TomandJeri
Senior Member
Good question. So I tried it, using a cheap 400W (continuous) inverter in an extruded case with twin outlets and a cigarette lighter plug in my Grand Cherokee. I tested a 75W incandescent flood light and a 10" 26W (nameplated) table fan on high speed.
Light (Utility)
Power 76.2W
Current 0.63A
Voltage 120.9V
Power Factor 0.99
Frequency 60Hz
Volt-Amps 76.3VA
Light (Inverter)
Power 70.0W
Current 0.62A
Voltage 116.0V
Power Factor 0.95
Frequency 58Hz
Volt-Amps 72.3VA
Fan (Utility)
Power 28.4W
Current 0.23A
Voltage 120.9V
Power Factor 0.99
Frequency 60Hz
Volt-Amps 28.4VA
Fan (Inverter)
Power 28.5W
Current 0.29A
Voltage 122.3V
Power Factor 0.78
Frequency 58Hz
Volt-Amps 35.5VA
To see how close the voltages were, I checked the utility and the inverter with a Fluke true RMS DMM, at idle (on, no load) and with the fan running (inverter only).
Utility (no-load)
KAW 122.3V
Fluke 122.9V
Inverter (Idle)
KAW 120.4V
Fluke 119.1V
Fan (Inverter)
KAW 121.5V
Fluke 120.9V
It would seem the inverter has voltage regulation, as the voltage actually goes up with load. But the DMM reads higher than the KAW on grid power, which presumably is relatively clean compared to the 'modified sine wave' inverter, and reads lower than the KAW on inverter power.
The differences in power factor between inverter power and grid power is also interesting, especially how an incandescent bulb has less than unity power factor, and worse yet on the inverter, but I suspect that has everything to do with the harmonics of the inverter power.
I don't know if there's anything to do with the ability of the KAW to correctly read it, either (pretty far out of my comfort zone), but I'm sure it wasn't designed to handle really crude wave forms. Utility power may be a bit dirty, but it's nothing like what's coming out of my little inverter.
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