I've done some testing on our RV's generator. The generator is an Onan Microquiet 4000 and was added about 5 years ago. Less than 200 hours on the clock. I start and run it under 50% load monthly; have owned this particular rig for 7 months.
What I am noticing under load is some voltage fluctuation, up to 3 volts in a cyclical pattern. It is most dramatic when under the heaviest load, but quite stable when the load is light.
1) Roof mount A/C running on high (compressor not cycling).
2) A/C + Microwave
3) A/C Fan only
4) Microwave only
5) Minimal load (bath fan, charging batteries)
6) Shore Power, no generator
There are no apparent fluctuations in generator engine noise/RPM during these various tests.
What I am wanting to know is if others have ever performed these tests and if I should consider this to be "normal". My biggest concern is that some devices can be more sensitive to such fluctuations (the microwave, for example).
What this reminds me of is back in the day my brother had a 55 chevy with a generator. There were pretty significant fluctuations in the voltage like what I see here; replacing the voltage regulator didn't solve the issue. When he swapped the generator out for an alternator, power was stabilized. (he had not attempted to get the generator rebuilt). I realize that we are talking AC vs DC here with this story; just sharing a similar symptom seen in the past.
Could it be that the windings have not been exercised enough in this generator? Should I care about the fluctuations? I wouldn't feel comfortable using a computer in the above scenerio.
See this youtube video I took this afternoon to show what I am talking about.
RV Generator Microquiet 4000 Fluctuation - YouTube