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Motorcycle Stator Coils

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Motorcycle Stator Introduction

This is the ultimate guide to motorcycle stator coils.

We’ve included a whole host of learning material and educational data, to help get to grips with these apparently simple devices.

Thinking of sourcing a new stator?

Start with the basics. Skip out the waffle.

Find out all that you need to know before making your next purchase.

motorcycle stator
A photograph of a motorcycle stator

Converting mechanical power from the engine into electrical energy…

Explanations everyone can understand. Layered into what you need to know. Before building on complexity until you’ve had enough and beyond.

We’ve even stripped down the motorcycle stator to its basic engineering principles.

Wrapping up each principle into an everyday system that does exactly what a motorcycle stator needs to do…

“Converting mechanical power from the engine into electrical energy in the form of AC (alternating current).”

Motorcycle Stator Technical Data

Browse below to find detailed, technical data about motorcycle stators. If you think we’re missing something get in touch and we can publish it here for everyone to see.

The Basics

What is a Motorcycle Stator?

A motorcycle stator is a series of coiled wires. Forming the stationary part of the motorcycle alternator.

A complete alternator converts the rotational energy of the engine into electrical energy.

How Does a Stator Work?

Attached to the crankshaft of a motorcycle is the flywheel. This is used as the rotating part of the motorcycle alternator, called to rotor.

Shaped a little like a cake tin; the flywheel fits over the stator coils. Covering them up but leaving just enough room to rotate freely.

The flywheel has powerful magnets built into its sides.

As this magnetized flywheel rotates, it induces a current flow in the stator coils. This current is then fed to the regulator rectifier. Which in turn provides power to the battery.

How Do You Wire Up a Replacement Stator?

Motorcycle stator coils are now sold as bolt on, plug in and go devices. This is a list of common wires that may need be connected:

  • Yellow, White, Pink or Brown = AC Outputs
    • to supply the regulator rectifier
  • Green = Ground
    • reference voltage. Such as a common ground connection (usually the engine casing)
  • Blue or Blue/White = Ignition timing trigger
    • timing trigger for the ignition circuit, usually connected to a CDI unit
  • Red or Black/Red = Ignition AC supply
    • a separate AC supply for an ignition circuit. Also, usually connected to a CDI unit

Of course, not all manufacturers use these same wire colours. Especially in their wiring looms. It is highly advisable to cross reference your bikes wiring manual.

Alternatively, talk to your local auto-electrician before starting. However, the majority of aftermarket wired stators have adopted these same wire colours.

The Right Regulator Rectifier…

The number of AC outputs a stator is important. As this determines the number of AC phases it generates (a phase being a source of AC power). And therefore, the type of regulator rectifiers that will be compatible.


Although the principle operation of motorcycle stators are the same, there are many different specifications, formats and designs.

As always, the overall build quality of motorcycle stators varies between manufacturers.

Therefore, when sourcing a new stator, it’s important to consider evaluating the following before diving straight in:

  1. Output voltage
  2. Power output
  3. AC phase count
  4. Ignition supply and timing phase
  5. Mechanical dimensions
  6. Connectors
  7. Negative and positive earth wiring

Continue to read the sections below to gain a more detailed understanding…

Output Voltage

Stators with a different voltage rating are not cross compatible.

12-volt rated stators must only be used with 12V systems.

And therefore, 6-volt units must only be used in 6-volt systems.

Power Output

It’s important to match the power rating of a stator to that of the regulator rectifier.

Too little power and the stator won’t provide enough power for the regulator rectifier to perform efficiently.

If the stator generates too much power the voltage regulator inside the regulator rectifier will overheat and fail.

The same thing will occur by sending too much power to a condensing system. Ultimately any excess power must go somewhere.

Therefore, matching the stator and regulator rectifier specifications is essential.

AC Phase Count

Most motorcycle charging systems are either a 2 phase or 3 phases.

For practical purposes, this means that the stator and regulator rectifier have either 2 or 3 AC inputs wires to connect.

It is essential to use all the AC outputs from the stator coils.

It’s also important to match this to the motorcycles engine specifications to ensure smooth running and prevent engine damage.

To keep it simple, the number of AC output wires on the stator must match the number of AC input wires on the regulator rectifier.

Ignition Supply & Timing Pulse

Depending on the type of ignition system used on the bike. It is likely that a CDI supply coil and hall sensor will be required as part of the stator assembly. And the location of these is critical.

Use the bikes workshop manual to maintain that the accuracy of ignition timing and circuit charging.

Mechanical Dimensions

Getting the dimensions right when buying a new stator will save you whole lot of headache when it comes to installation.

Consider these two things:

  1. The space that is available
  2. The specific design of the original

It’s also wise to check the length of cable that’s available on your loom. Just to make sure that it will reach.


Unless you plan on crafting your own electrical connections – connectors can make sourcing a replacement stator rather problematic.

Connector Care Top Tips

Most motorcycle connectors have replaceable terminal pins. This means that the pins can be relocated in the connector housing.

So, there’s no need to worry don’t worry about wire positioning in connectors. This can be remedied easily with a sewing needle at home…

  1. Lightly bend down the latch on the terminal pin to remove it from its connector housing.
  2. Then, make sure that the latch is still in good condition, before finally clicking it into the location you need.

Negative & Positive Earth Wiring

For most motorcycles this section can be overlooked.

The bulk of motorcycles on the market are negative earth.

And motorcycle stator manufacturers have accommodated this trend nicely.

Positive Earth Wiring

For those classic renovators among us that love positive earth set ups…

You can use just about any stator coil assembly that meets your needs. Providing that the coils come with a separate earth wire.

However, always check that this wire is the central tap of the star wound coils, and that is it isolated from external metal casings and fittings.

Wiring in Star vs. Delta

This is an advanced topic. And like most great questions, it comes down to maths…

In order to keep it simple; star connected coils generate a high voltage at lower current. Whereas, Delta connected coils generate lower voltages at higher current.

Motorcycles stators are wound in star. The key benefit of star connected coils is the lower current. The creates less heat loss.

Consequently, the size of any wires and cables can be reduced. Ultimately, saving cost of manufacture.

Motorcycle Stator Coil Testing

Fault finding on set of motorcycle stator coils can be straight forward, providing you have the right equipment.

Testing for short or open circuit coils

With a basic household digital multimeter. Carry out a resistance test between each coil.

If each doesn’t have a equal resistance, then there is likely to be a short between the tested coils. In this case the stator will need replacing. Unless of course the stator manufacturers specifications state otherwise.

A multi-meter can also be used to test each of the coils to ground to make sure that they have the same resistance. This is because motorcycle stator coils are wound in star with a ground as the common connection.

Enamel insulation testing

Using a proper insulation resistance tester, one can also test the resistance of the enamel insulation. This is the insulation material used on the copper wires of each coil winding.

This will provide an insight into the electrical wear at tear of the stator coils themselves.

Be cautious though. Applying high voltages during this test can itself cause damage to the enamel insulation. Therefore breaking your stator.

FREE Stator Wiring Diagrams

Huge buttons to navigate to Lamberts Bikes motorcycle stator wiring diagrams. Download them direct to your device or view them online!

6V-12V Stator Conversion Wiring Diagram Links

6 Volt to 12 Volt Stator Conversion Wiring Diagram

Learn more…

To learn even more about your motorbikes power circuit, view “how do regulator rectifiers work?

Don’t miss our motorcycle parts knowledge database!

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