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Re: New Coiler


From: 	Mark S Graalman[SMTP:wb8jkr-at-juno-dot-com]
Sent: 	Wednesday, September 10, 1997 7:28 AM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: New Coiler



          Hi Patrick,

   Here's my 2 cents worth:

On Tue, 9 Sep 1997 22:22:57 -0500 Tesla List <tesla-at-pupman-dot-com> writes:
>
>From: 	Patrick J. Gustafson[SMTP:gustafpj-at-uwec.edu]
>Sent: 	Tuesday, September 09, 1997 4:12 AM
>To: 	Tesla List
>Subject: 	New Coiler
>
>Hello all, 
>
>I have been patiently reading the list for quite some time now, but I
>could not get my questions to post on the list.   Thanks to Chip, this
>problem has been finally resolved. Here are the concerns that I have 
>as
>of yet:
>
>
>1.   I have a two layer secondary coil with 28 gauge wire close wound
>for 21.6" (both layers).   The first layer is at 6" in dia. and the
>second layer is at 6.125" in dia.   The calculated resonant freq's are
>108.71 kHz and 106.45 kHz respectively, and the calculated inductances
>are 91.84 mH and 95.49 mH also respectively.   Now since I layered in
>parallel, can I add together the inductance values directly? ( i.e. 
>the
>new value would be 187.33 mH)   

    No, when inductances are placed in parallel the total value goes down
and will be less than
the least value of inductance, in this case the total inductance would be
about 46.8 mH
  
   Thats alot of inductance for a 21" tall coil, The concern I have at
this point is I feel for the amount
of power your going to run into this coil the height of the coil maybe
too short.

>2.   Should I be concerned with the differing resonant freq's when
>calculating the needed primary capacitance?


   No, the two frequencies are close enough, you could just call it 107
khz. But, in reality this 
frequency means little because the actual secondary frequency will go
down with the addition of
a top load such as a sphere or a torus and then drop maybe another 10-15
khz while under sparking
conditions.

>3.   How do you determine  (a) the inductance (of chokes) needed to 
>stop
>the voltage spikes from reaching the NST's, and  (b) what ratings the
>parallel resistors that accompany these chokes should have?

  Here IMHO there is no need to calculate, I would shoot for about 50 -
100 uH in a air wound
choke and a few mH in a ferrite core choke. The De-Qing resistors are not
placed in parallel with
the chokes but are placed in series with them and for a NST I would use a
1 K ohm 25 watt wirewound.


>4.   What capacitance should I use for my protection cap. given the
>power supply below?

      Two old TV style doorknobs (500 pf 20 kv) in series from each HV
terminal to the transformer
case work well. This value really isn't critical, I'd just try to stay
between 100-250 pf and keep the
leads short. What you really DON'T WANT is to have a resonate point in
your filter (choke) system
anywhere near the actual operating frequency of you coil.

>5.   For the protective spark gap for the NST's, how is the ground
>electrode incorporated into this?      

       The ground electrode is the center electrode and it is tied to the
transformer case which is tied to
   earth ground.

>Here are the specs. of my Tesla coil:
>
>Primary Coil - 16 turn, 1/4" soft copper tubing with 5/16" spacing.  
>Inner dia. is 8" and outer dia. is approximately 25".
>
>Secondary Coils - As stated above.   Note: Went for inductance by 
>using
>28 gauge wire, also to see if it can withstand the punishment.
>
>Power Supply - 15 kV -at- 90 mA NST's.   ((3) 15 kV -at- 30 mA in parallel)
>
>Toroid - 25" outer dia. with a 5" cross section.
>
>Spark Gap Electrodes - 3/4" thick by 2" long highly polished steel, 
>with
>3/8" radius of   curvature on one end.
>
>Spark Gap - Single static.
>
>Components not made yet:
>
> - Primary capacitor (Calculated to need about .0226 uF.   Anyone have
>problems with using mylar for the di-electric?)
> - Protective capacitor.
> - Chokes.

   Under no circumstances use mylar for a pulse cap, it will melt at
best! Mylar cannot tolerate HV AC
voltages and peak currents. 

>
>Some info:
>
>I am a Physic's major, mathematics minor at the University of 
>Wisconsin
>Eau Claire, so I am quite familiar with most of the terminology 
>involved
>in Tesla coils.   This is my first Tesla coil project, which I am
>building for the Physic's Dept. (and they are funding!!) for
>demonstrations on inductance and E&M fields.   I can already see the
>limitations of these 2 coil systems, and may soon have to start
>researching into magnifiers.
>
>Any help greatly appreciated.
>Patrick Gustafson

                           Mark Graalman