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.


Next Step

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Recent Alternator Repair reviews

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6,722
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Attila

19 years of experience
906 reviews
Attila
19 years of experience
Infiniti G37 V6-3.7L - Alternator - Basking Ridge, New Jersey
He was faced with a difficult situation due to unexpected rusted bolts, poor access, etc. but he got the job done on time and on budget.
Honda Accord - Alternator - Scotch Plains, New Jersey
Mr. Paniti was punctual and very professional. He kept me up to date on what was going on. He had to go pick up the right alternator, he called me and informed me of the situation. The car started and he made some recommendations. Great service Thanks

Collins

12 years of experience
488 reviews
Collins
12 years of experience
Acura RL V6-3.5L - Alternator Repair - Atlanta, Georgia
Collins is a true professional. Arrived on time and answered all of my questions. I would use him again.
Nissan Altima - Alternator - Atlanta, Georgia
Collins was incredibly kind, professional, and went above and beyond to get my car running. So thankful to God of all the mechanics that I was blessed with him. ❤️❤️❤️ Thank you 

Thomas

12 years of experience
96 reviews
Thomas
12 years of experience
Jeep Patriot L4-2.4L - Alternator Repair - Grand Prairie, Texas
First time using your mechanic app and Thomas was great! Attentive, kind, and professional. Made sure everything was good to go before leaving.
Honda Civic - Alternator - Fort Worth, Texas
Thomas was very knowledgeable in both mechanical and electrical issues with my car. He was great with explanation of the issue, as well as making the repairs to my car efficiently. I highly recommend him as a mobile mechanic to anyone I know!

Robert

20 years of experience
1089 reviews
Robert
20 years of experience
Mercedes-Benz C300 V6-3.0L - Alternator - Thornton, Colorado
Was on time and completed the job to my satisfaction. Will use again when any of my cars or trucks needs work done to them. Thank you.
Toyota FJ Cruiser - Alternator - Westminster, Colorado
Robert is a great mechanic, and I will definitely be looking to use him for further work. I used to troubleshoot and work on cars, but I lack the expertise to tackle modern electrical systems. Robert efficiently diagnosed the problem, and fixed the car within the estimated timeframe.

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