Samlexpower VR175 Owner's manual - 3.
3.
HOW YOUR INVERTER WORKS
The inverter converts low voltage DC (Direct Current) from a battery or other
power source to standard 230 volt AC (Alternating Current) household power.
3.1 PRINCIPLE OF OPERATION
The inverter converts power in two stages. The first stage is a DC to DC
conversion process that raises the low voltage DC at the inverter input to 280
volts DC. The second stage is the actual inverter stage that converts the high
voltage DC into 230 volts, 50 Hz AC(rms). The DC-to-DC converter stage uses
modern high frequency power conversion techniques that have replaced the
bulky transformers found in less technologically-advanced models. The
inverter stage uses advanced power MOSFET transistors in a full bridge
configuration.
3.2
THE OUTPUT WAVEFORM
The AC output waveform of the VR-series inverter is known as “modified sine
wave”. It is a waveform that has characteristics similar to the sine wave shape
of utility power. This type of waveform is suitable for most AC loads, including
linear and switching power supplies used in electronic equipment,
transformers, and motors. (See Figure 4).
The modified sine wave produced by the VR175/VR250/VR400 inverter has an
RMS (root mean square) voltage of 230 volts, which is the same as standard
household power. Most AC voltmeters (both digital and analog) are sensitive to
the average value of the waveform rather than the RMS value. They are
calibrated for RMS voltage under the assumption that the waveform measured
will be a pure sine wave. These meters will not read the RMS voltage of a
modified sine wave correctly. They will read about 20 to 30 volts low when
measuring the output of the inverter. For accurate measurement of the output
voltage of this unit, use a true RMS reading voltmeter such as a Fluke 87III,
Fluke 8060A, Fluke 77/99 series or Beckman 4410.
FIGURE 4: Modified Sine Wave and Sine Wave Comparison
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