AC POWER FROM INVERTERS FOR CATAMARANS
By Kevin Jeffrey
While it’s easy to cruise successfully with only DC electrical appliances, it’s natural to want the option of using inexpensive household galley appliances, power tools, and work or entertainment electrical devices on board. Imagine a silent, lightweight, affordable AC power system on a sailboat. A few years ago this was unthinkable, but the new generation of efficient DC-to-AC inverters have made these type of AC power systems a reality, creating a quiet revolution in the way multihull owners use electrical power.
There are two basic methods for supplying AC power on a sailboat: 1) Directly–from a dockside outlet, AC genset, or modified AC alternator run off the main engine; and 2) Indirectly–from a DC-to-AC inverter. Dockside power is convenient, but it has a major drawback for most cruising sailors—it’s only available at the dock. AC gensets or other engine-driven alternatives are effective, but in addition to their weight, cost, and maintenance, an engine must always be running for AC power to be available, the time when most of us would prefer a good dose of peace and quiet. Silent operation is the beauty of a DC-to-AC inverter.
Instead of creating electricity, an inverter simply “inverts” DC power from the house battery bank into useable AC power, similar to that found dockside or in a house. Despite an inverter’s numerous advantages over engine-driven AC sources, it is critical to understand that an inverter is contributing to your DC electrical load, sometimes to a great degree, and that the battery power an inverter uses must be replaced during routine DC charging, whether by renewable or engine-driven sources. Your total inverter load depends on the power draw of the individual AC appliances, the efficiency of the inverter, and the length of time the appliances are used.
New inverters are over 90% efficient when actively inverting and consume truly miniscule amounts of electricity in their idle mode. Most models produce a modified sine-wave output that is “clean” enough for TVs, VCRs, computers, and most other electronics. Only a very few appliances actually require pure sine-wave output (laser printers come to mind), and almost nothing that is typically used on a boat. Check with your inverter supplier regarding specialized electrical devices on your boat.
Inverters are available in a range of power ratings. 50-watt mini-inverters can operate laptop computers, while pocket inverters in the 150- to 250-watt range can operate computers, TVs and VCRs, blenders, fans, small power tools and more. Larger inverters are needed to operate appliances with heating elements, such as toasters and microwave ovens (1000 watts), coffee makers (1200 watts) or hair dryers (1500 watts), or appliances that have motors with high initial electrical surges, such as refrigeration compressors. A 1500-watt inverter is a convenient size, since it can operate any appliance that can be plugged into a standard household AC plug. Inverters with over 2000 watts of power allow you to run multiple AC appliances simultaneously.
Many of the larger inverters have a charging mode, eliminating the need for a separate battery charger. When a direct source of AC power is available, the inverter-charger automatically begins giving the batteries a high-performance charge. 1500-watt inverter-chargers have about 70 amps of charging current; 2500-watt models roughly 120 amps.