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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
**************Vote for your city's best dining and nightlife. City's Best
2008. (http://citysbest.aol.com?ncid=aolacg00050000000102)
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