FW: How should we measure coil efficiency, was neon vs.

From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Wednesday, July 30, 1997 3:41 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: How should we measure coil efficiency, was neon vs.    

Hi John,
> From:   John H. Couture[SMTP:couturejh-at-worldnet.att-dot-net]
> Sent:   Wednesday, July 30, 1997 12:49 AM
> To:     Tesla List
> Subject:    Re: How should we measure coil efficiency, was neon vs.    potent
> At 04:33 AM 7/28/97 +0000, you wrote:
> >
> >From:  Alfred A. Skrocki[SMTP:alfred.skrocki-at-cybernetworking-dot-com]
> >Reply To:  alfred.skrocki-at-cybernetworking-dot-com
> >Sent:  Saturday, July 26, 1997 1:37 PM
> >To:    Tesla List
> >Subject:   Re: How should we measure coil efficiency, was neon vs.   potent
> >
> --------------------------------------------------
>   Alfred -
>   There is no contradiction because I have said several times in the past
> that the spark length test and the efficiency test are two completely
> different tests. The reason is because the efficiency requires finding the
> output energy and spark length cannot be converted into energy. The energy
> for that one special long spark cannot be measured out of a group of 120 or
> more sparks per second.
>   Tesla coils appear to have an optimum operating frequency because small
> coils use high op freqs and large coils use low  op freqs. This implies that
> a certain size coil would have an optimum op freq. This means that a coil
> could be improved by increasing it's op freq if it is operating at a freq
> below it's optimum and vice versa.

But operating frequency is largely dictated by coil size. True, you 
can arbitrarily increase inductance but as you do so, wire losses 
increase as well. The reverse applies to reducing (up to a point).

>   Some coilers are now saying that a smaller pri cap and more pri turns are
> better compared to past coils. That appears to be contrary to the fact that
> more energy can be stored in a larger pri cap. At present we do not know
> enough about how a TC operates to know which way to go. 

Hmmmm....  Well, I think you cannot separate air ionization effects 
from coil operation. The two are inextricably linked when one is 
producing sparks. Trying to analyse a sparking resonator without 
taking discharge characteristics into account is bound to give non-
real world answers isn't it? In those systems with small Cp, high BPS
gives the same average throughput power-wise as a large C low BPS but 
the peak power is a lot lower. Using a high surge impedance in the 
primary definitely reduces gap losses and would also make quenchng 
easier I would think. I hope to check this in the lab. 

>   Selecting an operating frequency is at present an arbitrary choice and the
> builder cannot explain why he has chosen a particular freq for his coil. It
> is important that he pick the optimum op freq to get the most from his coil.

To a large degree, it is chosen by the choice of coil size.
>   Note that in developing a TC computer program like the JHCTES an optimum
> op freq for the power input selected must be determined because many
> parameters depend on this freq. The JHCTES method of finding the optimum op
> freq cannot be compared with other methods because I have not heard of
> anyone who has worked out a method. 

Given that Cself is invariant for a particular coil form, increasing 
turns => decreasing wire size and the losses progressively increase.
My modified guideline for good Q's is wire diameter = 3 skin depths 
minimum for a space wind and 4 for a close wind. I have seen Q's 
heading downwards as more turns are crammed onto a particular coil 
form. Increasing wire size beyond the above guideline does not seem 
to increase Q enough to be worth it.
    The highest Q I've ever measured was for a space wound coil on a
H/D = 1 HDPE coil form and was approaching 500 taking generator 
impedance into account. I have heard of Q's of around 600 being 
    Secondary Q's are generally so high relative to the primary that 
small variations don't seem to make a great deal of difference beside 
the influence that different inductances can have on spark quality.