Re: MOT-powered coil questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <Tesla729-at-cs-dot-com>

In a message dated 5/30/03 4:27:57 AM Pacific Daylight Time, 
tesla-at-pupman-dot-com writes:
>Captain, In regards to the last email...
>
> >I disagree whole heartedly.  Even 3kVAC is enough
> >for a reliable spark-gap
> >driven tesla coil.  Plus many of us, Ed Wingate,
> >Steve Ward, Gary Lau, and
> >others have built
> >very successful tesla coils utilizing only 4kVAC
> >transformers.  Theres more
> >than enough margin for reliable operation.
> >
> >The Captain "...
>
>While Steve Ward has made a very nice 142 watt mini
>coil with a 4 thousand volt transformer, and others
>with other succesful low voltage designs, does this
>hold up for higher currents? Are these designs(
>besides Ward's) high current? The 6,000 watt MOT coil
>I was working on with Steve Ward had serious quenching
>trouble even at 8Kv... at least when operating with
>our sucker gap. My advice, like I said before, is to
>go with higher voltage...
>
>
>Steve K.


Hi all,

I would have to agree with Steve on this, too. At higher current and
power levels (> 5 kVA), there is a whole lot more plasma in a small
area at lower (< 10 kV) voltages, which renders quenching
difficult, at best. I don't understand the idea of having to employ
monumental  quenching efforts for the < 10 kV -at- > 500 mA when
we all must realize that the capacitive discharge energy goes up
as the square of the voltage (E= 0.5  X CV sqrd). That means that if
you double the voltage, at a given capacitance, you quadruple
the discharge energy. And more energy into the primary coil is
what it's all about if you want those huge sparks coming off the
toroid :^) I realize that many coilers have obtained impressive results
from their large coils using the relatively low voltaged MOTs as their
power supplies, but most of the time they either end up doubling
the output of two seriesed MOTs or series 4 or even 6 of them
for serious power levels and that would place the final output
voltage in the 14.4 kV pole pig range.

Also, the primary capacitor size (nFD, uFD) requirements are
obviously substantially lower with higher voltages. Of course
the down side of this is the  higher voltage rating require-
ment of the primary capacitor. All in all, it would seem to me
that the 10 kV to 20 kV range seems to be the optimal primary
voltage range for most of our coils. Primary voltages that are
 > 20 kV seem to present a whole other set of problems ---
(corona losses, excessive stand-off clearances to prevent flashover,
very high cap voltage ratings $$$, ect.). I think Scot (bunnykiller) found
this out with his seriesed 14.4 kV pigs for over 30 kV output when
overdriven by variacs.So an x-ray transformer powered coil wouldn't
prove to be practical, either.

Coilin' in Memphis,
David Rieben