Samlexpower Pure Sine Wave PST-1500-12 Manuel Du Propriétaire page 10

Section 2 |
2.2 OUTPUT VOLTAGE WAVEFORMS
180
160
140
120
100
80
60
40
20
0
20
Pure Sine Wave
40
crosses Zero Volt
60
instantaneously
80
100
120
140
160
180
TIME
Fig. 2.1: Pure and Modifi ed Sine Waveforms for 120 VAC, 60 Hz
The output waveform of the Samlex PST series inverters is a Pure Sine Wave like the
waveform of Utility / Grid Power. Please see Sine Wave represented in the Fig. 2.1 that
also shows Modifi ed Sine Waveform for comparison.
In a Sine Wave, the voltage rises and falls smoothly with a smoothly changing phase
angle and also changes its polarity instantly when it crosses 0 Volts. In a Modifi ed Sine
Wave, the voltage rises and falls abruptly, the phase angle also changes abruptly and
it sits at zero V for some time before changing its polarity. Thus, any device that uses a
control circuitry that senses the phase (for voltage / speed control) or instantaneous zero
voltage crossing (for timing control) will not work properly from a voltage that has a
Modifi ed Sine Waveform.
Also, as the Modifi ed Sine Wave is a form of Square Wave, it is comprised of multiple
Sine Waves of odd harmonics (multiples) of the fundamental frequency of the Modifi ed
Sine Wave. For example, a 60 Hz Modifi ed Sine Wave will consist of Sine Waves with
odd harmonic frequencies of 3rd (180 Hz), 5th (300 Hz), 7th (420 Hz) and so on. The high
frequency harmonic content in a Modifi ed Sine Wave produces enhanced radio interfer-
ence, higher heating effect in inductive loads like microwaves and motor driven devices
like hand tools, refrigeration / air-conditioning compressors, pumps etc. The higher
frequency harmonics also produce overloading effect in low frequency capacitors due to
lowering of their capacitive reactance by the higher harmonic frequencies. These capaci-
tors are used in ballasts for fl uorescent lighting for Power factor improvement and in
single-phase induction motors as Start and Run Capacitors. Thus, Modifi ed and Square
Wave inverters may shut down due to overload when powering these devices.
10 | SAMLEX AMERICA INC.
General information
V = 169.68V
PEAK
V = 140 to 160V
PEAK
V = 120 VAC
RMS
Modi ed Sine
Wave sits at
ZERO for some
time and then
rises or falls
16.66 ms
Sine Wave
Modi ed Sine Wave