Geek alert! Geek Alert! Just a couple (dozens?) of words regarding ''inverters'', ''modified'' sine waves, ''real'' sine waves, average responding meters and true rms meters.:zz
I saw these postings about low voltage out of a power inverter so I just had to do a little experiment.
I just happen to have a little 300W inverter sitting on my junk pile... errr uh I mean my instrument bench, just waiting for a purpose in life. A ha! I thought, I might just hook it up to a 12 volt battery
and measure the no load output voltage.
With a 12 volt input that lousy thing only put out a measly 104.1 Vac. I thought to myself Costco sure screwed me when I bought that piece of junk! Uh but wait a minute, I seem to recall some of the fine print that mentioned something about "true RMS" responding meters........
Soooooo When I measured the no load output of that piece of junk with a true RMS meter it said 123.2 Vac. Much closer to the promised 120 Vac that the inverter advertisement barked about.
Beware of this idiosyncrasy! When measuring the ''modified'' sine wave voltage with an average responding meter the value you get is BOGUS! Most average responding meters measure the average ac voltage and scale it to an RMS (root mean square) value for a pure sine wave, just like you get out of your wall socket. This trick won't work with a square wave, or a triangle wave, or a rectangular wave, or a sawtooth wave or ANYTHING except a true sine wave. Each of these signals have a different scaling factor that relates the average value to the RMS value. The scale factor that equates the average of a sine wave signal to the RMS value of said signal is NOT the same factor that equates a modified sinwave signal to its RMS equivalent. Using an '' average responding'' meter to measure ANYTHING except a purely sinusoidal signal is kinda like trying to measure the dimension of a square hole with a round pin gauge.
The moral of the story is that to measure the actual heating power of juice from a modified sine wave inverter takes a good, and of course, more expensive True RMS meter.
End of Geek alert. Hopefully, this makes things less murky.