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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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