Thanks Bart,
Very helpful, thank you. I was wondering what was the origin of the 8
Mhz superimposed spikes I see on my scope trace?
At the moment my secondary is 5 cm below the primary - I will calculate
the corresponding k, and try to rig something to move it up or down to
see the effect on performance. I still have not finished the Terry
filter, but the static spark gap is now on PPE instead of wood
Cheers
Thomas
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of bartb
Sent: 12 April 2008 02:51
To: Tesla Coil Mailing List
Subject: Re: [TCML] Tesla Coil tuner - scope traces questions
Hi Thomas,
I revamped my model for your coil with the new primary specs. This is
how JAVATC interprets the coil:
http://www.classictesla.com/temp/ThomasRyckmans.gif
and here's a JAVATC output for my inputs and outputs for your coil (most
everything is in centimeters):
http://www.classictesla.com/temp/Thomas%20Ryckmans.txt
JAVATC showed 828kHz and the tune point should be about 3.25 turns
(pretty darn close to your 833kHz measurement). According to your
primary tapping measurements, this area was giving the greatest voltage
rise. I think your analysis for what you observed is fine. The primary
should be off by about 270kHz from turn 2 to turn 3 and this will affect
voltage rise by about 35% on the primary scope observations.
I put your primary even with the bottom secondary turn. Coupling is
0.135 which is nice! You should be sparking away. BTW, in the .txt file,
look near the bottom at the static gap. I calc'd the 4 electrodes in
there (ignore the RSG stuff as it doesn't apply). But in the static gap
section, pay attention to gap spacing between electrodes. This spacing
is a ballpark for your transformer. Opening that gap up will increase
breakdown voltage and although this is certainly easy to do, it's not
wise as the voltage can kill the transformer, especially if it's an NST.
Take care,
Bart
Ryckmans, Thomas wrote:
Hello,
I've used a signal generator to try and tune my small coil. Because of
the small secondary (Diameter=70 mm, about 480 turns, 15 turns/cm, 32
cm
height; measured L is 3.5 mH; top load a bit more than 7 nF and coil
self capacitance 5 nF) resonance frequency is quite high - about 760
kHz
calc and 833 kHz measured using a source.
I am using http://deepfriedneon.com <http://deepfriedneon.com> to
calculate values
thanks for having a look!
For all measurments, secondary and primary were physically separated
1. Here is a picture of my scope's trace when off resonance (1)
http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#518789176
5716440722
<http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#51878917
65716440722>
then I tuned the signal generator until I got (2):
http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#518789179
1486244514
<http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#51878917
91486244514>
strange looking wave form. It collapsed very near that frequency but I
could not take a picture. Is this the resonance frequency? Removing
the
secondary and reading the scope I got 833 kHz.
Then I kept my source at 833 kHz and plugged in the primary in
parallel
with the tank caps and shorted spark gap. My salt water caps is now
11.6
nF and my primary is inside diameter 110 mm, tube 8mm diameter, side
to
side spacing 10 mm as per bartb recommendations - I did rebuilt the
whole primary].
Calculated inductance is
1.3 microH for 2.5 turns,
1.9 microH for 3 turns
2.6 microH for 3.5 turns
3.4 microH for 4 turns
And to reach "around" 833 kHz with my 11.6 nF cap I would need a bit
more than 3.5 turns.
Now for measurments:
When tapping at 2 turns I get trace (3) with amplitude about 2.5
squares
x 50 mV = 125 mV
http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#518789180
8666113714
<http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#51878918
08666113714>
at 3 turns (Picture 4) I get amplitude 4.4 squares at 50 mV = 220 mV
http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#518789181
7256048322
<http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#51878918
17256048322>
And at 4 turns I get picture (5) 3.6 squares at 50 mV = 180 mV
http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#518789175
7126506114
<http://picasaweb.google.co.uk/Thomas.Ryckmans/TeslaStuff/photo#51878917
57126506114>
So I think I should get correct tuning between three and four turns...
Is this analysis correct?
Are these traces the ones I should expect?
I thought I would get a much more marked effect around resonance!
Also - what is the origin of the small spikes in the three last
traces,
especially picture 5?
Is this what is called ringing? I estimate the frequency of the small
spikes to be around 8 MHz or so...
And why is the amplitude so low? My source delivers about 4 volts
without load
Many thanks for your comments - as usual
Thomas
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla