How does an ATV charge its battery?

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You may have noticed that ATVs do not use alternators to charge its battery as a car do. And you know that keeping the battery topped off is essential for the bike to function properly.

Quite many 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 its battery. This is a fairly simple and robust system 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. What’s 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 your vehicle’s various systems are actually working.

This gives you a better understanding of its capabilities and limitations and makes 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) spinning at the same speed as the bike RPMs. The more throttle you give, the faster this shaft rotates.

The engine power is what powers the charging system. The charging system will “rob” your engine for about 0,5 hp on maximum output, which practically makes it a non-issue.

Three main components; the 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.

stator housing
The stator and flywheel are located inside the engine behind this cover.

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 bar works like a coil.

The number of bars varies from manufacturer to manufacturer and model to model, depending on the power output the bike requires. The shaft goes through this ring of coils, but the stator itself is not spinning.

One typical charging system style has the rotor mounted directly to the shaft, inside the stator. On the outside of the rotor, you’ll have several magnets.

Most common, however, 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 an alternating current.

However, this current is too unstable to be let directly into the bike’s 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 is achieved by sending the current through a 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 regulator on my Polaris.

The power that comes out of this box is ready to be used by the rest of the bike’s 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 bike’s electrical system. This may cause bulbs to go out, heated grips to die, and batteries to boil dry.

It’s important to measure your regulator’s output 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 bike’s electric components.

The charging system and the battery are designed to work hand in hand, and the power that’s left goes to charging the battery. When the ATV only needs a small current to power electric components, the battery gets a good charge.

Other times like when you use a winch, hand warmers, or other power-hungry accessories, 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 can create 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 cannot handle the wet and dirty conditions it likely will be exposed to when fitted to an ATV.

On the other hand, Stator systems are well protected inside the bike’s crankcase and do not require a constant airflow to keep them cool as they are designed to tolerate relatively 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 are also a deciding factor when the designers choose to use 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 have been and still are being fitted with an increasing number of power-hungry electric components. This puts ever-increasing stress on the bike’s charging system and 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 uses more electricity than the charging system can deliver, the power needs to come from the battery.

ATV batteries have low amp-hour capacities and are primarily meant to power the starter for just some seconds at a time.

Over time, overuse will drain the battery, resulting 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 in between each time you ride it.

Related: How to Charge Any ATV or UTV Battery; All You Must Know

I recommend getting a fully automatic battery tender that can be left connected without the risk of overcharging the battery.

The Ctek Multi XS 3600 is a cheap charger/tender that works well.

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 such 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 a 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 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 faster recharge and a slower discharge than the flooded acid-lead batteries. This is due to lower internal resistance.

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Haavard Krislok
Haavard Krislok
I'm an ATV and offroad-enthusiast, an engineer, a farmer, and an avid home-mechanic. I'm also the owner and editor of If you have any questions or suggestions regarding this article, please feel free to contact me.

Welcome to BoostATV

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