Re: [TCML] VTTC Poor Performance.

["Phillip Slawinski" <pslawinski@xxxxxxxxx>]

I'm using 30 turns on the primary and a 2nF cap.  I tried adding extra turns
and it only makes a small difference.

I should mention that my VTTC pulls 30A before I get to 120V.

I tried using just one transformer and I was able to achieve similar results
as far as spark length goes.  It seems when I add the other transformer in
series the arcs just get brighter and thicker.

On Thu, Sep 11, 2008 at 4:42 PM, <futuret@xxxxxxx> wrote:

> Here I'll discuss a number of issues relating to VTTC
> operation.
>
> When only one normal MOT is used, then it helps to
> remove the shunts.  This increases the spark length
> from about 21" to about 24".  Using two large MOT's
> as you are, I would think you'd have enough power to
> get longer sparks even without removing the shunts.
> I'm not 100% sure since I never used two MOT's in
> series along with doublers.
>
> Your voltage is dropping to 100 volts because the
> coil is drawing so much current.  Are your power
> line wires thick enough to help prevent line voltage
> drop?  The power wires should be at least 12awg especially
> if long.   I think the high current
> draw is not due to the nature of the MOT's nor
> is it due to saturation of the MOT's.  Instead it's
> due to an aspect of the VTTC ( I discuss this
> below).  By the way,
> I'm surprised you don't get any arcing in the tube
> since I've always gotten arcing when I went over
> around 5 to 7kVAC to the plate.  I realize that
> Cameron Prince also used 8kVAC or so and didn't
> get any tube arcing.  The only explanation is that
> the circuit is being heavily loaded thereby holding
> down the voltage.
>
> Here's an important key to all this.  The power
> draw of a VTTC is proportional to the
> input voltage.  If you double the input voltage, the
> coil will try to draw 4 times the power.  Steve Ward
> used probably around 5kVAC for his coil, and I used
> that same voltage for my coils.  But if you go to
> 8kVAC, you have to throttle things back, but not
> by ballasting.  VTTC's should not be ballasted.
> It's the VTTC circuit itself that limits VTTC current draw.
>
> Now I'll mention the key to all this which is
> the issue of tank impedance.  The higher
> the input voltage that is used, the higher the tank
> impedance must be.  The tank impedance is increased
> by using more turns in the primary and a smaller tank
> capacitor to stay in tune.  For example if you're using
> 22 turns in the primary, you may need to increase this
> to 27 turns or more to limit the current draw of the system.
> This I believe is why your coil is drawing so much current.
> If you remove the MOT shunts, the system will probably
> draw even more current.  However removing the
> shunts will not do any harm, if you have a suitable
> number of turns in the primary.  Removing the shunts
> will probably make the transformer saturate slightly
> easier, but it's generally not a problem.  I always run
> 140 volts into my single MOT VTTC coils with shunts
> removed, and all is well.
>
> However, consider Cameron's system.  As far as I know
> he kept the same number of turns that Steve used for his
> primary.  However Cameron runs with staccato, and
> probably cannot run without it... the system would
> draw too much power.  So by using staccato, you
> can run the tube at higher voltages and higher peak
> powers, yet keep the total power within suitable limits.
> This is what let Cameron obtain 36" sparks using a
> single 833 tube.  Cameron mentioned that he had
> to raise his grid coil very high above the primary.
> I suspect he had to do this to control the system
> due to the high input voltage and high peak powers of
> the system.  At such voltages, the tube is no lower
> running within its design parameters.
>
> Cheers,
> John
> --------------------
>
>
>
> -----Original Message-----
> From: Phillip Slawinski <pslawinski@xxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Sent: Thu, 11 Sep 2008 1:54 pm
> Subject: [TCML] VTTC Poor Performance.
>
>
>
> I recently built a 833C VTTC.  I've been toying around with the coil and
> made little changes here and there which made minor improvements to the
> performance.  The coil is pretty close to being in tune I believe.  Even
> with the coil in tune I only get 18" streamers.  I'm beginning to think
> that
> the MOTs I'm using may be to blame.  I have a 30A panel meter hooked up to
> measure total system current.  At about 70V or so I reach 20A current draw.
> If I push the variac further I hit 100V and never seem to get above that.
> The VTTC causes a volt drop which pulls down the filament voltage.  Lately,
> I've been running the filament transformer off a seperate line.  The system
> current still soars off the meter when I try to run the coil at full
> voltage.
>
> I have two very large MOTs that came from older microwaves.  I wired the
> MOTs in series for 8kV after the voltage doubler.  I have not removed the
> shunts from the transformers.
>
> Would removing the shunts from the transformers help in my situation?  Does
> the presence of the shunts cause the transformer to saturate any faster
> than
> it would otherwise?
>
> My system is almost exactly like the single 833A coil on Steve Ward's site.
> The major differences being that I have a 9x3 topload, my MOTs are wired in
> series,  I have an 833C, and I used a 10K resistor in the feedback circuit.
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