# Re: first post (fwd)

```---------- Forwarded message ----------
Date: Thu, 16 Aug 2007 18:55:45 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: first post (fwd)

Hi Garry,

is recommended by most on the list to stay away from the resonant value
capacitance. Bert Hickman just posted an excellent iteration of cap
selection and also stated within that post about resonant cap values and
STR (smaller than resonant) cap values causing high stresses on both the
cap and transformer.

Something I want coilers to be aware of: The use of a static gap
self-limits the voltage to a specified arc voltage. Yes, resonant and
str values of caps can cause voltages to rise very high (if allowed). If
coilers use a spice program or similar to look at the voltages in a TC
circuit and adjust the cap value towards the resonant value, they will
see the voltage climb as the approach cap resonance. But for a reality
check, most who look at this are not accounting for the clamped voltage
level (via static gap spacing). In reality, the break rate is what
actually climbs (faster and faster).

Resonant transformer C values and resonant Tesla Coils are one and the
same. It's resonance. Electrical resonance is when reactance's (both C
and L) are minimum (ideally zero). Remember Ohms Law: If V/R=I, then
V/smaller R = larger I. Thus, resonance transforms to a maximum current
characteristic. Thus, in this discussion, bps is increased because the
current rises thus charging the cap faster and faster. Very simple to
understand situation.

There are downfalls to this which affect both the cap and the
transformer. The arc at the gap temporarily shorts the transformer and
collapses it's field, then when the gap opens, the transformer is
allowed to again charge the cap including all associated inrush
currents. The faster this occurs, the more often the transformer and cap
see this chaos of events and can be dangerous to both cap and
transformer. Although STR values will not share the resonant rise
effects, they can still rise the bps if the supply current is high
enough. Far more trouble with resonant value caps however.

In your case, I think STR is the best approach from a cost standpoint
and capability of running a static gap without too much trouble (a good
static gap is still required). I recommended .02 through .04 uF. But, if
you really would like it bullet proof, then I would suggest 0.1uF in an
LTR setup. The downside of this is that you should be running a rotary
gap due to the high energy in that mode (which means a "real" rotary,
not some little low current cobbled together thing, and that can be
expensive). Also, an MMC setup for this particular LTR gets really
expensive. After weighing in on those basics, I recommended the STR system.

It's always your choice. When it comes to understanding resonant cap
situations, I highly recommend looking through some of Richie Burnett's
web pages on this subject. Here is a direct link to that particular
analysis:

http://www.richieburnett.co.uk/resonant.html#resonant

Understand the pro's and con's before you decide on what to do. Also,
use a design program that can look at these characteristics like Javatc.
http://www.classictesla.com/java/javatc.html

Take care,
Bart

Tesla list wrote:

>---------- Forwarded message ----------
>Date: Thu, 16 Aug 2007 07:49:08 -0500
>From: Terri Neeley <neeley_111@xxxxxxx>
>To: tesla@xxxxxxxxxx
>Subject: Re: first post (fwd)
>
>
>Dang now im confused.  What value should i go for my cap.  My
>transformers output approx.9kV225mA.
>
>Garry Neeley
>
>________________________________________________________________________________
>
>      From:  "Tesla list" <tesla@xxxxxxxxxx>
>      To:  tesla@xxxxxxxxxx
>      Subject:  Re: first post (fwd)
>      Date:  Thu, 16 Aug 2007 06:10:13 -0600 (MDT)
>      >
>      >---------- Forwarded message ----------
>      >Date: Wed, 15 Aug 2007 18:41:30 -0700
>      >From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
>      >To: Tesla list <tesla@xxxxxxxxxx>
>      >Subject: Re: first post (fwd)
>      >
>      >Hi Garry,
>      >
>      >I understand the transformer hookup but I don't understand
>      >capacitance. You mentioned 0.066uF. This is the "resonant"
>      capacitance
>      >value that will cause the transformer to operate in a 100%
>      resonant
>      >charging mode. Are you sure you want to do this? Can be a
>      >for your transformers. Even giant pole pig coils usually run
>      smaller
>      >than resonant by some margin. And NST's typically run larger
>      than
>      >resonant by some margin. The idea is to stay away from the
>      resonant cap
>      resonant
>      >charging. That means large safety margins in the voltage
>      category of the
>      >cap chosen and the windings voltage standoff capability of
>      the transformer.
>      >
>      >I was kind of surprised no one else had mentioned this
>      >would do just fine in the 0.02 to 0.04 uF range. Good for
>      MMC with
>      >regards to the number of caps vs. voltage and current
>      ratings.
>      >
>      >Examples:
>      >2 strings of 14 caps per string (CD 0.15uF type) [28 caps)
>      >= 0.0214uF total capacitance at 28KV rating (rms derating of
>      3.1)
>      >
>      >3 strings of 10 caps per string (CD 0.15uF type) [30 caps]
>      >= 0.045uF total capacitance at 20KV rating (rms derating of
>      2.2)
>      >
>      >Where:
>      >4 strings of 10 caps per string (CD 0.15uF type) [40 caps]
>      >= 0.06uF total capacitance at 20KV rating (rms derating of
>      2.2)
>      >
>      >Just food for thought. The 0.06uF value is unnecessary,
>      problematic,
>      >component dangerous, and expensive.
>      >
>      >Take care,
>      >Bart
>      >
>      >
>      >
>      >
>      >Tesla list wrote:
>      >
>      > >---------- Forwarded message ----------
>      > >Date: Wed, 15 Aug 2007 07:34:54 -0500
>      > >From: Terri Neeley <neeley_111@xxxxxxx>
>      > >To: tesla@xxxxxxxxxx
>      > >Subject: first post
>      > >
>      > >Hey guys im new to coiling but I am building my second
>      coil and I need some
>      > >help.  I don't want to make the same costly mistakes as I
>      did on the first
>      > >coil.  I will have 2 ge 5021g10 wired for 9000v 225ma for
>      a spark gap coil.  My
>      > >question is:  What capacitors should i go with?  I need
>      > >thought about the maxwell you see floating around ebay?  2
>      in parallel of the
>      > >35k .03mF would work but would it survive?  Any
>      suggestions would be great Thx
>      > >Garry Neeley
>      > >
>      >>______________________________________________________________________________
>      ________
>      > >
>      > >Find a local pizza place, movie theater, and more�.then
>      map the best route!
>      > >
>      > >
>      > >
>      > >
>      > >
>      > >
>      > >
>      >
>      >
>      >
>
>
>________________________________________________________________________________
>