RE: Res cap size charge

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

Original poster: "Luke" <Bluu-at-cox-dot-net> 


I was looking around the list archives and making up a spread sheet for
joules of the cap after charge time of 1/4 cycle and voltage on the cap
and number of rc time constants in the 14 cycle etc............

When I ran across a post on the archives pointing out the obvious. :(
The voltage is always changing so the rc time constant thing kind of
falls apart.

Thanx for the info.


Looking at the infor on the first link you sent I ran across something I
would like some opinions on.

Seems a good value for c would be 1.357 times c res.
That is where you hit the 120bps mark.  Going below this obviously gets
too close to c res and going above this slowes down the bps while also
giving less real power on the cap.   Why is the rule of thumb them 1.6
times c res for a static gap?
Luke Galyan
Bluu-at-cox-dot-net

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, January 21, 2004 7:29 PM
To: tesla-at-pupman-dot-com
Subject: Re: Res cap size charge

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi Luke,

At 06:41 PM 1/21/2004, you wrote:
 >I know it is not recommended to use a resonant size cap and that is not
my
 >intent.
 >
 >Using ohms law for the impedance of an NST of 15KV 60mA gives 250k ohms
 >Using the capacitive reactance formula there the capacitance at 60Hz is

 >0.0106mfd

Yes.

 >
 >Using 250k ohms and 0.0106mfd the RC time constant would be 2.65ms
 >Since the time to charge a cap is ¼ of the wave the time for cap
charging
 >at 60Hz is 4.17ms.

Nope.  It get's real messy now...  Although the time constant thing
gives
sort of comfortable numbers at first.  It is all screwed up in this
case.

 >This works out to the cap going through 1.57 RC time constants for each

 >charge cycle.
 >This is about 75% charged and 75% of 15KV is 11.2KV.
 >
 >So using a resonant sized cap will give max voltage of 75% (11.2KV in
this
 >case).
 >
 >Does this mean setting the spark gap (static) to fire at 11.2KV would
give
 >the same voltage to the system as if the gap were set to fire at 15kv?
 >Since the 15kv from the NST would fire the gap but only 11.2KV would
 >discharge from the cap into the primary.
 >
 >I know that the amount of energy is not the same as the amount of
 >voltage.  Energy is will be related to joules which is dependent on
both
 >voltage and cap size.  I am only talking about the amount of voltage
 >present not the amount of energy.

When F = 1/ (2 x pi x QSRT (L x C)) , or, 250k = 1 / (2 x pi x 60 x
C),  all kinds of factors start dividing out and things "theoretically"
get
explosive as infinite amounts of energy are transferred.  But in
reality,
resistances and losses keep the mess under theoretical control.  At that

point, simple equations we learned at school start to fall down and we
need
to crank the mess through the computer to get results that reflect the
"real world".  Here is a nice thing that deals with all this here, that
a
surprising amount of theory is based on, but nobody realizes it :o)))

http://hot-streamer-dot-com/TeslaCoils/Misc/NSTStudy/NSTStudy.htm

You "might" also want to see:

http://hot-streamer-dot-com/TeslaCoils/OtherPapers/TeroRanta/CurrentLimitedT
ransformers/NSTModel.htm

http://hot-streamer-dot-com/TeslaCoils/OtherPapers/TeroRanta/NSTCapMatching/
ResonantCapacitorMatch.htm

but this is getting into areas that makes my brain hurt too -at-:o)))

Cheers,

          Terry



 >
 >Luke Galyan
 >Bluu-at-cox-dot-net
 >