Re: Still confused on LTR sized Caps

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Dan,

On 27 Aug 2002, at 12:40, Tesla list wrote:

> Original poster: "Mccauley, Daniel H by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
> 
> 
> 
> Still a little confused on the LTR sized primary capacitors.  I assume the
> standard way to choose a primary capacitor is to choose a value which is
> charged to a maximum over the ac cycle of the high voltage output so that
> when a spark gap fires, the cap is charged at maximum at the peak of the
> high voltage output sine wave.  For this a 0.0106uF would be optimum for a
> 15kV/60mA NST.

That is so but by using a cap twice the size, you can store more 
energy as the voltage drop doesn't match the increase in capacitance. 
Another good reason for getting away from a resonant charging regime 
when operating with an AC supply is that the resonant charging is 
rather particular about the variac setting - it only happens smoothly 
at a particular setting. Above and below that setting I've found 
operation becoming "lumpy" and erratic. I've found that a larger cap 
and slightly smaller gap setting gives better results and more 
regular firing overall. The transformer (NST in particular) exhibits 
parametric changes in its characteristics with applied voltage and 
load.
 
> Now I am very confused about LTR sized caps.  First, I assume the entire
> primary tank circuit's resonant frequency would change as a result of the
> larger primary capacitor.  Secondly, why are LTR sized caps used in the
> first place and what are their benefits?

Any change in the tank capacitor affects the primary's tuning. 
Another benefit of LTR operation is that the voltage step-up ratio of 
the TC is increased (SQRT(Cp/Cs)).

Regards,
malcolm