Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx> Hi Jim,If you do go the route of "bottle caps", you may want to check out Mason Jars sold at grocery stores. Includes a screw on metal lid that aids the construction. The basics are to mix a salt water solution and poor into the bottle cap. The lid should have an electrode that penetrates down into the solution (a carriage bolt is often used) and this bolt also allows for an electrical connection (with a mason jar lid, a large carriage bolt can be used for the electrode and a smaller screw used for bottle to bottle connection). Add about 1/2" to 1" of mineral oil (it will float at the top of the salt water solution). Use aluminum foil to wrap the outer bottle with (keep about 1" below the lid). I like to use a smooth 5/8" socket head to smooth the aluminum foil to the bottle (reduce corona points).
The aluminum foil serves as one plate. The saltwater serves as the second plate. The bottle is the dielectric between the two plates. This is a basic capacitor. Now, line the inside of a bucket with aluminum foil, drill a hole in the side of the bucket and fasten a screw which protrudes out the side of the bucket. Next, place several of your bottle caps inside the bucket. This connects the bottle foil to the bucket foil and everyone of those bottle foil plates are electrically connected to the screw at the side of the bucket. Finally, connect bottle lids with a wire (bottle to bottle). You'll then have all the bottles in the bucket in parallel with one another. The capacitance of each bottle adds when placed in parallel. You can then add or remove bottle caps to adjust to the capacitance desired. The output of the cap is then simple one wire coming from the lids and the other from the screw at the side of the bucket.
I do have a bottle cap java thing which you might play with if you decide to go this route. Check out the "Help" link for definitions of inputs. Very simple calcs. Although it doesn't show mason jar bottles, it shows the basic idea.
http://www.classictesla.com/java/bottlecap/bottlecap.htmlNow, with all that said, I highly recommend MMC's for real performance. Bottle caps can be very lossy (lot's of corona). But for a nostalgia thing, bottle caps are still fun to build (and they work, not always great, but they work). Got one in the garage right now. I don't use it, but I've got it. (grin).
BTW, one thing with bottle caps is to keep corona at a minimum if possible. Corona is simple "power lost" not getting to the coil. Sharp edges enhance the mechanisms which cause corona. Try to keep everything as "smooth" as possible.
Take care, Bart Tesla list wrote:
Original poster: Jim <branley1@xxxxxxxxxxx>Thanks for the advice. It sounds like cheap solutions for someone cheap like myself. I like the "beer bottles with salt water in white poly bucket." What is the science behind this?Tesla list wrote:Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx> At 09:19 PM 2/3/2007, you wrote:Original poster: Jim <branley1@xxxxxxxxxxx> Hello Gentleman:My son and I would like to build a tesla coil with a 15,000V, 450VA, 30MA neon sign transformer. Does anyone have a material list that we can use to assist us in our scavenger hunt? Also any pearls of wisdom would be greatly appreciated. I have been on this mailing list for a few days and have been reading the posts and have found them to be highly invaluable.An easy and robust spark gap at that power is laying several short (1-2") pieces of copper pipe next to each other. (the tubes are all parallel). The "two bolts as spark gap" tends to get too hot too quick and not work very well.You need to track down capacitors. The two alternatives that are reasonable are:#1- beer bottles with salt water in a white poly bucket (search for "bucket cap")... basically free, but bulky and it can spill#2 - the MMC (multi mini capacitor).. a string of appropriate capacitors in series. Not just any capacitor will do here.. you need polypropylene dielectric (for low loss) and with the right construction to handle the current. Search for "MMC".... for a typical NST (neon sign transformer) buying them will cost about $30.Toroidal topload: metal dryer vent host and piepans are your friendThank You! Jim