Symptoms of a bad car alternator. How to check it.

The alternator is an electromechanical device that converts mechanical energy into electrical energy in the form of alternating current. Most alternators use a rotating magnetic field, but alternating current linear alternators are rarely used. In principle, any AC generator can be called an alternator, but usually, the word refers to small rotary devices driven by car engines and other internal combustion engines. Alternators in power plants that are powered by steam are called turbo-alternators.

How does the alternator work?

The alternator is driven by the thermal motor, through the accessory belt. Depending on the electronic systems of the car, the maximum electricity consumption can reach 1.7 – 2 kW. The alternator must be able to produce this energy and additionally, charge the battery.

When starting the engine, the battery supplies both the electric consumers of the car and the electric motor (starter). After the engine becomes autonomous, the alternator assumes the role of electricity supplier for consumers, while charging the battery.

The alternator has 2 coils: an external fixed coil and an inner rotary coil. If there are problems with the alternator and you go with the car in service for a correct diagnosis of the fault, it may be that the mechanics refer to the first of them calling it a stator, and the second, a rotor.

When the engine of your car is running, the rotor is driven by a belt, thus generating alternating current in the fixed coil of the stator. Subsequently, the alternating current is transformed into DC, using the alternator diodes. Indeed, there is an output voltage which is however limited by the voltage regulator. The faults occurring at the level of this voltage regulator are only one of the causes of the faults occurring at the alternator.

car alternator functioning parts

Symptoms of alternator problems

The alternator is the heart of the car, being part of the car charging system, alongside the battery and the voltage regulator. The alternator not only charges the battery, but also powers the entire electrical system of your car such as lights, AC system, ECU, stereo, etc., and when it fails, it is easiest to replace the alternator. If the alternator fails, the car will show some obvious signs.

1. Battery light in the dashboard

It usually lights up when contact is made, but usually disappears after the engine starts. If it stays on, chances are high that there will be problems with the alternator or other parts of the charging system. This is a general indicator, it doesn’t necessarily mean that the alternator is faulty. 

2. The engine has a burning odor.

When the alternator is faulty, the engine area begins to have a burning odor. This odor is caused by higher pressure on the belts with the help of the transmission and incorrect operation of the transmission wheel. If the transmission wheel does not work properly, one of the consequences would be increased pressure on the belts and hence the smell of hot rubber. Also, a faulty alternator could overheat, emitting a specific odor.

3. Strange sounds coming from the engine

If there are problems with the alternator, the sounds of your car’s engine may be different. If you notice that the car no longer runs smoothly, but makes clogged sounds, go to the car for a car service, as the alternator may show signs of fatigue.

4. Fluctuations in headlights and lights.

Sometimes, when the alternator starts to stop working properly, it shows certain fluctuations in the car’s lights, especially when the engine is idling.

5. The car does not start

If the car does not want to start, it’s surely a problem with the alternator and you need to change it. Better do it quickly before the battery is drained!

6. The battery is draining

If the car battery is in good condition, but it is draining, then your alternator is faulty and needs to be changed.

There are other signs that the alternator is defective. Thus, some mechanisms no longer function properly, such as closing or opening electrically operated windows. Also, the car starts with great delay. This may be due to a faulty alternator or battery, which may be discharged or too morally worn. In this case, each part must be checked to see which one is defective.

How do we check the load level of the alternator?

There is a relatively simple way to check if the machine alternator is working, but for this, you need a multimeter or a voltmeter. You will compare the results obtained by measuring the value obtained from the car alternator with default values for it.

The steps to be taken are the following.

1. You will first identify the alternator on your car, then check that all the belts are correctly seated.

2. Set the measuring device to 20 V, then start the engine. If the transmission wheel and belt behave normally, the next step is to connect the positive (red) clamp of the multimeter to the alternator’s red terminal, and the negative (black) clamp will touch a metal element of the car such as a screw from that area or the negative terminal of the car battery.

3. It is important not to touch the alternator with any of the clips.

Following the contact between the clamps of the multimeter and the components of the machine, the measuring device should indicate certain values. How many volts should the alternator charge, if it works well, the multimeter display should indicate values as close to 14V, usually between 13.8V and 14.2V.

If the voltmeter or multimeter indicates more than 15V, the regulator may be defective. If the values indicated by the measuring device are lower than 13.5V, the causes can be varied: either the engine is not sufficiently revved for the alternator to operate at normal efficiency, it is recommended that the engine be run at 2,000 rotations per minute, or the alternator connectors are too tight and then the transmission wheel and belts do not rotate properly.

In short, an alternator must generate about 14V to charge a 12V car battery. If the battery is almost fully charged, the alternator will no longer operate at full power, which is why the battery must be checked before the alternator is checked.

To check the battery, the engine must be stopped and the headlights switched on for 10-15 minutes, so that the battery consumes some energy, to see later how much power the alternator generates to compensate for the energy deficit. If the battery is charged, then the Meter display will indicate 12-13V (when the engine is not started). If after a long time of operation of the car the display is between 13V-14V, but after stopping the engine it drops sharply below 12V, then the battery is the one to be replaced.

Alternator replacement and cost

First of all, you need to have the old alternator removed from the car, and then see what kind of alternator should be ordered. On the market, there are different types of alternators that have different characteristics such as rpm, number of poles, how it is assembled, rotors, coil type.

After ordering the alternator, the specialist must order it according to the specifications mentioned in the car book. It is important to take the car to an authorized service because the mounting of the alternator is a repair that must be done very carefully considering the sensitivity of the alternator.

After the alternator is mounted, the car battery can also be reconnected, and after the transmission belt is checked and placed in place, the alternator’s output voltages should normally be measured, and the values should be compared.

If these meet the requirements of the manual, the alternator has been successfully replaced, and if not, a few small changes must be made. After installing the new alternator it must be checked if the battery control is still on the board. If yes, then there is a problem, and if the witness is switched off, then the alternator has been successfully changed.

Before replacing the alternator, however, you must be sure that the battery is in perfect working condition, and you must carefully check the alternator. You have to make sure that everything is fine before you replace this piece.

A good alternator should cost between $200 and $300 plus labor costs.

Here is a video about how to test the alternator.

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