MERCEDES BENZ ALTERNATORS
Alternators and Bosch regulators with internal regulators
DESCRIPTION
The alternators manufactured by Bosch are conventional three-phase alternators of the self-rectifying type.
Bosch 75 to 55 amp alternators use 3 negative 3 positive and diodes connected to the stator windings to rectify current, Bosch 90 and 80 amp alternators use 14 diodes.
All alternators use 3 exciter diodes connected to the stator windings, while the engine is running, these diodes turn off the alternator indicator light and supply power to the voltage regulator, Bosch regulators are solid state transistorized and integrated with the alternator .
ALTERNATOR APPLICATION
Model Volts / Amps
(1) Manufacturer Part Number
190E 14/70 489928
190D 14/70 489 897
All others 14/70 N / A
(1) Bosch alternators part numbers are preceded by the numbers 0 120 or start with an AL and write a number and end with an X.
1. You can connect a voltmeter to the “B +” terminal of the alternator and to ground, the voltmeter should indicate the battery voltage, if not, check the wiring between the battery and the alternator.
2. Turn on the ignition and verify that the alternator indicator light comes on; If the light does not come on, check the wiring between the warning light and the alternator, including the indicator bulb.
1. Make sure the connections at the battery, alternator and starter are clean and tight, make sure the engine and alternator body are properly grounded, make sure the alternator belt is tight and on good condition.
2. Connect the ammeter following the manufacturer’s instructions, connect the voltmeter leads to the battery terminals.
3. Start the engine and run it at 3000 RPM. Adjust the carbon pile to get the maximum output from the alternator, do not allow the voltage to drop below 12.6 volts.
4. The output of the alternator should be equal to the rated output of the alternator, minus 16-20 amps, if the reading is 16-20 amps below the alternator rating, replace the regulator and retest, if the output still too low, repair or replace the alternator.
REGULATOR CONTROL VOLTAGE TEST
1. Connect the ammeter following the manufacturer’s instructions, connect the voltmeter leads to the battery terminals, run the engine at 3000 RPM
2. Run the motor until the voltage stops rising, the voltage should be 13.5 to 14.5 volts, if the reading is wrong, remove the regulator and make sure the brushes are longer than 6mm .
3. If the brushes are OK and the regulator does not maintain the voltage within the specified limits, replace the regulator and retest, if the voltage is still incorrect, repair or replace the alternator.
REVISION
DISASSEMBLY
1. Remove the nut, lock washer and pulley, remember the position of the spacers, then remove the fan assembly and the wrench, write the mark on the front and rear housings, remove the voltage regulator and remove the screws , separate the front and rear covers.
2. Disconnect the capacitor from the terminal; Remove the nut, insulators, bolts, and washers.
Remove the stator assembly.
3. Unwind the stator from the diode assembly; Remove the wave bearing washer or o-ring from the rear of the housing.
3. Hold the front casing and carefully press the rotor, do not allow the rotor to fall, remove the screws holding the bearing retainer, remove the front bearing retainer, and remove the rear bearing seal from the slip ring at the end rotor.
TESTS AND REPAIRS
Diode assembly
1. Set the ohmmeter scale to x100 scale, connect the ohmmeter leads through the “B +” terminal and the 3 terminals of the stator, one at a time, the reverse leads, the ohmmeter should indicate continuity in only one direction .
2. Reconnect the ohmmeter leads across the negative and 3 stator terminals, one at a time.
Reverse cables; The ohmmeter should indicate continuity in only one direction.
3. Connect the ohmmeter leads across the “D +” terminal and all 3 stator terminals, one at a time.
Reverse wires, ohmmeter should indicate continuity in only one direction, if diodes are found to be bad, replace diode assembly.
FIG. 3: Diode array test 55 amp alternator diode array shown, others are similar.
1. Set the ohmmeter to the lowest scale, connect the ohmmeter across the stator leads, the resistance between the leads should be 14-15 ohms for the 55 amp alternator and .09 10 ohms for the 65 amp alternators 90 amps, if resistance is incorrect the stator has open or shorted windings and needs to be replaced.
2. Place the ohmmeter on the X 1000 scale. Connect the ohmmeter between the stator core and the stator wire, there should be no continuity, if there is continuity, the stator is grounded and needs to be replaced.
1. Set the ohmmeter to the lowest scale, connect the ohmmeter through the slip rings, the resistance should be 3-4-3.75 ohms for 55 amp alternator and 2.8-3.1 ohms for alternators from 65 to 90 amps.
2. If the resistance is too low, the rotor has a short circuit and must be replaced if the resistance is infinite without continuity, the rotor has an open circuit and must be replaced.
3. Place the ohmmeter on the x1000 scale, reconnect the ohmmeter between the slip ring and the rotor core, there should be no continuity, if there is continuity, the rotor is grounded and needs to be replaced.
4. Clean slip rings with very fine sandpaper, worn or pitted rings must be turned on a lathe, minimum ring diameter is 1 1/16 “26.8mm if slip rings cannot be repaired, replace slip rings as described in steps 5 and 6.
5. Remove the rear bearing from the rotor slip ring end, desolder the slip ring leads and bend the rotor winding ends, remove the slip rings and make sure the rotor winding ends are not damaged.
6. Insert the ends of the rotor winding into the slip ring and press the new slip ring into the rotor, the end of the slip ring should be 9/64 “3.5mm from the end of the collar, weld the rotor winding to slip ring terminals, rotate rings on lathe and retest rotor, maximum slip ring runout is 0012 “.03 mm.
Bearings
Always replace the bearings, if the replacement front bearing is sealed on one side only, the open side should face the rotor, if the replacement rear bearing is sealed on one side only, the open side should face out of the rotor.
Brushes
Make sure the brushes are longer than 6mm, replace if necessary, unsolder the voltage regulator brushes, solder the new brushes, and do not allow solder to enter the brush lead wires.
The brush should be able to slide freely in the holder with a normal spring tension of 10-14.
MOUNTING
1. Install bearing, retainer and screws in front casing, press rotor onto casing.
Press the bearing at the end of the rotor slip ring, weld the stator to the diode assembly, be careful when welding near the diodes due to possible heat damage.
2. Install insulators on the stator assembly, assemble the stator assembly and rear casing, install a wave washer or O-ring on the rear casing, align the scribing marks, and mount the front and rear casings.
3. Install wrench, fan assembly and spacers, install pulley, lockwasher and nut, tighten nut to 23-29 feet. 3-4 Nm Make sure the rotor turns freely and install the voltage regulator and capacitor.