Battery Equivalents and Replacements

Do Motorcycles Have Alternators?

Alternators are electric generators that transform mechanical energy into electric energy in the form of alternate current, hence their name.

Alternators are commonly found in cars, where they are used for charging the onboard battery which is in turn used to start the engine and power other electric loads. But the question remains - do motorcycles have alternators?

Published: March 28, 2022.

alternator w400px

Car-Style Alternator vs Stator

A car-style alternator is an electromechanical device driven via a drive belt that may be used for powering other devices as well (water pump, AC unit, etc.).

Anyway, a car-style alternator is a clearly visible device and it can't be found on most motorcycles, raising the question if the motorcycles have alternators at all...

Well, something has to charge the motorcycle's battery, right?

Motorcycles feature very compact engines without much room left for a car-style alternator.

Thus, motorcycles have their alternators built in the engine itself in the form of a stator with coils and outgoing wires that transfer alternate current to the diode bridge (Graetz bridge) or some more complex battery charging controller.

alternator s stator

As the motorcycle engine spins, the magnets on the rotor (axle of the engine) generate electricity (alternate current) in the coils of the stator which is then transferred outside the engine via wires.

The diode bridge (Graetz bridge) rectifies AC current into the DC current which is filtered further with few capacitors in order to reduce radio interferences and to stabilize the voltage.

In the end, the motorcycle battery itself stabilizes the voltage to its final value.

Note: some motorcycles feature a diode bridge within the engine, but since it may be difficult to repair the diode bridge in such a location, many models have a diode bridge outside - this also helps with cooling. Of course, modern bikes feature much more complex charging controllers providing more stable output voltage.

motorcycle w400px

Long Story Short: Motorcycles rarely feature car-style alternators - instead, they come with stators that produce electricity as soon as the main engine is started, thanks to the magnets on the rotor (axle of the engine).

So, do motorcycles have alternators? Yes, they do, but rarely car-style alternators.