Re: Skin Effect & Primary Current?
Tesla List wrote:
> >From MALCOLM-at-directorate.wnp.ac.nzThu Jul 25 21:02:05 1996
> Date: Thu, 25 Jul 1996 18:10:42 +1200
> From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> To: tesla-at-pupman-dot-com
> Subject: Re: Skin Effect & Primary Current?
> Hi Richard,
> > How did you capture the damped wave? You should have a good calibrated
> > Rogowski coil and mesure the exact peak current for a true idea of the
> > spark gaps actual resistance which in most tela circuits amounts to as
> > much as ten ohms! The more normal value is 1-4 ohms. Arcs of the low
> > value you measured are usually not normally encountered until the current
> > is over ten thousand amps. The decrement is, indeed, used to calculate a
> > number of loss factors in an LC circuit, but without a very accruate
> > value of peak current it would be tough to use. The ultimate would be to
> > get a current transformer reading as well as a second channel voltage
> > reading across the gap and integrate the two to yeild the actual power
> > loss and resisatance of the gap over time.
> You're right. I didn't include enough data to make sense of this. Cp
> was 0.1uF, Lp about 12uH. The waveform was captured on a digital
> storage scope with an aerial hung a few feet away from the primary.
> I repeated this with a range of L/C's. I was stunned to find that in
> all cases, the decrementing waveform gave a Q of about 10. The range
> of capacitances tested was 25 to 100nF and L's ranged from the one
> given (the resident primary for the coil I mentioned elsewhere) to
> a coil wound from high quality 80 strand Litz measuring 330uH. Not
> only did all give that Q, but it was peripherally verified by the
> number of oscillations recorded until the gap extinguished (about 20
> - 22). I was able to changed the scope timebase and superimpose the
> captured waveform on top of a previously captured waveform. The match
> was amazing. In all cases, the gap was set for an identical firing
> voltage. In fact I was using the voltage decrement to do the
> Looking at Q = 1/R x SQRT(L/C) showed that for the higher L/C
> ratios the gap resistance was much higher than that earlier
> combination. It was clear then that gap resistance was inversely
> proportional to current. For 330uH and 25nF then, this Q gives a
> gap+circuit resistance of 11.5 Ohms which fits well with your finding
> I think.
> The most dramatic realization for me was that changing L/C ratios
> in the primary had no noticeable effect on dynamic Q. The other one
> was seeing just how much power is being lost in the gap. Looking at
> these results from several angles suggested that the gap had all the
> characteristics of a pair of back-to-back zeners with a voltage
> drop of about 60 which seemed a reasonable conclusion for a gas
> Further thoughts on this welcome.
All of this info has been spread out over a number of our report tapes
in the past. Also the fact that litz wire is a cruel joke played on Tela
coilers and that Q's of 5-20 are the norm for most any tesla tank
We have also shown measured dynamic Q's for resonators in the 150 range.
Most of the best, however, fall just below 100 with an average coil
being around 70. Once the toroid goes on, this can rise slightly or dip
based on a number of factors.
Richard Hull, TCBOR