Alternator & Regulator - Bosch Article Text

ALTERNATOR & REGULATOR - BOSCH
Article Text
1989 Volkswagen Golf
For Volkswagen Technical Site
Copyright © 1998 Mitchell Repair Information Company, LLC
Monday, August 23, 1999 11:38PM
ARTICLE BEGINNING
1989-92 ELECTRICAL
Alternators & Regulators - Bosch
Cabriolet, Fox, Golf, GTI, Jetta, Jetta GLI, Vanagon

1991 Corrado, Passat & Golf GL
NOTE: Some Golf, GTI, Jetta and Jetta GLI models may use a
Motorola alternator. Please refer to ALTERNATORS - SEV
MOTOROLA article. Vanagon models only use Bosch 90-amp
alternators.
DESCRIPTION
Bosch alternators are conventional 3-phase, self-rectifying

type alternators. Bosch 65 through 75-amp alternators use 3 positive
and 3 negative diodes connected to stator windings to rectify current.
Bosch 90-amp alternators use 14 diodes.
All alternators use 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.
Bosch regulators are transistorized and integral with alternator.
BELT TENSION ADJUSTMENT
BELT TENSION SPECIFICATIONS

ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
Application (1) Deflection In. (mm)
New Belt ................................... 5/64 (2)

Used Belt ................................. 13/64 (5)
(1) - Deflection is with 22 lbs. (10 kg) pressure

applied midway on longest belt run.
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
TESTING (ON-VEHICLE)
WIRING CONTINUITY TEST
1) Connect a voltmeter between alternator "B+" terminal and

ground. Voltmeter should indicate battery voltage. If not, check
wiring between alternator and battery.
2) Turn ignition on and ensure alternator indicator light
comes on. If light does not come on, check wiring between alternator
and warning light, including indicator bulb.
OUTPUT TEST
1) Ensure connections at battery, alternator, and starter

Article Text (p. 2)
(most vehicles) are clean and tight. Ensure alternator, engine and
body are properly grounded. Ensure alternator drive belt is tight and
in good condition.
2) Connect ammeter following manufacturer's instructions.
Connect voltmeter leads to battery terminals. Adjust carbon pile on
tester until voltmeter reads 13.5 volts. Alternator output should be
28-35 amps.
3) Repeat process at 1000 RPM. Alternator output should be
75-85 amps. Repeat test at 2000 RPM. Alternator output should be 89
amps. If alternator output is low, remove alternator for testing and
repairs.
4) Start engine and run at 3000 RPM. Adjust carbon pile on
tester to obtain maximum alternator output. Do not allow voltage to go
below 12.6 volts.
5) Alternator output should equal alternator rated output,
minus 16-20 amps. If reading is 16-20 amps below alternator rating,
replace regulator and retest. If output is still low, repair or
replace alternator.
REGULATOR CONTROL VOLTAGE TEST
1) Connect ammeter following manufacturer's instructions.

Connect voltmeter leads to battery terminals. Start engine and run at
3000 RPM.
2) Run engine until voltage stops rising. Voltage should be
13.5-14.5 volts. If reading is incorrect, remove regulator and ensure
brushes are longer than 7/32" (6 mm). Replace if necessary.
3) If brushes are okay and regulator fails to keep voltage
within specified limits, replace regulator and retest. If voltage is
still incorrect, repair or replace alternator.
BENCH TESTING
DIODE ASSEMBLY
1) Place ohmmeter on x 100 scale. Connect ohmmeter leads

across "B+" terminal and 3 stator terminals one at a time. Reverse
leads. Ohmmeter should indicate continuity in one direction only.
2) Connect ohmmeter leads across negative plate and 3 stator
terminals one at a time. See Fig. 1. Reverse leads. Ohmmeter should
indicate continuity in one direction only.
3) Connect ohmmeter leads across "D+" terminal and 3 stator
terminals one at a time. Reverse leads. Ohmmeter should indicate
continuity in one direction only. Replace diode assembly if defective.
Article Text (p. 3)
Fig. 1: Bosch Diode Assembly Test

Courtesy of Volkswagen United States, Inc.
STATOR
1) Place ohmmeter on lowest scale. Connect ohmmeter across

stator leads. Resistance between leads should be approximately .14-.15
ohms for 55-amp alternator and .09-.10 ohms for 65 through 90-amp
alternators. If resistance is incorrect, stator has open or shorted
windings and must be replaced.
2) Place ohmmeter on X 1000 scale. Connect ohmmeter between
stator core and stator lead. No continuity should exist. If continuity
exists, stator is grounded and must be replaced.
ROTOR
1) Place ohmmeter on lowest scale. Connect ohmmeter across

slip rings. Resistance should be 2.8-3.1 ohms for 65 through 90-amp
alternators.
2) If resistance is too low, rotor has short circuit and must
be replaced. If resistance is infinity (no continuity), rotor has open
circuit and must be replaced.
3) Place ohmmeter on x 1000 scale. Connect ohmmeter between
either slip ring and rotor core. No continuity should exist. If
continuity exists, rotor is grounded and must be replaced.
4) Clean slip rings using fine sandpaper. Rings which are
worn or pitted should be turned on lathe. Minimum ring diameter is 1
Article Text (p. 4)
1/16".
5) If slip rings are beyond repair, remove rear bearing from
slip ring end of rotor. Unsolder wires from slip rings and bend up
ends of rotor winding. Pull off slip rings. Ensure ends of rotor
winding are not damaged.
6) Insert ends of rotor winding into slip ring and press new
slip ring onto rotor. Slip ring end must be 9/64" from end of collar.
Solder rotor winding to slip ring terminals. Turn rings on lathe and
retest rotor. Maximum slip ring run-out is .0012" (.03 mm).
BEARINGS
Always replace bearings. If replacement front bearing is

sealed on one side only, open side must face rotor. If replacement
rear bearing is sealed on one side only, open side must face away from
rotor.
BRUSHES
Ensure brushes are longer than 7/32". Replace if necessary.

Unsolder brushes from voltage regulator. Solder new brushes. Do not
allow solder to run into strands of brush leads. Brushes must be free
to slide in brush holder with normal spring tension of 10-14 ozs.
(283-397 g).
OVERHAUL
For alternator disassembly and reassembly, refer to Fig. 2.
Fig. 2: Exploded View of Typical Bosch Alternator

Courtesy of Volkswagen United States, Inc.
Article Text (p. 5)
END OF ARTICLE

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ALTERNATOR & REGULATOR - BOSCH

Cabriolet, Fox, Golf, GTI, Jetta, Jetta GLI, Vanagon

Bosch alternators are conventional 3-phase, self-rectifying

BELT TENSION ADJUSTMENT

BELT TENSION SPECIFICATIONS

New Belt ................................... 5/64 (2)

(1) - Deflection is with 22 lbs. (10 kg) pressure

WIRING CONTINUITY TEST

1) Connect a voltmeter between alternator "B+" terminal and

1) Ensure connections at battery, alternator, and starter

REGULATOR CONTROL VOLTAGE TEST

1) Connect ammeter following manufacturer's instructions.

1) Place ohmmeter on x 100 scale. Connect ohmmeter leads

Fig. 1: Bosch Diode Assembly Test

1) Place ohmmeter on lowest scale. Connect ohmmeter across

1) Place ohmmeter on lowest scale. Connect ohmmeter across

Always replace bearings. If replacement front bearing is

Ensure brushes are longer than 7/32". Replace if necessary.

For alternator disassembly and reassembly, refer to Fig. 2.

Fig. 2: Exploded View of Typical Bosch Alternator

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