12 | SAMLEX AMERICA INC.
Resistive Load:
A device or appliance that consists of pure resistance
(like filament lamps,
cook tops, toaster, coffee maker etc.)
and draws only Active Power
(Watts)
from the
inverter. The inverter can be sized based on the Active Power rating
(Watts)
of resistive
type of loads without creating overload
(except for resistive type of loads with Tungsten
based heating element like in Incandescent Light Bulbs, Quartz Halogen Lights and Quartz
Halogen Infrared Heaters. These require higher starting surge power due to lower resist-
ance value when the heating element is cold)
.
Reactive Load:
A device or appliance that consists of a combination of resistive,
inductive and capacitive elements
(like motor driven tools, refrigeration compressors,
microwaves, computers, audio/ video etc.)
. The Power Factor of this type of load is <1 e.g.
AC motors (
PF=0.4 to 0.8)
, Transformers
(PF=0.8)
, AC to DC Switch Mode Power Supplies
(PF=0.5 to 0.6)
etc. These devices require Apparent Power
(VA)
from the AC power
source. The Apparent Power is a vectorial sum of Active Power
(Watts)
and Reactive
Power
(VAR)
.
The AC power source has to be sized based on the higher Apparent Power
(VA) and also based on the Starting Surge Power.
2.2 OUTPUT VOLTAGE WAVEFORMS
TIME
180
160
140
120
100
80
60
40
20
0
20
40
60
80
100
120
140
160
180
Modified Sine
Wave sits at
ZERO for some
time and then
rises or falls
V
PEAK
= 169.68V
Modified Sine Wave
Sine Wave
Pure Sine Wave
crosses Zero Volt
instantaneously
V
PEAK
= 140 to 160V
V
RMS
= 120 VAC
VOL
TS (+)
VOL
TS (
–)
16.66 ms
Fig. 2.1: Pure and Modified 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 Modified 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 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
SECTION 2 |
General Information