Skip the auto shop - Our mechanics make house calls
  1. Home
  2. Articles
  3. How the Alternator Works in Your Car

How the Alternator Works in Your Car

alternator

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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

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

More related articles

P0121 OBD-II Trouble Code: TPS "A" Circuit Range Performance Problem
P0121 code definition Throttle Pedal Position Sensor/Switch (TPS) A Circuit Range Performance Problem...
P0222 OBD-II Trouble Code: Throttle/Pedal Position Switch/Sensor B Circuit Low Input
P0222 code definition Throttle/Pedal Position Switch/Sensor B Circuit Low Input What the P0222...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...

Related questions

Q: How to tell the ignition coil is bad or good? Lexus

Hi there - basic testing of ignition coils can be done with a volt meter, checking for shorts or a specified level of resistance (measured in ohms) in the coil windings. Failing coils require an oscilloscope (or similar testing tool)...

Q: When my car starts I see my headlights and indash lights go dim.

A starter motor uses a lot of current and thus will cause a voltage drop at the battery. During the brief interval that a starter engages and runs, any other circuits that are also "on" could see the voltage drop...

Q: Q: Possible dead battery

Hello. The battery light turning on when the engine is running indicates that system voltage is low. Everything required to run the engine, and everything in the car, will drain the battery. Most likely, it is the alternator, but the...