Owner`s manual

General Information
ITC-Series
Inverter Page 24 7/18/03
as 32, 36, 48, or 120 volts. The most common inverter AC output power is 120 volts at a frequency of 60 Hz.
Some inverters, however, are designed to produce 240 volts, or both 120 and 240 volts at 60 Hz. Because
some countries use power of different voltage and frequency (e.g., 230 volts at 50 Hz), inverters are available to
conform to these requirements.
The three available inverter types are distinguished by the type of AC output waveform they produce. This
waveform affects the AC loads they operate. This section provides an overview of these inverter types, including
the advantages and disadvantages associated with using each type.
Sine Wave
Modified Sine Wave
Square Wave
Sine Wave Inverter
Sine wave inverters produce an AC output waveform like power produced by the electric utility companies and
rotating generators. The sine wave inverter’s waveform is characterized by the highest peak voltage and smooth
voltage transitions (no square wave components). Such inverters are the most costly of the three inverter types
because they contain additional electronics to produce the required waveform. A measure of the sine wave
quality is
Total Harmonic Distortion
(THD), and is expressed in a percentage. The lower the THD the higher the
quality of the sine wave power.
Modified Sine Wave Inverter
Modified sine wave inverters are sometimes called “quasi sine wave inverters” or “modified square wave
inverters.” Modified sine wave inverters generally cost more than square wave inverters because they contain
additional electronic circuitry to produce true RMS regulated AC output. Modified sine wave inverters have
higher AC peak voltages than square wave inverters, and automatically control the width of the AC output
waveform to regulate the output voltage (pulse-width modulation). The shape of the modified sine wave
inverter’s waveform includes a square wave component. It is stepped in such a way, however, to closely
approximate the true sine wave produced by the electric utility companies. Although this waveform has a higher
peak voltage than do square wave inverters, its peak voltage is not as high as a pure sine wave. Therefore, AC
loads containing power supplies might not always operate properly on the modified sine wave inverter.
Square Wave Inverter
The square wave inverter is a low cost device that produces a pure square wave AC power output. This AC
power can be an accurate 60 Hz frequency if it is crystal controlled. It does not have the necessary peak voltage
to properly operate many AC appliances that contain electronic power supplies (e.g., computers, TVs, and
VCRs). The square wave is appropriate when operating AC loads such as resistive heating devices.
5.2 Inverter Sizing
Output Power Rating - Power output is an important consideration when purchasing an inverter. Power is
defined as the rate that a device produces (or uses) electrical energy. This rate is measured in watts or kilowatts
(one kilowatt equals 1,000 watts), or sometimes in volt/amps. Volt/amps are roughly equal to watts and are
obtained by multiplying volts times current produced or used by a device
To properly determine an inverter size (in watts) for your application decide which AC loads you plan to operate.
Inverter size is the sum of the wattages of the AC loads that you wish to run at the same time, plus a safety factor
of 10 to 20 percent.
Continuous Output Power - Continuous power is defined as the AC power in watts (or volt/amps) that an inverter
can produce on a continuous basis at a given temperature.
Surge Output Power - Inverter power can also be rated in terms of surge power. Surge power is the short term
duration of AC power that the inverter can produce. It is often specified as the watts (or volt/amps) that can
operate a resistive load for two or three seconds. Sometimes this is specified in AC amps because the inverter