Inverter Sizing - Vanner SP00175 Owner's Manual

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General Information
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.

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
may allow output voltage to drop (which would reduce wattage). Like continuous power, the surge rating is
affected by ambient temperature.
Note - Regardless of an inverter's power ratings, an inverter's AC output capability is only as strong as the DC
source. To achieve optimum performance, an inverter must be installed with properly sized cable and have an
ample DC supply. Recommended cable sizes are listed in the DC Cable and Fuse Chart (Section 4.2). The
following sections in this manual will cover the basic information required to properly size the inverter battery and
the vehicle alternator. Keep in mind that if information in this manual directly conflicts with instructions from a
specific battery or other equipment manufacturer, Vanner recommends that the other manufacturer's
recommendations be followed.
Owner's Manual 8/5/17
ITC-Series Inverter Page 25