Re: Top Toroid
At 09:10 PM 1/29/97 -0700, you wrote:
>Subscriber: MALCOLM-at-directorate.wnp.ac.nz Wed Jan 29 21:02:26 1997
>Date: Thu, 30 Jan 1997 11:02:08 +1200
>From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
>Subject: Re: Top Toroid
> Thought I might add a brief note to yesterday's diatribe
>> 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).
>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 has a key and salient point here which can be learned by simple
dinkin' around but is backed up by solid theory. Best energy transfer may
or may not yield best spark based on a number of key factors. The secret is
to make the secondary as inductive as possible within the limits of your
terminal capacitance's ability to withstand the pressure. (Tesla mentions
this in the CSN.) Let the primary and its cap fall where they may within
synergisitic design priciples. I opt for the largest system capacitor which
will give a minimum of 6 turns in the primary. ( I prefer 8-12 turns) Stay
away from 1 and 2 turn primaries at all costs!!!!
Richard Hull, TCBOR