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Re: [TCML] Terry Filter

I recently purchased a 9kV 50mA OBIT or at least the seller says it is an OBIT. This appears a little bit hefty for the purpose. Anyway, do these transformers require the same sorts of protection that are used with neon sign transformers?
Paul
Think Positive

  ----- Original Message ----- 
  From: Dex Dexter 
  To: Tesla Coil Mailing List 
  Sent: Monday, December 21, 2009 05:23
  Subject: RE: [TCML] Terry Filter


  I run my static gap coil without any filter at all.
  NST is 5kv/20ma ,and safety gap is set for
  the breakdown voltage of aprox 10 kV peak.
  I've   never saw it arcing so the breakdown 
  voltage of my static gap is probably below 9 kV.
  Position and way of connecting the gaps with respect to
  NST is important.Both gaps should be paralleled with NST.

  Dex

  --- Gary.Lau@xxxxxx wrote:

  From: "Lau, Gary" <Gary.Lau@xxxxxx>
  To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
  Subject: RE: [TCML] Terry Filter
  Date: Mon, 21 Dec 2009 02:16:43 +0000

  If you build a filter with MOV's targeting a 15kV NST, and you use a 9kV NST, the MOV's will allow a peak voltage of something like 22-23kV before they kick in.  With a 9kV NST, the maximum voltage that *should* be allowed is 9000 x 1.414 = 12726, call it 13-14kV.  So it would be permitting too-high voltages that should have been clamped.  One needs to select the correct number of MOV's for the NST voltage used, for the same reason that one needs to set the safety gap for each situation.

  Regards, Gary Lau
  MA, USA

  > -----Original Message-----
  > From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
  > Behalf Of chipford@xxxxxxxxxxxxxx
  > Sent: Sunday, December 20, 2009 8:31 PM
  > To: tesla@xxxxxxxxxx
  > Subject: [TCML] Terry Filter
  > 
  > I have my terry filter about 50% done. While building it, I asked myself a question.
  > Why would a person build anything but a Terry Filter capable of protecting a NST of
  > 15,000 volts? I ordered 14 MOV's from dig-key. For 4 or 5 dollars more, I could
  > have had 16. Now if i want enough for a 15k trany, I gotta pay shipping
  > again.Correct me if I am wrong. If I build a Terry filter capable of protecting a 15K
  > volt trany, I can use it to protect my 9000 volt NST without any modifications. I bring
  > this up because, as we all know, parts get swapped from coil to coil and if I decide
  > to built a larger coil with my 15k trany later on, I could've just moved it over without
  > worry. Am I wrong?

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