PROBING MYSTERIES OF THE INVERTER: PART I

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PEAK VOLTAGE: The amount of power delivered by an AC waveform is equal to the area under the curve ... even if that curve happens to be square. Now if you refer back to Fig. 5B, you'll see that the sine wave must reach a higher voltage if it's to develop the same amount of power as the square wave.

Of course, the load (the power demand, that is) doesn't really mind the voltage difference between sine and square waves. It's interested only in receiving all the power it has coming. However, some electronic devices are designed to take advantage of the recurring peaks of a sine wave. For instance, many color televisions utilize this voltage to generate higher voltages inside the set ... thereby eliminating bulky power supplies. Obviously, the square wave can't deliver the voltage that such electronics require, and the set won't work properly.

VOLTAGE REGULATION: In most inverter applications, it's of primary importance to stablilize the output voltage. Without an internal regulator, a square-wave inverter will give a correspondingly lower voltage output as the voltage of the input drops (which is a regular occurrence in battery storage systems). And since most appliances are designed to operate within a specific voltage range, an extreme drop could result in damage.

When you shop for an inverter, then, you should be certain that it has voltage regulation and that its range of tolerance of input is in keeping with the generator or batteries that will be supplying it with power.

FREQUENCY. Devices that are sensitive to voltage peaks and regulation are also likely to be sensitive to frequency (clocks and timers are two examples). Ideally, the output frequency of the inverter should always be 60 cycles per second (in the U.S.). But in actual application, variations in input voltage, temperature, output power, etc. will influence the frequency. And, al though large inverters do an admirable job of limiting frequency drift, many small, inexpensive transistorized units have no means of stabilizing the output at all.

SYNCHRONOUS INVERTERS

Yet another member of the electronic inverter family is the synchronous inverter. Unlike the static units we've discussed so far—which take power from a source, invert it, and deliver it to a load—the synchronous type is designed to be hooked up to a local utility.

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