Re: [TCML] 12"/16" Large Coil Diameter Selection

[Futuret <futuret@xxxxxxx>]

 Amir,

My thoughts about the issue is that the aspect ratio is not too
important provided it's within an acceptable range.  One of the
key issues is the height of the secondary.  If it's too short,
you may get breakdown along the coil form or sparks may
hit the ground too often.  When I design a coil, I like to consider
first the input power, then consider the spark length, then work
backwards to determine toroid size, coil size, etc.  

I consider the limit to spark length to be based more on toroid
size (and power input of course), rather than on secondary size
(provided the secondary doesn't break down of course).  If the
secondary is too small, then the inductance will be low (using
reasonable wire thickness), and the coil will be less efficient
for the reason discussed below.

For example I think a 12" x 50" secondary can give basically
the same spark length as a 16" x 50" secondary if both coils
use the same size toroid.  It's true the narrower secondary
may result in a little less efficient Tesla coil.  It would probably 
not be the secondary which is less efficient but the primary,
since the primary surge impedance will be lower, resulting
in higher spark gap losses proportionally.  So the narrow
secondary coil may need to be driven with a little more power
for a given spark length, but should still be able to produce
the same spark length because the toroid is the same (large).  

Another consideration is whether you will drive the pole pig to
double its rated power.  Even break rate is a consideration.
A high break-rate coil can possibly tolerate a shorter coil form,
and smaller toroid for a given spark length.  However a lower
break rate is probably more "efficient".  Sparks may be brighter
at a higher break rate however.  Sparks may form coalesced
tendrils at times at higher break rates.  This is less likely
at lower break rates.  

If you have plenty of space to run and store your coil, then
you may want to keep the full 60" height, and use the 16" diameter
form.  Such a coil can easily produce 20 foot sparks using a large
enough (65" diameter) toroid.  Such a spark length would require 
about 20kVA which your transformer can provide for intermittent use.
I'm assuming a break rate of around 320 breaks per second.  

Cheers,
John

 


 

 

-----Original Message-----
From: Ln2guy42@xxxxxxx <ln2guy42@xxxxxxx>
To: tesla <tesla@xxxxxxxxxx>
Sent: Fri, Jun 3, 2011 5:14 pm
Subject: [TCML] 12"/16" Large Coil Diameter Selection


Hello everyone!



I am planning on winding a large secondary coil and have an option regarding 

diameter size.


I have on hand a large supply of 18 awg magnet wire as well as two segments of 

sonotube. They are both 60" in length, but one is 12" in diameter and the other 

is 16" in diameter. The coil will be powered by a 14.4 Kv 10 kw pole 

transformer. 


I have researched the archives and found that the main considerations in 

designing larger coils to be the lower aspect ratio (suggested to be 3:1), a 

larger diameter (for it is more "efficient" and can handle more power), as well 

as aesthetic design (overall coil size versus spark output length). 


I was wondering if anyone had any suggestions/comments on which coil diameter to 

use based on any criteria that are important in this decision.


I am also curious to know how a 4" increase in diameter of a secondary coil will 

make a difference (if any) in coil performance with regards to the above 

criteria.


Thank you so very much for any input and I appreciate all comments.


Amir M.



 
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