How Are Marine Alternators Different from Other Vehicle Alternators?

Commercial and industrial grade vehicle electrical systems require reliable, safe and robust power sources. These systems often charge battery banks under adverse conditions of temperature, moisture and dust. High-performance alternators are engineered with these and other considerations in mind.

ship sailing in the middle of the water with a marine alternator

Marine versus Automotive Alternator Requirements

Fuel-efficiency via weight reduction is a primary goal for automotive design. Thus, modern vehicle alternators are made from lighter materials, sized for small batteries and minimal electrical loads. They will not sustain high loads without external airflow for cooling.

Industrial alternator applications require continuous-duty, high-output alternators built to last while operating safely. Marine alternators, for instance, have higher power demands than regular cars and trucks to run lights, radio transceivers, navigating equipment, AC/DC inverters, water makers, pumps, winches and other high-amperage devices.

Additionally, marine engines are often installed in enclosed compartments to shelter them from moisture and salt spray. This means that marine alternators must be self-cooling at high loads or have an additional cooling subsystem. Marine alternators also comply with strict safety specifications not required of cars.

Marine Alternator Features

In order to meet these demands, alternators built for marine use have features not found in automotive-grade units:

  • Spark screens that meet U.S. Coast Guard standards to eliminate the alternator as an ignition source
  • Double-insulation to eliminate electrical shock in wet conditions and prevent sparks
  • Dual fans and large heat sinks for self-cooling under high, continuous loads
  • Stainless steel bearings, corrosion-resistant metals and heavy-duty coatings
  • High output at low RPMs to match marine diesel engine operating conditions
  • Battery sensing regulators for high-efficiency battery charging and detection of battery cell failure.

Marine Alternator Placement and Installation

Since most marine vehicle designs impose strict space constraints, it is important to select first the correct alternator case size:

  • Small case alternators are typically around 6 inches in diameter and 6 inches long. They often employ a single pulley. Typically, they produce less than 110 amps at 12 volts.
  • Large case alternators are about 7 inches in diameter and 7 inches long and supply greater than 110 amps. These may need a double pulley or multiple groove serpentine belt system.
  • The largest engines use an extra-large case alternator or multiple alternators to supply adequate power.

The other main feature when selecting a replacement marine alternator is the foot type. Alternator cases come in single foot or dual foot designs with varying distances between feet. Large foot spacing is used on larger diesel engines. Some fittings require spacers for proper installation. The most important considerations are that all pulleys match and that belts are in alignment.


Regulator Features

Automotive alternators rely on simplified voltage regulators, internally or externally, whose main task is keeping the starter battery topped off. Efficiency and battery life are of higher priority in marine applications, however, so the regulators are more complex, accurate and adjustable. Most marine alternators rely on external regulators to supply such features, although internally regulated alternators are available. Many can be adjusted to match the type and size of the house battery bank, monitoring equipment and ambient operating conditions.

Marine and Automotive Alternator Divergence

It used to be that automotive and industrial alternators were versions of the same basic underlying design. In recent decades, however, their design goals have diverged, which means that even for similar load requirements, their manufacturing and operating characteristics no longer make them interchangeable. Marine alternators, in particular, must supply higher performance under conditions more challenging than that of modern automotive alternators.

Give us a call to talk about the right alternator for your marine application today. We ship to the US, Canada and internationally via Air-freight or Ocean Freight utilizing all of the major couriers. Depending on how quickly you need the products..

Tug Boat photo credit to Rennett Stowe under cc 2.0
Washington State Ferry photo credit to A.Davey under cc 2.0