Reactive power - Reactive Generator research from GotoLuc - discussion thread

[itsu]

If you have a phase shift between voltage and current... which apparently you do... is it still legitimate simply to multiply RMS voltage by RMS current to get a power figure?

I think Itsu's scope is multiplying the instantaneous samples of current and voltage.  He should have simply written  (Ch1 * Ch4),  (Ch3 * Ch4),  (Ch2 * Ch4), etc...

I hope, his scope only displays the RMS averages for each channel but makes multiplications for each sample.
I'm not sure what type of average his math channel is displaying/applying to the results of these multiplications  ...I think it's an arithmetical mean - not RMS, because it displays the word "mean".

verpies,

not sure what the scope is using, i can try to use PP values instead of RMS and see the difference in the math function, if any.
The documentation is not very enlightening about this subject either, i have to do some digging here i guess

Regards Itsu

[itsu]

In the mean time i tried to replicate what Gotoluc is doing/measuring with this bifilar coil.
My bifilar coil is measured 1.3 Ohm and 127mH.

I tried to use the same setup as Luc did (625Hz square wave 10V rms as input)

I measure the voltage across and the current through the coil and using the math function (ch1 * Ch4) to show the power.
I am using a current probe which is set at 2mA/mV, meaning that the current (and the power) needs to be multiplied by 2

As i have a slightly higher ohms value in my coil, my signal on ch1 is somewhat stronger then yours.


Video here: http://www.youtube.com/watch?v=QgZcIavM_Oc&feature=youtu.be

Regards Itsu

[verpies]

I tried to use the same setup as Luc did (625Hz square wave 10V rms as input)

That's a good place to recall, that the inductive reactance to a square wave is always 81% of the inductive reactance to a sine wave of the same frequency and RMS value.  See here.

Video here: http://www.youtube.com/watch?v=QgZcIavM_Oc&feature=youtu.be

The first scopeshot shows that the green current waveform curves up inside one of the blue ellipses...most likely due to beginnings of saturation.
In an ideal inductor the current waveform would never curve up like this.  See here.

The second scopeshot shows a discontinous current (a current spike) in an alleged RL circuit.
The current in an ideal RL circuit will never be discontinuous like this. 
In other words - current spikes are abnormal in an ideal inductor, even if that inductor is switched rapidly (...but voltage spikes are normal).

However, the interwinding parasitic capacitance is capable of creating such current spikes when stimulated by a rectangular waveform.
This parasititc capacitance will and does form a parallel LC tank with the inductance of the coil. This LC tank will and does ring/oscillate. 
If you know this ringing frequency and the inductance of the coil, then you can approximate this parasitic interwinding capacitance as C=1 / [ L(2πf)²].

The third annotated scopeshot shows the energy returned to the power supply (the SG) as the blue area above the red curve and the energy delivered by the power supply (the SG) as the white area under the red curve.

P.S.
How high are these current spikes anyway?
If I were you, I'd place the current probe after the voltage measuring probe, as a matter of principle.  Imagine, that the red crocodile clip is a small resistor...and the voltage sensed by the scope is subjected to the voltage drop of that resistor.  Now the voltage sensed depends on the current flowing and no longer reflects the true voltage output of the SG....in this case by μV.

[gotoluc]

In the mean time i tried to replicate what Gotoluc is doing/measuring with this bifilar coil.
My bifilar coil is measured 1.3 Ohm and 127mH.

I tried to use the same setup as Luc did (625Hz square wave 10V rms as input)

I measure the voltage across and the current through the coil and using the math function (ch1 * Ch4) to show the power.
I am using a current probe which is set at 2mA/mV, meaning that the current (and the power) needs to be multiplied by 2

As i have a slightly higher ohms value in my coil, my signal on ch1 is somewhat stronger then yours.


Video here: http://www.youtube.com/watch?v=QgZcIavM_Oc&feature=youtu.be

Regards Itsu

Thanks itsu for the replication attempt and making a video to share your results.

Luc

[itsu]

P.S.
How high are these current spikes anyway?

Thanks again verpies for this piece of information.

Here a picture of the current spike.
Again  times 2 = 144mA pp @ ringing frequency 7.2MHz

Regards Itsu