How the Alternator Works in Your Car | YourMechanic Advice

How the Alternator Works in Your Car

Schedule Brake Pad Replacement
Service Area

$125.62 - $449.32

Price range for all vehicles
Average rating from 12,277 customers who received a Brake Pads Replacement.

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.


Next Step

Schedule Brake Pad Replacement

The most popular service booked by readers of this article is Brake Pad Replacement. Yourmechanic’s technicians bring the dealership to you by performing this job at your home or office 7 days a week between 7AM-9PM. We currently cover over 10k cities and have 100k+ 5-star reviews... LEARN MORE

SEE PRICING & SCHEDULING

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Recent Brake Pad Replacement reviews

Excellent Rating


YourMechanic Brake Pad Replacement Service

Average Rating

4.9/5

Number of Reviews

12,277

Rating Summary
11,730
348
73
35
91
11,730
348
73
35
91

Chris

21 years of experience
1861 reviews
Chris
21 years of experience
Mini Cooper Clubman - Brake Pads Replacement (Rear) - Silverado, California
He arrived early, went straight to work, and it should have been quoted higher as it’s a Mini which takes longer than the average break job. He didn’t try to get more than the quoted amount. He even set out to replace a running light for me when he was finished. I thought there would hard sales telling me I needed more work but there wasn’t. Because he didn’t try to sell me more work, I will use him again. When I hired a mechanic I don’t want a salesman. 
Land Rover Range Rover Sport - Brake Pads Replacement (Front) - Irvine, California
Chris again has provided great Service. Everything was great. I was very happy with the work and will definitely have him return for any other work.

Bryant

11 years of experience
408 reviews
Bryant
11 years of experience
Ford Fusion - Brake Pads Replacement (Front, Rear) - Indianapolis, Indiana
Bryant has done great work on my car before, the latest work is no exception. He's very flexible, and goes the extra mile to get you back on the road.
Scion iA - Brake Pads Replacement (Front) - Carmel, Indiana
This is my first time using this service. I am very happy with it. Bryant was very knowledgeable and did quality work. I will use this service more regularly.

Edmar

21 years of experience
184 reviews
Edmar
21 years of experience
Chrysler 200 - Brake Pads Replacement (Rear) - Euless, Texas
Edmar always does a very good job. He's done a few different things on my car the last two years. Each job was performed very fast and top quality. Thank you once again.

Mazyar

7 years of experience
255 reviews
Mazyar
7 years of experience
Jaguar XF - Brake Pads Replacement (Rear) - Lawrenceville, Georgia
He was early, courtesy and actually helped me save some money since i didn't need all the work that i thought i needed done. Honest guy. Very knowledgeable. Great attitude.

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE