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Re: Discharge impedance of a CW Tesla coil
--- Tesla List <tesla-at-pupman-dot-com> wrote:
> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
> Hi All,
>
> I have been playing with my patched together RF
> generator and measurement
> equipment. Today I took off work early to do
> something important. ;-)) I
> was able to measure the impedance of the brush
> discharge of my coil run
> from the generator in CW (continuous wave) mode.
>
> The secondary is 1180 turns of #24 wire on a 4.25
> diameter PVC form 26.125
> inches long with an inductance of 22.1mH (from my
> little 9kV/30mA coil).
> The primary is 10 turns of 0.092 inch Litz that is 6
> inches in diameter.
> That is about 2uH. I used the generator to drive
> the coil at 100, 200,
> 300, and 400 watts delivered power compensating for
> the small reflected
> power. All the coil components stayed cool so I
> assume almost all the real
> power was going to the discharge. I can adjust the
> frequency to get the
> lowest reflected power so it is very well in tune at
> each level. I ran out
> of tuning range at 400 watts with the fiber optic
> probe transducer on the
> top of the coil (added top capacitance). I will
> need to wind a new
> slightly higher frequency secondary to get the
> generator's full 900 watts
> forward power in tune with the probe in place.
> Hopefully, nothing will
> melt down at that level...
>
> It appears that the discharge is composed of a
> resistive region a few
> inches in diameter (the part you see) that provides
> a relatively low
> resistance path to a capacitive sphere around this
> discharge. Thus the
> discharge is a real resistor in series with a
> capacitance around the discharge.
>
> Obviously, I need to write one of my papers on this
> to fully explain all
> the details, but for a point discharge at around
> 330kHz, I got a discharge
> impedance of:
>
> Z = 20K + 3K ohms / 100watts delivered (real
> resistance) in series with
> 0.58pF + 0.070 pF / 100 watts delivered
> (capacitance).
>
> The actual numbers are as follows:
>
> Delivered power Resistance Capacitance
> 100 22887 0.665pF
> 200 26122 0.754
> 300 29409 0.827
> 400* 30779 0.892
-----
Hi Terry,everyone,
Just a small input.
Interesting figures for resistances.As power and arc
lenghts go up you have more resistance.This is in
oposition to the case of usual TC operation where arc
resistance remains more- less same or even drops down
to some extent in larger systems as more power is
added.
Regards,
Boris
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