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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,

Good, I'm glad your confused because that means your read the post. It 
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
>      your target
>      >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
>      very bad thing
>      >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
>      >value unless you design your components to take advantage of
>      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
>      issue. Your cap
>      >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
>      .06microfarad so I
>      > >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
>      > >in advance.
>      > >Garry Neeley
>      > >
>      >>______________________________________________________________________________
>      ________
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>      >
>      >
>
>
>________________________________________________________________________________
>
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