How A Car Alternator Works
If you know how a car alternator works it makes it all the easier to understand when/why it’s not doing its job. Understanding how an alternator works is half of the troubleshooting job.
List of parts making up a car’s alternator
- Stator
- Rotor Assembly(Made up of the following parts)
- Slip rings
- Rotor coil
- Bearings
- Brushes/brush holder
- Voltage Regulator
- Rectifier
- Fans(internal and external)
What each part does
Stator
The stator is a fixed set of coils that do not move. The coils in the stator collect and deliver the AC electrical current to the rectifier.
Rotor
The rotor rotates within the stator and generates a variable sized electrical/magnetic field with voltage/amperage provided by the voltage regulator
Slip Rings
One slip ring for each brush(2). Each slip ring is attached to one end of the coil in the center of the rotor. Allows the rotor to spin and yet keep constant electrical contact with the brushes and the voltage regulator.
Rotor Coil
The coil creates a variable sized electrical/magnetic field with voltage/amperage provided by the voltage regulator.
Bearings
The bearings support the rotor as it spins. The bearings are the only moving part and should be primary when there is noise coming from the alternator.
Brushes/Brush holder
The brush holder holds the brushes in place. One end of the brushes are connected to the voltage regulator. While the other end are being pushed against the slip ring by spring tension. The brushes connect the voltage regulator to the spinning slip rings.
Voltage regulator and slip rings
Voltage Regulator
The voltage regulator connects to the battery because it will need to draw power from the battery for the alternator. The voltage regulator has two functions. It monitors the state of charge(charged/charge needed) of the battery. The second function is to adjust the amount of voltage/amperage for the rotor coil based on the battery’s state of charge.
Rectifier
The rectifier connects to each of the coils in the stator. It turns AC current into DC current with the use of diodes and a capacitor. Thus electrical output of the rectifier connects to the car battery.
Fans(internal and external)
Fans remove heat from the alternator because the rectifier generates heat. The heat comes from converting AC current to DC current. The fans circulate air to keep the internal components cool which will reduce the chances of an early failure.
Electrical Magnetic Field At Work
Why an electrical magnet generates electricity
A Quick Test
If you want to test it without tools have your car running, pull the positive cable off the battery. Don’t let the cable touch anything. With the cable disconnected, this removes the battery from the electrical system. A working alternator will keep the car running. This because it is the only thing producing electricity. If your car dies your alternator is not working.
Related Article: Test Your Alternator Without Tools
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