The bifilar pancake coil at its resonant frequency

[itsu]

Haven't followed this (my own) thread anymore. But as it is mine, here is a related post:

I made some more coils. I earlier used bifilar coils to be pulsed. I now tried single wire coils:

I connected the two single wire pancake coil in series, to my IGBT pulse driver.
The IGBT became extremely hot (much hotter than with a pulsed bifilar coil).
I guess this is because of the back emf produced, by the pulsed coils.
To avoid it, i should use a diode and a resistor in parallel with the coil, to burn the energy of the back emf.

So, I guess I will be making another bifilar pancake coil, to pulse in series.

isnt it funny, that the bifilar coil doesnt produce this troublesome back emf?

Telsa in his patent states, the back emf of a normal single wire coil, can be fixed with capacitance... but how?

I must say... these bifilar coils have their advantage (the IGBT stays cool)

Hi Evo,

that would be great, but could you perhaps show some scope shots of your IGBT drain in both situations (Bifilar coil versus single wire coils)?

Thanks,  Itsu

[synchro1]

Re: what is the physical meaning of "Negative Inductance"?

"The most fundamental reason is that the electric energy stored in this element is more than the magnetic energy stored. Circuit designers interpret it as a capacitor".

Here's what I gathered: Increased inductor field strength creates a reluctance to changing current, but some current that fails to pass is stored in the inductor along with the magnetic field. Now, this is referred to as "Positive Capacitance" except the frequency reactance is reversed. The amount of positive capacitance in an inductor of charged magnetic field strength is measured in 'Negative Henries" of inductance, and has to be proportional to the intensity of the flux field.

[gyulasun]

Hi Itsu,

To refine this tuning procedure, both coils would need to be paralleled with a variable capacitor
and first both of these capacitors would need to be set to a half capacitance value (half opened capacitors).
This way you could tune any of the coils either above or below of the frequency established by
the half opened capacitors, and this then could help finding the best coupling where the response
has a single peak at the common resonance frequency for both coils.  Both LC circuits mutually detune
each other as they are coupled i.e. getting closer to each other hence the need to either increase or
decrease the individual coil resonancies and this can be done by opening or closing the capacitors.

But this tuning you nicely show in the video may also be enough already to test the load of a LED or
any other load connected to the pick-up coil how it influences the small current consumption of the
main TBP at the paralel resonance - this was the original goal for tuning the pick-up coil to be resonant
with the main TBP coil.

Thanks
Gyula

I made a similar TBP coil like the one i already had and which has similar specifications (1.4 Ohm each coil,
130uH each coil etc.)
With a fairly great distance between them, i can tune them (using a 45 - 450pF variable capacitor on the
driven TCP coil) to resonate around the same frequency.
When narrowing the gap between the TBP coils we see the resonance points getting split due to
overcoupling, see screenshot below.

Yellow is the driven TBP coil being sweeped between 200 and 400 Khz.
Purple is the pickup TBP coil at the same resonance frequency.
Blue is the FG sweep signal.

Video here:  https://www.youtube.com/watch?v=2iXfDTRQKZ0

Regards Itsu

[Magluvin]

Hi Itsu,

To refine this tuning procedure, both coils would need to be paralleled with a variable capacitor
and first both of these capacitors would need to be set to a half capacitance value (half opened capacitors).
This way you could tune any of the coils either above or below of the frequency established by
the half opened capacitors, and this then could help finding the best coupling where the response
has a single peak at the common resonance frequency for both coils.  Both LC circuits mutually detune
each other as they are coupled i.e. getting closer to each other hence the need to either increase or
decrease the individual coil resonancies and this can be done by opening or closing the capacitors.

But this tuning you nicely show in the video may also be enough already to test the load of a LED or
any other load connected to the pick-up coil how it influences the small current consumption of the
main TBP at the paralel resonance - this was the original goal for tuning the pick-up coil to be resonant
with the main TBP coil.

Thanks
Gyula

I was thinking on the tuning. If the coils are wound as neatly as possible and one coil res at one freq and the other at a say higher freq, then one could try unraveling the lower freq coil just a tiny bit at a time, where that would lower both capacitance and inductance thus raising the freq to equal the other coil.  No?

Mags

[gyulasun]

Yes, Mags  removing a few turns can also be a solution for fine tuning.  Especially in case when someone
has no variable capacitor in his junk box.  Tuning is surely easier by variable capacitors or trimmers though.

Gyula