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