I'm trying to calculate the Real Power consumption of my device in Stand-by mode, but to do that I need to figure out its power factor due to:
\$\text{Real Power} = V_\text{rms}\times I_\text{rms}\times PF\$
Now, my device like many other IT devices doesn't have a perfect sinusoidal current curve, so I can't just calculate the phase shift can do cos(theta).
I read through some documentation for an Arduino application and apparently you can calculate Real Power by doing several instantaneous samplings of current and voltage and multiplying them and just get the average. So I took out my scope and decided to get 1000 samples.
Here is the graph:
I exported this data to an excel sheet and got the following values:
\$V_\text{rms} = 118.96V\text{ (RMS)}\$
\$I_\text{rms} = 0.02024A\text{ (RMS)}\$
\$S \text{ (apparent power)} = 2.40792\text{ VA}\$
\$P \text{ (real power)} = 0.93713\text{ W}\$
This gives me a power factor of
\$PF = 0.93713/2.40792 = 0.38919\text{ ← This is a very low power factor.}\$
I used my Kill-a-Watt device and it tells me my power factor is somewhere around 0.6 average.
I tried investsigating online if I missed something, and I noticed a website that said that the current probe for the scope should have it's "flow arrow" pointing to the source, in my case my AC outlet. I noticed I had it the otherway around and corrected this. The graph is bellow:
The gives me almost the same RMS values, but when I try to calculate Real Power by multiplying instantaneous Voltage and current readings and averging them out I get a Real Power of:
\$P = -1.02W\$
Can any of you guys with more experience point me in the right direction. What am I doing wrong?
No comments:
Post a Comment