Power InvertersBack in the "old" days--that's ten years ago--the state-of-the-art in off-grid living was a twelve volt lighting and appliance system much like today's RV's. Contrast this with the modern home where everything is run from 120 volt power. The problem the 12 volt system is the very large wire sizes that are required to carry power at such a low voltage and the relative lack of choice in low voltage lights and appliances. The development of efficient power inverters has eliminated much of the reason for installing a 12 volt system. A power inverter is an electronic device that converts the direct current provided by one or batteries into the alternating current used in American households. The input battery voltage will typically be 12, 24, or 48 volts and the output household voltage will be 120 or 240 volts. Today's off-grid system is typically based entirely on 120 volt power supplied by a power inverter with no low voltage appliances use at all. This expands tremendously the available choice of appliances, reduces the cost and complexity of wiring and can might reduce total building cost because of the generally high cost of 12 volt appliances. Specifying an InverterInverters for home power use will provide either sine wave or modified sine wave output. The modified sine wave is popular because it is far cheaper for the same output power. Inverters are built for a given batter voltage and can not be modified to use a different voltage, so the battery bank must either be known or you must decide on one at the same time you select an inverter. The power output of the inverter is probably the single most critical concern for two reasons. First, if it is too low, then you will have problems starting appliance motors or may have brown-outs when too many lights and devices are turned on. Secondly, the price of an inverter is proportional to power output, so while one that is too small may leave you in the dark, buying a large one may put you in the poor house. Choosing an InverterSad to say, but one of the primary considerations in choosing an inverter will be cost. Inverters combine three characteristics that make them costly to build. On the one hand, they are precision instruments that contain advance digital control circuitry. These circuits are designed to be highly reliable and able to withstand wide variations in temperature and humidity. Secondly, inverters handle very large electrical power levels. This means that some of the components are larger, high current devices. Finally, while inverters are relatively plentiful, the some of the components like the transformers used are specialty items that will typically be custom built for the inverter manufacturer. Commercially Available InvertersThe leading manufactures of inverters for home power use are Trace and Heart. Several others do exist and may be of good quality, but these are the companies I am most familiar with. I personally use Trace equipment and have never had a problem (other than the initial sticker shock of course ;-). Trace has by far the largest selection of models. Their list prices are somewhat higher than similar models from Heart, but Trace distributors commonly provide aggressive pricing that makes the Trace generally cheaper. Trace builds literally dozens of different models for
different combinations of battery voltage and output power
level. These two main features are encoded in the model number
for easy reference. For instance: |