Re: Ok, what is an LTR cap.

["Barton B. Anderson" <tesla123-at-pacbell-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi David, Garry, 

Tesla list wrote: 

>
> Original poster: Tesla729-at-cs-dot-com 
>
> Hi Garry, 
>
> That would be LARGER THAN RESONANT. Normally, the natural 
> resonance of the power xfmr determined by the current and voltage 
> rating of the xfmr output and the mains frequency dictates a certain 
> size of cap. for resonant charging -at- the mains frequency (60 hz in 
> the US, 50 hz in Europe). I'm having a little trouble putting my finger 
> on the exact formula at the moment, but other more knowledgable 
> members could rattle it right off for you.


Cp uF =  1/ (2 * pi * Z * F) 

Z = xmfr impedance 
F = 60 or 50 Hz (0.00006 or 0.00005) 

>
> But, basically a 12 or 15 KV 
> 30 mA NST -at- 60 hz will need approximately 10 nF of tank capaci- 
> tance to be resonant.


12KV / 30mA = 400,000 impedance 

1 / (6.28 x 400,000 x .00006) = 6.6nF (.0066uF) 

>
> However, NSTs are notorious for succumbing 
> to the HV kickback peaks caused by operating with a resonant sized 
> cap, so many coilers opt for a larger than resonant sized cap. which 
> in turn keeps the HV kickbacks to a more managable level by the in- 
> creased surge impedance. So instead of using a 10 nF cap with a 30 
> mA NST, they may use a 15 or 20 nF cap. Of course, there are limi- 
> tations to how far one can go with this as a 30 mA NST would not be 
> able to charge a grossly oversized cap properly within the 8 or 10 msec 
> duty cycle of 50 or 60 hz operation, so the output would  decrease at 
> this point. 
>
> I hope this explains it somewhat for you. I'm sure more knowledgable 
> list members will respond as well with better explanations, though.


I think you did a great job! 

Bart 

>
> Hang in There, 
> David R.