The Latest in Outboard Tech: High-Output Alternators

Go ahead, add more electronics. These alternators can handle that.
Yamaha outboards employ an under-flywheel alternator that’s turned by the engine’s crankshaft.

Alternators often take a back seat to more compelling onboard technology. But without an alternator, an outboard engine can’t recharge batteries. Quite plainly, alternators are day savers. And with all the extra technology we now put on our boats, alternators carry an ever-increasing load.

In response, outboard makers have increased the amperage output of their alternators. Whereas a 35-amp alternator once seemed generous for high-horsepower outboards, now the larger engines feature 100-plus-amp units.

“This isn’t something we’re dreaming up,” says David Meeler, Yamaha technical marketing manager. “We’re responding to the demand of the consumer and the ever-increasing electronics loads they want to hang on their boats. You need power [from the alternator] to be able to do it, and you have to be able to store that power (in batteries).”

Improving Tech

Let’s begin with the basics: An alternator is essentially a generator that converts mechanical energy into alternating-current electricity. Most use rotating magnets that interact with a stationary armature or stator.

The vast majority of the onboard power demand—offshore or inshore—happens when the engines are operating at low rpm, such as when boaters cruise or troll. Thankfully, that’s also the point at which the engines themselves consume less power.
However, to compute their onboard amperage needs, boaters need to know the net amps generated by the alternator. Net amps equals the gross amps minus the engine draw.

Yamaha F450 outboard
Courtesy Yamaha Marine The new F450’s 96-net-amp alternator prioritizes the charging of starting batteries.

Yamaha’s new F450 delivers 96 net (102 gross) amps at idle, and that power is what Meeler calls “stackable.” If your boat holds five F450s, that’s 480 net amps of power. Note that amperage stacking is not automatically a characteristic of all outboard setups.

Yamaha uses what’s called an under-flywheel alternator as opposed to an automobile-style belt-driven alternator. The under-flywheel unit is turned by the crankshaft rather than by belts. Belts can create more failure points, and UFW alternators offer better corrosion protection.

Meeler says UFW alternators have become ever more efficient, taking advantage of technological improvements over the years. In 2009, for instance, Yamaha’s 4.2L Offshore engine alternators employed ferrite magnets. Ferrite combines iron oxide with a small amount of an additional metallic element such as zinc or manganese.

By 2018 and the introduction of the first F425, Yamaha built its magnets from a rare-earth element called neodymium. Rare-earth elements deliver greater holding strength at a smaller size, and they don’t rob power from the engine itself like other magnets can.

At the same time, Yamaha also explored phase angle control within its charging system, a first for outboards. PAC extracts the “juiciest” pieces of the charging wave, Meeler says. This technology manipulates the magnetism of the stator itself to make it more powerful.

Mercury V12 600 hp Verado alternator
Courtesy Mercury Marine Mercury’s V12 600 hp Verado comes with a 100-net-amp alternator.

Read Next: Adding High-Output Alternators

Belted In

On the other hand, Mercury Marine employs belt-driven alternators, citing speed and cooling advantages as well as better reliability based on the latest build techniques, including improved bearings. The alternator’s magnetic rotor turns at speeds 2 ½ or 3 times the engine speed.

“We continue to see more and more electronics on boats with more and more power needs. We see this trend in automotive as well,” says Jeffrey Becker, Mercury’s category manager for outboards 150 hp and above. “Even on the smaller boats for bass fishing, they have depth finders, big screens, trolling motors, livewell pumps, etc.”

As a result, Mercury introduced a 100 net (150 gross) amp alternator for its V12 600 hp Verado. (The newest V10 outboards—including 350 and 400 Verado, 400R and 350 SeaPro—also feature a 150 gross-amp unit while the V8 Verado engines come with a 115 gross-amp alternator.)

Mercury’s alternators employ electromagnets rather than rare-earth magnets. Electromagnets rely on a supplied electrical current. To enhance power, Mercury switched from using round copper wire, which allows minute air voids, to square copper wire that binds tighter. That simple substitution allows more wire to pack the alternator for a stronger magnetic field. Mercury says the company also employs newer and better materials such as a more magnetic steel.

Becker says the company has also responded to the trend for larger vessels—with generators—migrating to outboard power. As the outboards themselves grow quieter, the generator noise seems more pronounced. In addition, generators can be unreliable and sometimes necessitate two fuel systems aboard.

Fathom e-Power diagram
Courtesy Navico Group The Fathom e-Power System has been enhanced for outboard boats by Mercury’s new dual-mode alternator, an option for the new V10 400 hp Verado and 400R.

To resolve those issues, Mercury’s sister company Navico Group launched the Fathom e-Power System, designed to replace a generator with lithium-ion batteries. But without a big enough alternator to recharge the entire Li-ion bank in short order, boaters had to recharge using shore power.

Enter the dual-mode alternator, an option for Mercury’s V10 400 hp Verado and 400R. The 48V/12V alternator pairs with Fathom e-Power to charge the Li-ion battery bank at speed or at idle for all-day use and reuse.

“I think it’s going to be a pretty big game changer,” Becker says.


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