Do Outboard Motors Have Alternators?

Do Outboard Motors Have Alternators?

Note: As an amazon associate I may earn a small commission from qualifying purchases if you click to amazon from my site and choose to make a purchase.You can read my complete affiliate disclosure for more details

Do Outboard Motors Have Alternators?

Outboard motor alternators are a device that helps to convert mechanical energy into electrical energy.

You can use them in many outboard motors, including trolling motors, the most common type of alternator found on modern engines.

Yes! Almost all electric starter outboards have an alternator to recharge the battery.They have fixed-speed electric motors, which spin the propeller shaft simultaneously.The alternator is slightly larger than an outboard motor and fits on top of it like the cap on a soda bottle.

Because it does not need to change gears, the motor contains an alternator.

You use it to recharge its battery while running, so they don’t need another battery as some internal-combustion outboards do.

The motor, by necessity, doesn’t generate torque directly. Instead, you use it to get the propeller spinning at a constant speed. Three things happen to accomplish this:

The alternator generates electricity and charges the battery. The motor spins its propeller shaft at the same speed as the water flows through it.

The water pressure inside the motor drives its gears and shaft in a circular motion (around its hub), which turns the propeller.

The alternator spins in a clockwise direction, so the motor turns counterclockwise. The propeller shaft is at the bottom of the alternator, but it looks like it is at the top because it’s at a higher point on the water.

How Do I Know If My Outboard Has an Alternator?

Check Its VoltageIf it stays at 13.7 volts instead of fluctuating like the other batteries on your boat, it’s most likely an alternator. 
 It could be one if you can hear a humming noise or see a fan inside the battery compartment. 
Check Your Amp HoursAlternators also have significantly more Amp hours than traditional batteries and are typically rated in 20-hour increments (i.e., 55 Ah = 55 Amp hours). 
Check Your Voltage At RestIf your voltage is higher than your Engine is operating (10-12 volts), it could be the alternator. 
Check The Back Of The BatteryIt could be one if you attach a device or component to it. 
 Check The Engine CompartmentIf it has an additional wiring harness connecting to a battery within that compartment, you probably have an alternator on board. 
Check The Boat’s ManualSometimes, not all alternators are designed the same. If your boat has a maintenance manual, see what it says about this. 
Dump BatteryIf your battery is built so that you can easily reach your alternator with a long extension cord and disconnect it from the Engine, that’s usually an indication you have one. 

How Does an Outboard Motor Alternator Work?

During normal operation, the alternator generates electricity by spinning its rotor inside of its stator (the stationary part). The stator comprises wires that you can wrap around a core.

This creates a magnetic field that the rotor can pick up. This pickup occurs when a rotating arm called the rotor spins inside this magnetic field.

While it spins, it creates an electromotive force (EMF) that produces an electrical current. This current flow out through the stator wires and spins the core.

The resulting current produces an alternating current (AC). You can use a stepper motor called the output rotor to produce this alternating current.

While it rotates within a stator, it also creates an electromotive force that produces AC. This current from the input rotor flows into the output rotor and creates an AC output, which goes out of its stator and into the load.

The same basic concept occurs in an outboard motor alternator.

However, because you use them to create electricity, they are much larger than the crankcase of a car or the front wheel of a bicycle, which is meant to store energy for propulsion.

To put it into perspective, a large outboard motor will have an alternator several feet in diameter.

Can An Alternator Run Without a Battery?

Yes, it can, but you will burn up the alternator as the system uses the battery to help control the voltage regulator.

Just as many cars need a reference voltage of around 14.4 volts, and the alternator makes electricity at the rate of over a hundred Amps.

You may be able to bypass your battery for a short period by using an insulated alligator clip attached to your ring terminal on each end to attach directly to the battery post.

But this is only a temporary solution as you will fry your alternators wiring harness in no time due to voltage spikes that occur when attaching directly with alligator clips eliminating any chance of restoring power after removing them.

The procedure for bypassing the battery is simple. Still, it is time-consuming as you need to use a small alligator clip on each end of the 6- or 8-gauge wire.

Connect them to the positive and negative terminals on the positive battery post using an automotive relay with a minimum current rating of 5 amps. If your alternator fails, you will want to save the relay to use it again.

Do Outboard Motors Have Alternators?

The Boat will be impossible to start at first as you create a dead short by skipping the alternator and using your battery as the power source.

You will also get horrible grinding noises from the starter and a dim headlight.

The ignition may or may not work, but it’s better to avoid risking it until you fully bypass the alternator by ensuring that your alternator’s positive wire is connected directly to the positive battery post.

How Much Horsepower Is Required to Turn an Alternator?

The amount of horsepower required to turn an alternator can vary depending on the type of Engine you are using and its design.

For example, a boat engine could require as much as 150 Hp, while a motorcycle may need only 25 Hp. The amount of horsepower required also depends on how it is being driven.

A shaft connected to the Engine will typically require more power than a belt-driven system that requires less mechanical force.

The machine’s maximum current is the most important factor in determining how much horsepower is needed to turn an alternator.

Alternators are rated by the maximum amount of current they can push. The higher the rating, the greater the horsepower needed to drive it.

Type of AlternatorHorsepower
Marine Alternator10HP
Diesel-Electric Alternator2 HP
Car alternator2.345 HP
Brushless Alternator13404 Hp
Goldschmidt Alternator250 HP

The Connection Between the Engine and The Alternator

The connection between the boat Engine and the alternator Connecting an engine to provide electrical power. The two are connected by a drive belt made out of rubber.

If the rubber drive belt breaks, water will leak into your fuel tank, either drained or overflowing, causing an engine fire.

This is due to hydrostatic pressure from leaking fuel in a closed compartment causing it to reach over 1,000 Psi at sea level.

The rubber drive belt will also wear and tear over time, especially in salty conditions.

If a failure occurs in the direct drive between the Engine and alternator, water will get into the fuel tank, which can catch fire or cause a fuel pump to fail.

Only 1 in 2,000 of these failures occur at sea level, with 1/2 at sea level conditions. These things are called wet starts because they are caused by water entering the fuel system and not airlocks or clogged filters that cause wet starts.

Even if your Engine and alternator are completely dry, you can still have wet starts if the water enters your fuel system during a long period of cruising.

The main reason for a wet start is that the drive belt or hose becomes blocked or worn. It’s common for alternators to fail due to wear on the drive belt and hose, causing water to enter the fuel tank, which causes an engine fire.

How to Detect A Faulty boat Alternator?

First, check the battery. If it’s over 12 volts, the alternator is working properly and is not the source of your problem. Next, check the charging system.

Use a voltmeter to measure the voltage output at the alternator terminals. If you find more than 14 volts at each terminal, a faulty regulator is causing your problem.

The last step is to measure to see if there’s voltage on both sides of the regulator. If there isn’t any, the regulator is defective.

Do Outboard Motors Have Alternators?

It is also possible that you have an alternator problem. To test for this, disconnect one wire from the regulator and connect it to the ground. Now check that terminal with your voltmeter.

If you get more than 14 volts but less than the battery voltage (for example, 13 volts), proceed with tests using a voltage tester at different places on the field coils and diodes of the alternator until you locate the faulty component(s).

Proper charging voltage will also depend on the electrical system’s load (the current being drawn).

If you use many electrical accessories, such as lights and stereo equipment, you will notice that your battery does not go up to 14 volts.

Putting your voltmeter across the battery terminals with the Engine at idle and all electrical accessories off should read 13.5 to 13.8 volts.

If it reads less than this, you have a charging problem. The load on the Engine is what determines the charging voltage.

How Do You Check an Alternator with A Screwdriver?

To check that alternator is working properly, you need to do the following steps:

1. Take off (unscrew) the protective casing of the alternator. If a person has never looked inside an alternator, he will get confused with all those cables and wires immediately.

2. Check whether an alternator has a battery voltage or not. An alternator needs at least 12- V to work properly.

3. Screw back the protective casing of the alternator.

4. Power on the Engine, but wait to start it up. Please wait until you receive a voltmeter reading on an alternator and leave it alone for a while (a few minutes).

5. After some time, start the Engine (it should be running in AMP mode) and wait for a few seconds as it gets warm up (now you can drive your boat).

6. Start measuring the voltage again. If the alternator is not working, the battery voltage will drop significantly.

7. After that, stop the Engine and measure if any battery voltage is left on an alternator’s separated cable.

8. If there is no battery voltage, you need to do something with an alternator immediately!

9. It is better to get a boat maintenance specialist to do this as they have special diagnostic tools and equipment to check whether that alternator has enough output power.

10. If an alternator works properly, you should change the cables and wires.

What Do Outboard Motors Contain?

1. The Engine

The Engine is the heart of the outboard motor. It’s attached to a gearbox. The gearbox changes mechanical rotation from the Engine into rotational motion that will produce thrust on a propeller blade or foil.

2. Fuel Tank

The fuel tank provides fuel for your Engine to use when generating energy to turn its gears and generate thrust on a propeller blade or foil.

The fuel tank is made of rubber or plastic. Plastic can withstand the pressure inside a boat’s Engine much better than rubber.

3. Fuel pump

The fuel pump is attached to the fuel tank. It is a small-sized pump that moves two hoses and one filter through its hose connections.

The hoses pass through the filter, into and back out of the fuel tank, and to and from the Engine to send fuel to it when a propeller blade or foil turns on a propeller shaft from an outboard motor.

4. Compression System

The compression system consists of a piston and cylinder enclosed within an engine cylinder. The Engine compresses the fuel in the fuel tank and sends it to the Engine’s combustion chamber.

5. Timing Belt

This is one of two major components of an outboard motor. The timing belt is typically located above the crankshaft and connects the camshaft to the crankshaft.

An outboard motor’s timing belt helps convert the cyclical motion of a crankshaft into the rotational motion needed to spin a propeller blade or foil.

What can Cause Low Voltage in the boat System?

CorrosionMarine Battery corrosion usually starts at the battery’s negative terminal, where marine-specific corrosive and environmental elements can get into.  

Battery corrosion harms the performance of marine electrical systems and starts slowly but will quickly build up.

Chemical formulas can cause corrosion faster, so you should consider adding new ones.
 High VoltageIncorrect wiring or fault in wiring can bring about short circuits that result from the high voltage being introduced in the boat’s electrical system.

High voltages usually result from un-grounded wiring systems or short circuits that result from poor-quality electrical cables, connectors, or faulty components.  

This causes an increase in the boat’s voltage, which can lead to equipment damage and component burning.
Loose ConnectionA loose connection in the boat’s electrical system is a common source of voltage failure, especially if you need to detect it early enough.  

A loose connection can cause a high resistance, which results in the wire melting, burning, or heating. The increase in resistance causes the voltage to drop, reducing the electrical system’s efficiency.
Electrical FailureThe human error involved in working with batteries or changing their position is a major cause of low voltage on boats.  

In extreme cases, such as changing a battery’s position while the boat is on, you can experience a range of voltages. The voltage change may be sufficient to cause damage to the electrical system.
OverheatingOverheating can occur when the boat is exposed to high temperatures. This is usually caused by a malfunction in the Engine or other electrical parts connected to a battery.  

You can encounter the highest voltage usually when the Engine is running, and the battery may be in danger of overheating and explosions.
AccelerationAcceleration can cause voltage drops that can lead to the failure of electrical components, especially when batteries are electrically shorted.  

A short circuit will develop at the disconnecting point between a battery and its electrical ground, which may cause overheating, melting, or burning of components at this point.
 UnderchargingIn some cases, when batteries are left in a discharged state, they may suffer from overcharging.  

Also referred to as ‘priming,’ this can result in higher voltages, leading to the melting and burning of components.  

This process is much like what happens with lithium batteries, which are highly sensitive to charge.


Alternators on cars, boats, and other vehicles work similarly. A voltage regulator controls the alternator’s output, helping to stabilize the voltage on your boat.

When something goes wrong with your boat’s electrical system, a low voltage in the boat can be caused by other issues.

Corrosion and overheating are two common causes, especially when your boat is not maintained regularly.


Hi! I' am Tom. I was a manager in one of the biggest stores for over 10 Years, am also an SEO by night. I don't like to call myself a blogger; they are very analytical, do email marketing, and know all SEO stuff. I faced many questions from customers about different products, and there was hardly any help on the internet. After learning all the things about these products as a manager the hard way, I decided to start a blog and help other people.

Recent Posts