You may have noticed that ATVs do not use alternators to charge its battery like a car do. And you know that keeping the battery topped off is essential for the bike to function properly.
Quite a lot of its functions like the starter, cooling fans, lights, winch, power steering, heated grips, GPS and other accessories require electricity to work.
So how then is it being charged? What is generating its juice?
An ATV uses what is called a stator system or magneto system to charge it’s battery. This is a fairly simple and robust system that’s located on the inside of the ATV’s engine. Any time the engine is running, the stator is continuously generating an electric charge. Some of the electricity is used to power the bikes different electrical components. Whats left is being used to charge the battery.
How does a stator charging system actually work?
If you’re anything like me, you want to know how different systems on your vehicle is actually working.
This gives you a better understanding of its capabilities and limitations, as well as making troubleshooting a bit easier when things do not work as it’s supposed to.
A stator system can be designed in several ways, but they all share the same working principles.
Inside the engine crankcase, you have a shaft (the crankshaft) that is spinning at the same speed as the bikes RPM’s. The more throttle you give the faster this shaft spins.
The engine power is what powers the charging system. On maximum output, the charging system will “rob” your engine for about 0,5 hp, which practically makes it a non-issue.
Stator, rotor and regulator rectifier
The charging system is connected directly to this shaft and basically consists of three different components. This is a rotor or flywheel, a stator, and a regulator rectifier.
The stator looks like a drum or a ring that’s made up of multiple laminated non-conductive bars, wrapped in thin copper wire. Each individual bar works like a coil.
The number of bars varies from manufacturer to manufacturer, and from model to model, depending on what power output the bike requires.
The shaft goes through this ring of coils, but the stator itself is not spinning. One common style of charging system has the rotor mounted directly to the shaft, inside of the stator. On the outside of the rotor, you’ll have several magnets.
Most common on ATV is another variation of the system where the magnets are connected inside a flywheel that spins on the outside of the stator.
Both systems basically work the same way: When the magnets on the rotor or the flywheel spin past the coils on the stator, the magnet will induce a current in the coils. With each revolution, this current reverses itself, and you get alternating current.
This current, however, is too unstable to be let directly into the bikes electrical system as the voltage varies in-line with the engine speed, and at full speed is way too high.
The current also needs to be converted from alternating current (AC) to direct current (DC) before it can be used to charge the ATV battery.
This process is done by the regulator rectifier.
This is usually a small black or metal box with heat fins on the outside to better dispose of the heat created by the semiconductors inside.
The power that comes out of this box is ready to be used by the rest of the bikes electrical system.
A common fault on ATVs is when the regulator-part of this box fails, and you’ll get too high voltage pumped out into the bikes electric system. This may cause bulbs to go out, heated grips to fail and batteries to boil dry.
It’s important to measure the output from your regulator as soon as you suspect it has gone bad.
Is all the power being used to charge the battery?
No, it’s not. A big chunk of the power the charging system generates is being used right away to power the electric components of the bike.
The charging system and the battery are designed to work hand in hand, and the power that’s left goes to charging the battery. Sometimes you use small amounts of power, and the battery gets a good charge.
Other times like when you use a winch, you actually use more power than the charging system can deliver, and power is taken from the battery.
Why do ATVs use stator systems and not alternators?
Belt driven automotive style alternators are capable of creating a substantially higher power output than the magneto style systems used on ATVs. Why do the manufacturers choose an inferior system to be used on our bikes?
Well, it all boils down to technical challenges. An alternator needs a lot of air blown by it to keep it cool. But it has to be relatively dry and clean air. The alternator simply cannot handle the wet and dirty conditions it likely will be exposed to when fitted to an ATV.
Stator systems, on the other hand, are well protected inside the bikes crankcase and do not require a constant airflow to keep them cool as they are designed to tolerate quite high temperatures.
Different combinations of engine coolant, engine oil, and internal fans are used to keep the stator system operating within its rated temperature range.
Space limitations is also a deciding factor when the designers choose to us stator systems over alternators as the latter typically require a lot more room.
This is no problem in the relatively spacious engine compartment of a car, but on ATV’s the design needs to be compact which can more easily be achieved with a stator system.
But over the years, ATVs has been and still is being fitted with an increasing number of power-hungry electric components. This puts an ever-increasing stress on the bikes charging system an battery.
To keep up the engineers have been busy making improvements to stator type charging systems. The systems have evolved tremendously and the average power output has increased by as much as 3-4 times from the 1990s up to today.
And for the most part, they still manage to keep up with the demand.
Changes that have been made are the use of a better type of magnets, amping up the number of coils and magnets by increasing the diameter of the flywheel and moving from a 1 phase to a 3 phase power output system.
Only the future can tell us if ATV’s will still be using stator systems for the years to come, or if the ever-increasing demand for electric power at some point will force the engineers to start looking for alternatives like the alternator or others.
What happens when the charging system cannot keep up with the power draw?
When the bike use more electricity than the charging system can deliver, this power needs to be taken from the battery.
ATV batteries have low amp-hour capacities and are primarily meant to power the starter for just some seconds at the time.
Over time, overuse will drain the battery, which can result in you not being able to start the bike. And even worse, it can permanently damage the battery.
This can happen when you only use the bike for short periods of time each time you ride. The starter will drain quite a bit of power from the battery, and the charging system will need some time to charge it back to where it was.
Also if you do a lot of winching, for example when plowing, you may find you use more power than the system can deliver. Riding in low gear range may solve this as the higher REVs will give more power from the charging systems.
But sometimes this is not enough. Then your best option will be to hook up a charger to top off the battery between each time you ride it.
I recommend getting a fully automatic battery tender that can be left connected without the risk of overcharging the battery.
Does it matter what battery you use?
ATV’s generally use one of two types of batteries. These are flooded acid-lead batteries (flooded batteries), and Absorbed Glass Mat batteries (AGM).
The acid batteries are the cheapest, but cannot handle as bad of a beating that gel batteries can. They are prone to spillage which is not ideal for motorsport or off-road applications. Maintaining them can also be quite the hassle.
The AGM batteries are filled with gel and are practically maintenance free. There is no risk of spillage, and they usually will last a lot longer. They do cost a bit more to purchase, but the added cost will more than likely pay off in no time for the average ATV owner.
In my opinion, they are the perfect match for ATV’s.
As for charging, the AGM batteries allow for a faster recharge and a slower discharge than the flooded acid-lead batteries. This is due to lower internal resistance.