As others have said, an induction motor has a large start up current. The start up current itself isn't a constant but wants about 6x the full load current for the first cycle or two (1/30 to 1/60 of a sec) and then drops off following a decay curve assuming the power source (generator) can meet the load. Years ago, when I was young and naive (high school_, I worked on a job where the owner flew a "3hp" Craftsman 240V air compressor and 5kw generator into a remote site for some work we were doing using pneumatic nailers. The motor was rated for 10A so the owner assumed the 5kw was plenty. We were dropped off for a week yet the compressor wouldn't start off of the generator.
With the owner being willing to risk burning up the generator or compressor at this point, once we used the tank down to where it was unusable (~60psi) and it still wouldn't start, he fully drained the tank and restarted the unit with the generator throttle overridden on full-bore. The motor started spinning but only reached about 1/2 speed, eventually bringing the air tank up to pressure however by that time the paint on the motor and generator was discoloring from heat. It was a stupid move but it worked albeit putting a tremendous amount of wear on the generator and compressor motor.
The real solution is, as said here, is to try it. It may come down to the mass of the moving parts having enough stored energy to kick the motor up to full speed or it may just work off the bat. If it doesn't you know you need a larger generator.
Jim
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Originally Posted by William C Rogers
