The vehicle’s alternator is a device that converts the mechanical energy from the crankshaft rotation into electrical current. When the engine is running, this energy is used to charge the battery and power various electrical devices. In some vehicles, this device is also used to start the engine.
Alternator: Structure and Function
The alternator, also known as a “lima,” consists of static (fixed) and dynamic (moving) components. During driving, its role is to supply power to the vehicle’s electrical devices and charge the battery. The static components include an aluminum housing, diodes, covers, stator, and a charge controller with carbon brushes. The latter provides the required voltage and adjusts it in response to the corresponding load. This ensures that electronic components are not damaged by voltage fluctuations. The dynamic components include the pulley, rotor, ball bearings, and slip rings. The alternator is driven by a V-belt or multi-ribbed belt, providing the necessary power to the battery and other important electrical devices in the vehicle (such as headlights, seat heaters, and auxiliary and safety systems). The battery acts as a voltage buffer and energy storage device, supplying power both when the engine is running and when it is off.
Types of Alternators
With carbon brushes. This is the most common type. In such devices, the excitation winding is mounted on the rotor shaft. The excitation current flows to the rotor through the carbon brushes.
Brushless motors. These are less common but reliable and durable. In this type of alternator, the excitation winding is directly connected to the stator. The electromotive force is generated by changes in the magnetic permeability in the air gap between the rotor and stator.
These devices also vary in size, the relative positions of some components, performance, and strength.
In addition to traditional alternators, combined starter/alternator assemblies are also used. These components are typically installed in hybrid vehicles or those equipped with start-stop systems.
Purchasing an Automotive Alternator
Alternator Usage Tips
After repairing or inspecting the device, always check that the wiring connections are correct. Reversing the terminals can lead to failure of the rectifier diodes and voltage regulator. Disconnecting the alternator from the battery while the engine is running can also damage the vehicle’s electrical system. Therefore, do not attempt to test the device’s operation by creating sparks and connecting the device’s positive terminal to the body. It is strictly forbidden to jump-start another vehicle while your own engine is still running.
Ensure the engine compartment is clean. Contamination poses a risk to the engine housing, leading to corrosion; it also poses a risk to electrical connections, leading to oxidation. When cleaning the engine, protect the alternator from water splashes, for example, by covering it with a thick plastic bag.
Regularly inspect the drive mechanism. Overtightening the idler pulley or improper installation can cause premature damage to the idler bearings. Note that the idler pulley is also a consumable item. The service life of the idler pulley is specified by the vehicle manufacturer in the manual. It must be replaced once it reaches the end of its service life.
Avoid driving through deep puddles. If unavoidable, at least try to drive slowly and carefully. Temperature fluctuations can damage the device.
Signs of Alternator Defects
Diode bridge failure, voltage regulator failure, drive belt breakage or looseness almost always lead to insufficient battery charging. If the battery warning light continues to flash during driving, the alternator usually needs to be checked. If the headlights are dim while the engine is running and the horn makes a clicking sound, this may also indicate a fault. You may notice a buzzing sound under the hood due to bearing wear. A whistling sound usually indicates belt breakage or oil leakage on the belt.
Causes of Defects
If water or an oil-contaminated mixture enters the diode bridge’s circuit board, or if the terminals are reversed, the diode bridge may burn out. Reversing polarity also endangers other alternator components, including the voltage regulator, which can also fail after a short circuit in the vehicle’s electrical system. Incorrect installation of the tensioner pulley and pulley, as well as improper belt installation, can lead to pulley failure. Brushes can fail due to normal wear.
Checking the Generator with a Multimeter
Checking the alternator for problems is easy. Measure its charging voltage with a multimeter. Before checking, ensure all power-consuming systems are turned off. Then follow these steps:
Set the multimeter to DC voltage.
Connect the red clip to the positive terminal and the black clip to the ground terminal. The car battery voltage should be at least 12.2 volts.
Start the engine and read the voltage. The charging voltage should be about 13.5 volts or higher, and higher than the battery voltage. At this point, the battery is charging.
Connect electrical devices. Increase the engine speed to 4000 rpm, then measure the voltage again.
The allowable voltage range varies depending on the vehicle brand and model. For example, many newer models are equipped with electronically controlled alternators.
If the voltage does not reach the manufacturer-specified value when the engine starts, it indicates a fault in the vehicle’s alternator. If a fault occurs, the alternator regulator should also be considered as a possible cause, especially if the voltage is not higher than when it is at rest while the alternator is running. In most cases, the regulator’s carbon brushes are simply worn out. In this situation, replacing the charge regulator is the wisest choice, as the cost is relatively low. However, the replacement process varies by model: it may require removing other components in the engine compartment first to access the regulator. In such cases, it is recommended to visit a repair shop.
