Recently a friend was arguing with me how motorcycles have stators and not alternators (sigh!).
I wanted to bash the head (not sure mine or his).
But I understand this is a widespread confusion. That prompted me to write this article.
So, do motorcycles have alternators?
Yes. Motorcycles have alternators. Motorcycle alternators are commonly referred to as stators, even though a stator is just one alternator component.
Compared to conventional alternators, motorcycle alternators are far different and simpler in setup – containing a stator, rotating magnets, and a regulator-rectifier.
A motorcycle alternator’s working principle, functions, how different they are from a conventional alternator are all detailed below.
Does a motorcycle contain an alternator?
Of course yes.
Motorcycles contain alternators in them.
The alternator in a motorcycle converts the mechanical energy derived from the crankshaft through the engine into electrical energy in the form of alternating current.
But there is a teeny tiny difference.
The motorcycle alternator is very different from a conventional alternator. Simpler as well.
But the working principle and the functions remain the same.
Motorcycle Alternator Parts
Here’s what a motorcycle alternator consists of:
- A stator
- Rotating magnets
- A regulator-rectifier
The stator is nothing but a stationary coil of wires.
And as the name suggests, is the stationary part of the alternator.
The stator has copper windings (coils) on it. The number of coils on a stator can range from 6 to 18 depending on the make.
Next. The rotor.
The engine flywheel has permanent magnets attached to it, which revolve around the stator. Thus making the flywheel the rotor in this setup.
The rotating part is the rotor. The stationary part is the stator. As simple as that.
As the magnets rotate along with the engine flywheel, it creates a rotating magnetic flux, which generates alternating current (AC) within the stator coils.
That’s the short version of how a motorcycle alternator works. The long version is boring and headache-inducing. So I am skipping that part. You can wikipedia-it.
The current output from the stator coils has different purposes.
These include – battery charging, ignition, lights, etc.
One more thing. I swear this is the last.
The current generated must pass through the regulator-rectifier, which is another alternator component (you can say they are not, but either way the regulator-rectifier has a significant purpose).
A regulator-rectifier converts the alternating current (AC) from the stator to a direct current (DC). In addition, the regulator moderates the current voltage as well.
So although the alternator produced AC, the motorcycle wants it in DC, and the regulator-rectifier bridges that gap.
‘Motorcycle stator’ is the more common term used
Even though the motorcycle alternator consists of both the stator and the rotor, the alternator in motorcycles is commonly called the stator.
In a way, it does make sense.
The engine flywheel exists for other purposes. Only the magnets attached to the wheel are specifically for the alternator. So, the rotor is not specifically made for an alternator here. It already exists for other purposes.
Only the stator is an exclusive component dedicated to generating current.
As a result, people use stator and alternator interchangeably when it comes to motorcycles.
Whether you agree with the terminology or not (heck I don’t), the stator is the commonly used term to refer to a motorcycle alternator.
Functions of a motorcycle alternator
The motorcycle alternator has 3 main functions:
- Battery charging
- Powering the lights
Let’s dive deep into each of these functions.
One of the windings on the stator is called an exciter coil. The exciter coil has far denser windings than the other coils on the stator.
So that the exciter coil can produce higher voltage electricity. This high voltage is for the ignition.
Of course, the current doesn’t flow directly from the stator’s excitor coil to the spark plug for ignition.
The higher voltage electricity is first supplied to the Capacitor Discharge Ignition (CDI) unit. The CDI unit stores the electric charge and dumps the same when required.
The CDI unit is also connected to the pickup coil, which tells the CDI when to dump the charge for ignition.
How does the pickup coil tell?
Short answer. There is a small magnet on the flywheel. As the flywheel rotates, the pickup coil receives signals from the magnet and uses it to signal CDI.
As the CDI unit dumps the charge, the current flows through the ignition coil.
The ignition coil acts as a step-up transformer and increases the voltage as high as 200x.
The resulting high-voltage electricity is used to fire the spark plug and ignite the engine.
#2. Battery charging
The alternator also charges the motorcycle battery.
The electric charge produced in the stator windings is passed through the regulator-rectifier first.
The rectifier converts the AC into DC. The regulator modulates the voltage.
The resultant direct current (DC) is then passed onto the battery, wherein the battery stores the charge.
And that’s how the battery gets charged in the motorcycle itself.
#3. Powering the lights
The electric charge produced in the alternator is also used to power up lights and other electronic accessories in the motorcycle.
Of course, the battery performs the same function too.
Typically, the alternator powers up the lights and electronic accessories. And if the alternator is not producing enough charge, then the battery takes over and fills up the deficit.
So, both the alternator and the battery power up the electronic accessories in the motorcycle.
Motorcycle alternators are different from car alternators
Although the working principle remains the same, car alternators and motorcycle alternators are quite different.
Car alternators look more like the conventional alternators we are familiar with. Car alternators are also quite complex and bulky. Whereas the motorcycle alternator is quite simple in design.
To keep things simple, here are the two main differences:
First, the car alternator is an assembly of different parts encased in a housing.
They are like external all-in-one alternators. Containing lots of components as opposed to the motorcycle alternator which consists of fewer parts.
As a result, car alternators are bulky and take up a dedicated space in the vehicle.
Motorcycle alternators while do take up space are compact and are simply attached to the flywheel.
Second, motorcycle alternators use permanent magnets in the rotor to generate magnetic flux. But, car alternators use electromagnetic flux.
The car alternators have coils on the rotor as well. The rotor coil receives current from the battery and creates an electromagnetic field.
These differences are one of the reasons why motorcycle alternators are more commonly called stators. The ‘conventional’ alternator term suits more to the car alternators.
Difference Between Alternator and Stator
As discussed already (like a thousand times), the stator is an alternator component.
The stator, along with the rotating magnetic flux and regulator completes the alternator formation.
But a motorcycle alternator is not an all-in-one kind of alternator with all the parts packaged to provide a single component. Rather, it’s a setup with fewer independent parts.
You have a stator as the main component. The rotating magnets on the flywheel act as a rotor. You have a regulator-rectifier to complete the set.
That’s why, a motorcycle alternator is often simply referred to as the stator. Even though the stator is just another part technically.
Bottomline. The stator is one alternator component. But is often used interchangeably for motorcycles.
Difference between Alternator and Starter Motor
A starter motor is used to start the engine.
It provides the initial spin to get the engine running. The initial spin is triggered by the electric self-starter button.
Once the engine starts with the help of the starter motor, there is no need for the starter motor. The starter motor will stop working through a gear disengagement mechanism of the starter gear.
The alternator, on the other hand, starts working only after the engine starts.
The main function of the alternator is to generate electric current which will be used along with the battery to power up electrical accessories in the motorcycle.
Both these are completely different parts serving different functions.
Once the engine starts, the starter motor will stop working. The alternator starts working only after the engine starts.
Before you go…
Here are a few more related posts on motorcycle charging systems: