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Re: [TCML] Safety gap, secondary coil, and coil mounting
Hi Nicholas,
Comments interspersed:
Nicholas J. Goble wrote:
I have a few more questions (certainly not my last) about tesla coil
building. The project has taken off after obtaining my free NST. It's
rated at 9KV and 30mA. So far, I've purchased 1000' of 24 awg enamled
copper wire through eBay and have bought a 4"dia PVC pipe in hopes of
building a secondary. I'm just waiting for the wire to arrive. In the
meantime, I bought some supplies from Lowes hardware to build a safety
gap. I ended up getting 3 brass egg-shaped drawer knobs. I think
these will work. Here are my questions for you all:
1) How can I determine the spacing for the safety gap?
Gary just mentioned a day ago about testing the safety gap across the
transformer by itself and then setting the spacing so that the gap does
not fire. This is perfect for a starting point. The electrodes you
purchased should be fine. Once the gap is in place with the coil, there
may be a need for some adjustment. If the gap fires very often, it's gap
may need to be increased slightly. But first, check the gap spacing of
the main gap. If it is too wide, it will cause the safety gap to fire
more often.
2) The safety gap goes after the NST but before the spark gap and cap, right?
The safety gap should be directly parallel with the main gap. The safety
gap is the second switch which is designed to fire in the event the
first gap does not (for whatever reason). If you have 2 spark gaps, the
one with the widest setting is the "safety gap". Think of it in that
type of connection and it's then very easy.
3) Can I wind the secondary by hand? I don't really have a lathe to
help me with that.
Absolutely. I've wound many coils by hand and even wound a rather large
coil by hand. It is time consuming and you need to pay attention to
detail as your winding (spacing, tension, etc..), but no problem other
than hand fatigue. Take a break now and then. If you want to count
turns, slide a small piece of paper under ever 100th turn. You can later
just pull our the piece of paper. It's a good idea to count turns for
future reference, but you can also estimate turns based on the length,
wire size, and measured resistance of the coil.
4) Do I have to seal the ends of the PVC pipe used in the secondary?
No, but it is a good idea. If you want, you can simply lay your top
terminal on the top of the pvc. However, it is nice to have end caps.
They help with mechanically attaching the top and bottom winding
connections for the base wire as well as the top terminal. I use
Plexiglas for the top and bottom caps, but for a 4" size pvc, you can
probably find an end cap of pvc that fits the form. Much easier when the
coils are 6" and smaller.
5) Should I varnish the PVC pipe before and after winding it? If yes,
then why? How many coats? What type of varnish?
Yes. Lightly sand the pvc to clean it. Then give it a light coat of a
spray on varnish (most anything will do). This helps seal the pvc from
absorbing moisture. Do this inside and out. Real easy and quick to do.
Then your ready to wind it. Once it's wound, use a good insulating
coating to help keep the wires in place during handling. Some use the
Dolph coating that DC has recommended for years (it's probably one of
the best to use). I personally use Marine Spar Varnish because it goes
on thick, is flexible for temp changes (no cracks), and it's available
at most hardware stores. It's been a great coating for every coil I've
built. I allow a full day of drying between coats and I lightly sand
each coat before I put on the next. I apply enough coats to get past the
wire turn to turn ripples. Here's a pic of the SISG coil I'm working on
which shows this coating on one of my secondaries.
http://www.classictesla.com/sisg/SISG1%20014.JPG
BTW, that is a 24 awg wire size on a 8.5" diameter secondary. When I
coated this coil, it was spinning at a slow rpm horizontal. I applied
the spar varnish with a stain brush and then let it spin all day while
it dried (helps for an even spread of the coating).
6) How much room should I leave on the ends of the PVC pipe so I can
attach the toroid and whatever goes underneath?
If you want to attach the top terminal directly to the pvc pipe of the
secondary, then leave at least enough room so that the bottom of the
secondary is even with the top secondary winding. That's a pretty good
starting point. You can always shim up the top terminal if needed.
7) I see that many coilers have a two level table to keep their coil
on. Why do you need that? My guess is that the streamers from the
coil would short out the components unless they're underneath it. Is
that true?
I'm not sure what your describing? It's nice to keep components below
the coil in a cabinet of sorts, but each coiler does his/her own thing.
You don't want strikes hitting your main components. Those 300 to 500 kV
strikes pretty much go where they want to go. But, those strikes have no
brain. You can direct them anywhere you want with a grounded target
nearby. Best to put one up horizontal with the toroid as opposed to a
target near your main components which simply puts your components in
harms way.
Take care,
Bart
Thanks again.
Nicholas Goble
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