Alternators

In this section of the course we looked at the different components of the alternator and how they work. An alternator provides electrical charge to electrical components of the car and charges the battery when the car is on. We dismantled the alternator and performed tests on the different components as we went along.

Rotor winding to ground test
This test is done to see if there is a circuit between the rotor shaft and the the slip rings. There should be no circuit between the rotor shaft and the slip rings. The slip rings supply the electro multi pole magnet with a positive and a earth. If there was a circuit between the rotor shaft and the slip rings, it would mean that the rotor winding has shorted and would result in no magnetic field from the rotor. No magnetic field would mean no current is induced and as a result no current is produced or supplied by the alternator. You use a multimeter to perform this test. You set your meter on 2K. Place the black lead on the center of the rotor shaft and the red lead on either one of the slip rings. The meter should read infinity.

Rotor winding internal resistance test
This test is done to see how much internal resistance the rotor winding has. The rotor winding has to resist current to produce a magnetic field and thus the resistance has to be within the spec of 2-6ohms. If the internal resistance is lower than the spec (which can be caused by an internal short circuit), the magnetic field produced by the rotor will be weaker and as a result less current will be induced by the stator windings. This will mean that the output of the alternator is low. If the internal resistance is higher than spec (which can be caused by corrosion), the magnetic field produced by the rotor will also be weaker. This is because the winding will be restricting too much current. This will also result in lower output from the alternator. This test is done by setting your meter on 200ohms. You then place one end of each lead on the slip rings to obtain a reading. (Note: the internal resistance of the meter must be subtracted out of the reading).

Testing Stator winding resistance
This test is done to see how much resistance the stator winding has. The winding resistance should be no more than 0.2ohms. If the winding has a resistance higher than that, it would then mean that current induced buy the winding will be lower as  has a higher resistance to current flow. This will result in less current being induced and therefore the alternator's output will be lower. To do this test set the meter on 200ohms. Connect the black lead to the common terminal (one with the most wires) and the red lead to the other terminals one after another. Record each different result.

Testing Stator winding to ground test
This test is done too see if there is a circuit between the stator windings and ground. There should be no circuit between the two.  If there is a circuit it would mean that the winding has shorted to ground. This is not good as it would then result in no current withheld by the stator. Resulting in no output created by the alternator. This test is done by setting your meter on 2K. Then placing the red lead on the common terminal and placing the black lead of the meter on the body of the alternator. 

Testing the rectifier positive diodes
This test is done to see how much voltage is being used up (voltage drop) by the diodes, and to ensure that the diodes are letting the current through the right way. A rectifier converts AC in DC, so it is important that the diodes pass this test. To test the voltage drop you put the black lead on the B terminal and then touch the positive lead on each of the P terminals and record the readings. The meter has to be set on diode test mode. The resistance of the diodes should be between 0.5VD to 0.7VD. If the VD of a diode is higher, it will mean that the diode will be using up more voltage and this will result in a less affective rectifier. A higher voltage drop means less voltage can get through resulting in an loss of output from the alternator. There is nothing wrong if the VD reading is less than the spec. All it means is that the diode needs less voltage to operate. To test which way the current flows through a diode is done by placing the red lead on the B terminal and then the black lead on each of the P terminals. The result should be infinity. This result means that there is no circuit through the opposite way of the diode. This is good as it means that the diode will let the current go through the right way.

Testing the voltage regulator
The voltage regulator controls the alternators output by increasing and decreasing the strength of the rotors magnetic field. It regulates the voltage. Different regulators have different specified voltage spec. This test is done to see if the voltage regulator (when performing) regulates the correct voltage. If the voltage reading is lower than the spec, it will mean that the magnetic field provided by the rotor is weaker. Thus less current is induced by the stator windings and therefore results in lower output by the alternator. If the voltage reading is higher than the spec, it will mean that the voltage regulator is allowing more voltage and therefore is overcharging the battery. This can cause the hydrogen levels in the battery to rise which potentially be dangerous for the car and its occupants.

Checking the brush protrusion lenght
It is important to check the length of the brushes as they supply electricity to the slip rings and if they are too short the brush springs can't apply enough pressure to maintain constant contact. This causes excess sparking that damages the slip rings and reduces the output of the alternator. The minimum length of a brush should be no less than 4.0mm.


On car testing
The on car testing of the alternator is simple. It is done in stages. The first thing we do is we perform a visual inspection of the alternator, drive belt and tension, leads. What we are looking for here is to see that all the components are in good order. The alternator should be mounter firmly (no movement). The leads should be attached properly and firmly (to prevent them from shorting out or grounding anywhere). The belts should have no cracks on it (cracks are sigh of wear and belts with cracks can snap). The belts should be of the right tension (should only flex 5mm). After you perform the visual check you record the OCV of the battery (should be higher than 12.4V).
After this all the tests performed should be done when the car is running and at 1500 to 2000 rev's. The reason for doing this is that the alternator is actually supplying current to the engine electrical components and charging the battery like it would if the car was running.

No Load Test
The no load test is done to check how much amperes is produced by the alternator when all the accessories are turned off in the car (no load). All the ampere drawn out of the alternator during no load is supplied to components such as your ignition system (spark plugs), your EFI (electronic fuel injection), your ecu (on board car computer) etc. In a fuel injected car the no load amp output should be between 10 - 18amps. Any more can mean that you have a fault in one of your electronic component, or that there is a wire that in causing resistance. Any less can mean that your alternator is not working as well as it should be. Reasons can be faulty alternator, The rotor winding can have a internal short circuit causing the magnetic field to be weaker. The brushes inside the alternator can be of a low length (lower than 4.0mm) therefore causing spark and reducing alternator's output.
An alternator also bneeds to charge the battery. So during the no load test the regulating voltage of the battery needs to be between 13.5V - 14.8V. Any lower and that means that the alternator is not supplying enough charge to the battery, resulting in the battery to take longer to charge or never be fully charged. This can be caused by corrosion on the terminals causing resistance and therefore a voltage drop. It can also be caused by the voltage regulator of the alternator (not regulating enough voltage to charge the battery). If the regulating voltage is higher than the spec, it means that the voltage regulator on the alternator is regulating too much voltage. This is dangerous because it will end up overcharging the battery and increasing the hydrogen levels inside the battery (danger to the car and its occupants).

Load Test
Before you do a load test you first need to turn off the engine, turn on all accessories other than the radio and the wipers and then record the current being drawn from the battery. This is a good indication of how much amps the alternator needs to be supplying the engine with. You then turn on your engine (engine speed 1500 - 2000 revs) with your accessories on, take down your amp output from the alternator. (Note: this reading will be higher than the reading taken from the battery as current will be drawn to supply your basic engine functions such as your ignition and EFI as well). The current draw should roughly be the sum of the the current draw recorded from the battery and the no load current draw recorded from the alternator. If the current draw is lower than that it means that the alternator is not able to supply all the current needed and therefore the battery has to compensate the alternator by supplying amps. This is not good for the battery as it means that it still has to supply charge even with the alternator on. This in the long run can reduce the battery life as the battery is in constant use and is not being able to get charged under load. The charging voltage under load should be your OCV + 0.5V (E.G: if your OCV is 12.5V then your charging voltage under load should be 13V). This is just an indication of what the figure needs to be and can be more. If the charging voltage reading under load is lower than OCV of the battery, it will mean that the battery will not be fully charged. This will lower the battery's life as it never reaches full charge. The low figure will also mean that the battery has to compensate for some of the voltage needed, and as a result you will end up with a drained battery.

Voltage Drop Test
This test shows you the amount of voltage being lost from the alternator to the battery. To obtain a valid voltage drop reading a reasonable amount of load needs to be applied to the circuit. (Voltage drop in a circuit is the highest when the circuit is under load). You check the voltage drop between the battery positive post and the alternator output (B terminal), and the voltage drop between the battery negative post and the alternator body. (The engine is still on with a speed of 1500 to 2000 rev's). The voltage drop on each side of the circuit should be no more than 0.2V. If the reading is higher than that would mean that your battery is getting less voltage supplied to it. Thus reducing its regulating voltage. This drop in voltage can be caused by corrosion on the battery terminals. It can be caused by faulty wiring (high resistance in the wire). It can be caused by black marks caused by spikes on the battery terminal and it can also be caused by dirt building up between the terminals and the wires.

Those were the tests performed on the alternator by me both on and off the car.