Re: [TCML] design idea

[Steve Ward <steve.ward@xxxxxxxxx>]

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

On Sat, Feb 4, 2012 at 4:59 PM,  <lightningfor@xxxxxxxxxxxxxxxxxxxxxx> wrote:
> Thanks Steve,
> I appreciate the feed back.
> My reason for asking relates back to the big VTTC coils I have been
> developing.
> Basically, the 10kv that I am applying to the tank is not enough to give
> me the arc length I need.
> I figured that if I fed the 10kv into the primary of the Ferrite
> transformer I could use the stepped up voltage of the secondary to put
> accross the tank circuit.
> I am experienting with a drive circuit on the grid of the valve to drive
> the ferrite with...
>
> I also like the fact that one side of the tank can be grounded (as you
> mentioned)...
>
> I am really wishing I had started with IGBT's instead of valves!!! and may
> still have to go that way yet... We will see.
> The big problem I am having at the moment is my drive circuit seems to
> suffer badly (has a fit) every time there is a mismatch of tuning with any
> of the tuned stages. My first attempt did not have any feedback from
> primary or secondary into the frequency generating part of the circuit, so
> I will re design and see if I get better results.
> One observation is that the valve seems to "feed back" out of tune energy
> into the circuit... where as IGBT's etc don't appear to do this as badly...
>
> Any feed back welcome...
>
> Carlos
>
>
> On Sat, 4 Feb 2012 01:01:19 -0600, Steve Ward <steve.ward@xxxxxxxxx>
> wrote:
>> Hi Carlos,
>>
>> This works just fine, and i have done similar things before, and plan
>> on doing this in the future.  What it does for you is allows impedance
>> matching between a low voltage bridge that is low impedance, and a
>> tank circuit that might be more economical to build at a higher
>> impedance.  But, if you do the engineering, you will find that adding
>> such a transformer in there is not going to really help the efficiency
>> (though if done properly, it wont hurt noticably either).
>>
>> So sure, it can work, but i suggest thinking about *why* you would add
>> such a transformer.  My reasons were to combine multiple H-bridge
>> drives, and to conveniently alter my drive impedance (so i could run
>> more volts on the bridge at less current, so same power but less
>> Silicon conduction loss) to better match the capacitors i had
>> available.  The cost is of course, you have added a transformer and
>> its losses.  Though, one distinct benefit i see is that it allows you
>> to directly RF ground your tank circuit providing good robustness to
>> primary strikes (though you gotta make sure your transformer's
>> insulation is good!).
>>
>> Thats how i see it, anyway.
>>
>> Steve Ward
>>
>> On Fri, Jan 27, 2012 at 1:21 AM,  <lightningfor@xxxxxxxxxxxxxxxxxxxxxx>
>> wrote:
>>> Hi All,
>>> I have an idea on an electronic tesla coil that I am thinking about
>>> playing with, and I'm looking for feedback.
>>> This may not be a new Idea, but I haven't seen it before...
>>>
>>> The basic concept is to drive the primary tank circuit with a ferrite
>>> transformer...
>>> So you would have the typical HF driver circuit with a pair of big
> IGBTs
>>> or similar on the end, driving the primary of a suitable ferrite
>>> transformer at the correct frequency.
>>> The secondary of the ferrite transformer would step the voltage up,
>>> providing HV and HF to drive the tank of the tesla coil...
>>>
>>> I am not looking for a better way to do things, just a different way.
>>>
>>> As far as I can understand, this would work, but I am looking for
>>> feedback...  been done before,why not, potential problems, potential
>>> advantages, dissadvantages etc.
>>>
>>> Carlos
>>>
>>>
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