Measuring Output Voltages of Invertors? Tech/Math Question

Olly

Bronze
Mar 12, 2007
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This has been a bit of a puzzle and is really for the Tech/Maths minded people.
Measuring A/C voltages with a conventional A/C voltmeter gives you the RMS voltage -Root Mean Square and this assumes a Sine Wave.

Invertors generally give out a stepped square wave - two or three steps. What is the correction factor on what you would read on a RMS voltmeter to get the "SAME" ?

We usually set Stepped Squarewave invertor to read 110 V A/C on an RMS voltmeter but if you switch from street to invertor incandecent lights get brighter. Street Voltage is 120 V A/C measured with the same voltmeter.

Cant find this googling it - any ideas/formulas, correction factors?

Olly and the Team
 

donP

Newbie
Dec 14, 2008
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True Sinus VAC

My simple volt meter gives me 194 VAC, whereas my panel meter says 230 VAC.
However, the factor 1.1856 does not corelate with the 93/115 VAC reading when measuring the "110V system".

From this I deduct that the voltage range has to be considered, too and a simple multiplying factor cannot be applied.

But maybe this helps:
http://www.wikihow.com/Calculate-RMS

donP
 
Last edited:

beeza

Silver
Nov 2, 2006
3,480
732
113
If I recall from my apprenticeship days (which was over 25 years ago), multiply the peak voltage by 0.707 to get equivalent "DC heating effect" of AC. But that's on a pure sine wave.

You would need an oscilloscope to see what waveform your inverter puts out and do an area rule percentage calculation.