One model of L2 can run at several different frequencies. But which is the best?

[VNTC]

To certify the title is real, I do the following things
List the hardware:
First we have L2 then we make additional in order some main component:
C2; L1; C1; discharge wire that all for the resonance transformer of a DRSSTC.
There are all parameters:
L2= 1900turn s copper wire awg34; 3.5’ diameter ;15” long = 61mH (JavaTC)
C2= include 4 size’s 20cm; 25cm; 40cm; 50cm
L1=8turn flat spiral coil copper tube 1/4” 4.4 inner diameter 9.5’ outer diameter =
11.5uH (JavaTC)
Image 1 the coil.

Depend on the size of the toroid (C2 capacitance value) we can choose some size of the primary coil and capacitor tank. I think everybody want to choose the ratio L2/L1=C1/C2 as high as better. But practice show that higher 10000 (voltage gain factor=100)is not so good and lower 5000 of course not so good too. May be 7000-8000 is better. In this case this factor is about 5500 to save the low quality IBGT at low Apk I done a set of tests as follow:
Electrical control established and keeps them constant.
Halt bridge FGH60N60SMD low price China’s product.
Bus =320VDC.
Burst duration =100us.
Break per second= 200/s.
Image 2 several size toroid’s.

I replace the toroid step by step from small size to big size, tuning the coil until hit good tuning at every step, record the result on the notebook as follow:
 
After that i make double test set by reverse route to verify what was done.
Finally look at the information table and summary review:
First i saw the positive and reasonable signs between columns 2;3.
Last column give me a sudden contradiction.
Combine all information easily can answer the question in the title
140 kHz the best frequency for this coil with the conclusion “lowest consumption, highest power out”
One more special result I think need to report running at that point the frequency is very stability, from 20us to 140us burst duration it change very little, hard to recognize simply by looking the wave on oscilloscope.
I need to talk more about my L2 coil details
The copper enamel wire length of my coil is
1900*π*9=537.2m= λ/4
λ=2148.8m
F=300000/λ=139.6 kHz (this is frequency that the coil run at quarter length wave λ/4)
There was a coincidence of the results of the 1st line and quarter length wave law of the ." US Patent No. 645576, Nikola Tesla, System of transmission of electrical energy, filed September 2, 1897; granted March 20, 1900” from source  The History of Tesla coil (Wikimedia)
To be honest, I did not expect this result. On the contrary, I was looking for intense sparks of toroid 40cm like DRSSTC2 3.5 "of laboratories Loneoceans because the results were impressive. This is only surprising, not heartbreaking.
Say something about RF alternating current.
Image 3 RF Alternating current in transmission line. (from Wikipedia English)

Let’s look at image3 and image4 they show that to  obtain 1/4λ rule no need to fall into the correct position 25% of the wavelength, just stay in the area from the position 20% to 30% wavelength has been the perfect area.
For example the frequency matches 1/4λis 100 kHz that range will be 80 kHz to 120 kHz.
Image 4 RF Voltage/position of wavelength.

Of course I know what i wrote may be something isn’t true. So need to verify by other one.
Please let i say something about myself.
I am 69 year old, i play Teslacoil to find the spark as long as possible for fun 40% the rest i would like understand thorough and exactly how it work 60%.
 In modern times the science side of Sir. Tesla's patent has not been confirmed or denied in the Teslacoil player community. That is  DRSSTC is a quarter resonators or is not?
I look forward to invite 2 more enthusiastic coil man make the tests  to verify this article true or fails. Need to make the tests on 2 different level of frequency, one at 200kHz and other at<100kHz.
Theoretically in knowledge resources about Tesla coil. We find the position of the resonant frequency point on the L2C2 reference point and then add the L1C1 reference point. We will get many results just like geometry positioning by 2 reference points if there is a 3rd projection we will immediately locate a single result quickly,λ/4is that point! So we can say that after finish wire winding a secondary coil we can know what frequency it will run better by the parameter “
The length of wire winding”
A short video clip (140us; 200b/s; 500w consumption; 2.5joules/bang) this result get after I have done a 5nd step: tape primary coil at 6.3turns (8.8uH) to increase primary current to 250Apk at 140us burst duration.
    Many people succeed without caring about it because most normal models accidentally enter the green area very easily because this range is so wide or very badly enter the yellow zone so they still run. Only a few schools with incredible shapes will lot in the red and it will run very badly.
   Quote:
   Tesla was not the first to invent this circuit.[21][15] Henry Rowland built a spark-excited resonant transformer circuit (above) in 1889[2] and Elihu Thomson had experimented with similar circuits in 1890, including one which could produce 64 inch (1.6 m) sparks,[9][22][23] [1] and other sources confirm     Tesla was not the first.[14][24][15] However he was the first to see practical applications for it and patent it. He even realized that the secondary coil functioned as a quarter-wave resonator; he specified the length of the wire in the secondary coil must be a quarter wavelength at the resonant frequency.[25][8]
    I think if anybody can make a Tesla coil run at red range in this image. That job may be an affirmation that Tesla coil is not a quarter-wave resonator.

  Dear forum admin board, if this topic has been reviewed initially, I request the administrator to invite 2 members directly to do the verification tests. To conclude the question of whether a 1/4 wave length has any role in DRSSTC.
Thank you so much.

[Teravolt]

hi there VNTC, have performed these expieiments before to. my goal was to increse the Q of the secondary circuit. like you I wanted to make a secondary frequency that I wanted around 500khz so i decided to make it with a lengt to diamiter ratio of about 2:1 so with a 4" tube it was about 10" high. I did this to reduce distibutive capacitance. distibutive capacitance is in parallel with the secondary inductance witch would be great for a parallel tank. by adding torides to the top it makes a more series resonant tank circuit witch is what we need for voltage amplification. having said that I found the wave length of 500 Khz and derated it because all the extra capacitance that was being built into it will decrese the resonant frequency. I guessed at what this may be about 15% lower. eventualy I got it in an accepible range for sword sparks. for me adding capacitance to the top increases the topload voltage. others may have seen or expieinced this and may be able to eplain it more clearly. I found a good websight for a better explination. it doesn't refer to teslas bu tank circuits and a tesla is a tank/antena circuit. check out Series Resonance Example No1

https://www.electronics-tutorials.ws/accircuits/series-resonance.html

[Uspring]

VNTC wrote:

In modern times the science side of Sir. Tesla's patent has not been confirmed or denied in the Teslacoil player community. That is  DRSSTC is a quarter resonators or is not?

It can be seen that way. The grounded bottom of the is a node of a transmission line and the toroid on top an antinode. But don't make the wrong deductions from this. A coil runs best, if the operating frequency is near the secondary resonance frequency, which is determined by the secondary inductance L2 and the topload capacitance C2. The quarter wave frequency, as you calculate it, depends only on the length of wire. It does not depend on the topload capacitance, so in general the resonant frequency will not be the same as the quarter wave frequency.

That your coil works best at the quarter wave frequency is just a coincidence. Empirical knowledge suggests, that a good impedance for the secondary, i.e. 2*pi*f*L, should be around 50kohms. In your case, that turns out to be 54k at 140kHz, which is close enough.

[Teravolt]

hi Uspring I agree with everything you are saying but I have found that if you are in space and you strech your wire out it as a quater wave length and then put back the quater wavelength will be lengthend by the added destibutive capacitance and top load capacitance by a factor of what I dont know.  by using the 1/4y method you can ballpark a teslas top resonant frequency. crtanly if you more turns and or smaller wire this afect is larger. I have tested this out with short tesla,12x6" inductors with 20awg wire and I can almoast get the resonant frequency. I thought the the tesla has always been considered a 1/4 wave to get the high voltages at the tip thus I think it is a type of antena. corect me if I am wrong but antenas are usaly tuned circuits.

[Uspring]

@Teravolt:
Indeed, a stretched out wire, used as a quarter wave antenna, resembles electrically a base fed Tesla coil. The antenna resonant frequency is given by the quarter wave rule. Once you coil up the wire, the inductance rises and the capacitance drops. With respect to the resonant frequency, these effects cancel out to a certain extent. If you add a top load, then the resonance frequency drops and cannot be sensibly determined by the quarter wave rule. Better use JavaTC 

[Teravolt]

hello VNTC and Uspring, yes Uspring you are right that a tesle wave length or resonant frequency can not be carictorized by wire length however it will still behave like a 1/4y or 1/2y antena depending what type of tesla is built . I have never herd of a 3/4y or 1 1/4y tesla.
my understanding is that when we tune a tesla it is for a 1/4y because we want maximuim voltage at the top and max current at the bottom.

my point is that there are 2 types of capacitance to determin resonant frequency.  they are the paracitic capacitance between each winding and the top capacitance with the earth. what I have found from seeing this myself and form others that paracitic capacitance is not desireable and that capacitance is. By adding capcitance with the earth as series tank whitch is what you want to create voltage at the node where the cap and inductor connect we do this with a DRSSTC primary because the voltage is peak whare the MMC and primary connect. Not only can a DRSSTC be tuned at its primary but buy adding more torides where it makes it behave more like a 1/4y antena than a tank circuit

[VNTC]

Hi,Uspring.
Quote (from Kraiser Power Electronic, Secondary coil design and construction for Tesla coils)
The impedance of the secondary coil and topload is also calculated with a regular expression

In this page
A micro coil 40mm diameter (1600-200 turns) secondary impedance=57-59kΩ
And V. large coil 400mm (1600-2420) secondary impedance=57-61kΩ
It is not depend only on L2

[Uspring]

It is not depend only on L2

I agree, but I didn't claim otherwise.
The 50kohm prescription for the secondary impedance is based on the observation, that DRSSTCs capable of producing big arcs seem to have an impedance near that value. A theoretical justification is difficult, since it must be based on the impedance properties of the arcs produced. There must be some kind of impedance matching between arcs and secondary tank. Arc impedance measurements are involved and scarce.
Teslas goal was to produce large and high frequency electric fields for wireless transmission. The occurrence of big arcs was an undesired side effect. Why should he provide for a recipe to create big arcs? And how would a frequency derived from quarter wave considerations lead to a particular value of secondary impedance?

Think of a DRSSTC operating on Mount Everest. Due to the big differencee in air pressure, the arc properties like impedance will be quite different from ground level. That will change the optimum secondary impedance for big arcs. The quarter wave frequency does not change up there, since it is based on the wire length. So how can it be relevant, if arc length is the goal of TC builders?

[VNTC]

quote from Uspring:
 "There must be some kind of impedance matching between arcs and secondary tank."
Many people think as you. It is right but not enough.
To obtain the max power dissipation at a load (resistor) includes 4 elements:
1-Output voltage of the power source V.1rst prioritize
2- Internal impedance of the source Zin. Second prioritize
3- Impedance of the load Zload. Depend on the nature of itself .
4 Zin=Zload( the key condition is impedance match )
W=V*V/(Zin+Zload)
This empressive show that this statement is correct if Zload is the variable that people can intervene together Zin.
in contrast, Zload is a variable outside human intervention. there is only one way to reduce Zin as low as posible
 λ/4 is condition for the 1rst, it plays an most important role because it is in squared form . The second term depend on the design of the technician. The last term may be out of beyond the scope of intervention of human.
So I think this rule is necessary. Except if anybody can prove it is wrong.
The US patent agency does not grant a degree of uselessness unless they make a mistake.

[Uspring]

1) You cannot choose priority 1 and priority 2 independently of each other. The resonance condition in the secondary, which maximises Vout, causes Zin to be large.

2) The λ/4 condition is not the condition which maximises Vout. The secondary resonance condition does this.

[VNTC]

I like this discussion because it will bring a deeper understanding for us.
Of course good resonance should be the initial condition as the base for anything after. I want to mention about another one follow it that can make a second important contribution to the overall results

I strongly think that λ/4 that is it. Did you have been seen a coil generate the longest spark at middle height and none at the top?. Because current through it is double frequency of that will be, means at that position is according  λ/2.
I am going to try of proves 2 more test a 2 frequency for this topic.
Thank you, good luck.

[Uspring]

Did you have been seen a coil generate the longest spark at middle height and none at the top?

I've never seen that, but I heard about it and I think it is possible. The secondary winding acts like a transmission line since it has a distributed capacitance. So it can have a node at the at the bottom and an antinode at the top. That is the usual mode of operation. At some higher frequency there can be a node at the bottom, an antinode somewhere in the middle and another antinode at the top. This is not a desirable operation mode, since it will cause the arcs to break out from the antinode in the middle, which will destroy the winding.

The f = c/(λ/4) condition will act as a separate constraint to the design of a secondary with top load, since in general, it will not be the resonant frequency. I.e., you have to choose a top load to also meet this condition, as you did in your experiment. Numerous other coils work well, though, with a different kind of constraint, i.e. the secondary impedance being about 50kohm. I believe, this is caused by impedance matching issues, although I've difficulties proving this, since arc impedances are a big unknown. Now, in principle, the 50k and the λ/4 constraint could actually be identical, although I doubt this. Playing around with JavaTC will probably show this.