Alternating Current and AC Equipment
AC Generators Just as with inverters, advanced troubleshooting and installation procedures for AC generators go way beyond the scope of this book. These things are best left to the ABYC-certified professional marine electrician. However, some general knowledge of these workhorses is still important for the boatowner and will help to ensure that your generator is of the proper size and is performing as it should. The basic troubleshooting checklist at the end of this section will help you to at least point the service technician in the right direction if you do have trouble with your generator. Fig. 11-21. A typical inverter monitoring panel, the Xantrex “Link” 1000.
Inverter Waveform On the subject of voltage output, there is one additional point that needs to be made regarding inverters. Most (but not all) inverters produce what is known as a modified-square waveform. Shore-based power supplies, on the other hand, produce what is known as a sine waveform. Early inverters produced a standard square waveform. This technical mumbo-jumbo is all great information for electrical engineers and of little value to boatowners, except for several issues. First, older square-wave inverters had trouble running things like TVs, microwave ovens, and older computers, and could even damage or destroy these appliances. Today’s modified-square-wave and true-sine-wave inverters have pretty much licked that problem, and the new inverters run just about anything. The second problem caused by waveform is measuring voltage and amperage. As I mentioned earlier in this chapter and in chapter 3, the meter used to measure voltage from an inverter should be of the true RMS variety to give the best results. Typically, modified-sine-wave inverters will show low voltage when measured with an average-responding meter. This is no cause for alarm and not indicative of a fault with the inverter!
Rating AC Generators
AC generators are rated the same way inverters are. Wattage is the key here, and the basic AC use-analysis chart for inverters will work just as well for determining your generator requirements. The essential difference between generator and inverter ratings is that typically, generator manufacturers have rated their units in kilowatts (kW). One kilowatt equals 1,000 watts, so, for example, if your generator is rated at 4.5 kW, it’s a 4,500-watt unit. As with inverters, boaters are inclined to over- or underrate their needs with generators. Underrating will give poor electrical performance, for what should be obvious reasons by now. But a point that many people don’t realize is that overrating of a generator can wreak havoc with the generator itself. Generators are designed to operate at a very specific rpm to govern and control the AC frequency. They must be able to maintain this rpm over the entire operating range of the unit under all levels of electrical load. The problem is just that—load. Underworked generators will simply freewheel along, eventually gumming up the cylinders, valves, and rings of the engine. Slight overrating in terms of average combined wattage consumption is OK, but manufacturers recommend that a generator be rated to average 75 percent of its total wattage most of the time. Knowing this, it should be clear that running a TV from even 175
