Re: 8 kHz Tesla Coil

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Gerry,

The plotting might be of value if there were no proximity losses, 
current flowing in dielectrics, etc... Unfortunately, all that is 
real and likely far more important to R.

Have you measured the Q on the 82 kHz coil and compared?

Take care,
Bart


Tesla list wrote:

> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
> Hi Malcolm,
>
> I found a set of formulas on the web for skin depth (SD) of round 
> solid conductors that are said to be conservative and overpredict 
> the AC effect (with no proximity effect).  The author compared the 
> results to measured Rac to verify his claim.  The following 
> equations were given:
>
> for SD < r ;
> SD = 2837 / sqrt(f)      (Skin Depth - mils)
>
> Rac = Rdc * (r^2) / (r^2 - (r-S)^2)  [based on effective area 
> reduction due to SD]
>
>
> My coil uses 1440 turns of 23awg where Rdc is 61 ohms.  At 82KHz, the skin
> depth is 9.9mils.  The copper diameter is 22.6mils (~2 SD's) so Rac 
> is 2% higher than
> Rdc (or 62 ohms).  Seems like the resistance is hardly affected by skin
> effect for this case.  The Q for a series RLC circuit is:
>
> Q = sqrt(L/C) / R
>
> R = 62 ohms
> L = 83mH  (Les)
> C = 46pf    (Ces)
>
> Q = 685
>
> I just got my 8x36 coil with the larger toroid (8x32) working, 
> tuned, and optimized for spark length.  The wall power is 2100 
> watts. My longest power arc currently is 86 inches.  Granted, 
> proximity effects have not been included, but this coil, using wire 
> that is only 2 SD's thick, performs with a Freau factor of 1.9
>
> I think by using this formula, one could easily make a table for a 
> given coil size and plot the Q and L as a function of AWG.
>
> Gerry R.
>
> > Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>
> >
> > HI Gerry,
> >
> > On 23 Sep 2005, at 10:53, Tesla list wrote:
> >
> > > Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
> > >
> > > Hi Malcolm,
> > >
> > > No comment is a waste of time in the persuit of knowledge and
> > > truth.  I think I understand what you were getting at.   If one uses a
> > > wire size where the current density is low in the center (that I
> > > called a waste of copper), one might opt to fix that by using a
> > > smaller guage and this will result in an increase of AC resistance.
> > >
> > > One question unresolved in my mind is how important it is to have the
> > > optimum unloaded Q considering that once breakout starts, the coil
> > > becomes loaded and Q drops to a low number.  Is the issue just one of
> > > power dissapated in the wire or are there other issues???
> > >
> > > Gerry R.
> >
> > A lot of people place a strong emphasis on the low loaded Q of the
> > system and claim that this makes secondary Q relatively unimportant.
> > However, it is demonstrably true (and a waste of money) that even an
> > unloaded Q as low as 40 (c.f. a loaded Q of about 10 e.g.) results in
> > an abysmal performance. I have always found that high unloaded Q
> > secondaries perform well. I put that down to two things: maximizing
> > output voltage on first ringup and maximizing energy retention with
> > light loading (e.g. air streamers) for a second bite of the cherry
> > within a single primary shot. At some stage I'd like to see (or
> > produce) a formula which produces an optimal secondary (nominated
> > topload included) for a given size coilform. By optimal I mean with
> > the highest inductance before or about the point where Q starts
> > dropping.
> >
> > Malcolm