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Re: [TCML] Caps



Hi Christian,

LTR is a child of computer investigation on TC behavior, evaluated IRC by Terry Fritz. It revealed that using an LTR capacitor, more Power could be transferred to the sparks, while at the same time stressing less the primary cap, voltage-wise. But first of all, I'd recommend studiing the basics of TC's (especially "Resonant Loading" on Ritchie Burnett's excellent Website:

http://www.richieburnett.co.uk/tesla.shtml

There exists no such thing, useful to the operation of TC's as a multiple LTR cap! - Two(2) resonant circuits are involved and resposible for the sucessful performance of a TC (and oftly they are not distinguished in a clear way):

1.) The resonant circuit of the primary with the main capacitor, which has a resonant RF frequency in the range of 60kHz to say 500 kHz. Frequently this is thought of the only relevant resonance, which is erronous thinking...

2.) Another resonant, LOW f frequency, which is formed by the leak- or ballast inductance of the HV-Transformer (i.E. NST), seen from the HV side, with the primary capacitor. The resonant frequency in in the order of magnitude, with your 60Hz or 50Hz Line frequency.

Essentially. these 2 regimes can be threated independently, which really facilitaes the analysis.

A so called "resonat Cap" is one, which has in No. 2. a resonant frequency of 60Hz(US) resp 50Hz(EU &..other). At this point, it must be remembered, that resonant loading has the potential, to stress a cap and HV-Xfrmer to perhaps 80kV ... 100kV, IF no safety-gap would prevent this. If you don't rely on safty-gap ignition: resonant loading is to be avoided.

However, the quesion is: How high a voltage your prim-cap will be charged, when the main gap fires? - The energy in the cap, for ONE firing (=1 bang) is Ebang = Cprim * (Vcap^2 ) / 2 - meaning the power is going up linearly wit the cap size, but SQUARED by the voltage at charge end. This means, your power for transferring energy to sparks, is depending on the power of the HV-Supply, included leak- and ballast inductance. If the primary cap is too big, it will not stress the cap, but it will not charge to a high voltage, giving little bang-energy, which would be true for higher than LTR caps

Another case is the smaller than resonant cap (STR). An STR is oftly a need to use in high power TC's, with PT or "Pole Pig" power systems, because LTR would lead to uneasy big primary capacitors and too low winding primaries. The power supply is no more again an obstacle for charging the the cap: it can do too much! Here the maingap comes to play: if static or ASRSG, it will fire more oftly (high BPS). If SRSG, things have to be tuned (after evaluation) to a reliable compromise... well that's beyond this reply.

Well, you may use STR to save some $, but please use at least a reliable safety gap. The recommandation is: use simple LTR, if you have an NST.

Regards, Kurt


-----Ursprüngliche Nachricht----- From: Christian Hill
Sent: Wednesday, August 29, 2012 8:22 AM
To: tesla@xxxxxxxxxx
Subject: [TCML] Caps

Hello. I am building my first coil and have a few questions. I read that
you should stay away from using a resonate sized capacitor as it can cause
a "condition called resonate rise." Multiple sources say to use a "larger
that resonate" capacitor to keep this from happening. I've read that you
can also use a multiple of the LTR capacitance value as well. Let's say
that the optimum LTR capacitance is 10nF. Since I can double it and use
20nF would I also be able to half it and use 5nF? (Assuming that my voltage
needs were met, of course).

I would assume that the closer I get to the resonate capacitance value, the
better chances of resonate rise I have. So I should stay as close as
possible to a multiple of the LTR capacitance, correct? Or should I just
meet my voltage needs, tune the coil accordingly, and make use of safety
gaps?

I am asking all of these capacitor questions because I want to get the most
out of my money. Those Cornell-Dubillier 942C20P15K-F's can really add up
when you're on a budget. I tried searching through the archives and have
poured over dozens of tesla coil guides but found nothing that really
answered my questions. Thank you very much for your help.
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