Re: My 4 inch Tesla Coil (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Thu, 25 Oct 2007 19:55:56 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: My 4 inch Tesla Coil  (fwd)

Hello Amir,

The reason the NST died is because the NST was overvolted. NST's cannot 
handle voltages beyond their rating well. When you run an async spark 
gap, the cap charges along the AC line frequency. The phase of the 
firing rate vs. the charging frequency is constantly varying. There are 
points along the frequency where no firing's will occur. This can cause 
an overvoltage at the cap which is seen at the NST hv winding.

With an NST, it is best to either use a synchronous rotary or a static 
gap in order to stabilize firing voltage. A Terry filter would be an 
excellent component to add to your coil. Also, with the new 15/30 you've 
purchased, check the value of the cap and the value of a capacitor size 
that cause your transformer to go into resonance. You want to use a cap 
size which is larger than resonance in order to prevent the voltage from 
rising beyond your NST's ability. Typically about 1.5 times larger for a 
static gap and 2.6 x larger for an srsg. A 15/30's resonant cap size is 
0.0053uF. So, in the neighborhood of 0.008uF for a static gap and 
0.0138uF for an srsg.

Take care,
Bart

> I was wondering if anyone could explain to me why my other NST died. 
> I was trying it with an asynchronous rotary spark gap with the TC and I had  
> only run it for about 10 seconds for the first time that day, when it just  
> stopped arcing. I had no filters or any rf chokes which is what I suspect was  
> what caused it. I didn't think I needed them because I was dealing with such 
> low  power.
> On my next transformer I will definitely put in a terry filter on it. 
>  
> You guys are really nice!
> Thank you
> Amir
>