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Re: [TCML] Secondary Damage (Large Coil)

Oe way to make a smooth coupling is to drill a small hole through the form, strip the wire ends, and feed them through the hole. Then twist them together inside the form and solder them. Then rewind the rest of the coil. Putting epoxy around the splice couldn't hurt.
The sharp ends will not go into corona inside the form since the field inside is only longitudinal. I have (unfortunately) made many of these splices and they have all worked well. 

---Carl







Hi Amir,

Amir Mojarradi wrote:

Hi Bert,


That sounds fantastic.
Based off of your information, I have a clear idea of the necessary steps I will take: 


1). Remove bottom winding (~250 turns) - up until the damaged points.


OK.


2). Sand/scrape off the carbonized damage on the coil form
OK. If the removed areas leave deep gouges, fill these in with clear epoxy. After it has hardened, sand the filled-in areas so that they're flush with the rest of the form before adding the new wire. 


3). Apply thick epoxy resin coat onto the coil form
This is not necessary at this stage. Just splice in the new wire and then rewind the missing portion of the winding. 


4). Splice in a new wire
Do this before rewinding - it's much easier to make the splice before winding the rest of the bottom portion. 


5). Wind new bottom winding


OK


6). Apply thick epoxy resin coat onto the new winding.
Coat both the old and new portions of your winding with resin. It will cover both sections equally well and you'll end up with a complete layer of protection across your entire winding. 




Sound all right?
Would you recommend applying the Envirotex over the entire coil, even parts which are already coated with several layers of varnish? 


I'll keep you updated about how the procedure goes.
Excellent! As others have mentioned, once you've repaired the secondary, you may also want to reduce your coupling and re-check the tuning of your system, since the coating may alter the resonant frequency of your secondary. Once the system is verified to be in tune, you can try increasing the coupling. Have s few folks stationed around the coil so that they can see all sides of the secondary. Run the coil at night or in a dark room. If you see any evidence of racing sparks, back off the coupling a bit. Also, look for (and fix) any abnormal corona between the primary and secondary, such as from the primary tap, between the innermost primary turn and secondary, or from the strike rail to the upper portions of the secondary (sort of like a corona "Christmas Tree"). Corona can quickly grow to become a potentially damaging flashover. 




Thank you for your kindness,


Amir Mojarradi


Best wishes and good luck!

Bert





-----Original Message-----
From: Bert Hickman<bert.hickman@xxxxxxxxxx>
To: Tesla Coil Mailing List<tesla@xxxxxxxxxx>
Sent: Thu, Apr 12, 2012 7:47 pm
Subject: Re: [TCML] Secondary Damage (Large Coil)


Hi Amir,

Many coilers have had excellent results using Envirotex Lite Pour On
High Gloss Finish. This two-part resin is available in many craft and
hardware stores and it can also be ordered through numerous online
sources.

http://eti-usa.com/envirotex-lite/
http://eti-usa.com/wp-content/uploads/2011/03/Envirotex-Lite-English-Instruction-Sheet1.pdf 

You'll need to set up a well-ventilated, but dust-free (and flying
bug-free!) work area. You will also need to set up a fixture that can
continually rotate the coil form at a surface velocity of ~4 - 5
inches/second. You'll want to apply a relatively thick final coating
(1/16"  - 1/8" max). You'll need apply the resin within ~25 minutes or
less after mixing. You'll need to continuously rotate your secondary
while applying the resin, and then continue rotation until the resin has
sufficiently hardened (typically 6-8 hours) to prevent sagging. Some
excellent practical information can be found in the TCML Archives. Look
for the "Envirotex Lite , High Torque drive" thread in the July, 2009
archives.

When done right, you'll get a beautiful, hard, crystal-clear coating
that completely imbeds and protects the entire winding. Be sure to allow
your coating to completely harden (2-3 days) before using it in your
system.

Good luck,

Bert

Amir Mojarradi wrote:

Hi Bert,


Thanks for your helpful advice. Is there a particular brand or type
of epoxy or polyester that you recommend? I know other forms of epoxy
exist, but the only products I have seen at major hardware store are
the small,  "5 min" epoxy tubes. Would these be sufficient?


Thank You,


Amir Mojarradi



-----Original Message----- From: Bert
Hickman<bert.hickman@xxxxxxxxxx>  To: Tesla Coil Mailing
List<tesla@xxxxxxxxxx>  Sent: Thu, Apr 12, 2012 8:18 am Subject: Re:
[TCML] Secondary Damage (Large Coil)


Hi Amir,

The insulation between turns has been damaged, possibly by a strike
to the winding, an arc-over from the primary to the lower part of
the secondary, or by handling. Strikes to the secondary can be quite
damaging on larger coils such as yours. At the very least you'll need
to remove the windings around the affected areas, or remove the
bottom portion of the winding since the coil form may now also be
carbonized underneath.

Once the winding has been removed from the affected areas,
scrape/sand away any traces of carbonization from the form before
applying new wire. Once you have repaired the winding, you may also
want to consider applying a thick 2-part polyester or epoxy coating
over the winding. This will protect it mechanically as well as
helping to prevent any future damage if you get another strike to the
secondary. The strike will harmlessly spread out along the surface of
the coating instead of destroying the insulation/wire at a single
concentrated point.

Bert




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