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Non-Linear Coil Winding Experiment.



---------- Forwarded message ----------
Date: Sun, 12 Oct 1997 21:16:27 -0600
From: terryf-at-verinet-dot-com
To: tesla-at-pupman-dot-com
Subject: Non-Linear Coil Winding Experiment.

To all,

	I have been experimenting with different types of coil windings.  Using my
computer-controlled Tesla coil winder, I made three coils.  They were all
wound with the following parameters:

	300 turns
	3 inches in diameter, wound on cardboard mailing tubes.
	10 inch long windings on 12 inch long tubes.
	#30 enameled magnet wire 0.0110 inches in diameter.
	235.6 feet of wire.
        No top terminal was used.
	
Coil #1 was wound with linearly spaced windings.

Coil #2 was wound with the winding spaced proportional to d=cos(x).  In
other words, the coil windings were spaced so as to give a linear voltage
distribution along the coil.  Assuming V is proportional to sin(x).  (x is
the distance along the coil).  This coil has windings bunched together at
the top.

Coil #3 was wound with the windings spaced proportional to d=cos(x)^2.  In
other words, the coil windings were spaced so as to give a linear
capacitance distribution (turn to turn) along the coil.  Assuming C is
proportional to V^2.  This coil has windings very bunched together at the top.

The results are as follows:

Coil #1
	F0 = 1597.6 kHz
	Inductance = 2.07 mH
	Self Capacitance = 4.79 pF

Coil #2
	F0 = 1815.7 kHz
	Inductance = 2.16 mH
	Self Capacitance = 3.56 pF

Coil #3
	F0 = 1829.0 kHz
	Inductance = 2.31 mH
	Self Capacitance = 3.28 pF

The field profile around each coil was mapped at resonance to determine the
shape of the field around each coil.  This was done by placing a sheet of
paper directly behind the coil and bringing a grounded rod near the coil.
As the rod approaches the coil it de-tunes the coil and the field strength
decreases.  (As measured with a short antenna connected to an oscilloscope).
The point at which the field strength decreased by 1/SQR(2) was marked on
the paper.  A signal generator drove the coils.

Coil #1 had an approximately 13-inch diameter field that was elongated along
the length of the coil.  No big surprise.

Coil #2 had a similar but smaller field 11 inches in diameter.

Coil #3 had a field that was very circular in shape.  This circle was
centered at the top of the coil windings and was approximately 8 inches in
diameter.

Conclusion:  

Coil #1 performed as expected.

Coil #2 appears to have succeeded in evenly distributing the winding to
winding voltage along the coil without harming any other parameters (they
improved considerably).  Such a coil would be much less likely to arc
between windings.  It would also have better field distribution around the
coil allowing higher voltages to be achieved.

Coil #3 has the lowest self-capacitance and the highest inductance.
Theoretically, this is optimal but the field distribution around the coil
would tend to promote early breakdown. 


In other news....

        My real time voltage and current probe project is going slowly.
Nothing useful yet.  Big problems with bandwidth but still very hopeful.
        
        I will write up the plans for the computer-controlled coil winder
sometime.  It is really cool and not too expensive (~$150).  

        Going to try to get a web page going for pictures and info.
Considering doing Tesla book on web page rather than the usual paper thing.  


Later

        Terry   

terryf-at-verinet-dot-com