Primary field strength

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: Primary field strength
From: Tesla List <tesla-at-stic-dot-net>
Date: Thu, 20 Aug 1998 23:15:22 -0500
Approved: tesla-at-stic-dot-net

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From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Thursday, August 20, 1998 3:56 PM
To:  Tesla List
Subject:  Re: Primary field strength

Hi Chris,

> From:  chris.swinson [SMTP:chris.swinson-at-zetnet.co.uk]
> Sent:  Wednesday, August 19, 1998 8:58 AM
> To:  Tesla List
> Subject:  Re: Primary field strength
> 
>  Hi Malcolm & All.....
> 
> 
> 
> >From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
> >Sent:  Tuesday, August 18, 1998 4:00 PM
> >To:  Tesla List
> >Subject:  Re: Primary field strength
> >
> >Hi Chris,
> >
> >> From:  chris.swinson [SMTP:chris.swinson-at-zetnet.co.uk]
> >> Sent:  Sunday, August 16, 1998 3:48 PM
> >> To:  Tesla List
> >> Subject:  Re: Primary field strength
> >>
> ><snip>
> >> so if the field is that big, I could easily make a 200" secondary, as it
> >> appears the field is huge when the caps are included.  Ok, I could not do
> >> this as I only have 80" hight in my room.  But you see what I'm getting
> at.
> >>
> >> This was only 1 gap as well, If I used all 5 gaps , the field would
> probably
> >> go 100's of yards away.  So what stopping me from building a bigger
> >> secondary ?
> >
> >The problem can summarised thus: You are transferring a fixed amount
> >of energy from the primary cap to the secondary capacitance with each
> >gap fire. Each gap fire is separate from every other. There is no
> >accumulation in the secondary with successive gap fires. The
> >capacitance of the secondary rises with its size.
> >
> 
> I'm not 100% sure of what you getting at.  Are you saying that if I did
> build a 200" high seconday and ( theory ) had the same capacitance as my 36"
> seconday, it would in fact give me a huge power increase ?

It won't have the same capacitance - it will be a *lot* higher which 
means output voltage will be a lot lower for a given primary energy.
 
> 
> >Since Vo = Vgap*SQRT(Cp/Cs),  you can see what is happening to your
> >output voltage as your secondary gets larger. Taken to an extreme, if
> >your secondary capacitance ends up being as big as the primary one,
> >secondary voltage only reaches that of the primary assuming no loss
> >in effecting the energy transfer.
> >
> 
> 
> Could you explain your calc a little better, Perhaps with a example or 5.

It is derived from Conservation of Energy. 

    0.5CpVp^2 = 0.5CsVs^2   where Vp = gap firing voltage

=>  Vp^2*Cp/Cs = Vs^2

=>  Vp*SQRT(Cp/Cs) = Vs

In other words, you can't get more out than you put in and that 
equality assumes no losses in transferring the energy from primary to 
secondary. Note that it also works by Vs = Vp*SQRT(Ls/Lp) since
LsCs = LpCp (tuning requirement).

Malcolm