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Re: Top Toroid
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On Fri, 31 Jan 1997 23:16:01 -0700, Tesla List
<tesla-at-poodle.pupman-dot-com>, you wrote:
>> Subject: Re: Top Toroid
>
>Subscriber: sgreiner-at-mail.wwnet-dot-com Fri Jan 31 23:10:25 1997
>Date: Thu, 30 Jan 1997 14:39:43 -0800
>From: Skip Greiner <sgreiner-at-mail.wwnet-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: Top Toroid
>
>Tesla List 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>
>> To: tesla-at-pupman-dot-com
>> Subject: Re: Top Toroid
>>
>> 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
>>
>Hi Malcolm and all
>
>I have been following with great interest the various posts on gap
>losses but not always accepting the conclusions put forth. I assume from
>your answer above that as the surge impedance goes down then the surge
>current increases. Are you then saying that gap losses go up due to this
>increased current? Doesn't this assume that the "resistance of the gap
>while it fires remains constant?
>
>My experience with synchronous gaps leads me to a different conclusion.
>I feel quite sure that the current in a firing gap is a function of the
>voltage in the cap as well as other factors. I note that the contacts in
>my gaps run much cooler when the gap is firing near the peak of the
>mains voltage. When firing ahead of the peak (by adjusting the gap
>position with respect to the motor shaft) I notice that the gap pins get
>much hotter. I attribute this increase in gap heating to increased
>resistance in the gap due to a lower current/voltage. I believe that the
>gap resistance is dynasmic and definitely increases at lower currents
>which can definitely be controlled when using a synchronous gap. My
>primaries usually are 3 to 7 turns and I think on the low impedance side
>and therefore have low surge impedance. Still at 1800va input I have no
>trouble using .25" brass contacts in the rotary and they give very long
>life.
>
>Flames and comments will be appreciated
>
>Skip
>
----begin include from sci.plasma-----------------------------------
> The conductivity in ohm-m of a fully ionized plasma (which a flame is
> not) is
>
> 5.2e-5 * Z * ln lambda / T_e^(3/2)
>
> where Z is the charge of the ions, ln lambda, known as the Coulomb
> logarithm, is a weak function of density and temperature usually equal
> to 10 or 15, and T_e is the electron temperature expressed in electron
> volts (eV). Thus a plasma is a poorer conductor than copper unless it
>X is hotter than about 1 keV (10 000 000 deg).
>Another rule of thumb for radiating plasmas, is that its conductivity
>varies with the current to the 3/2 power I^(3/2a).
>However, if really, really high voltage impulse is applied about a torus
>of plasma, the current electrons can be accelerated (run-away) to
>essentially light speed, and the conductivity of such plasma circuits
>may become several orders higher than ordinary copper conductivity.
>-------------end include--------------------------------------------
>Notice the inverse T_e^(3/2) section: I think that this matches with
>Malcolm et al's measured results.
Regards,
jim