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.
NICK ----- 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......Regards, Scott Hanson