Re: How to rise the secondary? (fwd)

---------- Forwarded message ----------
Date: Mon, 13 Jul 1998 15:34:54 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: How to rise the secondary? (fwd)

Hi John,
          Some points raised by this post:

> Date: Fri, 10 Jul 1998 05:47:05 +0000
> From: "John H. Couture" <couturejh-at-worldnet.att-dot-net>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: How to rise the secondary? (fwd)
>   To All -
>   Why are coilers building Tesla coils and raising the secondary to make
> them work properly? Raising the secondary of a properly designed and tuned
> coil only reduces the output. Why use a faulty design of excessive
> overcoupling then try to correct it by raising the secondary?

It would be too bad if one ended up with a less than optimally 
coupled design though.

>   If a proper pri/sec clearance is maintained to prevent flashovers 
> and the
> coil properly tuned raising the secondary is unnecessary. Tweaking is part
> of the tuning process and not necessary for coupling selection with a
> correct design. With a properly designed TC the quenching adjustments relate
> only to the primary circuit. Quenching always occurs after the first
> transfer when the secondary circuit has almost zero energy and has no effect
> on the primary circuit.
>   Critical coupling is the same for Tesla coils as it is for any dual
> coupled RCL system. If this condition can be determined at the time of
> design the correct amount of overcoupling can be determined and excess
> overcoupling avoided. It does not make engineering sense to deliberately and
> incorrectly design a coil with excessive overcoupling and then try to
> correct it by raising the secondary.

I think it does if one doesn't know the characteristics of the gap 
one is using or one wishes to experiment with different types of 
gaps. In a sense, adjusting k for optimal quench and output is 
"tuning" the system to suit the gap.

>   I have studied and researched this problem with over a dozen coils. My
> conclusion was that raising the secondary was not necessary with a properly
> designed TC. In fact a TC that requires raising the secondary can never be
> adjusted to produce optimum output. This is because moving the secondary
> away from the primary will reduce the output.

I beg to differ. If transfers do not go to completion (as they won't 
if k is not one of the loss-adjusted magic values), then raising the 
secondary could well improve peak voltage production.

> I have not solved the problem
> of finding the exact coupling for a particular TC. However, coupling is not
> critical as it does not affect the amount of energy transferred. Only
> sufficient pri/sec clearance is required to prevent sparkovers. I agree more
> research is needed.

I think coupling does affect the amount of energy transferred. If it 
is set between two of the magic values (again, loss-adjusted) then 
transfers will not go to completion. One can see this on the scope.