PROBING THE MYSTERIES OF THE INVERTER: PART II

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As a final requirement, you'll have to match the inverter's input voltage to your energy system. If your setup is already locked into a format-12 volts, for instance-you'll just have to seek out an inverter that uses 12volt input. If, however, you're still designing your system, it's wise to review the options and decide which one best fulfills your needs.. (Higher voltage inputs, for example, allow higher overall power capacities or longer transmission distances. On the other hand, the odd voltage appliances demanded by such units can be hard to come by.)

And don't forget that an inverter is simply a conversion device ... an AC system of I KW requires DC input power of at least I KW. All too often, users overestimate the capability of their energy production systems and consequently end up with disappointing results.

INSTALLING AN INVERTER

Wiring an inverter into your home energy setup is a very straightforward task, and you shouldn't have any trouble doing the job yourself. The basic circuit is illustrated in Fig. 1, andas you can see-it involves simply attaching the DC source to the input side and the AC load to the output. There are, however, some precautions to be observed if you're to derive the maximum benefit from the system and insure that it's safe.

WIRE SIZING

In most applications, the input wires from the DC source will carry a comparatively low voltage ... say, somewhere between 12 and 48 volts. So, remembering that volts times amps equals watts, we can see that a 300-watt, 12-volt inverter will be receiving 25 amps at maximum power. Now 25 amps is a pretty hefty chunk of current ... and some cables simply aren't capable of handling that amount. In fact, the smallest-diameter wire you would dare use with that amperage would be No. 10.

Moreover, resistance, in even that 10-gauge wire, will limit the practical lead length to a mere I I feet. Resistance robs the current flow of energy (it is released as heat), and is inversely proportional to the wire size. In other words, the larger the wire, the less resistance there'll be ... hence the loss will also be lower. As a matter of fact, the power loss in a conductor is equal to the square of the current. So if you double the amperage flowing in a wire, the losses will rise fourfold!

The maximum amount of loss that can practically be sustained by a conductor is 5% .. . the figure around which electrical codes are designed. The Wire Sizing Table is designed to show you what the maximum length of a particular size of conductor may be at a given amperage. Under the wattage column, the upper figures express power at 120 volts

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