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RE: [TCML] Could this be a breakout point?
Steve -
I think you may have a problem with corona from the "points and edges" on the nuts you are using to secure the wiring. Instead of the top nut you could use a tapped brass ball to increase the radius of curvature, but the increased overall height of the ball could also cause corona problems. Its not clear from your photo how much shielding this stud will receive from the toroid. In my experience, even a small projection from the last few turns at the top of the secondary will generate significant corona, even if the toroid is just a few inches above the bump in the wire
I share your concern about the vulnerability of the last turn of the secondary, and how it is connected to the topload. My solution is a bit complicated, but it completely isolates the secondary wire from any possibility of damage where it connects to the topload. Also, it (almost) completely eliminates the possibility of arcing inside the secondary coilform.
First, I install a sealed plastic baffle inside the secondary, about 3" below the last turn of wire at the top. This baffle is sealed in place with a large bead of electronic-grade RTV silicone sealant on both sides so it is completely air-tight. The baffle has a short ceramic standoff insulator mounted in the center, secured with a nylon screw. I run the last turn of the secondary through the wall of the coilform, and secure it to the top of the standoff with a small soldered-on ring terminal.
Then, I install a second, thicker plastic baffle (or top plate) flush with the end of the coilform, secured with multiple screws coming in through the side of the coilform. If you are using standard PVC pipe, this can simply be a PVC pipe cap (although I think an internal baffle looks better). In the center of this plate is a length of 1/2", 3/8" or 1/2" diameter threaded metal rod ("all-thread"), secured with nuts and washers on both sides of the top plate.The all-thread is long enough to position the topload at the desired height. I use a short piece of small diameter wire to connect the top of the standoff insulator to the bottom of the all-thread. The all-thread is what supports the topload, and the small piece of small-gage wire inside the coilform mechanically isolates the actual secondary windings from any mechanical stresses that might be "accidentally" applied to the topload.
It may sound like overkill, but I had an experience long ago where I broke off the wire at the very top of the secondary, and because the secondary had been meticulously epoxy-coated I could not "unwind" a few turns at the top of the secondary to get enough wire to make a new connection to the topload.
So, now all my secondaries are epoxy coated, have a sealed internal baffle, and have the actual secondary windings mechanically isolated from their connection to the topload. Having learned "the hard way" about internal arcing and broken secondary wiring, I make sure that I won't experience these types of failures a second time.
Regards,
Herr Zapp
--- On Sun, 9/7/08, Stephen J. Hobley <shobley@xxxxxxxxxx> wrote:
From: Stephen J. Hobley <shobley@xxxxxxxxxx>
Subject: RE: [TCML] Could this be a breakout point?
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Date: Sunday, September 7, 2008, 12:06 PM
My goal has been to terminate the coil wire on the cylinder.
The solution you describe is what I have now, and I'm concerned about
the fragility of the coil wire.
Steve
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of bartb
Sent: Sunday, September 07, 2008 2:01 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Could this be a breakout point?
Hi Steve,
It may be a problem. You'll of course have to try it to find out. It is
best to cap the top and use the top cap for the toroid connection. I
personally would not feel comfortable with this connection. It may run
ok at first, but at some point something will cause it to breakdown
(humidity, tuning, coupling, etc..). I recommend you consider this a
temporary solution and begin looking around for a more permanent top cap
connection. It's not that difficult to make a top cap. It would be nice
if we could find a ready-made cap, but sometimes that's not possible, so
we must then fabricate something. It's at that point we start taking
these shortcuts which can end up a hasty and poor decision. But top caps
can be made from many materials (even wood if necessary).
Take care,
Bart
Stephen J. Hobley wrote:
> I made some changes to the secondary today - creating a connection
> terminal for the toroid.
>
> http://www.stephenhobley.com/breakout.jpg
>
> But does this look like it might be creating an unwanted breakout
point?
>
> Steve
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