Marine Inverters allow you to use things like TVs, other home entertainment equipment, computers, printers, microwaves, and power tools when far from shore power and without using a generator. They can also recharge dead cell phones or hand-held VHF batteries with AC chargers.
120 Volt AC power on board usually comes from three sources: shore power, a generator, or an inverter. Assuming you don't wish to stay tethered to the dock, your choice between a generator or an inverter depends on your power requirements underway. Typically today, many boaters have both a generator and inverter aboard. They complement one another nicely.
Inverters have a variety of advantages. They are an economical, maintenance-free, and relatively compact source of AC power.
Inverters operate somewhat like battery chargers in reverse. They take DC power from a battery and, utilizing sophisticated circuitry, change it into 120 Volt AC current. The ship's batteries are the inverter's fuel tank and, naturally, inverters can consume a lot. They will only provide 120 Volt AC power provided that there is ample juice left in the 12 Volt batteries.
It is highly recommended that you have a separate, dedicated engine starting battery to avoid accidentally draining the entire 12v system.
Because inverters and marine battery chargers share certain electrical components, many models are available as combination inverter/charger units.
Most automatically switch almost seamlessly to battery charger mode when connected to shore power or if the generator is switched on, changing back almost seamlessly into an inverter mode when the AC power input is shut off. Most models have multi-stage chargers that prolong the life of your batteries by monitoring them and altering the charge rate according the battery's needs and condition. Since overcharging and poor charging are among the leading causes of battery failure, this is an important feature. Also, some inverter chargers may be set to optimally charge specific banks. You can program them regarding ambient temperature, battery temperature, bank size, battery type and other factors. This is a very desirable feature.
Before you can choose the appropriate inverter, you must first evaluate your power needs, including future additions. The key is to determine the maximum amount of 120 Volt AC power you and your crew will use at any one time, bearing in mind efficiency issues and the fact that the more you use the sooner you'll discharge the battery bank if you have no charging source, like a generator or engine alternator, running. Small inverters will operate a couple of smaller appliances simultaneously. If you wish to run the TV, VCR, and computer in the salon while a crew makes microwave popcorn, you'll need a larger capacity unit.
Add the wattage of all the appliances that you intend to operate simultaneously, ensuring you include any items, including a refrigerator, that run continuously. The total wattage run at one time is the minimum size inverter you should consider. However you should always purchase at the very least one size larger. You will probably discover more uses for your inverter after you've set it up-- and if you turn way too many loads on simultaneously, the inverter will overheat and shut down. Also adding up power requirements on labels of devices does not include efficiency loss and loss of voltage (leading to increased amp draw) through wire runs and possible resistance in connections and elsewhere.
Choosing Batteries To Power the Inverters
Inverters depend on adequate type, size and number of ship's batteries for proper operation. To estimate the size and number of batteries you'll need, expand your list of appliance wattages by adding a third column for the amount of time you'll want to run each piece of gear in a 24-hour day. Since battery capacity is measured in amp hours, you'll need to build a forth column for adding up the amp hours required. Convert the watts to amp hours using this formula:
All inverter installations require a large, dedicated 12 Volt fuse in the main power line from the battery to the inverter. Be sure to purchase the correct fuse block and fuse with the inverter-- it's always wise to carry a spare fuse if you plan a lengthy cruise. It is extremely important to follow carefully all the instructions in installation and operating the inverter. Larger inverters can consume a lot of DC power at times, and the wiring must be as specified by the manufacturer, not only to promote efficiency, but also to avoid fires and melt downs. A good unit will have a thorough set of instructions.
Remember also that AC power from an inverter can cause fatal electric shock, just as it can if it's the shore power or generator. Proper wiring and circuit breakers and all other aspects of installation and operation, according to applicable ABYC (American Boat and Yacht Council) standards is important. And post warnings in appropriate places that, although the boat isn't "plugged in" wires and components may still be hot with AC current.
Technology, knowledge and practices change almost daily therefore it is prudent to research for the very latest up to the date information on marine inverters and seek qualified professional assistance when needed.