Re: [TCML] design idea

[<lightningfor@xxxxxxxxxxxxxxxxxxxxxx>]

OK, I think I understand most of that.
It always amazes me just how complex this simple little circuit really is
when you start analysing whats really going on.
Especially when you add into the mix, the varying load that the secondary
arcs create...



> 
> Yes, look at any SSTC, they will operate with a very low primary
> impedance in order to get the voltage transformation from the tesla
> coil.  Think of it this way, the voltage gain of the tesla transformer
> is related to coupling and the square root of the inductances of the 2
> coils (im speaking loosely here since i dont remember exactly the
> equation), so if you make the primary coil less inductance, but keep
> them coupled the same, then the step up ratio of the tesla coil goes
> *up*, right?  Its like you have less primary turns, so the turns ratio
> went up.  BUT, this automatically implies a bigger tank capacitor
> because its still gotta resonate with less primary inductance, yes? So
> then it stands to reason that if you want more power out of your CW
> tesla coil, you need more top voltage, and one way to achieve this is
> to lower the primary/drive impedance.

So If what you are saying is correct, one should be able to get the same
performance from a properly designed Vttc, as with a DRSSTC, given similar
power input and duty cycle...?
Generally speaking, VTTC coils either get run in CW with short fat arcs or
staccato making longer sword like arcs.
I am yet to see a spark off a vttc that has the appearance of a sgtc or
sstc, but I guess its because nobody has taken the time to try and drive
one with the correct parameters.
> 
> This is not surprising to me.  If you must do CW, then id be
> interested in seeing a low frequency CW coil because i think that
> there might be a benefit of a higher streamer impedance in that you
> might have more electrostatic forces driving long streamers without
> pumping so much current which makes the root of the streamer really
> fat and power hungry!
> 
> What frequency did it operate at?

The original CW version ran at 140khz.
The secondary coil is physically very large which I fear is part of the
problem.
16 inch diameter and 10 feet long... the wire is also large about 3/16
inch diameter stranded...(4mm copper and 1mm pvc insulation)
I'm guessing the large internal capacitance of the secondary is not
helping things?
It was designed this way because in CW mode I have noticed heating of the
secondary near the base of the coil in my smaller test coils, so decided to
use a large wire on the big model due to the very long runtimes required
(sometimes hours).
The length was chosen because when run out doors at night, things like
wind and moisture from due etc, can cause problems with sparks tracking on
coils that are designed with "tighter" perameters.

> 
> Well, i would not suggest switching to Si unless you are really
> experienced with it... it seems to take most people many months of
> hard work to pick it all up and get something reliable.  Id recommend
> sticking with tubes if you got them, and focus on modulation and maybe
> tesla transformer design.

My experience with SI is limited, and even getting a good modulating
system working for the valve is proving hard.
So you are probably right.
 
> Well, honestly i considered buying some big vacuum tubes to make a
> bigger QCW tesla coil.  Ultimately i found some nice little IGBTs that
> i want to gang up 48 of, and make some 10-15 foot "trees" with i hope!
>  I go this route because im stubborn!!  You could likely get a tube
> big enough to out do my fleet of IGBTs, and not worry about the tube
> randomly exploding because you messed up some stray inductance
> somewhere that threw off the switching and caused it to overheat 1
> IGBT specifically.  But ive got a vision of this working and am just
> motivated enough to see it through... not because its the simplest
> way!

This is exactly why I chose to go down the valve path in the first
place...
I have given these BIG valves all manner of crap, and they have stood up
to all of it!
If I had started with SI, i'm sure it would have cost me a fortune in
spare parts...!!!
The question is, can I get them to cooperate with me to get the results I
need...
They have there own little querks that SI does not, so I guess they still
have there negative aspects despite being so ruggedly reliable.
 
> Of course, driving your tube coil properly might involve some special
> techniques depending on what you want.  Can you elaborate more on what
> you want the system to do in terms of spark characteristics?  I know
> its an art project and this is important, maybe i can help offer
> ideas.

The machine just needs to generate some juicy looking arcs that are
similar to a powerful SGTC, but perhaps change in fatness and texture with
the different audio inputs.
The top load on the secondary needs to distribute the arcs 360 degrees,
generating multiple streamers at once to "fill" the circumfrence of the 20
foot diameter cage. in other words, lots going on at once, instead of just
one big streamer branch...
I have found that removing the electrodes from the top load gives a more
random display with is more pleasing than static breakout points.

The audio side of things is not so important to my client, however my
experience with pulsed audio input (i currently use a Xenosonic board which
is monophonic) is that the quality is low, and it is very difficult to feed
live sounds into it without getting horible distortions, due to the
monophonic nature of the board...
The CW modeof operation means it is easy to input live sounds with good
quality results, but it is yet to be seen if I will be able to get the arcs
long enough in this mode of operation...
This leaves me with trying to find a method somewhere in between CW and
Pulsed, that offers a simple way to get reasonable sound quality from
polyphonic live sound input AND still get the longer arcs... 
> 
> And you say "multiple", well what if you just had a breakout point
> that move around quickly and let the human eye integrate all the
> sparks?  That is, have the spark emitted from a spinner or something
> and pump out a bunch of them in fast succession.  Certainly much
> cheaper than making all 8 sparks at once!

Wouldn't the fast moving breakout point mean each succesive pulse was
discharging into non ironised air. Meaning spark growth would be effected,
and arcs would be shorter as a result...?


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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