RE: [TCML] Terry Filter, Saftey Gap Distance?

["Lau, Gary" <Gary.Lau@xxxxxx>]

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of ConorPerry@xxxxxxxxxxx
> Sent: Saturday, June 14, 2008 12:05 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Terry Filter, Saftey Gap Distance?
>
> Thank you for your info.  I'm curious how you came up with your 11/64"
> (0.172") gap distance?

That would be the part about "properly" setting the gap.  A safety gap is not set by factoring the NST voltage into some equation or table, nor by asking what spacing others have used.  I reported what mine was set to just as a point of reference.  But everyone needs to set their own gap, simply by having only the safety gap tied to the NST secondary, placing full AC voltage into the NST, and set the width so that it just doesn't arc.

> How you mention the atmospheric effects I wonder if
> it's more from empirical data than by calculations.  Are you setting the
> gaps just larger than they will fire without the primary?

Yes.

> When I initially calculated for mine I used the 3,000,000 Volts/Meter as the
> dielectric of air (
> 76,200 Volts/Inch).  My 12/100 NST with a Variac is guessed to have an
> output of 14kV.  So I set my gaps just above that voltage at around 8kV per
> side, which is a distance of 0.11".
>
> Then I run your numbers with the same math, but with a 15kV NST on a Variac
> to make 17.5kV.  Your gap of 0.172 calculates to 13kV per side, and 26kV
> total.
>
> So am I set too conservative, or are you too high?  Do your safety gaps ever
> fire?  Maybe my assumption of using the 3,000,000 V/m is unfounded (since
> that's "standard air" at 1atm.)
>
> CP8071

I think you're being far more analytical than is useful (but I'll guess that your voltage estimate is probably close).  As Jim mentioned, calculating the breakdown voltage for such gaps is very difficult.  It's much easier to simply set the voltage and adjust the gap width.

My safety gap does indeed fire.  I use a sync RSG, and setting the phase is a very critical adjustment.  As I advance the phase, the firing voltage increases and performance increases, then without warning, it miss-fires (i.e. doesn't fire), the next charging cycle the voltage charges much too high, and the safety gap fires.  I back off on the phase, and the world continues to turn without trouble ;-)

Regards, Gary Lau
MA, USA
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla