I have a self wound coil with 52850 turns of 0,15 mm CuL on a plastic core (base diameter 32 mm, length 250 mm).
With an LCR meter I could measure an inductivity of 13,32 H.
Now I'm looking for the best way to measure the self resonance frequency SRF of that coil with my NanoVNA V2.
I think, the SRF could be a bit below the 10 or 50 kHz of the NanoVNA.
Is there anyway a possibility to measure the SRF?
How would you do it?

Look for where the phase crosses zero. With the inductance that high the
SRF will be very low. That could be a problem seeing it on the NanoVNA.


On Sat, Oct 30, 2021, 03:22 Dirk <dottensm@gmail.com> wrote:

> I have a self wound coil with 52850 turns of 0,15 mm CuL on a plastic core
> (base diameter 32 mm, length 250 mm).
> With an LCR meter I could measure an inductivity of 13,32 H.
> Now I'm looking for the best way to measure the self resonance frequency
> SRF of that coil with my NanoVNA V2.
> I think, the SRF could be a bit below the 10 or 50 kHz of the NanoVNA.
> Is there anyway a possibility to measure the SRF?
> How would you do it?
>
>

Maybe late but anyway how i would do it throught a indirect way:

I would take another coil for example 1mH and determine the parasitics of that from the resonance frequency. Then i would plug the 13.32H choke in parallell to the 1mH choke or similar, since 13.32 >>>>> than 1mH the parallel connection will not change the effective inductance at all as long as there is very low magnetic coupling between them by using a core material for the 1mH core or shield it from the magnetic coupling.

This means all change in SRF in the system going from 1mH to 1mH||13H would come from the parasitic capacitance of the 13H coil (which i assume is much larger than the 1mH coild) and you in this indirect way able to calculate the parasitic capacitance of the large coil and by that calculate the first SRF of the large coil.

With the dimensions provided,
and assuming enamel thickness of 0.0635mm with a dielectric constant of 3,
a crude estimate of the self capacitance is 17764pF per turn or 939uF total.
https://www.emisoftware.com/calculator/wire-pair-capacitance/
In parallel with 13.32H yields a self-resonance around 1.4 Hz.
The lowest frequency on my nanoVNA is 10kHz.

You could put the coil in series with a 16 Ohm resistor,
and sweep it with the audio generator function of the free PC software AudioDope http://www.audiodope.org/.
AudioDope can generate tones from .01 Hz to 5.5 kHz.
Use the AC voltmeter on a DMM to see the voltage peak across the coil, or a dip in the voltage across the resistor.

13.32 Henries is huge.
The back EMF of opening the coil in circuit may exceed the 5kV dielectric breakdown of the insulation.

Treat the setup as you would if the NANOVNA were a grid dip oscillator.
Attach a small coil to the source port of the NANO. Set the NANO up to
measure reflection from the source port, S11. Set tje NANO-attached small
coil close to your coil under test end-to-end - loose coupling. Sweep the
band(s) of interest. The reflection will exhibit a dip where the coil
under test is resonant.

Dave - WØLEV

On Wed, Jan 26, 2022 at 1:04 PM Torsor <ts.mixed.stuff@gmail.com> wrote:

> Maybe late but anyway how i would do it throught a indirect way:
>
> I would take another coil for example 1mH and determine the parasitics of
> that from the resonance frequency. Then i would plug the 13.32H choke in
> parallell to the 1mH choke or similar, since 13.32 >>>>> than 1mH the
> parallel connection will not change the effective inductance at all as long
> as there is very low magnetic coupling between them by using a core
> material for the 1mH core or shield it from the magnetic coupling.
>
> This means all change in SRF in the system going from 1mH to 1mH||13H
> would come from the parasitic capacitance of the 13H coil (which i assume
> is much larger than the 1mH coild) and you in this indirect way able to
> calculate the parasitic capacitance of the large coil and by that calculate
> the first SRF of the large coil.
>
>
>

--
*Dave - WØLEV*
*Just Let Darwin Work*

It sounds like the secondary of a Tesla coil. Measure the resonance through the coupled secondary, since that's what you actually have to resonate.