Hi Ratch,
>No, I believe you want the apparent power, also called complex power, with the designated symbol S*. Its units are VA. S* = VI*, where I* is the >conjugate of I. Another relationship is S* = |I²|Z
Wait a minute here:
P = VI and 120 x 1.41 = 169
Also:
Apparent power = |I²|Z = (1.41² x 85) = 169
Same thing??? So when we multiply V x I it gives us our va's which is apparent power!!!!!
Why do you say "NO"
Confused!
Getting back to the example. I have drawn the Voltage and current wave forms in approximation to my example. I didn't draw _every_ degree... that would take too long.
Please take a good look at the attachment below I have included in this post. Now let's put asside the fact that that a 120VAC main cannot just get connect to a micro-controller. We all know this. Obviously, the voltage and current will be attenuated by a conversion proccess. So let's set this asside for now. Let's just look at the AC theory.
My micro controller will read the voltage sine wave *instantaneously*. So this means that it will see:
@t1 = 2.96 v
@t2 = 119.98 v
@t3 = 167.1v
@t4 = 169.25v
@t5 = 167.1v
@t6 = 119.98v
@t7 = 2.96 v
plus I will see aaaaaall the other voltage values between t1 and t2 and aaaaaall the voltage values between t2 and t3 etc.... So what I am saying is that for the sake of this sample, I just did seven time slices. But bear in mind I will be reading the voltage at every degree of the 360 degrees sine wave. So all positive and negative voltage values will be read into my micro controller and logged in a table. Hence instantaneous voltage. The same goes for the current wave form.
Now what you have been explaining to me is to multiply every instantaneous values of VI at every time slice.
>So all you have to do is multiply each instantaneous current and voltage value, sum them up, and divide by the period
So let's do it:
VI @ t1 = 2.96 x 1.057 = 3.128 watts
VI @ t2 = 119.98 x 0.352 = 42.23 watts
VI @ t3 = 167.10 x 0.352 = 58.81 watts
VI @ t4 = 169.25 x 0.881 = 149.10 watts
VI @ t5 = 167.10 x 1.233 = 206.03 watts
VI @ t6 = 119.98 x 1.41 = 169.17 watts
VI @ t7 = 2.96 x 1.233 = 3.649 watts
So taking the absolute values of VI when in the negative part of the voltage sine wave, we get the same wattage values. So summing up all the wattages of the 7 time slices shown above and multiplying by 2 (to include the bottom part of the wave form) ... is:
632.11 x 2 = 1264.23 watts
Now we divide 1264.23 by the period of one cycle:
1264.23/(1/60) = 75853 watts of true power ?????
True power is supposed to be close to 120 watts???
confused.
Where have I gone wrong!
Thanks for your help.
r