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Re: [TCML] All of my tesla coil questions (for now)



Hi Nicholas, Welcome to the list!
Comments  interspersed below

Matt D.


In a message dated 6/11/08 9:20:30  P.M. Eastern Daylight Time, 
ngoble@xxxxxxx writes:
figure I should introduce  myself.  I'm a sophomore in college, 
Yea!!


studying  business. 

The gods may forgive you for this ;^)

I have only  a basic college level physics course 
under my belt,

Puts you ahead of  some folks.

but I've read a lot about Tesla coils on the Internet.  

SOME of what's on the Internet is accurate, some is ka-ka-poo, much is  in 
between.


I've always enjoyed building things and impressing people  with them.  I 
think the most fun is building them though.  My plan  is to build a 
small to medium coil over the summer.

Instead of  filling the archives and your inboxes with multiple 
questions that are  unknown to me but second nature to everyone else, 
I'll just clump them all  in one big message.  Here are all my 
questions; hopefully someone can  answer them:

1) Do I NEED a Terry filter?  I know they protect the  transformer, but 
I don't know how they work and what happens if I don't use  one.

Do you NEED a seat belt?, a bike helmet?, a condom?, fire insurance?  a door 
lock?
Taken over a large sample and over years, NST's with Terry  filters tend to 
live longer than those without. The Terry filter prevents a lot  of HV spikes 
from going back into your transformer. Any disruptive (spark gap)  coil will 
have occasional misfires which result in higher than rated voltages  across the 
secondary of the NST. Even without over-volting, the persistent RF  "hash" 
stresses the NST causing it to fail over time. The Terry filter includes  a 
safety gap. 


2) Do I NEED a safety gap?  Again, I know they  protect the transformer, 
but I'm in the dark as to how they work and what  will happen if I don't 
use one.

YES. Even if you don't want the added  protection of a Terry filter, a safety 
 gap is the minimum protection you  should use. If you have accidentally set 
your main gap too wide, or there is  that occasional missed discharge,  At 120 
breaks per second, it takes very  few seconds for that "occasional missed 
discharge" to occur. An NST can become a  door stop or boat anchor in short 
order. 


3) How much should I plan  on spending on a transformer (approx 10 KV, 
30 mA)?  I don't want  overpay because of inexperience.

Neon sign shops can  no longer legally use the type of NST that you want for 
their neon sign service.  Many places will part with them for the copper and 
iron scrap value. Some will  give one or more away, especially used ones.
Take a cheap  ohmmeter with you and check that the resistance from each HV 
terminal to the  case ground is the same within 5-10%. (should be several 
k-ohms) Also check that  the resistance from each primary terminal to the case 
ground is "infinite" while  the resistance between the two terminals is a couple of 
ohms at most. A  transformer may pass these tests and still be defective, but 
if it fails any one  of them, it's bad.
If you buy one on line, the shipping  will be a large fraction of the price. 
A good 15 kV/30 mA transformer will weigh  in at 20-25 lbs. and a 15 kV/60 mA 
will be in the 40-50 lb range. Expect to pay  near $1./lb shipping and 
handling.


4) How do I construct an  MMC?  What type of circuitry do I use?  I 
can't find any concrete  information on MMC's.

Capacitors (C-D 942 C series are best) are  connected in strings and strings 
are connected in parallel. If each cap used is  C uF at V volts and has a peak 
current rating of A. If there are P caps per  string and S strings in the 
array, then:
The total voltage rating is P*V, the  peak current is S*A, the capacitance of 
the array is C*S/P.
As an example,  assume each cap is rated 0.15 uF at 2000 V peak and 10 Amps 
peak current, and  that   there are 5 strings of 15 caps each. Then the whole  
array is rated 2*15 =30 kV, 5*3 =15 Amps, and 0.15 * 3/15= 0.03 uF. 

5)  Instead of building an MMC, would it be cheaper and/or more 
effective to  build a plate capacitor out of just window glass and some 
other  metal?

No, glass plate capacitors are very lossy, fragile, heavy, and  microscopic 
trapped air bubbles in the glass can expand and shatter the glass  when used in 
HV applications. So-called beer bottle caps are cheap and have been  used 
with some success (Tesla used wine bottles), but again, they are heavy,  lossy, 
prone to breakage,and sloppy. If you make one for the experience, your  next 
one Will almost certainly be an MMC or a big commercial pulse  cap.


6) This was my plan for a spark gap: Have 2 rods (preferably  Tungsten) 
form a gap inside a PVC pipe and have a fan or blower at one or  both 
ends.  Will this be sufficient?  Would a rotary gap be  better?  I just 
don't want to be replacing the rods every time I fire  this thing up.

Tungsten stands up to the wear & tear of TC's very  well, but it does not 
cool quickly which makes it hard to quench the gap once it  starts to conduct. 
Parallel copper pipes tend to quench better in a static gap,  and tungsten in a 
rotary gap where the 100 mph breeze created by spinning helps  to cool them 
and movement aids quenching.  

7) Should I use  insulated, magnetic wire on the secondary coil?

My biggest fear is that  my coil doesn't work after all the time and 
effort I invest into it.   My second biggest fear is that it dies 
shortly after I put it  together.  My third biggest fear is that I die 
from it.  I'm  pretty sure I can be safe around electricity.  Just don't 
touch the  thing when the cap is charged or it's plugged in, right?

You also don't  stand close enough for the streamers to "kiss" you. You keep 
expensive digital  equipment turned off and away from it while running. The EM 
fields can even mess  with battery operated stuff like calculators and 
plastic-cased sport  watches.

Don't let anyone you want to impress see your "first light"  attempt.


These are all my questions for now.  I appreciate all  of your past and 
future answers.  This has been an extremely helpful  list serve.  Thanks

You will greatly benefit from reading the  following website:

http://www.richieburnett.co.uk



Nicholas  Goble  




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