Re: secondary frequency problem (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Tue, 18 Sep 2007 00:16:25 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: secondary frequency problem (fwd)

Hi Chris,

2.7MHz is closer to 3 than 2. If you build a coil that with a 
fundamental frequency at 2.7MHz (calc), then you must have some means of 
driving it with 2.7MHz if using a signal generator and scope setup. If 
you can't get past 2MHz on your generator, how can you say that it 
doesn't ring at 2.7MHz? This must be an really small coil. Do me a 
favor, send me a Javatc output so I can see the details. Your probably 
just reading lower harmonics at the moment.

A resonant transformer isn't a typical turns ratio transformer such as 
an NST or other iron core transformer. This is a resonant transformer 
where the output potential is a function of the resonant condition which 
exist at the fundamental frequency. If you want to calc output, use the 
capacitances or inductances as follows:

Vout = Vin x sqrt(Cpri/Csec)

Cpri is a nice fat capacitance and your actual tank cap is all that is 
needed. Vin would be your cap voltage at the bang. Csec is a bit tricky. 
What you want there is the capacitance at the moment in the cycle when 
all the energy is stored in the capacitance. Javatc gives you this C 
value and is termed "Cee" meaning "equivalent energy capacitance".

Typically, coil potentials range from 200kV to 500kV. Imagine if the 
number of turns (pri and sec) were used. Say for example an average 1000 
turn coil with 350kV output. This means the primary would have to have 
350 turns! Can you imagine that? So, how do we get to 350kV with only 
say 10 turns? The answer is resonance (or that point where the inductive 
and capacitive reactances are minimum). At that point, we then get a 
high current characteristic due to reduced overall impedance which in 
turn provides the high output potential, so think of it as a function of 
the coils reactances.

As far as the Q output? Way off for your coil I expect (and is why I 
would really like to see your detail). Q is calc'd from the Fraga AC 
resistance and it's this AC resistance which is probably off. The value 
is usually good for coils greater than 3:1 h/d as stated in the help 
output of Javatc. But, your coil I'm sure is small and there are no 
actual Q measurements for a coil that small. If I were you, I would 
ignore those two outputs and simply measure it yourself. Just click on 
the Q text in front of the output box. I describe in the help file popup 
how to measure Q. It is a difficult measurement as far as accuracy and 
takes some practice. In my opinion, the greatest difficulty is equipment 
resolution.

Take care,
Bart



Tesla list wrote:

>---------- Forwarded message ----------
>Date: Tue, 18 Sep 2007 13:53:32 +0100
>From: Chris Swinson <list@xxxxxxxxxxxxxxxxxxxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Subject: secondary frequency problem
>
>Hi all,
>
>I spaced wound a coil which according to javatc and my own workings, should 
>be around 2mhz.
>
>However, when testing on my signal generator, I seem to find the frequency 
>is about 800khz with a harmonic at about 1.2mhz. I can only get to 2mhz on 
>my signal generator, but the voltage on the coil keeps dropping.
>
>The voltage ins and outs are as follows...
>
>10mv = 140mV  (x14)
>20mV = 325mV (x16)
>40mV = 700mV (x17)
>80mV = 1400mV (x17.5)
>1V    =  17V (x17)
>2V =     35V (x17)
>
>The "gain" seems to go form 14 to about 17 for some reason. I would have 
>thought the voltage gain would have been a lot higher aswell.
>
>Also seems strange that there does not seem to be any real relation to input 
>volts vs. output volts, the gain is always about 17. I would have expected 
>double volts in = double volts out or something along those lines, but does 
>not appear to hold true.
>
>going form 10mV input to 140mV, then double the input to 20mV would have 
>expected 280mV output. In any case the figures are hard to crunch as the 
>gain is altering a fraction which is probably throwing the results a little. 
>Going from 40mV to 80mV seems to work out better, x2 input (40mV to 80mV) 
>gives 700mV & 1400mV output. so it holds true I think that double volts in = 
>double volts out ??
>
>I think the actual gain is a fraction off 17, though it is hard to read 
>volts exactly on the scope also. so x17 is pretty close. I guess with 10KV 
>input I would obtain 170KV output. So does my x17 figure = the Q of the coil 
>?
>
>JavaTC states the Q as 1,000 which does not seem right. Also I still do not 
>understand the frequency problem. JavaTC says 2.7mhz. I don't know if that 
>is true as I can't get past 2mhz on my signal generator, but 800khz seems to 
>be the figure. 1.2mhz almost does nothing, and volts just keep dropping 
>after that. below 800khz it looks like about 300khz is another harmonic but 
>it is hard to tell. So assuming the coil is 800khz, why does it calculate as 
>2.7mhz ??
>
>Cheers!
>Chris
>
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