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RE: [TCML] Terry Filter



To the point suggesting caution if overdriving an NST with a Variac - Isn't that what this is all about? :-)  But seriously, if using a static gap, the gap width should be set running the NST at a nominal voltage, and OK, maybe just a "smidge" wider, though you didn't hear this from me.  But assuming one took no undue liberties with that smidge, it won't matter if you crank the variac up to 140V, as the NST won't see or generate any higher voltage, *IF* one is using a static gap, which is it's own voltage clamp.  Again I stress, the static gap must have been set responsibly.

I myself use my NST with a boosting Variac and wouldn't think of stopping at 120V.  This is with a SRSG.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Paul Brodie
> Sent: Friday, November 06, 2009 5:19 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Terry Filter
> 
> Herr Zap,
> Dan is getting the MOV's from me and I bought the ones Terry advised me to
> buy, way back when I was planning to use a neon sign transformer to power my
> coil in 2007. I decided to use MOT's instead and never used these. They are
> the P7215-ND, 1800 volt 2500 amp ones from Digi-Key.
> 
> I think he will be all right as far as these MOV's are concerned. I also
> went back and pulled out the Terry filter drawing I was using at the time
> and my memory is almost as bad as my vision. ;-) It does indeed specify 8
> MOV's per side and not the erroneous 9 per side I thought I remembered. Once
> again, I find myself having to apologize. I feel like a broken record. Maybe
> I will just keep my mouth shut.
> Paul
> Think Positive
> ----- Original Message -----
> From: Quarkster
> To: Tesla Coil Mailing List
> Sent: Friday, November 06, 2009 14:26
> Subject: Re: [TCML] Terry Filter
> 
> 
> Dan -
> 
> You need to carefully review the manufacturer's datasheet for your specific
> MOVs to verify their rated RMS voltage, and compare this to what you expect
> to see in your circuit. You also need to consider if you ever intend to
> "overdrive" the NST with a variac (apply more than local AC line voltage) to
> achieve greater coil output. If so, you might want to "design-in" physical
> space for additional MOVs, and just use  jumper wires at these locations
> until you are ready to increase NST input voltage.
> 
> Some useful technical data on MOV characteristics can be found at:
>  www.littelfuse.co.kr/data/en/Application_Notes/an9767.pdf
> 
> Regards,
> Herr Zapp
> ----- Original Message -----
> From: "Dan Casaregola" <ag2z@xxxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Friday, November 06, 2009 9:24 AM
> Subject: Re: [TCML] Terry Filter
> 
> 
> >I have no idea.  The legend on my drawing shows 12 movs for a 9kv nst,14
> >movs for a 12kv ;nst, and 16movs for a 15kv nst.  I can only assume that
> >your drawing would provide a greater safety factor.
> > ----- Original Message -----
> > From: "Paul Brodie" <pbbrodie@xxxxxxxxxxxxx>
> > To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> > Sent: Thursday, November 05, 2009 10:01 PM
> > Subject: Re: [TCML] Terry Filter
> >
> >
> >> My drawing shows 9 MOV's on each side. Why the discrepancy?
> >> Paul
> >> Think Positive
> >>
> >> ----- Original Message -----
> >> From: "Dan Casaregola" <ag2z@xxxxxxxxxxx>
> >> To: <tesla@xxxxxxxxxx>
> >> Sent: Thursday, November 05, 2009 6:38 PM
> >> Subject: [TCML] Terry Filter
> >>
> >>
> >> I'm in the process of building a filter for my 15k/30ma NST, and the
> >> drawing I have shows the number of MOVs required for the stated voltage,
> >> but it only shows 6 MOV. either side of center tap ground.  I remember
> >> reading somewhere that the number of caps should be the same as the
> >> number ov MOVs.  Is this correct?  Thank you  Dan
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> 
> 
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