The Mercury Alternator Advantage: More Power, More Fun 

Make no mistake, it’s a digital world. From the WiFi-equipped thermostat in your home to the touchscreen in your car to the smart watch on your wrist, everyday life is filled with innovative digital devices that make ordinary experiences richer and more convenient.

It’s no different in the marine industry. Visit any of the major boat shows each spring, and you’ll see dozens of vendors pushing new technology for just about any type of recreational boat or activity. And because of all that technology, the electrical demands from onboard battery systems are higher than ever.

As an industry leader, Mercury is at the forefront of this innovation movement. We’re continually engineering new, smarter technology for boats. To support all your devices, we’ve also set a new standard in the industry by outfitting our most popular mid- and high-horsepower outboards with high-output alternators. And though you may not have realized it, having enough alternator output is a key to keeping your batteries charged, so you can keep your devices – and your fun – running all day.

What is an alternator?

An alternator is a compact belt-driven generator that’s installed on an engine to convert mechanical power to electrical power. That electrical power helps recharge a connected battery and, more and more, is being used to directly power onboard systems. The higher the rpm of the engine while running, the more output that alternator can generate.

On a boat, the alternator typically charges the cranking battery, which is the battery that starts the engine and runs other essential systems. But depending on the setup, it can also be used to charge house batteries, which are the batteries that power all the “fun” devices on a boat. 

Why a high-output alternator is important for a boat

The more output an alternator is capable of, the more charge it can put on the battery. And when that alternator is keeping your cranking battery charged, having enough juice is vital. Plus, if the alternator is also supporting house batteries, not having enough output means the use of certain accessories must be limited to make sure the cranking battery stays charged.

“A cranking battery dumps a lot of power when it turns over the engine,” said Jeff Becker, Mercury senior category manager for high-horsepower outboards. “If the battery didn’t have an alternator to help recharge it and you were starting the engine repeatedly throughout the day, eventually you’d run out of juice to crank your engine.”

On many smaller recreational boats, the cranking battery also powers aerators, running lights, digital gauges, and bilge and livewell pumps. Even on boats with house batteries, the electrical demands are constantly growing, and so is the demand for higher output alternators.  

“What we’ve seen in the last decade is a huge surge in the popularity of heavy-drawing appliances and equipment,” said Becker. “For instance, gyro stabilizers are now being added to a lot of big offshore boats. Running multiple 12- to 15-inch digital displays is becoming more common, too. So is adding a refrigerator, power steering or a stereo system. We didn’t see that kind of equipment on typical recreational boats in the past, but today those are common items that draw a lot of power. Even with house batteries to handle some of that load, we’re still seeing bigger demands than ever on the overall battery system, especially on higher-end luxury boats that are powered by our high-horsepower outboards.”

Mercury’s alternator strategy: More power!

Mercury’s solution to meeting boaters’ electrical needs is to outfit our engines with high-output alternators. In particular, the Mercury V6, V8, V10 and V12 175 to 600hp outboards all have alternators that generate class-leading charging power.

“The smallest alternator in that range is capable of an impressive 85 amps,” said Becker. “Outboards in our Verado® lineup come standard with more powerful ‘upgraded’ alternators to support things like electric or electro-hydraulic steering, plus all the equipment that offshore boaters need.”

When comparing charging systems, there are two primary things to consider: rated output and net power. The rated output – what you see listed on manufacturer websites – is the maximum amount of power the alternator can produce. Net power is the amount of power that is actually available to the battery after engine loads (like ignition, fuel pumps, trim and steering) are subtracted. Mercury actually engineers outboards to minimize these loads, making more alternator power available for charging.

To help illustrate these two factors, here’s a chart that shows the max rated amperage for the alternators on popular mid- and high-horsepower Mercury FourStroke and Verado outboards compared to a couple of competitor brands.

Alternator output ratings based on published data from competitor outboard brands.

At the 350hp node, you can see that the Mercury V10 Verado outboard is rated at 150 amps, which more than doubles the next leading competitor’s alternator rating of 70 amps. To really test the capabilities, however, Mercury engineers put the V10 Verado to the test to gauge the alternator’s net charging power.

As you can see in the chart below, the V10 Verado outboard’s net power already exceeded rated amperage at just 1500 rpm. So you don’t even need to run wide open to realize the full charging potential.

The engine continued to deliver more than 150 amps of net power clear to max rpm, where it generated almost 5 1/2 times the published net charging output of the competitor.

This is just one example. Net power could vary based on how a boat is rigged and what the alternator is powering. But no matter how you slice it, the V10 Verado can churn out a whole lot of charging power. And so can the other high-horsepower outboards in the Mercury lineup.

*Mercury net power figures do not include amperage draw from the steering system, which is dependent on the specific system (electro-hydraulic or electric) and application.

**Competitor net power figures are based on published data from the manufacturer.

“Smart alternators” are also improving performance

All that battery-charging capability isn’t doing much for you if your engine isn’t running. And the faster you run the engine (in terms of rpm) the more output you get.

Rather than you having to worry about your engine speed, Mercury designed a system that does it for you. It’s called the Idle Charge Battery Management System, and it’s all about peace of mind.

“Basically, at idle the engine monitors the battery charge level of your cranking battery,” said Becker. “If it senses that the voltage is too low, it’ll automatically increase rpm at idle to increase the amount of power output from the alternator and put more charge on the battery.”

Idle Charge Battery Management is standard on all V6, V8, V10 and V12 engines and it works to help manage voltage on a 12-volt cranking battery. The V10 and V12 are also available with a dual-mode 12-volt/48-volt charging system for integration with the Navico® Fathom e-power system, which replaces the traditional onboard combustion generator with a much quieter advanced lithium battery system for managing power needs on large boats.

Need more power? Mercury offers an alternator upgrade kit

If you love your big-screen fish finders, there’s one more alternator innovation from Mercury that should “charge” you up. It’s an alternator upgrade kit that’s available for all V8 and V6 FourStroke, Pro XS® and SeaPro™ outboards.

“The kit increases max charging output from 85 amps to 115 amps,” Becker said. “That’s the same higher-output alternator that’s on our luxury Verado engines. It’s a really smart upgrade to make on fishing boats with big depth finders and live sonar technology, and for pontoons with a lot of accessories or just anyone who wants more peace of mind.”

The V8 and V6 alternator upgrade kit is available from Mercury Authorized Dealers. Mercury recommends having the dealer perform this install. It’s a great addition to your annual service or winterization, and it can give your battery system a big-time boost. 

Upgrade your boat’s performance today

Mercury’s high-output alternators are a big advantage for today’s boaters and just one more way we help to deliver a better overall experience. To learn about upgrading your boat to a new Mercury engine with a high-output alternator, contact your local Mercury Authorized Dealer today.