This engine uses two alternators. These are often arranged to be controlled by a single regulator, which synchronizes their output.
Steve D’Antonio

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For most sailboats, keeping batteries charged is one of the most pressing cruising challenges.

In the majority of cases, the main charging source is a standard alternator supplied by the engine manufacturer, which is controlled by an integrated, and therefore unsophisticated, regulator. While this setup might work, when it comes to loading large deep-cycle domestic banks, it is far from ideal.

Most manufacturers of deep-cycle batteries, and particularly those of the sealed-valve regulated lead-acid variety (such as absorbent glass mat and gel batteries), recommend three-stage “smart” charging for a maximum longevity and warranty coverage. If your bank is made up of lithium-ion batteries, sophisticated and intelligent charge control is not only recommended, but is also mandatory for efficiency and safety.

Virtually any vessel with a domestic battery bank will benefit from an alternator/regulator upgrade. Standard alternators/regulators will chronically overcharge or undercharge deep cycle batteries, shortening their life and reducing their performance. It’s easy to argue that an upgrade to these components will pay off.

heat sensor
Heat dissipation is essential. If an alternator generates heat faster than it can be dissipated, it will overheat.
Steve D’Antonio

For conventional lead-acid batteries, a proprietary high-efficiency alternator (an alternator designed to operate at near maximum capacity for an extended period) along with an external smart regulator will, with some caveats, provide the battery bank with the most desirable load profile under the circumstances. This means that during the time the engine is running, the maximum amount of charge can be produced. Outside of driving a car for long periods of time, in most cases the runtime of an auxiliary motor for charging purposes is less than ideal, making it more important than ever to wring out every last alternator ampere-hours.

In addition to using a high-efficiency alternator and smart regulator, look for two types of temperature compensation. A sensor wired to the regulator and attached to the battery will report the battery temperature to the regulator, allowing compensation in the alternator output. The cooler the battery, the faster it can accept charge; conversely, hot batteries should be charged more slowly. In addition, the regulator should also receive information from the alternator box. If it is too hot, the output can be reduced to prevent heat damage.

The ideal alternator/regulator should have the following features: multi-stage charging, temperature compensation, self-diagnostic indicator lights or display, programmability for different battery types (including flooded, standard and thin plate pure lead acid, AGM, gel , carbon foam and lithium-ion), a user interface (DIP switches or, preferably, a laptop) and an N or P type field control for safety. Alternators whose field is regulated by controlling the negative side of the input – the N type – run the risk of the alternator inadvertently producing unnecessary maximum output, which can lead to costly and potentially dangerous damage to the battery. Alternators whose output is controlled by throttling the positive side of the field – the P-type – risk a short circuit which can blow a fuse and stop producing, which, although undesirable, is not harmful. My preference is for N-type alternators, as long as the regulator can accept this protocol.

The regulators must be able to be programmed to charge several types of batteries.
Steve D’Antonio

Review installation and programming instructions before investing in a new alternator/regulator. Although you can have the installation done by a professional, programming guidelines should be clear, concise, and simple enough for the average sailor to follow. You shouldn’t need to be a marine electrician to program and understand the functions of the regulator.

Finally, when changing to a heavy-duty alternator, the existing belt arrangement (a single V-belt, in many cases) will likely be inadequate. For alternators 100 amps and above, at 12 volts, a double or serpentine belt will almost certainly be required. Both are available for some engines as aftermarket kits, or they can be custom made. Overloading a single belt can lead to slippage, heat generation, and failure of the alternator and water pump bearings.

Steve D’Antonio provides services to boat owners and buyers through Steve D’Antonio Marine.