Sine Wave Inverter Anomaly

SoundGuy wrote:

vermilye wrote:
There is little advantage to bonding a portable generator if there is no low impedance earth ground (i.e. an 8' 5/8" driven ground rod ...

SoundGuy wrote:
Which obviously none of us are going to do in a campground. However, bonding neutral to ground, as indicated by my measurements, does eliminate strange voltage readings where one wouldn't expect them so the question is whether there is still value in bonding to prevent these voltages from possibly causing any problems with the equipment being fed. :@

BUMP ... in hopes someone may respond to this question. :@

I notice my twin fan which exhibits no motor noise at all when powered with 120 vac shore power but does squeal like crazy when powered with an MSW inverter also does still squeal ever so slightly when powered with my new 1000 watt sine wave inverter. Curious whether this has anything to do with errant voltage readings between the inverter's neutral and ground when not bonded I just tested it with the output bonded and found no improvement, the fan still squealed slightly. That tells me (I think) this slight squeal probably has nothing to do with these errant voltages and that this inverter's sine wave output really isn't as "pure" as the manufacturer would have me believe and is likely still somewhat ragged compared to shore power. I'd still like to know though whether these unusual voltages between neutral and ground when the inverter output is not bonded present any danger to the equipment being powered. :h

Any comments? :@

While I obviously can't prove it from here, I suspect the "stray" voltages you are seeing are inductive leakage. The high impedance of your volt meter don't load the connection enough to eliminate them.

You could prove it by switching the meter to amps & see if there is any current between the neutral & ground. A safer (and possibly less exciting) test would be to get a pigtail lamp socket with a 15 watt incandescent lamp & use that to make the connection. I would be very surprised if it lights. If it is inductive coupling, the available current will be so low that it is unlikely to cause any problems with equipment.

As to the "noise" created by the pure sine wave inverter, the only way to really know if it is the waveform is to throw a scope on it. Without doing that I can only speculate, but you might try loading the inverter with a load around 10% - 25% of its capacity. Many devices (including non inverter generators) produce lousy waveforms unless loaded.

Some interesting examples of device waveforms is linked here.