Off car alternator test

Parts

• Regulator
• Rectifier
• Rotor
• Stator
• Brushes
• Slip rings

Function

• Slip rings and brushes are used to supply power to moving parts. The slip rings act as rails for the brushes to run on so that the electrical power can be transferred from the stationary regulator to the moving rotor shaft.
• Regulator controls the strength of the rotor. The rotor is an electromagnet, the strength of the magnet is controlled by the regulator changing the magnets input voltage.
• The stator consists of copper coils that surrounds the rotor. The rotation of the rotor causes an induced voltage in the copper coils. The voltage created is AC 
• The Rectifiers convert the the AC voltage into DC voltage so that it may be stored by the battery.

Reason for using alternators

DC generators have moving coils inside a magnetic field. The engine's speed is to fast for the DC generators to handle, the centripetal force pulls it apart. The AC alternators have the magnet in side of the coils. The magnets have a higher tolerance for the centripetal force.

Testing 

1. Rotor

To test the the rotor connect the mulitimeter (in the ohm setting) to the rotor shaft and the bottom slip ring. this test will check for a short circuit. the reading should be infinity

To see if the rotor is still in good working condition connect the multimeter to the two slip rings. Check that the ohm reading is the same as specified

     2.  Stator

Check that all the copper coils have an ohm reading that complies with the specifications. If there is no reading it means that a coil has become disconnected

    3. Rectifiers

Use the Diode testing setting on the multimeter. Connect the positive wire to the B+ terminal and the negative wire to the negative side of the diodes. Then connect the negative wire to the body of the alternator and the positive wire to the positive side of the other diodes. If there is no reading it means the diode is broken.  

   4. Brushes

Measure the brushes with a vernier caliper. If the the measurements are less the 4.0mm then the brushes need to be replaced