Page 12
DEVICES THAT MAY NOT OPERATE ON
MODIFIED SINE WAVE
The output wave form of these inverters is a modified sine wave. See the diagram under
“Principle of Operation” on page 11.
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 0 Volts 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) does not work
properly.
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), 5
th
(300 Hz.), 7th (420 Hz.) and so on. The high
frequency harmonic content produces enhanced radio interference, higher heating effect
in motors / microwaves and produces overloading due to lowering of the impedance of
low frequency filter capacitors / power factor improvement capacitors.
NOTE:
Electric motors and microwaves will run hotter when operated with
modified sine wave. Please ensure proper ventilation for adequate cooling.
Some examples of devices that may not work properly with modified sine wave and may
also get damaged are given below:
•
The built-in clocks in devices such as clock radios, alarm clocks, coffee
makers, bread-makers, 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)
•
Transformer-less capacitive input powered devices like (i) Razors, flashlights,
night-lights, smoke detectors etc (ii) Re-chargers for battery packs used in hand
power tools.
These may get damaged.
Please check with the manufacturer of these
types of devices for suitability
•
Devices that use radio frequency signals carried by the AC distribution wiring.
•
Oil burner primary controls / some new furnaces with microprocessor controls
•
High intensity discharge (HID) lamps like Metal Halide lamps.
These may get
damaged.
Please check with the manufacturer of these types of devices for
suitability
•
Some florescent lamps that have power factor correction capacitors.
The
inverter may shut down indicating overload
•
Sewing machines with speed / microprocessor control
