Charging Circuit Components

The following is a basic guide to the components in a permanent-magnet charging system, which is the most common type of system found on a motorcycle today.  We’ll go through the main components, where they can be found, and what they do.

Stator: Stators come in all shapes & sizes, but what they essentially come down to are a precisely machined component of high-grade steel with an insulator on it; which copper wire is then wrapped around.  When the magnets in the flywheel spin around the stator, it will induce Alternating Current (AC).  This AC is then directed to a rectifier to be converted to Direct Current (DC) to charge a battery.


Three-phase stators or single phase stators are found on virtually all current street bikes.  Three-phase stators have three wires coming off them & single-phase stators have two wires.  The stator is located in the crankcase since the flywheel is attached at the end of the crankshaft.  The stator may be referred to by a number of other terms depending upon the applications, including generator, alternator, or magneto.

Flywheel: The flywheel is mounted on the end of the crankshaft and turns with the vehicle’s engine rotation.  Along the flywheel’s diameter are a series of magnets arranged in a specific pattern to correlate with the configuration of the stator windings.  The combination of the two are necessary for the process of inducing AC.  The flywheel is also frequently referred to as a rotor.10-002H.jpg

Rectifier/Regulator: As the name implies, these components perform two critical functions.  The rectifier portion consists of a series of diodes, which are basically one-way valves for electrical current.  These diodes thus convert the AC from the stator into DC by only allowing the passage of one side of the AC waveform.  The regulator portion then controls the current being allowed to pass through the battery in order to keep the battery from being either overcharged or undercharged.  This function is typically performed primarily by use of a semiconductor switch such as an SCR or MOSFET, or in come cases only a Zener diode.  Rectifier/Regulators can be found in a wide variety of places on your bike as different manufacturers mount them differently.  Many older vehicles utilize a separate rectifier and regulator.  However, the two components are merged into a single solid-state device on virtually all modern motorsport applications.

Battery:  The battery is where the charging current is going.  Although there are many styles of batteries, they are all designed to hold & store current for potential and future use.

For a visual description of these components, please check out our Youtube Video!