Motorcycle Stator Introduction
This is the ultimate guide to the 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. And find out all that you need to know before making your next purchase.
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 the motorcycle stator down 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
Select a tab below to view detailed, technical data about motorcycle stator coil assemblies. If you think we’re missing something get in touch and we can publish it here for everyone to see.
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 crack shaft 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 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.
The number of AC outputs a stator has 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.
Different Stator Specifications
Although the overall build quality of motorcycle stator coils varies between manufacturers. When sourcing a new motorcycle stator, it’s important to consider evaluating the following before diving straight in.
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.
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. 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.
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:
- The space that’s available
- 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 this can make sourcing a replacement rather problematic.
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…
- Lightly bend down the latch on the terminal pin to remove it from its connector housing.
- Then, make sure that the latch is still in good condition, before finally clicking it into the location you need.
Negative and 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.
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.
Motorcycle Stator Diagrams & Schematics
Click on a pane below to find links to our motorcycle regulator rectifier mechanical and electrical diagrams.
Wiring a Stator in Star vs Delta
This is an advanced topic. And like most great questions, it comes down to maths. 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 multi-meter. 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.
Motorcycle Stator Compatibility
Here are a few things to extra points to consider regarding the cross compatibility of motorcycle stator coil assemblies.
Voltage and power
The rated voltage of a motorcycle stator must match system voltage of a motorcycle. This is because the stator must match the rate voltage of the regulator rectifier. Which in turn must match the rated voltage of the battery. Too much or too little voltage is never a good thing in such applications.
With regards to power output, our best advice is to research the power output of the regulator rectifier. Source a stator with a similar power output.
This is often completely bike dependant. But not necessarily model dependant. The key here is to do your research. Manufacturers workshop manuals are great for this kind of information. Check out our motorcycles data library where we tend to hoard such material.
Ohmic and inductance values
This is a bit heavy on engineering mathematics. In most cases it is nothing to worry about because motorcycle parts manufacturers have adopted standardised methods for manufacturing many components.
Complete bike manufacturers often use what is widely available. And so consequently many parts have become standardised.
More will be developed on this topic in due course.
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