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Alternator & Regulator Audi 90 B4

Charging System 2 illustrations ~835 words

DESCRIPTION

All models are equipped with Bosch 3-phase, self-rectifying, 110-amp alternator. (Scheme 1) This internally regulated alternator is equipped with 14 diodes, with 3 exciter diodes connected to stator windings. These diodes turn off the alternator indicator light and supply power to the voltage regulator while the engine is running.

Exploded View Of Bosch 110-Amp Alternator. Scheme 1

Scheme 1: Exploded View Of Bosch 110-Amp Alternator
Scheme 1: Exploded View Of Bosch 110-Amp Alternator

Current Test

Ensure battery voltage is at least 12 volts. Disconnect Blue (D+) wire from alternator. Connect digital ammeter between alternator Blue wire terminal and Blue wire. Set digital ammeter to 200-mA range. Turn ignition on. If amperage is not 150-185 mA (milliamps), check Blue wire between alternator and instrument panel, and check instrument cluster printed circuit.

Resistance Test

Disconnect negative battery cable. Disconnect Blue (D+) wire from alternator. Connect ohmmeter between Blue wire and battery positive terminal. Turn ignition on. Resistance should be 140-160 ohms. If resistance is not 140-160 ohms, check alternator bulb. If bulb is okay, replace instrument cluster printed circuit and retest.

ALTERNATOR OUTPUT TEST

  1. Ensure connections at battery, alternator and starter are clean and tight. Ensure alternator, engine and body are properly grounded. Ensure drive belt is adjusted and in good condition.
  2. Connect Ammeter/Voltmeter (VAT-40/60 ) according to manufacturer's instructions. Operate engine at 2000 RPM. Alternator output should be 90-110 amps.
  3. If alternator output is low, repair or replace alternator. If reading is 16-20 amps less than alternator rating, replace regulator. If output is still low, repair or replace alternator.

TROUBLE SHOOTING

Note. For additional trouble shooting, see TROUBLE SHOOTING - BASIC PROCEDURES article in GENERAL INFORMATION section.

Light Does Not Come On With Ignition On & Engine Off

  1. Disconnect Blue (D+) wire from alternator. Connect jumper wire between Blue wire and ground. Turn ignition on. If indicator light does not come on, go to step 3). If indicator light comes on, go to next step.
  2. Check for poor alternator ground and worn brushes. If alternator ground and brushes are okay, replace voltage regulator. If light still does not come on, replace alternator.
  3. Disconnect negative battery cable. Replace indicator light bulb and reconnect negative battery cable. If indicator light still does not come on, repair circuit between alternator and indicator light.

Light Remains On When Ignition Is Off

Defective alternator diode and/or rectifier bridge. Replace alternator.

Light Does Not Go Out When Engine RPM Is Increased

  1. Check drive belt tension. If tension is okay, disconnect Blue (D+) wire from alternator. Turn ignition on.
  2. If indicator light does not come on, perform «ALTERNATOR OUTPUT TEST»(/audi/90/b4-1992-1995/remont/charging-system/#alternator-regulator__alternator-output-test) under ON-VEHICLE TESTING. If indicator light comes on, check for short to ground in Blue wire between alternator and indicator light. If Blue wire is not shorted to ground, replace alternator.

Diode Assembly

  1. Set ohmmeter on x100 scale. Connect ohmmeter between alternator output terminal and each of 3 stator terminals in turn. (Scheme 2) Reverse ohmmeter leads. If ohmmeter indicates continuity in only one direction, go to next step. If ohmmeter indicates continuity in both directions, replace diode assembly.
  2. Connect ohmmeter between negative plate and each of 3 stator terminals in turn. Reverse ohmmeter leads. If ohmmeter indicates continuity in only one direction, go to next step. If ohmmeter indicates continuity in both directions, replace diode assembly.
  3. Connect ohmmeter between Blue (D+) wire terminal and each of 3 stator terminals in turn. Reverse ohmmeter leads. If ohmmeter indicates continuity in only one direction, diode assembly is okay. If ohmmeter indicates continuity in both directions, replace diode assembly.

Testing Diode Assembly (Bosch 110-Amp Alternator). Scheme 2

Scheme 2: Testing Diode Assembly (Bosch 110-Amp Alternator)
Scheme 2: Testing Diode Assembly (Bosch 110-Amp Alternator)

Stator

  1. Set ohmmeter on lowest scale. Connect ohmmeter between stator leads. If resistance is not about .09-.10 ohm, stator windings are open or shorted. Replace stator.
  2. Set ohmmeter on x1000 scale. Connect ohmmeter between stator core and stator lead. If continuity exists, stator is grounded. Replace stator.

Rotor

  1. Set ohmmeter on lowest scale. Connect ohmmeter between slip rings. If resistance is less than 2.8 ohms, rotor windings are shorted. Replace rotor. If resistance is more than 3.1 ohms, high resistance exists in rotor windings. Replace rotor.
  2. Set ohmmeter on x1000 scale. Connect ohmmeter between either slip ring and rotor. If continuity exists, rotor is grounded. Replace rotor.
  3. Clean slip rings using fine sandpaper. If rings are worn or pitted, turn them on lathe until smooth. Minimum ring diameter is 1 1/16"(27 mm).
  4. If slip rings cannot be repaired, remove rear bearing from slip ring end of rotor. Unsolder wires from slip rings. Bend up ends of rotor winding. Pull off slip rings. Ensure ends of rotor winding are not damaged.
  5. Insert ends of rotor winding into slip ring, and press new slip ring onto rotor until slip ring end is 9/64" (3.57 mm) from end of collar. Solder rotor winding to slip ring terminals. Turn rings on lathe, and retest rotor. Maximum slip ring runout is .0012" (.03 mm).

Brushes

Ensure new brushes are .47" (12 mm) long. Used brushes must be at least .16" (4 mm) long.