RE: Capacitor help

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

Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> 


Bart -

Do you take capacitor charging time into consideration when selecting a
primary capacitor? The calculations below using the standard capacitor
charge equation indicates that the TC pri cap is not being charged to full
voltage when the NST is the power supply. I have been researching this
problem and have reached an impasse.

For example the charging time for each half cycle of 60 Hz (120 BPS) is

  1/4x60 = 4.17 ms. The capacitor charging time to 98% of 15000 is 4 time
constants.

    t = 4(-RC)(ln(V2/V1))

For a 15KV/60 ma NST the R=Z=V/I= 15000/.06 = 250000 ohms

     .00417 = 4(-250000xC)(ln(1/15000))

      C = .00417/(4(-250000)(-9.62)) = 433 pf max size pri cap.

This is saying that a 15KV/60 ma NST cannot charge the pri cap to anything
near the 15000 volts if the cap is larger than 433 pf and the charging time
is 4.17 ms. This cap is 24 times smaller than the resonant cap! What is
wrong with these calculations?

What are other coilers doing regarding the charge time when selecting the TC
pri cap? I believe this TC design question has never been brought up before
on this List?

John Couture

------------------------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Saturday, December 13, 2003 8:47 PM
To: tesla-at-pupman-dot-com
Subject: Re: Capacitor help


Original poster: Bart Anderson <classi6-at-classictesla-dot-com>

Hi Mark, All,

I just noticed the "reason" you are looking for an LTR cap was to achieve
possibly longer sparks. I almost always run a PDT which forces me into an
STR cap. From my understanding, LTR values do not give longer sparks or
anything of that nature, but are used to reduce the stress on the NST in
SRSG situations. The static gap apparently is also to benefit in this same
respect. The tradeoff is capacitance for voltage.

I sometimes get the impression coilers think using LTR gives greater spark
lengths, but again, this is not my understanding from past posts on this
subject.

Comments, anyone?

Take care,
Bart

 >Tesla list wrote:
 >
 >>Original poster: "RIAA/MPAA's Worst Nightmare" <mike.marcum-at-zoomtown-dot-com>
 >>Javatc recommends .027 uF (2.7x resonant) for a 8750v/35 mA with a 120 bps
 >>synch rotary (using .0165 now, trying to get longer or at least fatter
 >>sparks). Does this sound right or did I screw up somewhere? I thought 2x
 >>res. was usually the upper limit for caps before they didn't charge enough
 >>before the next break.