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Re: [TCML] newer tesla coil parts (split Terry filter resistors)



Makes sense.

Perhaps in large coil systems, 5 kVA and up, they might be instructive to
detect mis-tuning.  We usually alligator clip a "bench gap" across the neon
xmfr bushings, and, if all is well we remove the gap letting the varisters
fall to this task.  I must admit, though, to smoking a few varisters before
Bart's excellent JAVATC was developed.

DC






On Thu, Nov 12, 2009 at 4:23 PM, Lau, Gary <Gary.Lau@xxxxxx> wrote:

> Hi DC,
>
> Yes, I agree that the safety gaps appear to be redundant if one also uses
> the prescribed number of MOV's.  However, even with a proper Terry filter
> using a properly set mid-point grounded safety gap, I still see these gaps
> fire on rare occasions following a primary strike or SRSG misfire.
>
> The MOV's are great because they keep us honest.  Short of disconnecting
> them, one can't open them up just a bit more.  But they are relatively
> fragile and won't endure a continued overvoltage for long before they fail
> (fortunately in the shorted state).  The ball gaps cost nothing, take up no
> significant real estate, and just look nice. I see no reason to suggest
> elimination them.  If we were all perfectly honest and meticulous in setting
> the safety gaps, I think the MOV's could be eliminated, but human nature
> being what it is, would not suggest this.
>
> Regards, Gary Lau
> MA, USA
>
> > -----Original Message-----
> > From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> > Behalf Of DC Cox
> > Sent: Thursday, November 12, 2009 5:38 PM
> > To: Tesla Coil Mailing List
> > Subject: Re: [TCML] newer tesla coil parts (split Terry filter resistors)
> >
> > Gary:
> >
> > Interesting question.
> >
> > I was also wondering the precise requirement for the spark gap balls.  In
> > the days before varisters came along we definitely used them.  But, now,
> the
> > varisters should shunt any overpotentials to ground directly,
> essentially,
> > make the spark gap balls unnecessary as there should not be any high
> > potentials present to fire the gaps.
> >
> > I would assume this might be of assistance in the rare event of horrible
> > mis-tuning, but with JAVATC this has almost become a thing of the past.
>  I
> > usually add 1/4 turn beyond JAVATC predicted pri tap point, and it's
> dead-on
> > at full power levels for most small and medium size coils.
> >
> > Comments on this idea (eliminating the spark gaps) welcome.
> >
> > Dr. Resonance
> >
> >
> >
> >
> > On Thu, Nov 12, 2009 at 9:22 AM, Lau, Gary <Gary.Lau@xxxxxx> wrote:
> >
> > > I'm not sure I see the value in having the caps & varistors at the
> midpoint
> > > of the resistors.  The R-C filter will only see one half of the
> resistance,
> > > so its low-pass frequency will be twice as high.  The only benefit I
> see to
> > > this is the bypass caps will be cushioned against the discharge current
> when
> > > the safety gaps fire.  But given that this should not be a frequent
> > > occurrence, I'm not sure this is worth compromising the R-C filter's
> cutoff
> > > frequency for.
> > >
> > > While splitting the 1K between two 500Ohm units is fine, I think it is
> bad
> > > advice to suggest placing the caps at the midpoint.
> > >
> > > Regards, Gary Lau
> > > MA, USA
> > >
> > > > -----Original Message-----
> > > > From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> > > > Behalf Of Jim Mora
> > > > Sent: Tuesday, November 10, 2009 3:30 AM
> > > > To: 'Tesla Coil Mailing List'
> > > > Subject: RE: [TCML] newer tesla coil parts
> > > >
> > > > Hi DC, All,
> > > >
> > > > I agree - nice, thoughtful construction! It never even occurred to me
> > > split
> > > > the halves.
> > > > We will all look forward to more pictures of our art form at work!
> > > >
> > > > Jim Mora
> > > >
> > > > -----Original Message-----
> > > > From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> > > > Behalf
> > > > Of DC Cox
> > > > Sent: Monday, November 09, 2009 2:46 PM
> > > > To: Tesla Coil Mailing List
> > > > Subject: Re: [TCML] newer tesla coil parts
> > > >
> > > > Nice construction work.
> > > >
> > > > Both Digi-Key and Mouser usually stock them.  I split mine into two
> 50
> > > watt,
> > > > 500 Ohm resistors putting one ahead and one behind the common
> > > varister/cap
> > > > connections.
> > > >
> > > > D.C. Cox
> > > >
> > > >
> > > >
> > > >
> > > > On Mon, Nov 9, 2009 at 10:53 AM, Shaun Epp <scepp@xxxxxxx> wrote:
> > > >
> > > > > Here are some pictures of my new NST filter.  I ordered parts from
> > > digikey
> > > > > this time and used the correct values and MOVs( before I was using
> > > 3Kohm
> > > > > resistors and door knob caps).  It's built so that I can change
> from 7
> > > > MOVs
> > > > > per side to 8.  After reading posts on this list, I think I'm going
> to
> > > use
> > > > > all 8 for my 12Kv, 60mA NST because it puts out more that 12Kv at
> 120V
> > > in
> > > > > and I'm using a variac.  I'm using 50 watt resistors for the
> 1Kohms, I
> > > > can't
> > > > > get ahold of the 100w versions, does anyone on the list have some
> for
> > > > sale?
> > > > >
> > > > >
> http://i487.photobucket.com/albums/rr239/growl99/NSTfilterfront.jpg
> > > > >
> > > > > http://i487.photobucket.com/albums/rr239/growl99/NSTfilterback.jpg
> > > > >
> > > > >
> > > > > Question:
> > > > > My capacitor bank is currently on 2 boards and I'm going to make a
> 3rd
> > > > > board of CD 942 caps (14 caps 0.15uf in series spaced).  What are
> other
> > > > > coilers using for board to board spacers?, I want to stack them one
> on
> > > top
> > > > > of the other, and legs to keep them off of the floor,  right now
> I'm
> > > using
> > > > > 1/4 inch nylon bolts with heat shrink tubing over them to
> strengthen
> > > them.
> > > > >
> > > > > thanks,
> > > > >
> > > > > Shaun Epp
> > > > >
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