10 | SAMLEX AMERICA INC.
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 Modified 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
Modified Sine Waveform.
Also, as the Modified 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 Modified
Sine Wave. For example, a 60 Hz Modified 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 Modified 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 fluorescent lighting for Power Factor improvement and in
single-phase induction motors as Start and Run Capacitors. Thus, Modified and Square
Wave inverters may shut down due to overload when powering these devices.
2.3 ADVANTAGES OF PURE SINE WAVE INVERTERS
• The output waveform is a Sine Wave with very low harmonic distortion and cleaner
power like Utility / Grid supplied electricity.
• Inductive loads like microwaves, motors, transformers etc. run faster, quieter
and cooler.
• More suitable for powering fluorescent lighting fixtures containing Power Factor
Improvement Capacitors and single phase motors containing Start and Run Capacitors
• Reduces audible and electrical noise in fans, fluorescent lights, audio amplifiers, TV,
fax and answering machines, etc.
• Does not contribute to the possibility of crashes in computers, weird print outs and
glitches in monitors.
2.4 SOME EXAMPLES OF DEVICES THAT MAY NOT WORK PROPERLY WITH
MODIFIED SINE WAVE AND MAY ALSO GET DAMAGED ARE GIVEN BELOW:
• Laser printers, photocopiers, and magneto-optical hard drives.
• Built-in clocks in devices such as clock radios, alarm clocks, coffee makers, bread-mak-
ers, VCR, microwave ovens etc. may not keep time correctly.
• Output voltage control devices like dimmers, ceiling fan / motor speed control may
not work properly (dimming / speed control may not function).
• Sewing machines with speed / microprocessor control.
SECTION 2 |
General Information
