Xantrex Inverter - Normal Behaviour?

[edpalmer42]

I picked up a used Xantrex Xpower 1000 inverter.  Typical 12V to 115 Vac @ 1000 W modified square wave inverter.

Everything seems to be working, but I noticed one odd thing.  When it warms up enough for the fan to kick in, the waveform changes; the non-zero part of the modified square wave gets slightly shorter and the zero time gets longer so the frequency doesn't change.  A scope shows that the peak voltage isn't changing.  A non-true RMS DMM shows the change as a significant voltage drop from 120V to 110V.  The output voltage is speced at 115 Vac +-5% so both 120V and 110V are within spec.

This is the first time I've played with anything like this.  Does this sound like normal behaviour?

Thanks,
Ed

[arclight]

Their output waveform will change based on the type of load you apply.  For instance, a transformer-style microwave oven will cause it to smooth out significantly.  I'd look at what is happening when the fan comes on (i.e. refrigerator kicking on, fans, etc).

Arclight

[edpalmer42]

In order to get things warmed up so that the fan would start, I was using a heating element from an electric stove (~43R) to apply about 300W of load.  The waveform didn't change until the fan started up.