6.ALTERNATOR INSPECTION, ASSEMBLY AND INSTALLATION In order to prevent the output voltage of the alternator from increasing beyond the specified limit, an electronic integrated circuit regulator is used. The setting of the regulator is non-adjustable. The regulator unit also carries the brushes. The alternator provides alternating current that is converted to direct current by rectifiers and then used for battery charging.
6.0
Objectives After going through this lesson, you will be able to: Inspect components of the alternator viz. rotor, stator, rectifiers, diodes and brushes Assemble the alternator. Install the alternator in the car.
i. ii. iii.
6.1
Inspection of Rotor First touch the test probes together and check the multimeter for proper working.
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6.2 窶｢
6.3
Touch the test probes of the multimeter to the slip rings to check the rotor for continuity. The resistance shown should be between 3.4 to 3.7 ohms. If there is no continuity, the field coil is open窶田ircuited and must be replaced. Touch the test probes of the multimeter on each slip ring and the rotor to check the rotor for grounding. There should be no continuity. Presence of any continuity indicates that the insulation on the field coil has failed, making the replacement of the rotor necessary.
Inspection of Stator Touch the test probes of the multimeter on the stator core and on each coil lead one after the other. If continuity is detected, the stator should be replaced.
Inspection of Rectifiers
The positive rectifiers are checked first. The rectifiers are considered to be acceptable if continuity is present when the positive test probe, which is red in color, is touched to positive side heat sink and the negative test probe is touched to the rectifier lead. At the same time, continuity should be absent when the test probes are reversed. All the three rectifiers are checked in a similar manner.
The negative rectifiers are checked next. In this case, the continuity between the negative side heat sink and each rectifier lead is checked. The rectifiers are considered to be acceptable if continuity exists when the tester negative probe is touched to the negative side heat sink and the tester positive probe is touched to the rectifier lead. Also, there should be no continuity when the tester negative probe is touched to the rectifier lead and the tester positive probe is touched to the negative side heat sink. Fig. 6.1: Rectifier plate.
If any malfunction is detected, defective part should be replaced.
6.4
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Inspection of Diodes
All diodes are checked for continuity, one at a time. Touching the probes to the two leads of the diode should show continuity only in one direction, so that when the probes are reversed, continuity should be absent. The positive side of each diode can be recognized by a silver line on that side.
6.5
Inspection of Brushes
There are two brushes that project out from the regulator. • Check the brushes for free movement in their holders. • Check the length of the brushes, which should not be less than 8 mm. The length of both the brushes should also be equal. The standard length of each brush is 18.5 mm. Fig. 6.2: Checking length of brush.
Self-check Questions 1. Continuity should be __________ between the 2 slip rings 2. What is the resistance of the rotor winding? 3.4 to 3.7 ohms 3. Continuity between the slip ring and rotor indicates that ____________________ _________________________________ 4. Continuity should be ________ between the stator core and each coil lead 5. Diodes should show continuity in both directions. State whether True/False. 6. __________ side of each diode has a silver line 7. Length of brushes should not be less than __________
6.6
Inspection of Regulator
The regulator cannot be checked as a unit or repaired by itself. It is an electronic integrated circuit unit and must be replaced when it becomes faulty. A faulty regulator can be diagnosed during troubleshooting.
6.7 • • • •
Assembly Install the regulator onto the rectifier plate and join the two by soldering where it was removed. Place the cover on the brush holder. Insert the rotor front bearing in the bore in the drive end housing and tap it into place with a plastic hammer. Screw in the three screws and tighten them with a Philips head screwdriver.
The triangular plate into which these screws are tightened holds the bearing in place at that end. •
Insert the bush and place the fan. The fan is provided to blow cooling air over the alternator.
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Place the spacer over the fan and then the two halves of the generator pulley.
The pulley halves as well as the shaft have flat portions which should be matched for fitting. • • • •
Match the flat portions and install the pulley halves onto the shaft. Place the washer and screw in the nut. Hold the rotor between wooden blocks in a vise and tighten the nut with a No 24 ring spanner. Loosen the vise and remove the rotor.
The half assembly is now complete. Next the stator is assembled in the rotor housing. • • • • • • •
Install the stator in the housing and screw in the screw, which holds the regulator assembly in the housing. Tighten the screw with a Philips head screwdriver. Install the stator properly and then keep the rotor housing upside down. Place the insulating bush on the positive terminal and then place a washer in the bush and screw in the nut. Place washers and spring washers on the other two screws and screw in the nut. Tighten all the three nuts. Place a washer on the ‘B’ terminal and screw in the nut over it.
The connector of the output lead will be placed on this nut and it will be tightened fully after the alternator has been mounted on the car.
• • • • • •
Press the brushes inward and keep them in position by inserting a steel wire from the outside. The wire will project inwards. Install the rotor housing over the rotor. Screw in the bolts holding the drive end frame to the rotor housing. Remove the wire. Tighten the bolts fully. Rotate the fan and check for free rotation. This completes the assembly of the alternator.
6.8 • • • • • • • • • • • • •
Installation Place the alternator over the brackets and screw in the bolts on both sides. Screw in the bolt through the mounting stay. Tighten the bracket bolts lightly with an open end spanner. Mount the belt over the alternator pulley and the drive pulley. Pull the alternator outwards and tighten the mounting stay bolt. Check the tension in the belt. If it is found to be satisfactory, tighten the bolt fully after pulling it outwards with a lever. Tighten the bracket bolts fully. This is followed by making the electrical connections to the alternator. Connect the output lead to the ‘B’ terminal and mount the insulation cap. Fix the coupler. Mount the bumper and tighten the bolts on both sides with an open end spanner. Insert the two projections of the grille in the lower member and tighten the two screws in the upper member to fix the grille. Connect the ground cable to the negative terminal of the battery. Close the bonnet.
Self-check Questions 8. Regulator is connected to the rectifier plate by ___________ 9. Cooling fan is provided in the alternator. State whether True/False. 10. How is alternator belt tension adjusted?
6.9
Summing Up
We studied the procedure of overhauling the alternator in this unit and the self-starter in the previous unit. In the self-starter, direct current is provided and mechanical energy is obtained to crank the engine. In the alternator, mechanical energy is provided from the engine and electric current is obtained which is used to charge the battery. The common element between the self-starter and the alternator is the battery. The self-starter draws electric current from the battery while the
alternator provides a charging current to the battery. We will study about the battery used in an automobile in detail in the next unit.
6.10 Assignments 6.10.1 Class Assignment 1. Compare the self-starter assembly with alternator assembly. 2. Discuss the differences between the functioning of self-starter and alternator. 6.10.2 Home Assignment 1. What could be the causes of a discharged battery? Write in detail.
6.11 Possible Answers to Self-check Questions 1. present 2. 3.4 to 3.7 ohms 3. insulation on the field coil has failed, making the replacement of the rotor necessary 4. absent 5. False 6. positive 7. 8 mm 8. soldering 9. True 10. by pulling the alternator outwards and then tightening the mounting stay bolt
6.12 Terminal Questions 1. How are diodes and rectifier checked?
6.13 References 1. Maruti 800 Service Manual
6.14 Glossary Continuity
Instrument setup to check wiring, circuits, connectors, or switches for breaks (open circuit) or short circuits (closed circuit).
Ground
The earthing provided to the negative terminal of the battery by connecting it to the body of the car.
Insulation
Any substance or material provided to a nything that needs protection or separation from a certain environment.
Ohm
The unit of electrical resistance.
Resistance
The opposition to the flow of current through a circuit or electrical device, and is measured in ohms. Resistance is equal to the voltage divided by the amperage.
Rotor
Field winding and electromagnets mounted on a steel shaft.
Slip ring
Continuous ring over which brushes make contact to provide current to the field winding.