How to check the performance of a car alternator

Alternator malfunctions can manifest themselves in many different ways, but it is most often worth paying attention to the alternator if you hear some noise coming from the alternator, or if you often notice insufficient or no battery charge.

This can be noticed very easily. The car does not start, you have started it with a cigarette lighter from another car. Somewhere you went, there stopped the engine, and then again you can not start the car, the starter does not turn. That is, either the battery has served its time, or the alternator does not charge it. If the alternator is out of order and its repair will cost several thousand dollars, and in addition the other parts of the car are in disrepair, it is easier to send the car for recycling:

Diagnosis of mechanical failures of the generator

Here, in general, everything is simple. If the noise, squealing, whistling, rattling, howling, then the problem is either in the bearings, which should definitely be checked for grease and wear. Sometimes it is enough to add grease and the noise disappears. In more serious cases, the bearings must be replaced with new ones.

In addition to the bearings, noise and howling may occur in case of winding short circuits either in the stator or in the traction relay. Also the cause of the unpleasant sound can be a short circuit of the windings to the housing, bad contacts. That is, it is obvious that the sound appears in the case of mechanical interaction of any parts of the alternator during its operation. All this can be detected visually by inspecting the alternator. Where there is contact, you will probably see traces of this contact.

Having detected a breakdown, you should assess the degree of its seriousness the possibility of repair. But mechanical malfunctions are not the only thing that can disrupt the operation of the alternator.

Checking Car Alternator Voltage

In order to establish the operability of the alternator it is necessary to check its output voltage, and then diagnose the main causes of malfunction. To measure the voltage most often use a voltmeter, which is connected to the battery terminals, less often – ohmmeter or multimeter.

When starting the engine, the voltage on the engine terminals should not exceed 8 V. It is better to perform the procedure not on a cold engine and ambient temperature not lower than 20 degrees Celsius.

To continue the experiment you need to “give the gas”, thus increasing the engine speed. This should be done until the tachometer needle reaches 3000 rpm. Then the voltage on battery terminals should be measured again. If the reading is less than 12.5 V, it is time to repair the alternator.

Dismantle the faulty alternator by disconnecting the ground terminal from the battery. Then, using a screwdriver, it is necessary to disconnect the voltage regulator mount.

Before proceeding to a more detailed diagnosis it is necessary to make an external inspection of the generator, namely to check the wear of brushes and contact rings and in the presence of carbon deposits grind.

The most common cause of failure of the alternator is a faulty voltage regulator, so it is better to change it periodically before the expiration date of the part.

Mounting the alternator in its original position is done in reverse order, at the end the mass is carefully connected to the battery.

After performing these simple actions, you need to connect the voltmeter to the battery poles again. When starting the engine and raising the rpm to the value of 3000 rpm, the meter should show a voltage value in the range of 13.5-14.5 V. This value of the voltmeter will mean that the cause of the problem has been eliminated.

Checking Voltage Stabilization

The next step should be to check the voltage stabilization. It is carried out as follows. With the headlights on, use a voltmeter to make the necessary voltage measurements. If the obtained figure does not differ by more than 0.4 V from the previously measured – then everything is fine.

The method of checking the alternator of your car described above is simple and uncomplicated and requires only the presence of a measuring instrument, basic skills of an automobile craftsman and a desire to understand the causes of failure of an iron horse yourself.

Checking the circuit of the power supply of the car

With the help of a measuring device we will be able to check the power supply circuit of the car.

To check the diode bridge it is necessary to connect a voltmeter to the alternator terminal and “mass”. The probability of diodes failure will be obvious when the voltage reading is over 0.5 V.

To determine the diode breakdown, connect the instrument between terminal “30” and the disconnected wire of the generator. A discharge current reading of less than 5 mA will be acceptable.

To test the voltage regulator, you will first need to warm the engine in medium speed mode with the lights on for at least 15 minutes. Then using a voltmeter you should measure the voltage on one side at “ground” and on the other side at terminal “30”. Voltmeter readings may be different for different cars.

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