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RE: Another Terry's filter question



Original poster: "MakingLightning" <MakingLightning@xxxxxxxxxxx>

What if you put a small metal plate over the filter, would that protect it
if you had the transformers and filter under the coil?
If you were using an open transformer, by that I mean one that was not
potted in a metal can, would the primary induce anything into the
transformer that you would have to worry about.
It seems like a lot of people put everything underneath the coil.

Can you use a rotary sparkgap with neon transformers?

Kevin

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Wednesday, March 29, 2006 2:44 PM
To: tesla@xxxxxxxxxx
Subject: Re: Another Terry's filter question

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

At 09:54 PM 3/28/2006, you wrote:
>I recently posted a question to the list about
>Terry?s filter.  I wanted to know
>if my string of twenty, 56 ohm, ½ Watt resistors (in place of the 100 Watt
1k
>resistor) would fry when the safety spark gap
>fired.  I mistakenly assumed that
>the safety gap was across the NST rather than the primary gap.  If the
safety
>gap were across the NST, and fired, the primary cap would discharge back
>through each of the 1k resistors, resulting in a large momentary current
>through the resistors.  It was this large momentary current that concerned
me.
>But, since the safety gap is not across the NST, the current that will flow
>through the 1k resistor is only the 30 mA of the NST.   30 mA times 56 ohms
is
>only 0.168 Watts per each ½ Watt resistor.  The resistors are at 1/3 of
their
>rated power and will survive.   Several people
>replied that the resistors would
>run hot.  Am I missing something?  Also, I do not think that the 1k
resistor
>will ever see the full 7500 volts of the NST.  7500 volts across a 1k
resistor
>calculates to 7 amps - from a 30 mA NST??  But again I may be missing
>something.  Perhaps the small filter capacitor (charged to 7500 volts) on
one
>end of the 1k resistor, and the firing (shorted) primary gap on the other
side
>of the resistor, might momentarily place 7500 volts across the resistor?

For a 15/30 NST the current might really be about
45mA depending on the system and all.  That gives 0.045^2 x 1000 = 2.025
watts.

The filter resistors are discharged at every
firing through the resistors.  The power there is:

1/2 x C x V^2 x BPS

1/2 x 3300pF / 6 x (7500xSQRT(2))^2 x 120 = 3.7 watts.

The MOVs also act like capacitors normally.  I
forget the value, but I think it is close to the
caps.  So they add another say 4 watts.

So if we add it all up, it is about 10 watts.  So
I think you will be ok with 10 watts of resistors.

For the 100Watt resistors, that is 10% of there
rating.  With an astounding 300C them rise for
100 watts they will heat to 30C above the ambient temperature.


>So, now that I realize that the safety gap is
>not across the NST, my question is
>why was it designed that way?  Since I want to protect the NST and not my
>resistors, why not put the safety gap across the NST?

The more reliable MOVs directly protect the NST.

Cheers,

         Terry



>Norman Scheinberg