAM AND TEST CIRCUIT |
ELECTRICAL SYSTEM REPAIRING CAUTION - Reversed polarity or excessive voltage will result in extensive damage to alternator system. Note the following to prevent damage.
Battery Installation - Negative battery terminal must be connected to ground (negative ground system only), and positive terminal connected to starter. DO NOT reverse battery leads.
Battery Charging - If a Quick Charger is used, both battery cables must be disconnected from battery. DO NOT use a Quick Charger to provide starting voltage.
Circuit Interruption - The battery must never be disconnected while alternator is running.
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| MINIMUM OUTPUT CURVE - 42 AMP ALTERNATOR |
Alternator Removal - Always disconnect battery ground before alternator removal and replacement.
High Voltage - DO NOT use a high voltage source to test diodes.
Booster Battery (For Engine Start) - Booster battery must be connected with negative lead to negative terminal and positive lead to positive terminal. DO NOT reverse battery leads.
DESCRIPTION
Fiat alternators are conentional three-phase, self-rectiying type alternators. Six silicon rectifier diodes are connected to form a full-wave, three-phase rectifying bridge. The three negative rectifier diodes (identified by black wording) are pressed directly in the end frame. Three positive diodes (identified by red wording) are located in a heat sink which is insulated from the end frame.
Application Model No.
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| MINIMUM OUTPUT CURVE - 47 AMP. ALTERNATOR |
850....................................* A 12 M 124/12/42M
124....................................* A 12 M 124/12/42M
* - Alternators A 12 M 124/12/47 and A 12 M 124/12/60 are optional.
TESTING
BENCH TESTING
Field Winding Resistance - Resistance must be measured across terminal "67" and ground, by the volt-ampere method, at alternator speed of 500 RPM. At 68 degrees Fahrenheit measured resistance must be as listed (see specifications).
Output Test - 1) Place alternator, compete with pulley and fan, on test bench equipped with gradual speed control. Wire as shown in illustration.
2) Run alternator for 30 minutes at 5000 RPM with output listed under Current Output (see
specifications).
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| MINIMUM OUTPUT CURVE - 60 AMP ALTERNATOR |
3) After thermal stabilization, determine the output curve at 14 volts, it is first necessary to run alternator until obtaining a given output, then reducing in speed to an output current of one to two amps. At this point, disconnect the load rheostat and the battery by operating switch "I" (see illustration). Then bring the voltage up to 14 volts by adjusting the speed.
4) The output curve must be identical or slightly greater than the ones shown (according to alternator model).
OVERHAUL
DISASSEMBLY
1) Remove the drive and ventilation components from rotor shaft. Remove brush holder (with brushes) by backing out its mounting screw on diode end head. Remove Woodruff key on shaft.
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| DIODE TEST |
2) Unscrew nuts of the four through bolts, remove drive end frame and rotor. Before removing stator, unscrew from inside (of housing), three nuts securing stator winding phase ends to diode ends. Remove stator.
3) To disassemble diode end frame, unscrew the nut of terminal "30". The frame negative diodes and the support with positive diodes will be separated.
TESTING
Diode Assemblies - Use a test lamp exceeding 24 volts or on ohmmeter. Always disconnect the diodes from the stator windings before individual testing commences. Due to the three-phase bridge connection of rectifier, a faulty diode could not otherwise be detected. Connect test lamp in series to diode to be tested. The diode is efficient if lamp lights in only one of the two connection arrangements (reversing test leads). Diode is open if lamp does not light in
either direction. Diode is shorted if lamp lights in both connection arrangements (see illustration).
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| REMOVAL OF NEGATIVE DIODES |
Stator Winding Resistance - Resistance of the stator windings can be checked only after opening connector joining stator phase ends to rectifier ends. Resistance must be measured between the end of each phase and the center terminal by volt-ampere method. As resistance values are very small, it is essential to use a high-precision ammeter. The recorded values must be the same as listed (see specifications).
Rotor Winding Resistance - Rotor resistance can be checked with ohmmeter. Connect across slip rings at 68 degrees Fahrenheit (see specifications).
Brushes - The spring pressure on slip ring brushes should be about one pound (0.43 kg), with new
brushes in operation position.
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| CENTERING OF NEGATIVE DIODE SEATS |
PARTS REPLACEMENT
Positive Diodes - On the aluminum positive diode heat sink, replacement of positive diodes is not possible. In case one or more positive diodes is damaged, change heat sink plate complete with diodes.
Negative Diodes - NOTE - The new diode must be of the type especially designed for replacements. Besides identification marks, spare diodes bear the letter "R" stamped on container shell. Also shell diameter in knurled areas is oversize. The seat hole of the damaged diode that was removed must be rebased to a larger diameter to ensure efficient operation of the replacement diode.
1) Removal should be performed using a suitable hand arbor press (see illustration).
2) A drill press should be used to ream diode seats. Support end frame with suitable fixture (A. 76035). Center seat to be reamed to fixture brushing by inserting guide and then locking end frame to fixture.
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| PRESSING NEGATIVE DIODES |
3) Re-bore diode seat using reamer (A. 90340) chucked in drill at about 1000 RPM. Reamer must be oiled continously with kerosene during operation.
4) Install negative diodes using hand arbor press. Diode axis must always coincide with hole axis. Drift (A. 76028) used fro installation of diode must apply its pressure exclusively on the container areas marked in illustration. Before pressing, be sure to prevent arbor rotation by securing lead screw in its vertical groove.
Brushes - To ensure best results, brushes should be replaced with a new brush holder as a complete assembly. Before installing holder assembly, clean all parts of grease and carbon dust. Lubricate bearings with suitable grease (Fiat MR 3).
REASSEMBLY
The alternator is reassembled by reversing the order of disassembly procedure.
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| BRUSH HOLDER ASSEMBLY |
