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What Does a Stator Do on a Motorcycle? (& How to Test One)

Working on motorcycle charging systems can be quite a challenge, especially if you don’t have much experience with electronics.

However, the majority of motorcycle charging system components (including the stator) are quite straightforward and appear to be more complex than they actually are. If you set aside a few minutes to get yourself familiar with all of the components of the charging system, then you’ll easily get the basics down rather quickly.

But if you’re wondering what does a stator do on a motorcycle, then this article is for you. We’ll briefly touch on the basics of how a stator works, why do they go bad, and how to test them.

What Does a Stator Do on a Motorcycle?

In short, the stator creates and outputs electrical current, which is used to charge the battery and power the motorcycle’s electrical systems.

Every motorcycle has an AC generator (also known as an alternator) that consists of two main parts: the stator and the rotor. As the name suggests, the stator is the stationary half of the motorcycle’s alternator, while the rotor is the rotating half.

The stator is made up of a series of coils (often referred to as “coil windings”), which are connected to the Regulator/Rectifier and the motorcycle’s battery. When the rotor spins around the stator, it induces an electrical current inside the copper windings of the stator.

This electrical current is then sent to the Regulator/Rectifier, where it is converted into DC current, stepped down to ~14 volts, and used to charge the motorcycle’s battery and power the bike’s electrical systems.

Why Do Motorcycle Stators Go Bad?

The motorcycle stator is extremely simple – it’s just a piece of iron with a bunch of copper windings around it. There’s really not much that could go wrong with it, right?

Well, kind of. While the stator itself will almost never go bad, other components of the motorcycle’s charging system can easily fry the stator windings.

1. Overloading

One of the most common reasons why stators go bad is because they’re overloaded. This usually happens when the motorcycle’s electrical system is trying to draw more current than the stator can provide.

For example, if you’re running a lot of aftermarket electrical accessories (like heated grips, heated vest, GPS, etc) at the same time, it’s quite easy to overload the stator. In other cases, a bad or partially shorted battery could also draw too much current from the stator.

Once the stator is overloaded, it starts to get really hot and eventually gets so hot that it melts the insulating coat, which then causes it to short out.

2. Damage From a Bad Rectifier

motorcycle rectifier

Another less common, but still quite important reason why stators go bad is because of a bad rectifier.

The rectifier is what converts the AC from the stator to DC. If it fails and starts dumping AC back to the stator, it will easily melt the stator windings.

Related: 6 Most Common Bad Stator Symptoms on an ATV

Will a Bad Stator Cause no Spark?

Yes, a bad stator can cause a no spark if the stator contains the exciter or the source coils used by the motorcycle’s ignition system.

If those coils are shorted to ground, then they won’t be able to send power to the CDI, and you won’t be able to start the engine.

How to Test a Motorcycle Stator

We’ll now go over a few different ways that you can test your motorcycle stator. These quick and easy tests will help you determine if the stator is going bad or if it has already failed.

Motorcycle Stator Short to Ground Test

To do this test, you’ll first need to locate the three yellow stator output wires. They will usually exit the generator and snake around the frame straight to the regulator/rectifier.

Once you’ve located the stator output wires, find the connector and disconnect it from the regulator/rectifier.

Next, use a multimeter to check for continuity between each of the three stator wires and the ground. If there’s enough room like in the picture above, try to back probe the wires. If there is continuity, then the stator is shorted to ground and needs to be replaced.

No Load Performance Test

This test is a bit more involved, but it will give you a good idea of the stator’s condition.

First, locate the stator output wires and disconnect them from the regulator/rectifier.

Now, start the engine and raise the RPMs to cruising speed (around half of the rev limit).

Next, set your multimeter to VAC (~V) and touch one probe to one of the stator output connector pins and the other probe to another pin. Make sure to test out all three combinations – a total of three measurements.

The stator output voltage should be above 70 VAC at cruising RPM. It may be different depending on your motorcycle’s make and model, so consult your service manual if possible. Also, the voltage should be roughly the same for all three terminals.

If the stator output voltage is below 70, then the stator is going bad and needs to be replaced.

Final Thoughts

A bad stator can cause all sorts of electrical problems on your motorcycle, from a no spark condition to charging system issues.

Fortunately, testing a motorcycle stator is relatively easy and can be done with just a multimeter.

If you think your stator might be going bad, make sure to test it as soon as possible. The sooner you catch the problem, the less likely it is to cause major damage to your motorcycle’s electrical system once it melts and shorts out.

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