How the Alternator Works in Your Car

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Your car alternator, at its most basic, is what works along with your battery and the rest of your charging system to keep your car running. When you start your car, you’re running on battery power. Then the battery transfers power to the alternator to power the vehicle. The alternator is comprised of the following parts:

The alternator rotor

This is simply a coil of wire that is wrapped around an iron core. The wire delivers a magnetic field via DC (direct current) – in other words, a current that flows in only one direction. The current is delivered to the coil by means of slip rings and brushes, and the alternator pulley rotates when the engine runs.

The stator

There is another set of three coils around the rotor – together, they form the stator. The stator is attached to the alternator shell, and it does not rotate. The rotor turns inside the stator and creates an AC, or alternating current.

The output diodes

AC voltage is weak, so before it can be used, it has to be converted to DC. This happens in the output diodes. They convert the current so it moves in only one direction, and blocks the flow of the current in the opposite direction. Six output diodes form the bridge rectifier, which regulates the voltage output of the alternator. The DC current pulsates six times for each rotation of the rotor – it’s not a pure DC current, but for most automotive purposes, it’s good enough.

The diode trio

These three diodes provide the alternator regulator with field current.

The voltage regulator

The voltage regulator is the part of the alternator that senses any drop in the battery voltage, and delivers more field current to the rotor, increasing its voltage output. If the battery voltage goes up, then the voltage regulator sends less field current to the rotor, reducing the output.

The field current supply

Field current is supplied from the alternator by way of the diode trio, and from the battery by way of the alternator warning lamp. When you first start your car, voltage is supplied by the battery. Assuming that your charging system is working properly, the output shifts to the alternator.

The alternator or battery light

The alternator or battery light alerts you to problems with the alternator, or possibly with other parts of your car charging system. A mechanic can perform diagnostics that will identify the problem, which can then be corrected.


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Michael

15 years of experience
518 reviews
Michael
15 years of experience
Mercedes-Benz GL450 - Brake Pads Replacement (Rear) - Atlanta, Georgia
Micheal was punctual and friendly. Work was completed within promised time. Will definitely use again.
Volvo S80 - Brake Pads Replacement (Front) - Roswell, Georgia
Michael was SUPER QUICK with doing my brake and rotors. Great communication throughout the whole process. Will always recommend

Kenneth

19 years of experience
509 reviews
Kenneth
19 years of experience
Toyota Sequoia - Brake Pads Replacement (Front) - Newport Beach, California
Kenneth did a great job and very knowledgeable. He has a great attitude and I will for sure be using him again.

Chuy

13 years of experience
129 reviews
Chuy
13 years of experience
Honda Civic - Brake Pads Replacement (Front, Rear) - Cicero, Illinois
Excellent work on doing the breaks for my car and the break and steering system flush I’ll definitely recommend and take into consideration for chuy’s work whenever I need a fix on my car

Richard

16 years of experience
72 reviews
Richard
16 years of experience
BMW 328i - Brake Pads Replacement (Rear) - Dublin, California
Richard was an outstanding mechanic. After he arrived, the first thing he did after taking the initial pictures of the car is an assessment into what work was asked. He quickly verified that I did not need brake fluid and my front brakes even-though it affects his personal commitments and time, which I think is highly appreciate and thorough professional. He was detailed oriented - took time to make sure that all the issue are fixed. He paid attention to detail in overall car assessment- he goes above and beyond. He was also teaching me through the process which I found highly educational and appreciate him providing the information ensuring and making me comfortable what he was doing and explaining patiently all the questions that was thrown at him. When he works - you know he's highly skilled and experienced and knows his stuff. He is highly experienced. He is a "Master" mechanic in true sense :)

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