[FwdX: [TCML] High Primary Q]

[David N. Van Doren]

Hi Bart
I don't see what the issue is.
Q has always been Reactance divided by Resistance.
The trick it to determine the real resistance.
Copper losses are just one source of losses.
One can calculate the skin depth of a tube and
use the resulting thin walled tube as the conductor.
But according to Dr Gary L. Johnson's Tesla Coil Paper,
Table 1, Proximity effects, skin depth R can be multiplied
by a factor of a little over 1 to as much as 5, depending
on the coil design.
But for me the biggest uncertainty of primary circuit losses
is in the spark gap. The conditions the determine the gap
Resistance can and do vary wildly. The gap resistance of
a coil running kiloAmps is most like very different
from a coil running a couple hundred amps.
This is what prompted me to ask the list what
it knew about Spark Gap Resistance.
Gap resistance is very tough for me to measure and
until I have some definitive data I can only assume that
It could range as high as the R's of the copper.
Than I would like to prove to my self the effects of
Dielectric losses in the capacitor. I don't know
how to equate loss factor to equivalent resistive losses.
Maybe someone here can show me?
Then there are radiative losses and I don't know
any thing about this.
So in the end Q may in fact maybe quite abit lower.
Maybe this is why Tesla turned to the Magnifier,
to in crease the coefficient of coupling to reduce
the number of loss cycles the energy had to endure.

Dave 

----- Original Message ----- 
From: "bartb" <bartb at classictesla.com>
To: "Tesla Coil Mailing List" <tesla at pupman.com>
Sent: Friday, December 28, 2007 8:21 PM
Subject: Re: [FwdX: [TCML] High Primary Q]


> Hi All.
> I posted this to the TCML in early December but didn't receive a reply.
> I've kept it around but have been busy with other stuff.
> Thought I would repost and see if anyone has any disagreements or 
> additions.
> 
> It's not highly discussed on the list except in generalizations. So, as 
> I did this little mathematical analysis, I was surprised myself.
> Bart
> 
>> Hi All,
>>
>> How high does the primary Q have to be? Reason I ask is I don't think 
>> it's as high as assumed and I include myself in that initial assumption.
>>
>> I was looking at Rac and Rdc in primary's this weekend and came across 
>> an interesting find. Rac is amazingly high in the primary and 
>> culminates into a rather low Q. How low? How's the 50 to 100 range 
>> sound excluding proximity effects.
>>
>> For example, 8.5 turn primary with 1/4" tubing. Length = 789.1cm, 
>> thickness is .254cm, and equivalent height if shaped into a ribbon is 
>> 1.995cm (using ribbon strip calculations).
>>
>> Rdc = p*length/cross sectional area
>> p is resistivity in ohm per cm = 0.000001678
>> Rdc = 0.000001678*789.1/(.254*1.995) = 2.61 mOhms
>>
>> Rac = length*sqrt((p*pi*u*f)/ht)
>> p = resistivity in ohm per cm = 0.000001678
>> u = relative permeability of annealed copper = 0.000001256629
>> f = frequency = 229106
>>
>> Rac = 789.1/sqrt((0.000001678*3.14*0.000001256629*229106)/1.995) = 
>> 688.3 mOhms
>>
>> Q = sqrt(L/C)/Rt = sqrt(0.000025669/0.0000000188)/(.00261+.6883) = 53.5!
>>
>> I am only looking at a significant portion of impedance but haven't 
>> included surge impedance which in my particular coils case is 37.3 ohms.
>>
>> So, where is the high Q? I can't find it.
>>
>> Take care,
>> Bart
> 
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