Re: Secondary resonant frequency vs. Skin Effect

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi,

The skin depth at ~~200kHz frequencies has been estimated at 1 to 3 meters 
in humans.  So, unless one ate way too much these holidays, or one's size 
merits their own zip code, skin depth will not "save" you!!

The RF currents tend to travel along the higher conductivity nerves and 
blood vessels in ones body.  So that is also where the damage is done!!  I 
know of an RF engineer that was holding the end of a high power coax with 
his thumb over the end "open load test" and noticed a burning smell..., and 
a tech that had a tuner arc to the back of his hand at about 10kV...  They 
were "hurting units" for a very long time!!!  But both "lived" through it 
very well considering the power behind it...

On the good side, nerves do not react to RF currents.  That is why you 
can't feel them unless they start burning holes in you.  In the burning 
case, the holes are super painful, super deep, and may require surgery to 
help heal!!

However, one may note the "super experts" in the field:

http://www.krampf-dot-com/

http://www.wondersofscience-dot-org/sfs/BIOGRAPH.HTM

These folks "do" let the RF currents run through them without ill 
effects.  But they have been doing it longer than most of us have been 
alive!!!!!  Don't do this at home or you "will die"....  A game for the 
super expert, or the super stupid...

I also note that Cynder Moon and Danielle Stampe are women performers who 
also do this.  One place where women seem to thrive in this mostly male 
hobby...

But do note that really screwed up things can happen, like your hair 
bursting into flames...

Austin Richards has a great suit of electrical armor too....

One may wish to refer to the lively posts under the search term "Arcs off 
the fingers and getting killed in the process..." in the Tesla list's archives:

http://www.pupman-dot-com/htsearch.html

Of course, we can't forget the person that died...

Henry L Transtrom - Electrocuted while working on a stage and using a
large Tesla coil.  He inadvertently allowed a power arc to go from his body
to some metal framing that was part of the stage backdrop.  He authored the
following book:

  "ELECTRICITY AT HIGH PRESSURES AND FREQUENCIES"
Henry L. Transtrom, originally published: 1913, second edition
1921, Joseph G. Branch Publishing, Chicago; Reprinted 1990, ISBN
1-55918-054-4, Lindsay Publications, Bradley, Illinois, 60915.
Paperback, 247pp, Lindsay # 20544.

He was considered an "ultimate master" of the "arcs off the fingers" thing...

We super highly discourage anyone from doing these stunts, while noting, 
that is it done by some very gifted few...

Most of use here that have been around for a long time have indeed been 
shocked by Tesla coils and lived,  those that have died have never reported 
back...  Our advice is just stay darn far away and don't get 
shocked...  There is no reward for getting zapped, but there is a giant 
penalty out there just waiting!!!

Cheers,

         Terry







At 02:22 PM 1/1/2004, you wrote:



> > Hi All,
> >
> > I am new to the list, but jus  twanted to warn of the low frequency which
> > can be typical of a large coil. I built my first coil 28 years ago. It was
> > 20" diameter x 48" and easily produced a 50-60" discharge. The resonant
> > frequency was 278Khz. This is actually a very low frequency and "skin
> > effect" does not apply at these low freqencies. In my opinion it is the Q
> > of the secondary that produces the high voltage rather than a turns ratio.
>
>
>On the contrary.  Skin depth applies equally well at those frequencies.
>However, the skin depth is related to
>conductivity.  Whereas highly conductive materials have shallow skin depths
>where skin effect is greater, less conductive materials
>(such as human flesh) have much higher skin depths and less skin effect.
>
>Skin Depth is approximately equal to:  1 / (sqrt(f*pi*mu*conductivity)
>(where skin depth is defined as the point where current flow decreases to
>about 37%)
>
>For a round frequency of 100kHz, the skin depth of copper would be about
>0.008 inches.  Based on the average resistance of human flesh,
>the skin depth would be about 10.5 feet.  So unless you were enormous, skin
>effect is basically non-existance for the human body.
>
>Also, the gain of a standard tesla coil (magnetically coupled) is equal to
>the SQRT (primary capacitance / secondary capacitance) - of course in
>actual practice, the theoretical gain may never be reached due to losses,
>premature break-out etc...
>
>Dan