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Re: [TCML] Toroid question

Hi Jim,
What you mention is very common practice and probably good advice to ensure breakout (but not necessarily performance). Coils have been built with toroids whose minor diameter is quite a bit larger and they worked fine. For example, I use a 6.5" minorD on my 4.5" sec. I also used a 9" x 30" toroid on the 4.5" sec when I hooked it up in the hybrid maggy configuration. I believe power and bang size are major contributors to the performance of a top loads ability to perform well run well. As long as the top terminal is sufficiently charged so that the surface field strength achieves breakdown in relation to the surrounding.
As Gary points out, we really don't have good hard numbers to predict exactly when too big is too big. Considering the cost and/or labor of toroids, it is something we should attempt. I personally have an academic problem with toroid sizing. To relate a toroid size based on a secondary diameter will not be best for all cases. It's simply an empirical probability that many coils will do ok with, so it does become good advice from that standpoint only. 

Take care,
Bart

Jim Mora wrote:

Hello List,
I seem to remember reading 2 thirds the winding length or a bit more as a
guideline for the major diameter. I have had pretty good results with a
minor diameter (which has a major effect on the capacitance if the major is
not oversized) close to the secondary diameter. Can anyone concur with that?
Jim Mora

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Lau, Gary
Sent: Saturday, May 30, 2009 2:37 PM
To: Tesla Coil Mailing List
Subject: RE: [TCML] Toroid question

Yes, there surely is a topload size that's too large for every coil.
Unfortunately no one has yet discovered a means of predicting what that size
is, so all we have is some very crude rules of thumb and trial and error. 
When a top load is too large, it doesn't just make the sparks smaller; it's
an all or nothing proposition.  Beyond a certain size, the topload simply
won't break out - even with a breakout point.

Regards, Gary Lau
MA, USA


-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Dex Dexter
Sent: Saturday, May 30, 2009 3:13 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Toroid question

John,in your formula
Spark lenght = 1.7*SQRT(P)
is P in watts power delivered to Tesla coil circuit or total power drawn

from the

mains?
Also,I heard that you developed the formula on the basis of SRSG , 120

PPS,and

equal bang sizes coils.
Does that mean  it is not so accurate for static gap coils,ARSG coils,and

higher

PPS coils.


Gary,there is surely a possiblity of a too big toroid for a power

level.Let say ,if you

put 48"x12" (with a braekout point on it) toroid on 360 W coil.That would

probably

decrease a spark lenght output,right?That size of the toroid is optimum

for a 1 kW+

range coil.

Dex

--- futuret@xxxxxxx wrote:

From: futuret@xxxxxxx
To: tesla@xxxxxxxxxx
Cc:
Subject: Re: [TCML] Toroid question
Date: Fri, 29 May 2009 18:18:23 -0400

Andrew,

at my website, I show my TT-42 coil with a 4" x 13" spun toroid.  The
coil
produces 42" sparks using a robust 12/30 NST.  An ordinary 12/30 gives
about 38" sparks.

 http://futuret.110mb.com

Cheers,
John


-----Original Message-----
From: Lau, Gary <Gary.Lau@xxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Fri, 29 May 2009 9:13 am
Subject: RE: [TCML] Toroid question



Hi Andrew,

As you noted, bigger toroid equals bigger streamers but fewer of them.

Personally, between the two choices you gave, I would choose the larger
4.5x18
toroid.  I haven't personally built a coil powered by a 12/30 so I
can't say how
much larger than that one could go.  Do you already own both of those
toroids?
If so, try stacking both of them and see how that performs, assuming
that you
have sufficient primary turns to accommodate the lower frequency.

The final answer will depend upon how much time and cash you have
available.
Big spun toroids are expensive.  If cash is limited, you may want to
try the
custom-made foam toroid that I had made -
http://www.laushaus.com/tesla/foamtoroid.htm


Regards, Gary Lau
MA, USA


-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Andrew Robinson
Sent: Friday, May 29, 2009 3:23 AM
To: tesla@xxxxxxxxxx
Subject: [TCML] Toroid question

I asked this once before but dont remember getting a very clear

answer.

With a 4" x aprox 22" secondary. 12/30 NST what would be an

appropriate

sized toroid? I've heard bigger toroid equals bigger streamers but

fewer

of them. I guess looking at it from the physics point of view, bigger
toroid = more capacitance = bigger streamer but longer charge times.

Basically we're looking at either a 3" x 12" spun toroid or a 4.5" x

18"

spun toroid. Also is there a better place to get these other than

ebay.

Can someone out there sell us one?


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