Re: ideas to drop resonant freq?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Larry, 
Comments intersperced below: 

Tesla list wrote: 
>
> Original poster: "Laurence Davis by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <meknar-at-hotmail-dot-com> 
>
> I've tried various things to drop the resonance on my coil. its tapped at 
> between the 4th and 5th turn. its using a about 2500w with 4 12kv/30ma NSTs. 
> I've learned a few things in the process, but haven't dropped the freq yet.




The resonant frequency of your coil should be based on your secondary L and
your secondary C+Ctop values. The transformer will have nothing to do with it.
The transformer is nothing more than a power supply to charge your primary
capacitor. 

The secondary resonant frequency = 1/(2*pi*sqrt(L*C)), where L = sec
inductance, and C = (secondary + topload capactance). 
The primary resonant frequency = "same" formula, where L = primary inductance
from tap, and C = primary tank capacitance. 

>
> heres a list of what I've tried. I'm looking for suggestions on what to try 
> or what to test. 
>
> 1) tried wrapping a new secondary. but miscalculated, and have fewer turns 
> than first secondary (which will raise resonance, right?).




Yes, if all else remained unchanged, fewer turns will "increase" the secondary
resonant frequency. 

>
> 2) removed 300ft spool of RG6/u that was being used to connect to my ground 
> rods.  essentially an air core inductor.




Nope, has nothing to do with it. 

>
> 3) removed 1 or 2 NSTs to better match resonant cap needed. here's my logic 
> on that.  java tesla calc says resonant cap for 12kv/120ma is 26nf or so. 
> which my cap is within 5pct or so.  supposing that cap value needed is more 
> than what i have, then reducing number of NSTs will reduce the cap reqd. 
> therefore will lower resonance. it didn't.




Ok, I think possibly there is a confusion here between "resonant charging" and
"resonant frequency". 
First, reducing the primary cap size will "increase" the primary resonant
frequency, BUT (this is important), the primary circuit (primary coil and tank
cap) must be tuned to the same resonant frequency of the secondary resonant
frequency. Therefore, if you reduce your tank cap to half it's value, you will
then need to increase your primary turns in order to tune the primary resonant
frequency to the secondary's resonant frequency. When you do this, the resonant
frequency matches the secondary's and nothing changes. First, lower the
resonant frequency of the secondary then tune the primary to the secondary. 

To tune to a lower frequency at the secondary either increase L or C. Since C
is a function of the turns, simply add more turns to the secondary. This will
increase both L and C and the frequency will be reduced. You could also go to a
larger diameter secondary which will increase the inductance (even if you leave
the turns the same). Another method is to increase the top load capacitance
(larger top). Because Ctop is added to Csec as part of the loaded resonant
frequency (loaded meaning top load is accounted for), a larger top load will
reduce the resonant frequency (to a degree). If you go too large, you may not
be able to breakout. Like I said, there are limitations. 

JavaTC has a BIG BLUE "README" link right next to the transformer resonant cap
size value. You really should read this. 
Here is what you will "read" if you click the link: 

*************************** 
Transformer Resonant Capacitor 
The 3 words above are used to describe the condition when the tank capacitor is
resonant with the transformer at the natural line frequency (50 or 60 Hz). 
This resonant charging effect is in the form of a higher current which charges
the cap to a higher voltage assuming the spark gap fires at a consistent rate.
Although this looks desirable, be aware that a resonant charging condition will
cause the output voltage to rise substantially and may over-volt the
transformer and/or tank cap. The charge and discharge sequence is controlled by
the spark gap. If the gap can be designed to conduct at the same rate and same
point along the AC half-cycle, resonant charging can be beneficial. 

Although JavaTC identifies the Transormer Resonant Capacitor for your design,
JavaTC by no means is telling you this is the size of the tank capacitor which
should be used. In some cases, it is telling you the value to stay away from,
and in others cases, the value to use (if your planning to operate the coil in
resonant charging mode). For an excellent study of resonant charging, visit
<http://www.richieburnett.co.uk/resonant.html#resonant>Richie Burnett's
study of
AC Resonant Charging." 
*************************** 

I highly recommend visiting Richie's web site. 

>
> 4) learned that there are "diminishing returns" from increasing the spark 
> gap distance. Also interrelated was the top load required changes per the 
> spark gap dist.  meaning: the spark length maximum is not at a wide open 
> spark gap. (does this sound accurate?) this I would guess affects charging 
> time of the cap.  in essence, there is an "optimum" spark gap maximum 
> distance with regard to spark output(which could be read as spark length, 
> more or less branches, decibel level, etc)




The spark gap "gap" should be set to the arc voltage of your transformer. If
you have 1 transformer or 4 in parallel, you will still have 12000 volts. When
you parallel more transformers, you increase the power supplies ability to
charge the tank capacitor at a faster rate as there is more current available.
This "can" allow the use of a larger cap size, but ONLY if your system is
designed for the larger cap size (primary turns are considered, secondary, top
load, etc...). However, it will not increase the arc distance. 12000V will arc
at some determined distance (defined by your electrodes and air desity). Just
because there is more current, doesn't mean you can arc a larger gap, it simply
means that the cap can charge to potential faster. A higher voltage would allow
a gap distance increase. 

NOTE, if you have a gap which is wider than 17kVp arc capability, then you risk
overcharging the cap and possibly damaging the cap and/or NST. 

>
> 5) next tries will include a smaller dia secondary with less turns, and a 4" 
> secondary with more turns. significantly. perhaps 30-50% more.  and a larger 
> cap that is adjustable AND in a smaller box.  i'll aim for 40nf with 5nf 
> steps, and break the last 5nf into 5x1nf.




Larry, would you be so kind as to provide your secondary dimensions, wire size,
turns, top load type and size, primary wire, ID and OD, turns, tank cap size,
etc.. 
This would help a great deal. Reducing the resonant frequency of a coil is
easy, but there are "physical limitations of practicality" which rule the
world. Also, could you provide your "desired" frequency? 

>
> experimentation helps me see the truth behind the math.  I wish i had a 
> stronger grasp of the fundamentals behind it all.  with time it will come. 
> thanks for any comments. 
>
> Larry.




Experimentation is the ONLY WAY to learn. I commend you for going the
experimentation route. I'm the guy who wrote JavaTC, but no computer program
can take the place of experimentation, however, it programs and measurement go
hand in hand. It keeps us on the right track and prevents us from going down
"myth road". 

Best regards, 
Bart