The power rating commonly associated with microwave ovens is the "cooking
power" which is the power being "delivered" to the item being microwaved. The
actual operating power requirement rating is higher than the cooking power
rating and typically is referenced on the back of the microwave. If the operating
power requirement does not appear on the back of the microwave, check the
owner's manual or contact the manufacturer. As a thumb rule, the electrical
power drawn by the microwave oven can be taken as 2 times the cooking power.
USING THE INVERTER TO POWER MICROWAVE OVENS
TECHNICAL INFORMATION
Basic Operating Principles of Modified Sine Wave Inverters.
Inverters work in two stages. During the first stage, the DC to DC converter
increases the DC input voltage from the power source (e.g. a 24 volt battery) to
approx. 155 to 170 VDC. In the second stage, the high voltage DC is converted
to 110 to 120 volts (60 Hz AC), using advanced power MOSFET transistors. The
output waveform resulting from this conversion is a "quasi-sine wave" or a
"modified sine wave" as shown below.
This stepped waveform is nearly similar to the sinewave power generated by
utilities and has a broad range of applications.
The modified sine wave produced by inverters has a root mean square (RMS)
voltage of 110 to 120 volts. The majority of AC voltmeters are not calibrated to
measure true RMS voltage and assume that the measured waveform will be a
pure sine wave.
Consequently, these meters will not read the true RMS modified sine wave
voltage correctly and when measuring the inverter output, the meters will read
about 20 to 15 volts too low. To accurately measure of the output voltage of the
inverter, use a true RMS reading voltmeter such as a Fluke 87, Fluke 8060A,
Beckman 4410, Triplett 4200 or any multi-meter identified as true RMS.
+155 to 170V, Peak
110 to 120V, RMS
0V
-155 to 170V, Peak
Time
Sinewave: Smoothly increases to
its peak and smoothly decreases.
It crosses 0 V sharply at a slope.
Modified Sinewave:
Shoots straight up,
levels off at peak &
drops straight down.
Also, it sits at 0 V for
some time.
Page 12
