tesla coil top loads and rough edges - Page 1
Forum section: electronics / beginners

author: Pirateguy
author_rank: Regular Contributor
timestamp: July 25, 2018, 05:39:44 pm
content: i m wondering, would covering a rough edge on a tesla coil top with some kind of insulator improve anything?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 25, 2018, 05:59:45 pm
content: How rough, and how insulating?Projections need to be a sizable fraction beyond local curvature to matter, in terms of reducing the voltage where corona or breakout occurs. Just because it's made of sharp metal that will cut your hand open if you fondle it, doesn't necessarily mean it's electrically worse.There are three kinds of treatment you can apply, to insulate or smooth it out:- Metal: smooth over it directly, say with aluminum tape. This brings up the nearby material and reduces sharpness of the area.- High quality insulator, strong but low-k: a lot of layers of polyimide tape, say, or a goopy silicone rubber or something. Local curvature is not significantly affected, so some corona will still be produced by the point, at a somewhat higher voltage. This puts a lot of stress on the material, hence demanding high quality. (Polyimide has excellent corona resistance.) The current drawn by the corona, from the surface of the insulator (more correctly, a dielectric barrier discharge), is the current flow that's able to drop so much voltage across the insulator, and thus prevent the point from breaking out quite as early. Note that, if it does break out, the insulator is screwed, nothing can withstand direct plasma.- High-k insulator: not sure what material would count here -- presumably one could make, like, ceramic-loaded tape, analogous to fridge magnets (plastic loaded with ferrite), but with dielectric material instead. Anyway, this has the effect of bringing up the nearby surface again, but with an insulator rather than a conductor. Because the k is large, the internal voltage drop is small (but not as nearly zero as for a conductor). This acts like an intermediate between the two cases. Breakout will still occur, much as with the conductor case, which isn't such a great thing for any nonmetallic material you'd place here...So, in conclusion: maybe, it depends.Tim

author: Pirateguy
author_rank: Regular Contributor
timestamp: July 25, 2018, 06:51:24 pm
content: ok well what we are talking about here is mini coils with top loads made from soda cansand i was wondering about the thin edge of where i cut it.i gave it a good sanding, and for the insulator i was thinking of maybe the mantle of some wireor just running the edge through some epoxy.but if i understand correctly this isn't really an issue at a small and relatively low powered scale?

author: Simon123
author_rank: Regular Contributor
timestamp: July 25, 2018, 11:19:44 pm
content: Made from soda cans?Will that provide proper capacitance?

author: Pirateguy
author_rank: Regular Contributor
timestamp: July 25, 2018, 11:45:29 pm
content: i am copying something i saw in a video.

author: Jwillis
author_rank: Super Contributor
timestamp: July 26, 2018, 05:41:17 am
content: You can use just about anything for your top load.But you don't want too rough because that's where your arcs will generally propagate from.You can find calculators online for spheres ,toroids and plates.So using pop cans would be a matter of experimentation.Make sure you clean the paint of the can or you might get undesirable results. Coat the coil well with varnish. The top load will show you where the varnish is thin when arcs come from the coil.A few coats of clear spray lacquer works really well .An extra layer of insulation between the primary and secondary is a good idea as well depending on how close they are together.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: July 26, 2018, 06:39:06 am
content: Quote from: Pirateguy on July 25, 2018, 06:51:24 pmYou might find these videos interesting:The two empty tuna cans, held together, open ends facing, with carefully applied aluminum duct tape, make a good top capacity for a small lowpowered coil like shown in the clips. There are many little details of construction that will each add a slight increment to performance.I would not use beverage cans, especially if they need to be cut. Although I have used them for toy VDG static machines, just to prove the concept.Good top capacities can also be made from materials such as flexible metal dryer ducting, styrofoam forms covered with heavy aluminum foil or duct tape, constructions of wire, etc. You can also find mirror spheres from China that are cheap and work exceptionally well.

author: Pirateguy
author_rank: Regular Contributor
timestamp: July 26, 2018, 11:06:03 am
content: on the issue of arcing to the coil, i will prolly add a spark ring to protect the coils as well as insulate things well, but i also intend to experiment and makemore then 1 coil. in fact i want to see how small i can get it and still have some visible sparks.right now i have 2 soda can based topload ideas. one i made out of a single bottom of a can and simply sanded the edge of it.like this one: (but better)and the other idea is to take 2 bottoms and join them togetherlike this one:i also have some steel balls and a pingpong ball and a doorknob wrapped in tinfoil.

author: Jwillis
author_rank: Super Contributor
timestamp: July 27, 2018, 04:04:44 am
content: The ping pong ball thing is something I'm working on .But I'm going to electroplate it instead.Just about ready. I just need to pick up some copper sulfate.I'm going to try with copper chloride first to see how that works since I saved the etching solution from PCB builds .Just need to boil down to collect the crystals.Who would have thought that electronics would lead to chemistry.