On 12/27/11 12:01 PM, Brian Hall wrote:
I got to thinking about the equations for inductance commonly used in Tesla Coil construction, and there tend to be four main shapes used: Helical (Cylindrical column)Flat spiralConical (cone with the point at the top)Inverted Conical (cone with the point at the bottom) Given that p = primary coil and s = secondary coil, which configurations have not been tried or discussed all that often? Which configurations have you found to give the best performances (given that everything is in tune) or interesting effects?Coupling issues you might run into with some of these? 1. p = Helicals = Helical 2.p = Helicals = Flat Spiral 3.p = Helicals = Conical 4.p = Helicals = Inverted Conical ---- 5.p = Flat spirals = Helical 6.p = Flat spirals = Flat spiral 7.p = Flat spirals = Conical 8.p = Flat spirals = Inverted Conical ---- 9.p = Conicals = Flat spiral10.p = Conicals = Helical11.p = Conicals = Conical12.p = Conicals = Inverted Conical---- 13.p = Inverted Conicals = Helical 14.p = Inverted Conicals = Flat spiral15.p = Inverted Conicals = Conical16.p = Inverted Conicals = Inverted Conical---- I know that 1 and 2 are common configurations, followed by 4, and one message a while back about 6 being easy to make with decent results. 15 has those rumors of 'antigravity' affects ... And if the inductive properties and construction of the Conical and Inverted Conical Coils were the same, then could one make as few as 6 interchangeable parts (3 primaries and 3 secondaries: 2 helical, 2 flat spiral, 2 conical) of compatible values with which to attempt all 16 configurations? -
These are all sufficiently well modeled by modern Tesla Coil modeling codes that one doesn't actually have to build any of them.
Verifying the model by experiment would make an excellent science fair project, if done well. You've got good theory, so you can formulate a great *experimentally testable* and *quantitative* hypothesis by running the model, then building the article and seeing if it matches.
In general, for a given size top load and secondary winding, there's really only two factors left: inductance of the primary and coupling factor. The physical shape of the primary doesn't have a huge effect, at least to a first order.
Looking at other effects:1) the primary (particularly flat ones) can serve as a "ground plane" to give a better defined E-field along the secondary, which has an effect on things like "racing sparks" 2) There's a difference in ease of access for things like adjusting the primary L for tuning. Some shapes lend themselves to "non-interacting" tuning. 3) There's a big difference in construction convenience, depending on the kind of tools you have available and what "prettyness" you are looking for: e.g. Bare AWG12 on cardboard and masking tape works pretty well, but looks kind of ugly compared to some of the really gorgeous coils out there. Kind of like the difference between a $5 battery quartz clock and a multikilobuck grandfather clock: they both work pretty much the same, but one is more pleasant to look at, and is basically "art".
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