Altenator

Alternator test

As in starter test this test is divided into two part

On car

Off car

Part one On car testing

Step 1

As usual did visual inspection to make sure battery is ok, connections and wiring are good, alternator is mounted in place firmly and there is no sign of damages. Also special care should taken to make sure that alternator belt is in good condition – no damages, cracks or contamination etc.

Everything is good condition apart from battery mounting as usual. Unitec seems couldn’t afford it.

Step 2

Removed surface charge and did an OCV test on the battery to make sure battery’s state of charge is at least 12.4V as in starter testing. If battery is not charged up to this level, there is not much point to continue our testing on the alternator because result will be misleading.

Battery OCV or the base voltage is 13.1V – 100% charged.

Step 3

Battery is ok, now let do a no load test to see if altenator is working. When engine started the battery voltage should increase at least 0.5V compare to the OCV or base voltage of the battery, therefore should give a reading of at least 13.6V.

Turn on the engine and put a voltmeter across battery terminals. The voltmeter gives a reading of 14.6V. This is well above minimum.

This test also shows us another important fact is that alternator’s voltage regulator is functioning properly. This 14.6V we just measured is also the alternator regulator voltage. Specification is between 13.5 and 14.5V, a little higher but I think it is ok. This test shows that alternator’s regulator is actually controlling output voltage. If the voltage goes too high such as above 15V or so low – the voltage regulator is probably faulty.

Step 4

Output amperage of the alternator should also be check. This is done with a clamp on amp meter, clamp around the positive cable directly connected to the battery terminal. This car showed a good reading of 5.5V where specification is 10 to 18A max. If the output amp is higher than specified then further test is needed to find out why. Amount of current flowing out the alternator is an indication of load. If there is no load then there shouldn’t have too much current.

Step 5

We see that this alternator is producing a good regulated voltage. Now we need to see that it could also provide enough current to the consumers under heavy load. This is called a load test. I attached a load tester to the battery terminals. While engine is running I use the load tester to applied 50A to the battery terminals. This alternator immediately responded to this load and increased it output amp from 5.5V to 68.8A while output voltage remaind at 14.2V.

Now we can say that this alternator is healthy. It is providing good regulated voltage and right amount current to the charging system.

Step 5

We know that the alternator is healthy, but we still need to make sure what coming out this alternator is going to get to the battery. Therefore we have to do 2 voltage drop tests to make sure it is connected to the battery properly from positive and negative side.

Voltage drop between altenator body and battery negative terminal is the negative path which give a reading of 0.06V. While specification is 0.2V.

Voltage drop between the alternator B terminal and positive terminal of the battery is the positive path gives a reading of 0.02. While specification is 0.2V.

The results show clearly that this alternator is properly connected to the battery through good path with low resistance.

Part two Off Car test

As with starter this test is only neccerray if we are certain problem is within the altenator.

Step 1

Dissemble alternator as instructed

Step 2

Make a visual inspection that nothing is obviously damaged and there is no strange smell.

Step 3

Check that there is no short between rotor winding and shaft by connecting ohm meter between slip ring and rotor shaft. Our result shows infinity. This shows that winding are not shorted to rotor shaft.

Step 4

Check there is no open circuit within the rotor winding. Connect ohm meter between slip rings. Meter reading is 2.8 ohm. Specification is 2-6ohm. The connectivity of the rotor winding is good.

Step 5

Check stator winding. Make sure there is no open cct in these three windings. Connect each terminal to the common terminal with ohm meter. Returned reading are all 0ohm. This shows that there is no open cct within stator windings.

Step 6

Check winding are not shorted to ground. Connect the ohm meter between the common terminal and the earth. Return reading is infinity. This shows that no winding is short to ground.

Step 7

Once we make sure windings are good. We can now test the rectifier. Rectifier are made of 6 diodes to convert ac to dc. Three positive and three negative. Use the diode test mode on the multimeter test positive diodes first. Make sure they conduct in one direction only. If any diode conduct in both direction or does not conduct at all, that diode or diodes are faulty needs to be replaced.

Use the meter to test from both directions. All positive diodes only conduct in one direction give a reading of 0.5V and the other direction with infinity. Do same thing with negative diode. Negative diodes give same result.

Well sound like our rectifier is in good condition.

Step 8

Rotor, stator and rectifier are all in good condition. Now lets test voltage regulator with a voltage regulator tester. Followed instruction and found the right setting for my regulator which is M3 126000 – 1190. This regulator use Field setting A, 12V and set point spec is 14.6v.

After we connect the regulator and switched on the tester the following result returned:

Short cct light is off  - there is no short cct in this regulator

Warning light is on – cct to warning light on the dash board is working

Field Light is flashing – Current flow into the rotor is controlled accordingly by regulate

Set Point Voltage is 14.6V – correct voltage as determined

All this information is just saying one thing this regulator is good.

Step 9

Before we reassemble the alternator. We need to measure the brush length to make sure it contacts the slip ring properly. Therefore correct amount of current flow into the rotor. Our measured length is 5mm which is still longer than specified 4mm. brushes are still serviceable.

In conclusion this alternater we are testing is in good condition.

Any way we took these alternators up stair and put them on test benches. We see how they actually changing their output current according to amount of load while maintained their output voltage quite stable all thanks to Ian.