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All motorcycles need a source of electricity. Even simple single cylinder kick-start dirt bikes require current to supply the ignition system with the power needed to create a spark. Larger and more power-hungry motorcycles with a radio, heated grips
and accessories such as GPS and auxiliary lights will require a lot more juice.
Whether you’re a motorcycle enthusiast or an aspiring technician, it’s important to know about the different types of power sources for motorcycles. Keep reading to learn about motorcycle
alternators, stators and the differences between these two devices.
The term “alternator” is commonly associated with the power-supply device commonly seen on cars and trucks. It turns motion into current. It is an all-in-one style unit that supplies the needed power to the vehicle.
Image credit Krishna Auto Electric
While the term alternator is commonly associated with automotive style units, the official definition is: a device that creates Alternating Current (AC) power from mechanical motion.
A “stator” is one component of the system that generates power for a motorcycle. Motorcycles generate power like a car, however they do it in a slightly different fashion. Rather than being an externally mounted unit, a stator
is positioned inside the engine and looks like this:
Image credit DB Electrical
As you can see in the picture above, a wire will travel through the engine case to an external rectifier/regular, which converts alternating current into direct current.
The rectifier/regulator is also responsible for maintaining the proper current as to avoid overcharging the battery and other dangerous issues. As engine speed increases, the stator will put out more and more power, and if left unregulated, can cause
A motorcycle alternator is a device that takes the existing mechanical motion of an engine and creates electrical current. To generate electricity, three things are required: motion, a magnet, and a coil of wire. The motion comes from the rotational nature
of an engine, and the magnet and coil of wire are added to complete the requirements for generating power.
Additionally, motorcycles need DC, or direct current, to power the electrical systems. Motorcycle alternators produce AC, or alternating current, requiring the rectifier/regulator to complete the system.
The simple answer to this question is yes—however very few automotive style external all-in-one alternators exist on motorcycles. Rather, a stator and rectifier/regulator handles the power generation task.
Simply put, a stator works together with a rectifier regulator to accomplish the same outcome as an alternator—to generate the DC power required to operate the motorcycle, ATV, side-by-side, etc.
The stator is the coil of wire housed inside the engine case. A magnet on a shaft spins within the stator, creating alternating current (AC). That current travels along fairly heavy gauge wire through the case and into the rectifier/regulator which converts
it to DC power, and at a consistent output.
When trying to understand the difference between a stator and an alternator, we first need to identify what specifically we are comparing.
A motorcycle stator is a component of the electrical system that, when combined with a rotating magnet, creates AC current. Stators are inside the engine case.
An automotive style alternator is a fully self-contained, externally mounted unit that creates DC current. Another difference between stators and automotive style alternators is the type of magnet uses. Stators use a permanent magnet, and automotive alternators
use an electro-magnet.
As stated above, a stator is one component of the motorcycle charging systems. Motorcycle alternator refers to a collection of components that includes the stator, but also includes magnets and a rectifier/regulator (devices that convert AC current to
DC current and maintain steady output).
If a dead motorcycle battery causes a starting issue, we often assume the battery is faulty. Typically, this is correct, as motorcycle batteries fail more frequently than stators fail. However, before assuming the battery is at fault and installing a
brand new one, an experienced technician will rule out the charging as the cause of the problem.
If the motorcycle charging system is not properly charging the battery, simply replacing it will not solve the issue. Additionally, a discharged battery will need to be brought up to full charge prior to static or load testing it.
A technician uses a multimeter to test a stator, either with or without a running engine. With the engine off, a technician can test for a broken winding wire. With the engine running, a technician can test voltage going into the battery. Using a series
of tests and chronological steps, a technician can rule out faults in the charging system, determining if the battery is ultimately the cause of the no-start scenario.
Motorcycle and powersports technicians regularly work with and test electrical system components. Understanding how the components interact with one another is critical for effective diagnosis and
repair. Technicians won’t often see automotive style alternators on motorcycles, however understanding how they work is valuable information to have.
Stators, on the other hand, are a component that will require testing and a thorough understanding of how they work. As with any system on a vehicle, once we peel back the mystery and understand how they should work, and how they typically fail, a technician
will be more comfortable and confident with diagnosing, servicing, and replacing components.
Wondering what types of jobs motorcycle technicians can pursue? Check out our career guide.
Ever wonder what the differences between 2 stroke vs. 4 stroke outboard motors are? Find out here.
Learn the history about where Café Racers came from and the class we offer about these and other iconic vintage bikes.
Lance Smeal is a graduate of the Motorcycle Mechanics Institute. He's also an entrepreneur and the owner of L-N-C Cycle Repair in Cottonwood, Arizona. This is his story.
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