Alternators - Off car testing report.

After we removed the rear cover, the regulator and the brush holder on the alternator, we were able to carry out tests for the rotor winding to ground and the rotor winding internal resistance test. In the rotor winding to ground test, we are testing to see if there is a circuit butween the rotor shaft and the slip ring. There should not be a circuit here and the meter should read infinity, when the meter is set to 2k. If there is a circuit here, it means the rotor winding is shorting to earth, and will need to be replaced.
On the rotor winding internal resistance test, we are testing to see if there is a circuit between the two slip rings. There should be a circuit between the two rings, and with the ohms meter set to 200ohms, we should get a reading between 2 and 6 ohms. In my test we got 3 ohms which is a pass. The ohms meter did not have any internal resistance I did not have to subtract it from the reading. If there is no circuit between the slip rings, they need to be replaced.
To carry out the next tests, I had to remove the rectifier, and the housing of the alternator so that we could access the stator winding terminals. We tested the internal resistance in these by connecting the negative of the meter to the common stator winding terminal. The specifications of the resistance should be between 0 and .2 ohms. I tested them all and found they had a resistance of .2 ohms each which is a pass.
The next test was the stator winding to ground test. This is where we test to see if there is a circuit between the stator winding and ground. We test this by connecting the positve of the meter to the common stator terminal and the negative of the meter to the body of the alternator. There should not be a circuit here so the meter, set on 2k, should read infinity. My test read infinity so that is a pass.
Next we tested the rectifier positive diodes. The rectifier is what turns the AC current produced by the alternator into DC current. To do this we put the negative lead onto the main terminal and then the positive lead onto each of the four p-terminals. The readings for the meter should be between .5 and .7VD My readings were between .491 and .497, so that is a fail. The next test we put the positive lead onto the main terminal and the negative lead on the p-terminals. The meter should now read infinity, and it did so that is a pass.

The next test was to test the rectifier negative diodes. To do this we set the meter to diode test mode. The negative lead gets put onto the E terminal and the positive lead onto each of the p terminals. The meter should read infinity, which it did, so that was a pass. The positive lead was then put onto the E terminal, with the negative lead onto each of the p terminals. The meter should have read between .5 and  .7VD. I got readings between .485 and .492, which are all fails.
The next test was to test the voltage regulator. The regulator controls how much current and voltage is sent away from the alternator. To test a regulator, we used a device called the Transpo Voltage Regulator Tester. After testing the regulator, I found that the set point voltage of the regulator was 12.1v, which does not meet the specification of 14.5v, so this tells us that the regulator needs to be replaced.
The bearing should also be replaced when servicing an alternator. The bearing is what allows the rotor shaft to spin. It turned smoothly and without any resistance.

The final check was to check the protrusion length of the brushes. On the brushes that I pulled of the alternater, the brushes were so worn that they popped out of the holder. I found new brushes and measured the protrusion length of these ones. The first brush measured 10.5mm and the second measured 11.5mm. The minimum length is 4mm, so these were both passes.