Generating electricity — how the alternator and regulator produce their magic
Issue 33 : Nov/Dec 2003
Although sailboats are usually small and compact, they have the infrastructure of a large city: the waterworks, the sewage disposal plant, and the electrical generating and distribution systems. And, just as happens on land, when one of these systems fails, it reminds us how dependent we are on that system’s technology.
The loss of dependable electricity aboard your boat can jeopardize your enjoyment as well as your safety. It means the loss of the electric bilge pump; lights (navigational as well as cabin lights); the VHF-FM radio, Loran, and GPS (unless you have handheld ones); electronic chart systems; and the radar. Also, and perhaps more importantly, you will be unable to start your engine — unless you can hand-crank it.
Except for some megayachts that have motor generators constantly running, our electrical needs, when away from the dock, are completely supplied from a storage battery or batteries, which have the capacity to “store” electricity. These batteries, which usually supply 12 volts of direct-current (DC) power, have a finite capacity and must be kept charged, or supplied, from an outside source.
At a marina, that source can be from a shorepower connection to an onboard battery charger, which converts the shorepower’s alternating current (AC) to the DC required to charge the batteries.
On the water, the source of this DC charging power comes from an alternator, which is driven by the engine. This alternator, as its name implies, creates alternating-current electricity (similar to shorepower) that is then converted, within the alternator, to DC electricity. A boat’s battery, then, is like a city’s reservoir, and unless that reservoir is periodically supplied with water, it will run dry. The alternator replenishes your boat’s electrical reservoir — the battery — and keeps it from “running dry.”
Controlled output
The output from the alternator is controlled by a regulator, which can either be built into the alternator or exist as a separate remote device. This regulator controls the amount of current (the amperage) that the alternator is supplying to the batteries.
The alternator and regulator, then, are the keys to dependable onboard electricity, and that’s contingent on being able to run the engine. This, of course, assumes that the alternator and regulator are functioning properly. But how do we know if the alternator and regulator are working? We can check the voltage of the boat’s electrical system, when the engine is running, with an inexpensive digital voltmeter; analog meters are just not accurate enough.
This check can be made most easily and safely at a cigarette-lighter outlet in the cabin — provided you’re not using any lights or appliances at the time. The test is done by placing the voltmeter’s probes on the socket’s two contacts. For added safety and convenience, or if you’re not sure where to check inside the socket, a Radio Shack cigarette-lighter adapter with test terminals can be used (Radio Shack part # 270-1521, $6.99). This adapter reduces the possibility of accidentally causing a short circuit while testing and, for added safety, has a built-in, replaceable fuse. You can buy a simple, shirt-pocket-size digital voltmeter for this kind of test for less than $20.
If your voltmeter shows a voltage of 1 or 2 volts above the battery’s “normal” voltage, you can be reasonably certain that the alternator and regulator are functioning properly and the alternator is supplying electricity that is being stored in the battery. For wet-cell batteries, a “normal” voltage reading would be 12.6 volts for a fully charged battery and 12.2 volts for one that is 50 percent discharged. For gel-cell batteries, add 0.2 volts to these figures.
Across the terminals
A more professional and accurate check can be made by going directly across the battery terminals — but if you’re checking the voltage this way, inside the engine compartment with the engine running, be sure to stay well away from the engine’s spinning belts.
For the long-distance cruiser, the ultimate protection from an alternator or regulator failure is having a spare alternator/regulator on board. Since alternators on the engine are normally located at the forward end, they can be easily worked on from inside the cabin — and replacing an alternator is a relatively simple procedure from mechanical and electrical standpoints.
When on an extended cruise, we keep a spare alternator and regulator on board. Twice in the last 25 years — once from an alternator failure and once from a regulator failure — our onboard spares have allowed us to continue our cruise with only about a half-hour interruption.
Thank you to Sailrite Enterprises, Inc., for providing free access to back issues of Good Old Boat through intellectual property rights. Sailrite.com
