Why is modified square-wave bad on extremely cheap R-C series power supplies?

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I have a plug in power meter that had a warning sticker warning you not to use it on a generator or an inverter. I did it anyways with extreme
caution. The power meter can read the correct true RMS voltage from modified square wave. The meter is powered through a series resistor-capacitor power supply and the resistor gets extremely hot when used on modified square wave.
What causes this?
Secondly, I noticed shaded-pole motors run slower on modified square wave from inverter compared to powering from sine wave from the outlet. Why?
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Harmonics. These lead to losses (at higher harmonics the capacitive reactance is lower and there will be relatively high harmonic currents - all adding extra losses. In the motor case there can be some backward harmonic torques.
--
Don Kelly
snipped-for-privacy@peeshaw.ca
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