Alternator Component Inspection: Rotor, Stator, Diodes & Brushes
Alternator Component Inspection
Essential checks before testing: Ensure all components are free from clay, dust, and grease. Conduct visual, mechanical, and electrical inspections.
Rotor Inspection
Visual and Mechanical: Verify the rotor, shaft, and collector rings are in good condition, without signs of damage, wear, or excessive play. The rings should have a smooth surface, free from scratches or cracks. If any anomalies are found, machine the rotor to a maximum eccentricity of 0.05mm, adhering to the manufacturer’s minimum diameter specifications.
Electrical: Check the insulation resistance between the seals and the shaft. If the rotor resistance changes, replace it. Measure the resistance between the slip rings using a multimeter. A low reading indicates a short circuit. If the resistance exceeds the specified limits, there may be a faulty connection or a bad solder joint. An infinite reading indicates a broken rotor coil. In all these cases, replace the rotor.
Stator Inspection
Visual and Mechanical: Inspect the overall condition of the stator body, including the windings. Ensure the windings are in good condition, without damage or deformation.
Electrical: Use an insulation tester to check the insulation. Verify the resistance between phases, which should be very low (0.18 to 0.35 ohms). Apply a 6V voltage between two phases, inserting an ammeter and voltmeter in parallel. The ammeter reading should match the manufacturer’s specifications.
Diode Inspection
Testing Diodes: Test diodes with the diode function on a multimeter. Disconnect the diode bridge rectifiers from the stator before testing.
Rectifier Bridge Inspection
6-Diode Bridge: Use a multimeter and a current source to check the 6 diodes. Connect the positive terminal of the source to the positive terminal of the bridge and the negative terminal to a test lamp. Contact each of the stator terminals with the test lamp. The lamp should light up. Reverse the polarity and repeat the test. The lamp should not light up. If the lamp lights up in both tests, the diode is faulty and the bridge must be replaced.
9-Diode Bridge: The procedure is the same as for the 6-diode bridge, but with three additional diodes. Connect the positive terminal of the source to each of the coil terminals and the test lamp to the negative terminal. Contact the common output of the auxiliary diodes. The lamp should light up. Reverse the polarity. The lamp should not light up. If the lamp lights up in both tests, the diode is faulty and the bridge must be replaced.
Cover Support and Brush Inspection
Visual and Mechanical: Check the condition of the cover support and bearings. Ensure they rotate smoothly without breaks or axial play. Inspect the condition of the washers. Replace brushes if they are less than 10mm long. Verify the brushes sit correctly on the slip rings and within the brush holder. Check the insulation between the two brushes and between the brushes and the mass. Also, verify the continuity between the terminals and brushes.