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Secondary Coil Terminations

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Andyman

Sat Mar 08 2008, 10:27PM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

Hello, I was just curious how you all start and end the windings on your coils. I will share with you the method I used, and then I want to see your methods.

Here is how I secured the base wire.

A closeup:

At the time I wound my coil, I didn't think of this idea. If i had, I wouldn't have drilled a hole into the secondary and put the wire through. If I hadn't drilled the hole, the wire would be completely isolated from the inside. I drilled a hole, tapped it, and epoxied in a nylon bolt.

This is how I did the top

This time, excellent isolation from the inside. The nylon bolt and nut is epoxied in place as is the plexi disk. After I have run the coil for at least a total of an hour, I will epoxy on the second disk.

I've shown you mine, now I want to see yours!

ps. Yes, that is saran wrap on the coil

RogerInOhio

Mon Mar 10 2008, 03:59AM

Registered Member #1034 Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154

I have always heard that it is best not to run the wire into the inside of the coil form because there would be a tendency for the spark to arc though there. It might only mater if you plan to really push the limits of the secondary coil.

Everything else looks good. It should work just fine. I am guessing that coil form is 4" PVC . What size wire are you using ?

Andyman

Mon Mar 10 2008, 04:10AM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

The form is 4.5" gray pvc. I used 24 gauge heavy build enamel wire. And the place where the wire enters the form is heaped with epoxy. I know I still shouldn't have put it inside, but I didn't know that at the time.

Cain

Mon Mar 10 2008, 12:09PM

Registered Member #624 Joined: Tue Apr 03 2007, 07:50AM
Location:
Posts: 59

Ive been running a 4" secondary with brass bolt through the top and the bottom with the wire also going in through the side of the coil lol never had any problems... and have had 5'+ arcs from her (twin mot, ARSG, 0.1Âµf cap(way to big lol))

my ext coil will be terminated through the bottom but not the top (6" coil)

Hazmatt_(The Underdog)

Tue Mar 11 2008, 02:58AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Here's a couple of mine. Ordinarily with the bottom I do use a nylon screw as a stud and a metal nut to compress against the copper pad, but it's very similar, I just wanted 2 attachment points because the copper pad sometimes wants to come off the plastic. (hard to bond copper to plastic >.< so 2 points as backup).

I'm not so in-favor of a corona ring now because my design doesn't really do much to help. That's not to say someone else's design won't work, just that mine is insufficient.

There's some more pics in my 'homecoming' thread too
009f

HV Enthusiast

Tue Mar 11 2008, 11:55AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

I use this method and it works very well.
Just cut a small rectangle of copper. Use Loctite cyanoacrylic or similar super glue and wrap about 1-2" around secondary. Make sure to adequately "scratch and roughen" surface of PVC and copper. Then use wire ties (or tape) to apply pressure and hold for 24 hours. Remove and voila! Just solder your secondary and connection wire to this copper "pad."
Also, its easier to solder first before you glue as heat tends to destroy the glue bond.

Jrz126

Tue Mar 11 2008, 01:49PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

I thought I had a picture of it, but i guess not.

I used some copper foil that I had left over from my primary. For the base, I glued an 8"x8" sheet onto the bottom of the coil (the flat side of the cylinder), and also glued another 8"x8" piece to the bottom of the table. Then I soldered the wire to each sheet. When the coil is put onto the base, the connection is made. It made disassembly/reassembly really easy. I did the same thing for the topload as well.

I had a 12" diameter secondary though, so I dont know how well it would work for the smaller coils.

Hazmatt_(The Underdog)

Wed Mar 12 2008, 04:31AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

For a while I was using copper tape pieces on the outside of the form, and the other pipe coupler at the base would engage the secondary with another piece of foil and sometimes have a snug fit. But the trouble with the tape is that getting a snug fit was totally unpredictable, the tape tore eventually, and sometimes it would help to promote an arc inside the form because to keep the tape on the secondary from peeling back on insertion, I would have to tuck it around the bottom and inside the pipe.
I like the tape and the concept, but I couldn't get it to work on a pressure/contact basis. So eventually I moved to using thicker copper sheet.
the copper pad is a good idea and I should have tried that one. You can get enough contact pressure there, just not when you're trying to wedge an oval pipe into a round coupler >.<.

base copper pad, absolutely rough it up! mine fell off a couple of times before I got it good and rough.

Herr Zapp

Wed Mar 12 2008, 08:27PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Andyman -

I think you are at risk of breaking your magnet wire with your lower termination. Using a nylon screw, you can't apply much tightening torque, and any sideways force applied to your ground wire may cause the nylon screw to rotate, breaking the magnet wire. You need to find a way to mechanically secure the wire to the coil form ("strain-relieve" it) so it is completely isolated from any stresses applied through the ground wire. I have had good success in bonding a copper plate to the side of the secondary coilform, and soldering the bottom turn of the magnet wire to the plate. The copper plate also has a brass machine nut (or a drilled & tapped piece of brass rod) brazed to it as an attachment point for the ground connection. After forming the copper plate to the exact radius of the coilform, I rough-up the coilform and the back of the copper plate with medium sandpaper, and bond the plate to the form using high-temperature epoxy adhesive. I have never had a plate come loose, even when using large gage, very stiff ground wire, and accidentally trying to remove the secondary from the system with the ground wire still attached.

For the top termination, I bond a baffle inside the form a few inches down from the top using electronic-grade RTV sealant (GE RTV-162). I attach a small standoff insulator to the center of this baffle, and run the top turn through the side of the form and solder it to the top of the standoff insulator. Then I can run a separate wire from the standoff up through a second baffle or top plate, and up to the topload. In the attached photos of a 6" dia secondary, I installed a female "giant banana plug" socket in the top plate, and ran the wire from the internal standoff insulator up to the top plate and connected it to the banana socket. I assembled a large ceramic insulator with a mating male "giant banana plug" so it could simply plug into the top plate, where it was secured with nylon screws. This way, both the top and bottom ends of the coil's magnet wire were complete isolated from any mechanical stresses applied through the ground wire or the topload. See the attached photos, they show the concept better than I can explain. (The poor-quality photos of the top termination are very old, pre-digital camera days.) Also shown are a matched pair of 3" dia secondaries (for a bipolar system) with similar ground plates with brazed-on brass machine nuts.

Shan

1205353588 480 FT40759 Secondary Ground Termination

1205353588 480 FT40759 Bipolar Secondaries

Hazmatt_(The Underdog)

Thu Mar 13 2008, 02:07AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Awsome work! and very clever too!

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