A car’s alternator is a device that transforms the mechanical power of crankshaft rotation into electric current. The energy it produces is used to charge the battery and power various electrical devices while the engine is running. In some cars, this unit is also used to start the engine.

Types

• With carbon brushes. These are the most common alternators. In such devices, the exciter winding is mounted on the rotor shaft. The excitation current flows to the rotor through carbon brushes.
• Brushless. These are less common. They are reliable and durable. These alternators have the exciter winding mounted directly on a stator. Electromotive force is formed due to changes in magnetic conductivity of the air gap between the rotor and the stator.

Moreover, the devices differ in size, relative positions of some of their elements, power, and performance.

Apart from conventional alternators, there are combined starter motor/alternator assemblies. Typically, they are installed on hybrid vehicles or cars equipped with the “Start-Stop” system.

Operating tips

After performing any repair job or inspection of the unit, always make sure the wires were connected correctly. Reversing the polarity of connection may lead to the breakdown of rectifier diodes and voltage regulator. Remember, if you disconnect the alternator from the battery while the engine is running, this may damage the vehicle’s electrical system. Never try to check if the unit is operable with the help of a spark by connecting the unit’s positive terminal to the car body. Do not jump-start another car while the engine in your car is running.

Keep your engine bay clean. Soiling is dangerous both for the unit housing, as this can lead to its corrosion, and for electrical contacts because they might oxidise. But remember to protect the alternator from splashes when washing the engine, for example, by covering it with a durable plastic bag.

Inspect the drive mechanism regularly. An overtightened belt or improperly installed rollers can cause the pulley bearing to fail prematurely. Remember, the pulley is also a consumable. The car manufacturers specify its service life in the owner’s manual. Replace the pulley when it ends.

Avoid driving through deep puddles. If there is no other way, try to cross them carefully at low speed. Temperature variations can damage the unit.

Symptoms of malfunctions

Diode bridge faults, voltage regulator malfunctions, torn or loose drive belt almost always lead to the undercharging of the battery. Therefore, if your battery warning light is constantly blinking during driving, you will usually need to check your alternator. If your headlights are dim and the horn sounds rattling while the engine is running, this may also indicate malfunctions of the unit. You may notice specific humming from under the bonnet in case the bearing is worn out. Whistling noise usually indicates that the belt is torn or has oil on it.

Causes of malfunctions

Water or a mixture of oil and dirt getting onto the circuit board of the diode bridge, as well as reversing the connection polarity, can cause the bridge to burn out. Reversed polarity is also dangerous for other alternator parts, including the voltage regulator, which can also fail after a short circuit in the vehicle mains. Incorrectly mounted idlers and tensioners, as well as errors in belt installation, can lead to the pulley breakdown. Brushes fail because of normal wear and tear.

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