Re: [TCML] Largest Secondary Coil "Drivable" by Primary Circuit

[jeremyee@xxxxxxxx]

Ok...that makes sense. Sorry for not checking back in the message trail. I was only loosely following this thread. That makes me feel better too that I didn't waste my time making the bigger secondary. When I had the smaller coil with my smaller toroid, I still had to add a breakout point to get a discharge. It was a 4.5" x 26" toroid. Maybe the problem is in my multi-static gap. I guess I will have to finish things and experiment. Thanks for the insight!

Jeremy
Sent from my BlackBerry device from Cincinnati Bell Wireless

-----Original Message-----
From: Futuret <futuret@xxxxxxx>
Sender: tesla-bounces@xxxxxxxxxx
Date: Mon, 27 Sep 2010 10:43:54 
To: <tesla@xxxxxxxxxx>
Reply-To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Subject: Re: [TCML] Largest Secondary Coil "Drivable" by Primary Circuit

Jeremy,

My comments are just a way to "think about the issue" and provide
some general guidelines, etc.  I'm not saying that secondary size doesn't
matter at all.  I mentioned in prior comments that the original
secondary size relative to the input power has to be considered.  My 
comments have to be read in conjunction with my prior recent comments,
otherwise the context is lost.  

Yes, there are rules of thumb that suggest a particular secondary
size for a given input power.  For example in my TT-42 coil I use
a 4" x 19" secondary, driven by a robust 12/30 NST which uses
about 800 watts when powered by 140 volts and gives 42" sparks
with a 13" toroid.  A previous coil which was basically the same
but had a taller 4" x 23" secondary, gave similar results, I think
the sparks were slightly longer or I was using a weaker NST for
the same spark length, I can't remember.  As a test I tried using
a 6" x 24" secondary on that coil, and I obtained the same spark
length.  I consider the 4" x 19" secondary to be around the
minimum size for efficient operation for that coil.  I don't think anything is
gained by using a larger secondary on that coil.  Larger secondaries
tend to have lower losses which can give a theoretical benefit,
but then again as Matt mentioned, it may be best to have at
least 1/2 the C of the secondary--toroid combo, in the toroid.
This ratio suffers as the secondary size is increased.  So 
possibly we gain one way and lose another way by increasing
toroid size, while keeping the input power the same.  

If we assume that a 4" secondary diameter is "good" for
an 800 watt coil, we can develop the formula:

  secondary diameter (inches) = sqrt input power (watts)/7

Example: (to determine secondary diameter for an 11,000 watt coil)

  sqrt of 11,000 = 104.88.    104.88/7 = 15"

I should mention one caveat to all this.  If the original small
secondary has relatively few turns of a thicker wire, then it may
be inefficient.  In this case replacing it with a larger secondary
may give better results.  In my statements about secondary
diameters, I'm assuming the inductance of the
original small coil, and the new larger secondary, are about the
same.  This means the original coil would use thinner wire, and
the larger coil would use thicker wire.  

For a 2kW coil the formula above gives 6.3" for the secondary
diameter.  This is about half way between the sizes of your old and
new secondaries.  Since your original secondary was rather small
for the power level, you may see some benefit using the new 
secondary.  There are always so many factors however, this is
why the things I'm talking about can only be a guide, and just a way
of thinking about the issues.  Different people like to approach
issues in different ways.  What is helpful and gives new insight
to one person, may just seem like nonsense to someone else.

If your toroid on the small secondary was rather small for the input
power level, and if you go to a larger toroid on the larger secondary,
that will give you longer sparks too.  

John

  

-----Original Message-----
From: jeremyee@xxxxxxxx
To: Tesla List <tesla@xxxxxxxxxx>
Sent: Mon, Sep 27, 2010 8:42 am
Subject: Re: [TCML] Largest Secondary Coil "Drivable" by Primary Circuit


I find the statement that secondary size doesn't matter is somewhat misleading. 

This is assuming that the optimal secondary size was chosen when the power 

supply was decided upon. When designing a secondary for given power level, what 

factors do you use to determine the size. Has there been a rule of thumb 

developed relating input power to secondary diameter? The reason I bring all of 

this up is because I just wound a new secondary this weekend. :) on my 2 kW NST 

power supply I went from a 4.5" x 23" secondary and am upgrading to a 8.625" x 

37" secondary. Was all of this work in vain? Thanks a lot!



Jeremy







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