Gdetrailer wrote:
MrWizard is spot on.
AC "electronics" and DC "electronics" ARE two different creatures when it comes to mathematical computations..
To fully understand and make the math work can often lead to the use of Calculus.. You cannot simply add and subtract to make the numbers work in AC voltages due to Inductance, capacitance and resistance that your AC loads WILL present.
The cleanliness and accuracy of the generator WAVEFORM also plays a key roll in just how accurate your "Killowatt" meter will end up.. Poor quality sine waves OR Modified Sine waves do not "play well" with the Killowatt meter..
Additionally, you ARE using an instrument to measure AC that I suspect is NOT very highly "calibrated" and trying to use it as the source of "truth".
The "Kilowatt" meter is effectively like trying to use a sledge hammer and a railroad spike to to fix a Rolex watch, just not enough FINE DETAIL and most likely a lot of ERROR to work with..
Rather than spinning your wheels, sometimes you just have to "accept" that the results may be less than what you want due to variables like how accurate your meter is, how accurate the gen waveforms are and how reactive your loads are..
Nearly 30+ yrs of electronic tech experience talking..
exactly. in the OP's case to "add them together" you need to realize that each value has a magnitude and angle associated with it. It's called "vector" math as compared to "scalar" math, single values you add, substract, multiply, divide.
and you have to accurately determine what the magnitudes and angle is for each variable.
and if you have equipment to "measure" it you need to know the equipment limitations. The kilo watt is a nice qualitative tool, gives you a good idea of the power draw. Works well to give a reasonably good idea of current draw, power factor, VA and watts to help answer questions or solve problems. But it is NOT a tool to give accurate verifiable results. It can tell you that "yup you are likely pushing the limits of or have margin left in a generator, breaker etc."
It is NOT a good quantitative tool, one that gives a precise accurate answer under all conditions.
Consider that a good power quality meter that will give accurate answers for the same conditions run's in the thousands if not 10's of thousands of $$$.
