Re: [TCML] Massive VTTC!!!

[Steve Ward <steve.ward@xxxxxxxxx>]

Can you get any pictures of this machine?  Sounds fascinating.

CW mode will tend to make short sparks.  Id try removing any extra filtering
capacitors/inductors from the power supply and running it with "raw" DC
pulses (unless you are using 3 phase, in which case that wont help).
Certainly pulsing the system seems to grow much longer sparks, though its
mostly due to the fact that you can run higher power during the spark as the
duty cycle is reduced, keeping the average power in check.

As far as i know, i think my coil makes the longest "CW-like" sparks (that
is, sparks grown over 8mS+ time).  To do this i apply a ramped voltage
waveform (of 20mS length) to my drive circuit, and the peak input power is
350V@120A = 42kW.  In this manner i was able to get 66" sparks from my "QCW"
(quasi-continuous-wave) tesla coil (older photos):

http://www.flickr.com/photos/kickermagnet/

Early-on, true CW experiments, while fairly high power (4-5kW) were not all
that exciting or interesting, which is why i developed such a sophisticated
system for pulsing.  I also tried just using 60hz mains as my "ramp
generator" (which is how most VTTCs operate), but i found that there was an
optimum power supply dv/dt to produce reasonably straight, un-forked
streamers, so with 60hz period i could never get more than about 36" sparks
before they were forking so often that they would grow no longer.  I found
the optimum dv/dt to be rather critical to getting the longest sparks
possible, that is to have continued streamer growth as a single channel,
rather than one that branches.  Near the limits of my system (anything past
maybe 48" sparks) its very difficult to grow sparks that dont branch.  Too
much dv/dt causes branching early on, too low dv/dt causes the sparks to
shorten.  In a CW system, the dv/dt is ~0, which is why i suspect that just
"interrupting" the CW operation alone may cause the sparks to grow longer.
But, to simply cut the circuit on and off abruptly will tend to introduce
problems because the secondary voltage will likely surge too high and flash
to the primary.  I rely completely on the smooth growth in voltage to keep
my system from arcing over, indeed if it ramps too quickly it just sparks
over to the primary.

Steve

On Wed, Nov 3, 2010 at 3:30 AM, Carlos Van Camp <
carlos@xxxxxxxxxxxxxxxxxxxxxx> wrote:

> Hi guys (and gals),
> I have been building a VERY large VTTC for the past 2 years, and I am in
> the final stages of testing and tuning.
> This machine has been built with brand new high power components and has an
> input power capacity of upto 50kw.
> The valve is a tetrode (4CX15000a) with a plate dissapation of upto 15kw.
> I am an experienced builder of large SGTC, but fairly new to valve coils.
> The trouble is that dispite an input of 30-35kw of power (CW mode), I am
> only achieving arcs 2-3 foot long (6 arcs at once coming off the top
> electrode).
> I understand that VTTC's make much shorter arcs for the power applied, but
> I have heard of people making arcs 8 ft long with less power than I have
> available...
> So... What am I doing wrong...?
>
> Does using a stacatto system truely make arcs longer...? Or does it just
> reduce the input power?
>
> Does any body have practical experience using thyratrons in place of spark
> gaps, and would one be suitable to produce a musical coil? (ie changing
> pulse rate to play tunes etc)
>
> Thanks,
>
> Carlos.
> _______________________________________________
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>
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