How the Alternator Works in Your Car

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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Recent Alternator Repair reviews

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5,852
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Alexander

6 years of experience
126 reviews
Alexander
6 years of experience
Toyota Camry - Alternator - Columbus, Ohio
First time using this service for an alternator replacement. Very convenient and quick service repair. The only issue (nothing to do with the mechanic I had) is it takes too long to get an appointment and after the alternator repair, I cannot book future appointments because it states no mechanics available in my zip code? Seems like this will be a one and done for me and mobile repair. Disappointing.
Honda CR-V - Alternator - Columbus, Ohio
A fantastic experience. Alex was great very nice and personal. He did a great job and I highly recommend him.

Gustavo

15 years of experience
5 reviews
Gustavo
15 years of experience
Nissan Pathfinder - Alternator - Glen Ridge, New Jersey
Very helpful mechanic, definitely would recommend. Took the time to diagnose issue and show me the result.
Toyota Corolla - Alternator - Jersey City, New Jersey
Gustavo was prepaired, on time and professional. His understanding of the job is comforting. Many thanks....

William

34 years of experience
338 reviews
William
34 years of experience
Honda Pilot - Alternator - Surprise, Arizona
William was highly experienced with Hondas and finished in less than 3 hrs. We’re very appreciative that someone with his experience was sent.
Honda CR-V - Alternator - Glendale, Arizona
William did a great job with replacing the needed parts and was very consise and professional. Would definitely recommend him for any Honda service you may need

Dustin

7 years of experience
35 reviews
Dustin
7 years of experience
Dodge Journey - Alternator - Wilsonville, Oregon
This was my first experience with a mechanic and Dustin was absolutely amazing. He was kind and communicated what was needed and explained everything to me in a way I could understand. I greatly appreciate his time and the value of the service provided.

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