Inverters change DC current from a battery into AC current that can be used to power any light or appliance that demands no more than the rated wattage of the inverter. Small inverters have one or two grounded receptacles and can plug into a cigarette lighter socket. Larger ones have two or more receptacles and need to be clamped directly to the battery terminals. Inverters almost always have cooling fans, and demand a portion of the battery’s power for their own operations. This is why it’s always more efficient to use 12-volt appliances, or take DC power directly from the battery. Nevertheless, inverters let us run all sorts of gear and gizmos.
There are three levels of sophistication in inverters, according to the shape of the electrical wave form they deliver. The highest level is the true sine wave inverter, which will power pretty much anything that runs on AC without interference, interruption, or trouble. These are the most expensive inverters. At the other end of the scale are inverters that put out a “square” wave form. These can cause interference in some sensitive appliances like TVs and other receivers, and devices with rheostats/dimmers, but are fine for incandescent lights, pumps, and other “dumb” equipment. In the middle are “modified sine wave” inverters, which can often bridge the gap in wave form performance. Most inverters on the market today are modified sine wave models, and true sine wave models are coming down in price.
An inverter’s rated wattage should probably be matched to a battery’s amp-hour rating. Some experts say that a ratio of about 5:1 is best – so for a battery rated at 100 amp-hours, don’t use an inverter rated above 500 watts. A good combination of common elements would be a 90-Ah deep-cycle battery and a 400-watt inverter.
For the projects we’re covering here, we'd recommend a simple, modified sine-wave or square wave inverter. A 400-watt model from an auto-parts store or online retailer will cost about $35, and in most cases will run everything from a light to a TV. If it turns out later that you need a more sophisticated inverter, you won't have too much invested already.