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?

Hi Tinselkoala,

i guess its not, as when testing a simple 1.2uF MOV capacitor (with 10M Ohm bleeder) with a 1.3KHz sign wave signal,
it shows a phase shift of 76 degrees with 6.21V Rms at 62mA Rms current.

Doing the numbers by hand P= U * I * Cos Phi shows a power of 93mW, while my scopes math shows 84mW mean (remember, current and thus power times 2 because i use a probe terminator in 2mA/mV setting)
Its close but not spot on 

So allthough the above pictures of the in-/output show only a "slight" phase shift, we better forget the mentioned power figures.

Regards Itsu

   

[itsu]

Of course, such tuning can be a tedious process, the final goal would be to achive the critical coupling which would insure maximum power transfer with a single peak response (notice that you also get a single peak response when the coils are undercoupled). 

Hi Gyula,

yes tell me about it   

Whenever i moved a core, the whole setup had changed and i had to move the coil again etc.
Guess its best like you said to use a trimmer to fine tune this and leave the cores fixed.

Anyway, thanks for the link and info, allways good to have some information handy.
The over coupled picture in there i had in mind when i spoke earlier of my idea of an overcoupled bandpass filter

Regards Itsu

[gyulasun]

...
Whenever i moved a core, the whole setup had changed and i had to move the coil again etc.
Guess its best like you said to use a trimmer to fine tune this and leave the cores fixed.

...

Hi Itsu,

If you wish to tinker with this parallel-series LC circuit to get the maximum power transfer (i.e. to achieve critical coupling between the coils), first you would need to separate the two bobbins so that different distances could be set between the coils i.e. to be able to vary the coupling.
Then divide the tuning ring cores equally: I assume you have say 6 then 3 of them would be inserted for the left and the other 3 for the right hand side coil or if you have only 3 ring cores, then just use 1-1 and look for the new (increased) resonant frequency. I edited a snap shot from your video to show how I think the positioning of the ring cores inside the bobbins, this way the changing distance could influence the resonant frequency of the LC circuits in the least degree (the cores that give the permeability would be the furthest away from each other).

You could use an L meter for each separate coil to position the cores in each bobbin to their outer edge area as I tried to indicate in the photo by ring symbols, and adjust both coils separately for the same uH or mH value by fine positioning the cores and fix them, then attach the bulbs and the tuning caps and look for the new resonance at an initial distance of say 5cm.

Then try to decrease the distance by say 1cm and watch the brightness of the right hand side bulb whether it increases:  here I have assumed of course that the 5cm distance causes an undercoupled response. IF this turns out to be the case, then the brightness of the right hand side bulb will be increasing as you reduce the distance between the coils, till the brightness starts decreasing at certain closeness: it may indicate you have reached the overcoupled case where two voltage peaks start to appear below and above of the resonant frequency which so far has been kept more or less at the same value. (In the overcoupled case the response will have a dip at the original resonant frequency as you surely know.)  By positioning the cores towards the opposite edges of the bobbins, you may not have to use trimmer capacitors for fine tuning:  if you carefully retune the generator a little when you reduced the distance to say 3cm then you have compansated the detuning effect of the increasing mutual inductance (here I assume of course that at 3cm you still have not reached the overcoupled case and brightness would further increase when you go to a 2.5cm distance from the 3cm).  At the critically coupled state the single peak response widens with respect to the undercoupled case, meaning the bandwidth of the two LC circuits gets widened but still there is a single peak.

This is briefly the tuning process, if you have questions please ask.

Gyula

[verpies]

1 the output bulb (right) power at resonance            (2x 122mW  = 244mW), (Ch1 RMS x Ch4 RMS)
2 the input power of the whole system at resonance  (2x 147mW  = 294mW), (Ch3 RMS x Ch4 RMS)
3 the input bulb (left) power at resonance                (2x 13.5mW =  27mW). (Ch2 RMS x Ch4 RMS)

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".

[itsu]

This is briefly the tuning process, if you have questions please ask.

Gyula

Thanks Gyula,

Its a clear process to follow, i will take a shot at it later this week.

Regards Itsu