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Re: I Need some Help.



Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Alex,

At 03:41 AM 6/3/2002 -0400, you wrote: 
>~Hello
>       I have been working on my first coil for a few weeks now.  I finished 
>it and turned it on.  There was no discharge off of the Sphere on the 
>secondary.  However there is a little arc (and I mean little) when I place a 
>piece of metal next to it (something like a screw driver).  

My first coil did that too :o))  A "little" arc shows that 90% of it works!

>I've been 
>wracking my brain to try and fix this problem and I was wondering if one of 
>you fine gentlemen would help me.  I think it is something with the 
>frequency of my circuits. I believe they are mismatched...

Almost guaranteed ;-)

>
>The Dimensions of my coil are as follows:
>Secondary uses 30 gauge copper wire that is wrapped around a PVC pipe 7/8 
>in. diameter and 8.25 inches tall. (about 700 turns) the sphere on top is 
>.75 inches in diameter.  

A very small coil by most standards.  #30 wire wraps...

http://hot-streamer-dot-com/TeslaCoils/Misc/WireGaugeChart.gif

90.5 turns every inch.  So 700 is real close for the number of turns.  The
inductance of the secondary is an important number and can be found by
using the formulas at:

http://home.earthlink-dot-net/~electronxlc/formulas.html
http://home.earthlink-dot-net/~electronxlc/formulas.html#helic

L = (NR)^2 / (9R +10L) = (700 x 0.4375)^2 / (9 x 0.4375) + 85) = 1.054mH
(H = Henry which is a measure of inductance)

With a 1 inch terminal ball and guessing and Using E-Tesla6:

http://hot-streamer-dot-com/TeslaCoils/Programs/Programs.htm

The resonant frequency of your secondary system is around 3,000,000 Hz
That is VERY high but it is because your coil is small.

>
>The transformer is 9000 V NST and 30 mA.  It's rated at 120 V. 


That transformer should be able to put out 28 inch arcs in a "perfect" system:

http://hot-streamer-dot-com/TeslaCoils/MyCoils/SmallCoil/SmallCoil.htm

>
>The capacitor has 17 sheets of 5.5 in. x 6 in. separated by .1 in. window 
>pain glass.  (I don't know the dielectric value.)  If it makes any 
>difference, only 4 inches of the foil overlaps for each of the plates ( a 6 
>inch x 4 inch plate)

Glass plate caps are not recommended now days.  They blow up easily and are
hard to know what the capacitance is.  MMC's are nice but cost money:

http://hot-streamer-dot-com/TeslaCoils/MMCInfo/mmcinfo.htm

For a 9/30 with a static gap, this chart says you want a cap that has a
value of 0.0113 uF or 11 of the Geek Group's caps

http://hot-streamer-dot-com/temp/MMCcapSales.gif

Or maybe something cheap like their bucket cap:

http://www.thegeekgroup-dot-org/Flash/how%20to/bucket%20caps.html

>
>The spark gap is non-rotary and can be adjusted to any distance it needs to 
>be at.

Adjust it so just the NST transformer with nothing else connected arcs
easily.  DON'T open the gap wider or you may hurt the NST.

>
>The primary is helical and is basically 5 turns of wire.  3.5 in. in 
>diameter, spaced 1 inch from eachother.  (I would be most willing to change 
>this or the capacitor.)  

If you have more turns, you have more adjustment range.  You "might" need
more turns if it is not too hard to do.  But your frequency is really high
so you should not need many more turns on the primary.  But you will need
lots of adjustment room....  If all else fails, add more turns.

>
>I would be forever grateful if someone could help me work out the flaws in 
>this design.  Thank you very much for all of your time.

OK,  Here is what I would do...  First be sure the spark gap is adjusted
right!  You don't want to blow up the NST.  With just the NST connected and
nothing else.  Set the gap distance as far as you can apart but where you
still get a good consistent arc.  Like 3/16 to 1/4 inch...  Then the gap
will be set fine.  If in doubt, go for LESS.  You have tons of power there!!

Second,  Get a bigger top terminal.  Get like a 6 inch diameter kid's ball
or anything like that and cover it with aluminum foil.  A big top terminal
will make bigger sparks and get that resonant frequency down.  Lowering the
resonant frequency will help things a lot!

If you still don't get arcs, redo the primary coil for like ten or 15
turns.  That will give far greater (like 10X) the tuning range.  You should
not need many turns with your coil but you need to search for the tune
point and a primary with a wide range is really important for that. 

Still no arcs...  You need a better cap...  Start collect beer bottles for
a salt water cap or cold hard cash for an MMC...

One thing to think about is a bigger coil.  A 7/8 x 8.25 inch coil run off
a 9/30 NST is like a Yugo running off a 2000HP dragster engine :-))  Might
think about like a 4 x 24 inch secondary with like 24 gauge wire and a 15
inch top toroid shaped terminal...

Hope this helps...  If all else fails, find a nice working coil and the net
somewhere that you think you can copy and just copy it :-))  Tesla coils
are pretty messing for the first timer and just copying a design solves a
lot of little details so you can get a coil working without having to know
every darn thing.  Above all, be real careful!!

I have to admit, my advice for the first timer to "just copy a coil" seems
to work really well.  My friend Dave did that and he really knows nothing
about the math and theory but his coil works better than mine!!  Once you
get the first coil working, all that tuning and inductance stuff becomes
clear.  You just have to get over the hump in getting a coil that makes arcs...

Cheers,

	Terry


>
>Sincerely,
>Alex
>