Re: [TCML] design idea

[<lightningfor@xxxxxxxxxxxxxxxxxxxxxx>]

Hi Steve,
Thanks for such a detailed explanation.
My experience is hands on, largly with SGTC's, so I often lack an accurate
undestanding of the theory behind things.

So are you saying that a Tesla coil with a low voltage supply and a large
tank cap (for a given frequency), can give just as big arcs off the
secondary, as a Tesla coil with a small tank capacitor (with the same
frequency) and a higher voltage supply?
And this is assuming an impedance match of the supply to the tank
circuit...?

I never really thought of it that way before...

I know the principle behind the voltage rise in a Tesla coil is due to
resonant rise, but I guess I always thought that voltage transformation
between Prim and Sec coils still would play its part...

I.E Higher voltage in means higher voltage out...
Is this Still the case?

I have tried many ratio's of L to C in my tank, and found a point that
worked best.
The arcs were only half the length I needed for the display and was
drawing only 30kw out of the 50kw it is capable of.
In saying that, at 20kw the arcs were almost as long as 30kw input, they
just get fatter... (this is a CW system)

It is my hope that increasing the voltage input to the tank will cause it
to draw more power and if I need to I will reduce the duty cycle.

Given what you mentioned about having a single switch (the valve), do you
think it is worth trying...?
Or do you think I am going to need to abandon the valve etc, and start
using silicon etc...?

If I did start from stcratch, what type of switch(s) would you recomend to
give me multiple 8ft long QCW arcs off the secondary...
I would be using a rectified 400v 3phase supply...

Kind regards,

Carlos




On Mon, 6 Feb 2012 17:15:23 -0600, Steve Ward <steve.ward@xxxxxxxxx>
wrote:
> Hi Carlos,
> 
> I see the predicament you are in with the VTTC: simply cant get enough
> power through it.  I havent modeled this type of oscillator yet, but i
> suspect that if you do have other options available in terms of tank
> capacitor that you can increase the Q of the system by lowering the
> primary impedance (more C, less L) which should increase the total
> power throughput by driving the secondary to a higher voltage which
> makes it push more current through the plasma.
> 
> You *could* try the transformer thing, but this would be particularly
> tricky with a single-ended drive like most VTTCs are (just 1 switch
> element).  The issue here is avoiding saturation of the core by
> applying any DC voltage to it long term.  I personally have not worked
> out what issues there may be, but it does stray considerably from any
> type of power supply i have made (yes there are forward and flyback
> converters, but their output current is DC not AC like a tesla coil,
> and this messes up the basis on which these designs function).
> 
> Since you mention you are already starting with 10kV, and want to go
> higher still, you'd likely need to do an oil submerged transformer in
> order to keep the coupling high (and stray inductance down).  To me
> this seems like more work than its worth.  For my scenario i was
> simply working with hundreds of volts where insulation issues are
> rather trivial.
> 
> Personally, i would be investigating what changes could be made to the
> tesla coil design itself (the primary and secondary circuits) to get
> more power throughput at 10kV.  The main methods of getting more power
> through a CW-ish system is to raise the loaded Q of the system so that
> the secondary voltage is higher.  You can do this on the primary or
> secondary side, essentially by increasing the total capacitance but
> keeping the frequency the *same* (so that means less L).  It might
> sound "strange" that less secondary inductance will result in higher
> voltage, but ive done it myself and it can work, but usually the more
> appealing option is to use more tank capacitance and leave the
> secondary alone, since i dont think more secondary C is particularly
> useful for CW spark growth.  Another thing to check into is if any
> tuning or coupling changes might give the power increase you are
> after.  I know that at for my QCW DRSSTC, i can actually increase my
> power throughput by *lowering* the coupling, when tuned a specific
> way.  Just a thought, not sure if i actually would have a chance to
> look into this much for you.
> 
> Also, i got the note about the job in chicago, which is funny since i
> used to live there until i left to work with arcattack.  I dont think
> we can do that date since we will be across the country in california
> just a few days before that, but i do know some guys (who i worked
> with) that can do tesla coils in chicago so perhaps i can pass the
> information to them.  I appreciate the thought, either way.
> 
> Steve
> 
> 
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