RE: Re: T-24 Hours Until New (Really Bright 10KVA) Light...

["David Dean" <deano-at-corridor-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Ryan,

Actually it is not as simple as 240V/ 8 ohms = 30 amps. If you were only
running resistive ballast, that would be true, insofar as if the output of
the pig were to be shorted, that is Vout = 0, taking the pig as an ideal
transformer (which for all intents and purposes it is, or can be modeled as,
anyway) then Vin = 0 as well, so all the voltage drop would be across the
resistor, and the maximum current would then be 30A at an angle of zero
degrees. That is not to say that the 8 ohm resistance will absolutely limit
the current to 30 amps as a ballast for a TC power supply though. Although
it is very unlikely to happen, it is possible for there to be a "kickback"
which would put an aiding voltage across the input terminals of the
transformer which would add to the supply voltage causing the current to be
higher. Of course if that were to happen, and it is very unlikely, it would
just be a spike which would at worst trip the circuit breaker. The
probability of kickbacks is higher with inductive ballast than with
resistive ballast, and more likely with a rotary spark gap than a static
gap, and more likely with a non sync rotary than with a SRSG, and more
likely with a coil that is out of tune than anything else, the other factors
are just incidental, in most cases. If you have safety gaps that are
properly set, that will take care of the problem. But I digress...

As I understand it, you are planning to power your existing coil, the
veretus coil, right? And planning to use a blown static gap as well? I don't
recall what kind of capacitor you are using...The matched size stated on
your website shows to be 26nf and the "needed to tune" size shows to be
19nf, so I assume something in that range. And you don't have a variac large
enough to handle 30A, do you? Putting all these assumptions together, I
would suggest using the 8 ohm dryer element with a fan to cool it, and leave
the welder out to start with. I started with a furnace for a ballast, I
pulled all the wires and could adjust the resistance from 50 ohms to 3.125
by setting jumpers for series or parallel. (4 12.5 ohm elements) I found the
best results with 12.5 ohms using a 14.4 KV pig running off of 240VAC, an
air blown static gap, and a 16nf rolled poly/aluminum flashing in oil cap. I
got 34" arcs to a grounded target with that setup. When I added the welder,
performance dropped considerably, I had to go down to 1.5 ohms, and the
resister got hot. Amp draw was in the neighborhood of 22 amps, though that
was taken with an analog clamp on type ammeter, the needle jumps around a
lot, so that is probably close to average. I found I could not run at all
with the welder by itself, It wanted to thump and growl and the sparkgap
fired erratically.

After migrating to a SRSG, I found the 1.5 ohm resister was just barely
getting warm, the amp draw dropped to 4.5 to 5 Amps, the needle on the
ammeter was pretty steady, and spark length increased to 39". This of course
was using the welder, and I had changed to a MMC, still 16nf. I now don't
use any resistance, just the welder, and sometimes some other inductors in
series to increase the inductance trying to get LTR operation. (I blew out
my 10nf lower voltage rating EMMC which was in parallel with the 16nf MMC
when I got close to resonance in that configuration, but now I've got some
radar pulse caps, so all is well.)

After experiencing the smooth, predictable, low power consuming, and orders
of magnitude quieter operation of a SRSG, I have given up on building an
ASRSG, as I would not have anything else. Also, with the "variac to adjust
firing angle" trick now up my sleeve, operation of a SRSG is a cinch.
Bottom line, I'm trying to sell you on a SRSG as your next project. Should
make that veretus coil go to 15' off of that dryer outlet, with a little TLC
and a reasonable size cap.

Anyway, just my $0.02.

later,
deano



> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Thursday, September 14, 2000 6:19 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: Re: T-24 Hours Until New (Really Bright 10KVA) Light...
>
>
> Original poster: "Ryan Ries" <spud-at-wf-dot-net>
>
> 	Why is 8 ohms too much?  Is not as simple as 240v / 8ohms =
> 30A?  Or is it
> just because of the extreme heat/power loss?
>
> 	Ryan Ries
>
> ----------
> > From: Tesla list <tesla-at-pupman-dot-com>
> > To: tesla-at-pupman-dot-com
> > Subject: Re: T-24 Hours Until New (Really Bright 10KVA) Light...
> > Date: Thursday, September 14, 2000 12:53 PM
> >
> > Original poster: Esondrmn-at-aol-dot-com
> >
> > In a message dated 9/12/00 9:47:02 PM Pacific Daylight Time,
> tesla-at-pupman-dot-com
> > writes:
> >
> > <<
> >     My 10KVA pig has been sitting very patiently in the garage awaiting
> its
> >  moment of glory.  We have almost finished wiring up the big extension
> cord
> >  that is to be run from the big 240v dryer outlet.  Very
> convenient since
> >  that is only about 10 feet from where the transformer will be.  We have
> a
> >  great arc welder to work with for ballasting, but I also went to the
> local
> >  junkyard and ripped an element from a dryer.  With my DMM, it measures
> >  about 8 ohms.  Does that sound right?  I hope so, because I like the
> idea
> >  of my coil running at a cool 30 amps. :-)  Also, I imagine that that
> >  element is bound to get VERY hot.  What do ya'll suggest to keep it
> cool?
> >   >>
> > Ryan,
> >
> > 8 ohms of resistance in series with the inductive ballast is a bit too
> much.
> > You want somewhere in the range of .5 to 2.5 ohms.  I used to use an
> array of
> > about 7 oven elements wired so I could switch in only one or all 7 of
> them in
> > parallel.  I now use fixed resistors.  I use a large fan blowing on the
> > resistors to help get rid of some of the heat - and yes, they
> do get real
> hot.
> >
> > Ed Sonderman
> >
> >
> >
>
>
>