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Re: [TCML] hybrid coil

Carlos,

Comments within:

On Wed, Nov 17, 2010 at 11:18 PM, Carlos Van Camp <
carlos@xxxxxxxxxxxxxxxxxxxxxx> wrote:

> Hi Steve,
> thanks for your feedback.
> I haven't completely given up on improving the valve coil that I have
> built, by adding the stacato controller and a few other small mods that I
> have in mind.
>

Interrupting should help to some degree, but if you could significantly
decrease the tank impedance to get more peak system power, that would be a
large improvement i suspect.

I was well aware of the fact that the arcs would be much shorter, which is
> why I allowed 50kw to get the 3 meter arcs that I wanted.
> I have completely underestimated the power required to prduce CW arcs of
> this length.
>

My attempts at high power CW showed me that it was quite a challenge.  One
solid state system i made ran at about 7kVA (measured at the "wall") and
produced just about 2 foot sparks in CW mode.  Other, similar SSTCs could
operate ~30% duty cycle and make the same 2 foot sparks with maybe 2kVA.

I was not aware that electronic coils had come so far or I would have
> definately gone in that direction. Also, I had the preconcieved idea that
> electronics and Tesla Coils dont mix and as reliability is a big factor for
> my client, so I chose valves...
>

Well, the reliability is still questionable.  Tubes are certainly going to
be more forgiving, though still breakable.  The reliability issues can be
greatly mitigated with good design.  It sounds like your project is a static
display piece, so the fact that its not being moved around and re-assembled
in new locations will help with the reliability issue as well.


>
> As for my hybrid idea, it seems the best way (with the gear I have set up)
> to get long arcs, is with a spark gap coil. But this wont allow me to
> modulate the pulse rate to play music, so I thought I could just use the
> valve to interupt the charging of the tank cap at the required pulse
> rates...
>

Ah, sorry then, i did not understand this before.  It could probably work
but i think there would be a significant "jitter" in the firing frequency of
the gap despite this power supply control.  Really depends on the breakdown
voltage of the spark gap i suppose.


>
> Am I correct that DRSSTC coils have no mains power transformer (ie they run
> off rectified mains)?
>

So far, all of the ones im aware of do.  Basically the largest DR coils to
date dont use more than 1kVDC to supply the drive power.  With 650VDC bus
I've produced 12 foot sparks, and not really limited by bus voltage so
much.  I have simulations for a much larger system that I'd expect could
produce up to 25 foot sparks, also operating from only 650VDC.  The real
limit is how low of primary impedance can be realized, and the 25 foot
sparking system would still use a 2 turn primary which i think is
acceptable.


> I assume that they get the energy into the secondary by using a large tank
> cap, and run low frequency secondary coils to keep the switching frequencies
> down and the primary turns up?
>

Yes, except the primaries generally still have relatively few turns as the
tank capacitance is quite large.  For example, my 10 foot sparking machines
operate at ~40khz with a 500nF tank capacitance.  It takes about 8 RF cycles
to ring up the secondary to max output (estimate 500kV).  The primary
current peaks to around 1300A typically and about 8.5kV on the primary and
tank cap (the tank impedance is about 6.5 ohms).

My site is a bit out of date, but you can take a look at some of my
projects:

http://www.stevehv.4hv.org/

I still have yet to make up a general system diagram, but if you have some
questions i could answer them on the list.


> These DRSSTG boards that are availabe, do they run in pulses or CW or are
> they adjustable?
>

When i saw DC Cox's driver boards (not sure if they are the same as the ones
he recently advertised), they were just a copy of my design that i put on my
website (http://www.stevehv.4hv.org/new_driver.html).  Ive used them for CW
coil experiments with small modifications, but the driver card is just a
generic simple thing.

Steve

Sorry for all the questions, but there is a good chance I will have to go
> this way...
>
> Kind regards
> Carlos
>
>
>
>
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