How to Test the Stator on a Motorcycle, ATV or UTV
The electrical system on your motorcycle, ATV or UTV is made up of the battery, the regulator/rectifier and the stator.
If your electrical system is failing to charge, the problem lies in one of those three components. The only way to know for sure which electrical component needs replacing is to test all three. We'll walk you through testing the stator, and we recommend watching the video above and printing the walk-through below reference.
NOTE: You'll need a multimeter to test a stator. If you don't already own one, we suggest buying one not just for testing a stator, but because multimeters can also be used to run other tests on cars, motorcycles, ATVs, UTVs, and other machines in your home.
What is a Stator?
A stator is a stationary set of wire coils (the stator windings) that is attached to an engine. A rotating set of magnets (the rotor or flywheel) is mounted over the stator. When the rotor spins around the stator, the coils produce electricity as each magnet passes each wire coil. The stator/rotor assembly is collectively known as an alternator.
In simple terms, the stator generates the electricity that powers the battery in a motorcycle, ATV or side-by-side, and is therefore responsible for powering the vehicle itself.
Aside from wear over time, not much can go wrong with the rotor. However, the stator is much more prone to failure because it's made from thin strands of wire.
The stators found in motorcycles, ATVs and UTVs are generally 3-phase stators. These consist of three separate windings wrapped around a series of points that circle the unit, with the ends of the three windings leading to an electrical connector.
Testing a Stator
A stator test is either static or dynamic. The dynamic test is performed while the stator is on the machine and the engine is running. The static test is performed without the engine running, and the stator doesn't even need to be attached to the machine.
When you have a problem with the electrical system in which the engine on your motorcycle, ATV or UTV won't run, you'll have to do a static test.
Static Stator Test
The static stator test involves measuring from coil to coil — or phase to phase — within the stator, and also measuring from each coil/phase to ground. The exact range the stator should be within will vary from model to model, and manufacturer to manufacturer.
Step 1. Set the multimeter to ohms. With the multimeter's positive and negative leads apart, the display will show "OL" (open loop). This means the current circuit is open and isn't shorted or grounded. When the positive and negative leads are touched together, the display will read 0 or close to 0, because the loop is now closed.
Step 2. Measure between the coils/phases by connecting the multimeter's leads to the three terminals in the stator's electrical connector. Measure between phases 1 and 2; between 2 and 3; and between 1 and 3.
NOTE: For the following examples, click on each image to watch the corresponding video portion.
Example 1. In this example, a Honda stator with a range of 0.1 ohms to 1 ohm is being measured. Such a wide range is easily measured by most multimeters.
Example 2. In the next example, a Polaris stator with a range of 0.07 ohms to 0.13 ohms is being measured. This smaller range requires a multimeter going to at least 1/100 of an ohm.
Example 3. In the last example, a Yamaha stator with a range of 0.1 ohms to 0.132 ohms is being measured. This extremely small range requires special multimeters that aren't readily available at the hardware store. Therefore, it's not practical to perform a static test on such a close-ranged stator. Instead, you'll have to perform a dynamic test.
Step 3. Measure between each coil/phase and a ground source. Connect one of the multimeter's leads to a ground source, such as the body of the stator itself, and the other lead to each of the three terminals in the stator's electrical connector individually. The display should show OL, for an open loop that indicates the coil hasn't shorted or grounded.
If the stator fails any of the static tests, it will need to be replaced with an OEM stator for your motorcycle, ATV or side-by-side brand.
Dynamic Stator Test
The dynamic test measures AC voltage from coil to coil — or phase to phase — within the stator. Once again, the exact range the stator should be within will vary between stator models and manufacturers.
Step 1. Set the multimeter to AC volts.
Step 2. With the ignition off, measure between the coils/phases by connecting the multimeter's leads to the three terminals in the stator's electrical connector. Measure between phases 1 and 2; between 2 and 3; and between 1 and 3. There should be no reading between the terminals.
Step 3. With the ignition on and the engine running, measure between the coils/phases by connecting the multimeter's leads to the three terminals in the stator's electrical connector. Measure between phases 1 and 2; between 2 and 3; and between 1 and 3. There should be a positive reading between the terminals.
Step 4. With the ignition on and increasing the engine's RPM, measure between the coils/phases by connecting the multimeter's leads to the three terminals in the stator's electrical connector. Measure between phases 1 and 2; between 2 and 3; and between 1 and 3. The reading between the terminals should increase as the RPM increases.
If the voltage readings don't change from when the ignition was off to when the engine was running, the stator is faulty and will need to be replaced. Watch the video above to see the full process of how to do a dynamic stator test.