[Prev][Next][Index][Thread]

Re: first coil & help!!!




From: 	Adam[SMTP:absmith-at-tiac-dot-net]
Sent: 	Monday, November 03, 1997 1:08 AM
To: 	Tesla List
Subject: 	Re: first coil & help!!!

Ray wrote:

>I just built my first coil and fired it up and thought it was pretty
>good,but.
>Here's my spec's.
>1st     1 15kv-at-30ma  neon sign tran,  2 chokes one on each side of hv lines.
>Conected to 6 spark gaps.  Using 8 16 oz bottles as caps. Primary 3/16 solid
>wire at .25 spacing.
>wound 8 times. Secondary 4.5 at 20 inches #27 wire. wound at 1300
>times.Torid 4" dia x12"wide. First time I fired it I got a great spark from
>the center of the coil at least 12".
>As I understand it should'nt come from the center of the coil. Through my
>reading on Tesla info I figured it was overcoupled? 

Overcoupling, too much power input or improper tuning can all cause this 
breakout.  In your case, I think it is the latter.  You need more primary 
capacitance and inductance.  Sounds to me like you are exciting the 
second harmonic of your secondary, meaning your tank circuit is tuned 
near an octave too high.  Your big toroid and ground are anti-nodes, and 
the center of your secondary has the highest potential.  Focus on 
lowering your tank resonant frequency by winding a larger primary, and 
building bigger and better caps.  Your bottle caps are probably in the 
not up in the 0.01 microfarad range that you need for this coil. Do you 
have a capacitance meter, or any equipment with which to measure some of 
your circuit components?

BTW, are your 16 oz. bottle caps glass?  Don't use plastic coke bottles, 
these are made from Polyethylene Terphthalate, a polyester similar to 
Mylar.  This is extremely polar and has horrible RF dissipation.  I put 
aluminum foil on either side of a 2 liter pepsi bottle once, and hooked 
it to a bank of neons and it melted in a few seconds.

>I had a spare transfomer and added it to all the mess. Now I'm at 15kv-at-60ma.
>Seconday  still the same. Little spark and still from the center of the
>coil. 

Adding transformers is going to make things worse, since the more 
transformers you add, the more primary circuit capacitance you will need 
to achieve the correct capacitor charging rate.

>Again it would only fire with  the secondary ground disconnected. I'm
>ready to start all over again with a new secondary.  

God no! Don't undo all that work!  Work on tuning the primary to match 
your secondary.  If you don't have a signal generator & o-scope handy, 
you will need to experiment a lot more to get yourself in the right 
ballpark.  Using tesla coil design equations can also help you get to the 
right place faster (see www.pupman-dot-com, and search the archives!)

I hope this gives you some new hope.  It will work soon enough...

-Adam




--------------------------------------------------------------------------
Adam Smith
absmith-at-tiac-dot-net
Epoch, Inc. Digital Music Project

www.tiac-dot-net/users/absmith/     Now with MP3!     Musik. Macht. Macintosh.
--------------------------------------------------------------------------