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RE: [TCML] Terry Filter
While intuition suggests that one might obtain the clipping voltage of the MOV string by multiplying the number of MOV's by 1800V, it's more complex. It's been years since I dug into the specs of the MOV's, but 1800V is NOT the clamping voltage. I don't have time to reinvestigate; please just use the table of number MOV's vs. NST voltage that Terry Fritz published. It's tried and true. If you need to know the why's, Digikey should have the MOV specs on their web site.
Regards, Gary Lau
MA, USA
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of chipford@xxxxxxxxxxxxxx
> Sent: Monday, December 21, 2009 2:32 PM
> To: Tesla Coil Mailing List
> Cc: mddeming@xxxxxxx
> Subject: Re: [TCML] Terry Filter
>
> Yeah. Thanks for the feedback. I have built several coils. I have a dead 15k 60ma.
> NST. I want to protect this one. I would like to understand more about it this time.
>
> So, help me understand the math. I have a 9000volt x 20ma NST. My calculator
> says that(5)1800v MOV's/side in series equals 9000volts. The recommended
> (6)/side equals 10800 volts. In the calc. way below I see 9000v x 1.414 = 12726v.
> Question one is this. Why do I multiply by 1.414. Is this a conversion to DC. Is the
> 9000volts RMS? Seems to me that if you use (7) per side, It would still be short of
> 12726 volts? I am guessing that we want to stop the kick-back well short of that. As
> I write this I am thinking that if I only used (5) MOV's that they would be clamping all
> of the time from the output of the NST. So I think I am starting to get an
> understanding. Feedback please.
>
> Chip
>
>
> ---- mddeming@xxxxxxx wrote:
>
> Of course a SGTC will run without any filter, just as a car will run without seatbelts,
> wipers, or headlights.
> There are some of us who would choose not to drive such a vehicle.
>
> Matt D.
> "Are you feeling lucky today..."
>
>
> -----Original Message-----
> From: Dex Dexter <dexterlabs@xxxxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Sent: Mon, Dec 21, 2009 5:23 am
> Subject: RE: [TCML] Terry Filter
>
>
> I run my static gap coil without any filter at all.
> ST is 5kv/20ma ,and safety gap is set for
> he breakdown voltage of aprox 10 kV peak.
> 've never saw it arcing so the breakdown
> oltage of my static gap is probably below 9 kV.
> osition and way of connecting the gaps with respect to
> ST is important.Both gaps should be paralleled with NST.
> Dex
> --- Gary.Lau@xxxxxx wrote:
> From: "Lau, Gary" <Gary.Lau@xxxxxx>
> o: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> ubject: RE: [TCML] Terry Filter
> ate: 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,
> he MOV's will allow a peak voltage of something like 22-23kV before they kick
> n. With a 9kV NST, the maximum voltage that *should* be allowed is 9000 x
> .414 = 12726, call it 13-14kV. So it would be permitting too-high voltages
> hat should have been clamped. One needs to select the correct number of MOV's
> or the NST voltage used, for the same reason that one needs to set the safety
> ap for each situation.
> Regards, Gary Lau
> A, 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
> uestion.
> Why would a person build anything but a Terry Filter capable of protecting a
> ST of
> 15,000 volts? I ordered 14 MOV's from dig-key. For 4 or 5 dollars more, I
> ould
> 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
> rotecting a 15K
> volt trany, I can use it to protect my 9000 volt NST without any
> odifications. I bring
> this up because, as we all know, parts get swapped from coil to coil and if I
> ecide
> to built a larger coil with my 15k trany later on, I could've just moved it
> ver without
> worry. Am I wrong?
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