Marine electrical equipment explained

Today's pleasure boats have become increasingly dependent on electricity. Most engines can't be started without it; many boatowners can't navigate without it; a growing number of toilets can't even be flushed without it!

While the explosive growth of boat electrical and electronic equipment over the past decade or two has brought about a revolution in comfort and ease of boat handling, electrical equipment malfunctions have become the most common maintenance problem aboard boats, especially those with aging, hodgepodge, or rigged marine electrical installation.

The marine environment is a terrible place for electricity. To be troublefree, electrical circuits must be installed with great care and to the highest standards. But no matter how carefully a marine electrical installation is carried out, the entire system must be properly balanced in the first place or it will soon become a source of endless problems and a constant drain on the wallet.

Because of improperly set up systems, many boatowners repeatedly find themselves with dead batteries, outright battery failures, and lengthy charging times. Fixing immediate problems does nothing to resolve the overall imbalance in the system, guaranteeing that the next difficulty is just around the corner. A large number of boats come straight off the production line with these potential problems built in.

Thus the first requirement for electrical problem solving and repair is to understand the peculiar needs of a boat's 12-volt electrical system, and to make sure that the overall system is in balance. Marine electrical maintenance, troubleshooting, and repair for specific pieces of 12-volt electrical equipment is a large industry. Although the focus is on 12-volt systems, all information is equally applicable to 24 or 32 volts.

Boat electrical equipment

Consider first an automobile. A 12-volt battery provides the energy to crank a starter motor, normally for just a second or two, after which the engine fires up and the alternator cuts in. The alternator subsequently supplies all the car's electrical needs, plus an extra margin to replace the juice the starter motor withdrew from the battery.

The car's electrical system runs on the energy supplied by the alternator, not that supplied by the battery. Although starter motors use a tremendous amount of energy, they do so for a very brief period of time, and thus pull next to nothing from a battery. This drain is replenished by the alternator in just a few minutes. In normal usage a car battery is almost always fully charged, and the batteries do very little work. This holds true for all cars, regardless of size, electrical complexity, or use. The only variable from one car to another is the capacity of the alternator-cars with high electrical loads need bigger alternators.

Contrast this with a sailboat. The "average" boat spends most of its time in a slip. Periodically the owner cranks the engine, motors out of the slip, shuts the boat engine down, and goes sailing. Apart from the time spent motoring, a boat electrical installation runs directly off the battery. The battery will be discharged more deeply than an automobile battery, while the engine will be run far less than an automobile engine, providing minimal charging time.

Now consider the "average" powerboat. The engine will be run for longer periods of time than a sailboat's, with usage patterns often similar to those of an automobile. But even so, most powerboats, especially cruising boats, will have extended periods when the engine is shut down and the boat electrical system is running off the batteries.

Although larger powerboats may have a 24-hour-a-day generating capability, with a battery charger left permanently "on" so that battery service closely resembles that of an automobile, this is not necessarily the case; an increasing number of boatowners with onboard AC generators and substantial power requirements are discovering that with a good-quality DC/AC inverter, they can shut down their generators for most of the day, enjoying peace and quiet while at rest and saving money at the same time! In this case too, battery use closely resembles that of cruising sailboats.

What this adds up to is that in contrast to automotive use, one way or another at some time almost all boats run their DC systems off the battery, deeply discharging it. As a result, the working environment for all the major DC system components (boat batteries, alternators, and voltage regulators) is very different from that found in the automotive field, and yet, primarily for reasons of cost, it has been customary to use transplanted automotive equipment in marine applications with little or no modification. Not surprisingly, this leads to numerous problems, most of which have their origins in the limitations of existing battery technology.