Re: Top Toroid

• To: tesla-at-pupman-dot-com
• Subject: Re: Top Toroid
• From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
• Date: Thu, 30 Jan 1997 11:02:08 +1200
• Subscriber: MALCOLM-at-directorate.wnp.ac.nz Wed Jan 29 21:02:26 1997

Hi all,
         Thought I might add a brief note to yesterday's diatribe 
fyi.....

>      I think we are generally agreed that the output voltage is 
> going to be a function of the energy that gets to the secondary at 
> the end of the first primary ringdown, and the total secondary 
> capacitance including top load. From first principles, this turns out
> to be:  Vo = Vcap*SQRT(Cp/Cs).  As Bert Hickman has showed however,
> this ideal will never be reached because of significant losses in the 
> gap. I think in some instances, around 80% of the energy gets 
> transferred. Papers by others use the formula: Vo = Vcap*SQRT(Ls/Lp).
> This is true because Ls*Cs = Lp*Cp   (basic tuning requirement). 

<snip>
Worth noting that if the prim and sec coil geometries are identical
(same height and diameter), the ratio SQRT(Ls/Lp) reduces to a
straight turns ratio (Ns/Np). If you want convincing, do the algebra
on Wheeler's inductance formula. Note also that this does not take
k into account either. It can only be true for a lossless case (no
gaps or other losses in either coil), no matter what k is set at.
A key point from this is that the turns ratio doesn't count in typical
Tesla Coils. A cruel irony of this is that you can make Ls/Lp 
arbitrarily high, but the lower the surge impedance of the primary, 
the higher the gap losses.

Malcolm
 

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