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Re: the back of secondary winding

Original poster: "seanick" <edgarsbat@xxxxxxxxxxx>

I feel I should send an update about my damaged fiberglass-covered pvc secondary. After removing the failed windings from my secondary and applying some epoxy to cover the remaining ones that were now exposed to air, I ran my coil again and this time there was no problem with the secondary. There were other problems mind you, not to mention the coupling was not quite as good as it was before. That is also why there were no racing arcs, so it does mean that my secondary was not badly damaged other than the one failure point.

However, my spark gap rotor was burned to a crisp... I had to sand quite a few layers off to remove the charred fiberglass around the four electrode holes. I wonder if that is partially because of the larger holes I had made in the rotor (which were intended to act sort of like fan blades to help quench the arcs) and/or partially because of the 1725 RPM motor I was using since my 3600 rpm motor was no longer able to synch anymore (even with no load !? apparently the 3600 rpm motor's windings were bruised or bearings are shot or something- applying new grease in the bearings didn't help either, besides being a pain to get to).

I sanded all of the burned areas of the rotor off but now the disc seems quite a bit thinner in those points so I will have to carefully apply some epoxy to rebalance it. Also I am going to cover the open areas between the spokes with some contact paper or something, to keep the arcs from having such an easy discharge path through them.

I also am thinking about ordering a good heavy-duty 3450 RPM motor for turning into a 3600 rpm synch again, but this time a stronger motor than a bench grinder. I was thinking one of these http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200306767_200306767 as I recently got one for my air compressor that seems quite a bit more solid than the one I had before. the only drawback is the fact it has a 5/8" shaft. Since my rotor is in a separate enclosure from the motor and on a separate shaft, (which did actually turn out to work pretty well) I can easily just step it down with a larger piece of hose and a hose clamp.

For those interested, here are pictures from the coil run on June 24th (Aaron can be spotted in some of them :)) http://www.themotocam.com/gallery2/main.php?g2_itemId=4116


----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Saturday, July 08, 2006 11:07 PM
Subject: Re: the back of secondary winding

Original poster: Billy Watson <Aesops.Tech@xxxxxxxxxxx>

The boy's and I made a spark gap Tesla coil at work to play around with on our breaks.

We wound the primary on a two foot piece of fiberglass pipe insulation about 14" wide. it was somehow absorbing the RF current, and we could not get any output from the secondary. We rewound it on a cardboard form, OK then.

The secondary was 1000' of #14 THHN. I think the primary was 4 or 5 turns # 10 THHN.
The spark gap was HeliArc welding electrodes, in brass holders.
Cap was a 3' X 3' X 3/8" tempered glass. 15 Kv 60 Ma ignition trans.
when tuning it up, the boys thought I was crazy, because I kept putting my hand up to the discharge, but my mussels kept pulling my hand back. Finally resonance, and I was able to draw about 2' to 21/2' thick beautiful waving arcs to my hand. We played with that coil for weeks while on breaks. On one occasion, one of the fellas was holding a florescent tube in his hands, with the close end about a foot sticking out from his hand, when a bolt jumped about a foot from the tube end to his chest. scared him. Another time we had the tube on a stand about a foot from the sec.electrode, with the other end resting on an iron pipe hand rail, in the concrete floor,with a foot overlap from the tube end, At the end of the hand rail , about 4" away was a metal filing cabinet sitting on the concrete floor. next to that was a metal office chair with 5 rubber wheels. The arcs jumped the one foot gap to the end of the fluorescent tube, lite it up, jumped out the other end of the tube, wrapped around it, and jumped to the hand rail, jumped a beautiful thick arc the 4" to the cabinet, Jumped about 6" to the chair, and jumped around all 5 wheels to the floor. All the while the arcs were pulsating and flowing with the air currents, and were thick bluish white. We would store the parts in separate places in the shop so the boss's wouldn't know what it was. one nite while putting the plate glass cap. away, it slipped out of my hands about an inch from the floor and shattered into little 1/4" pieses but were still held together somehow , and it released a strong O-Zone odor. especially when shook while hanging from the hands.
Just a coilers experiences.

Tesla list wrote:

Original poster: "seanick" <edgarsbat@xxxxxxxxxxx>

Hi Scott,
It was my secondary. The fiberglass is 3 layers of fiber decking (woven) cloth, with polyester resin. The wire is 200 deg. Essex formvar covered 18 guage magnet wire from Whitmor wire, close wound.

I cut open the fiberglass to see the pvc underneath was charred badly. the inside of the fiberglass was burned at the failure point of course but the rest was fine, whereas the PVC had a blackened ring from where one turn was so hot it charred all the way around the tube. the magnet wire's insulation was black and crispy for about 10 wraps at that point, but had not actually broken through in any one location.

This PVC core has failed once before but the last time it was from internal arcing. the inside had since been sanded and covered in fiberglass and this time the inside was fine. so I am fairly certain the pvc and fiberglass are good materials in general, but it is possible that there was a part of the magnet wire's insulation sanded off - after the first coat of fiberglass was applied, I wanted to smooth out any bumps and make sure no air pockets made it between the first and second layers but got a bit aggressive with the angle grinder/sanding disc at the first go. This is mostly a theory, but nearby magnet wire to the failed part had some copper showing which tends to support the theory.

Also, I must correct Aaron slightly- when I first fired this coil up, the arcs were quite a bit larger than I had previously expected (partly due to his help :)). Also, the primary was a bit overcoupled and some of the initial arcs were from the primary to the secondary. I immediately moved the primary down before any of the later (and much more impressive) power-up's but apparently the damage had already been done.


----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Monday, June 26, 2006 9:00 PM
Subject: Re: the back of secondary winding

Original poster: "Scott Hanson" <huil888@xxxxxxxxxxxx>

Aaron wrote:

" I was watching a friend's coil this weekend, and his secondary suffered an interesting yet unfortunate fate: All of a sudden, a bright spot of light appeared on the side of the secondary. After turning off the coil and approaching, it was observed that a nice little hole had burned in the winding. It did not appear to have resulted from a strike or racing sparks or anything quite so obvious."

"His secondary was coated with fiberglass."

When you state that his secondary was coated with "fiberglass", what exactly do you mean? Fiberglass cloth or matt, impregnated with polyester or epoxy resin? Or just coated with resin, without any fiberglass? If it was truly covered with fiberglass, was it woven fiberglass cloth, or random-fiber matt?
If glass was actually used, can you find out how many layers were applied?
Also, can you find out what type of wire was used to wind the secondary? Conventional enameled magnet wire, or something else?
Close-wound, or space-wound?

Always interested in the conditions leading to a failure, and the results of the subsequent failure analysis......

Scott Hanson