Quote:
Originally Posted by cdotson
skids, you got pretty close with the "imaginary" power. Microwaves are just about the worst items for power factor, which is the phase shift of the alternating current between the mains. As you probably do recall the superposition of a sinusoidal voltage wave onto another wave that is phase-shifted produces a peak and average voltage that is less than the non-shifted voltage wave.
Microwaves have a power factor of about 0.3, meaning the voltage wave is shifted 30%. Running a microwave without voltage decay requires significantly more wattage than the rated power of the microwave.
Your generator's engine loses power with altitude. At 10k ft elevation you're down up to 30% from sea level. Between your generator putting out 30% less and your microwave drawing around 30% more, your generator isn't big enough.
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Absolutely correct! Your generator power rating was established using standardized tests (like ISO 8528-1). By specification, this testing is conducted at 500 feet MSL (mean sea level) and at 77°F. For every 1,000 feet above 500 MSL, you lose 3% of rated power; for every 10°F increase, you lose 1% of rated power. [These are the numbers for an Onan 5500W generator - your numbers may be slightly different, but in the same ball park.]
So, your (constant output) 2200 watt generator, operated at 8800' MSL and 81°F has an actual constant output capability of 2200 less [8 x 3.5% altitude de-rate] less [1 x 1% temperature de-rate] = 1,562. Available amps would be 1562/120=13.0 amps. Again, your generator testing numbers may be slightly different than the Onan numbers shown here. But the concept is exactly the same.
Generator selection is commonly based on the manufacturer's peak rated availability without a thought to the anticipated actual use of that generator. If your trips commonly include going to higher elevations and/or very high temperature, those factors MUST be included in your purchase decision.
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