When talking about power sports engines, a stator is the part of the charging system which generates the power needed to run all the electronics of the machine. The charging systems perform much the same function that alternators would in your truck or car.
There are two fundamental types of charging systems – field excited and permanent magnet. By getting a better understanding of each, we can begin to grasp what exactly a stator is and how it works.
Permanent magnet systems
Permanent magnet is by far the most common type of stator, especially in newer vehicles. The stator looks a bit like a large gear with copper wire wrapped around the outside. In this type of stator, a cup shaped permanent magnet called the rotor or flywheel mounts to the crankshaft and spins around the stator. The rotating magnet charges the stator, and the AC volt output is sent to a part called the rectifier/regulator. The rec/reg is responsible for changing the current to usable DC volts and keeping the charge from going over a specific set point; usually 14.4-14.7 volts DC.
Permanent magnet systems (which mostly all modern sport bikes have moved to) is exactly what the name implies; a permanent magnet which rotates inside or outside of the stator. The amount of power that comes out is governed by the design of the stator/rotor and how fast it rotates. The strength level is FIXED, not variable like the field coil rotor.
Field Excited Stators
Field excited systems work in a similar way. The rotor in this system is an electromagnet instead of a permanent magnet. This means the magnet only becomes magnetized when in use. The “electro-magnet” is of a variable strength, allowing it to put out the amount of power the bike is using & enough to keep the battery charged. The rectifier/regulator provides the same function in this case, but it does so by changing the strength of the electromagnet.
In short, The stator is one half of what you can think of as the motorcycles “generator” which mostly amounts to long runs of copper wrapped around a steel core; all built to produce power for your machine.