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Re: [TCML] Beginning Tesla Design



Taylor Skidmore wrote:
Well, no harm involved. I really want to use this Coil for a science fair project. My teacher, however, wants a project that really has no publicized results, so I'm having a little trouble on that end. I was thinking about something along the lines of adding a second toroid, letting it sit atop the first, but I really don't know what I could measure, or if that's a valid project at all.. Since I will be using the Coil in the fair, my budget grows exponentially, as my parents are suddenly willing to donate some money, heh. Any ideas?




build and demonstrate projects do not do well in fairs, as your teacher has told you. WHat you need is to either use the coil as a tool to test something else, or to do a parametric design study; change some part of the coil design systematically and see how the performance changes.


In any case, what you wind up doing has to be something that hasn't been done a 1000 times (e.g. colored light on plants) and something for which you can make a prediction of behavior BEFORE you actually do the experiment. The prediction should be based on your "book research", not just pulled out of thin air (as a judge at fairs, I hate seeing a hypothesis that runs along the lines of "I think it will get bigger", with no reason why they think that).


The other thing judges like to see is quantitative measurements, and repeated trials, with at least some simple statistics. An appreciation of the uncertainty in the measurement (measurement accuracy and precision) is also a big plus. If you measure the AC line voltage and just write down all the digits from the meter as 120.8V.. that's one thing.. if you look at the manual and find that the meter accuracy is only 5% so you write down 120V +/-6V, that's a much better statement.


Here's some suggestions.

If you build a MMC with enough capacitors, you can vary the capacitance of your primary circuit, and, as a result, the value of the primary inductace will change, to keep fres the same. You can use one of the modeling programs to predict the coil behavior and see if it matches.

Likewise, you can add a second toroid to the top, which will change the top load capacitance. (Your first challenge wlll be figuring how to measure the change).. that should change the tuning point of the primary for best output, which should be predictable. SO you have a prediction of how much the top load changes (based on some approximation or a modeling program), which you can then measure. YOu can take your modeled or measured change, and plug that into the modeling code and predict what the new primary tuning should be.


This kind of thing is generically called "model verification"... you're taking someone else's model and verifying that it works, which something important in science. It's the whole repeatability of results by another scientist thing.

You could also experiment with different shaped primaries. I assume you're working with a NST powered coil, so bare AWG12 house wire works nicely as a primary, and you can make cardboard/foamcore supports to make everything from a flat spiral/pancake, to a cone, to a cylinder. Again, there are theoretical predictions of the inductance and performance that you can use to check your measured data.

Looking at differences in coupling ratio (k) (how far the primary is from the secondary, for the most part) would be quite interesting.

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Those are all "tinker with the coil" experiments..
Then there are "coil as a piece of experimental apparatus" experiments.. I think st Elmo's fire is particularly interesting. It's not corona discharge in the classical sense, but more like electrospraying of salt water. You'd set a pan of salt water on top of your coil, with something like a piece of wood that's wetted in the middle, and fire it up. You do NOT want to have actual breakout of sparks here, just the HV, so the adjustments will be critical. Even more challenging will be figuring out how to photograph it (it's pretty faint). If you want some details on the physics behind St Elmos fire, I think I wrote something to the list a few years back. Actually you could put the coil upside down over the pan and wood, which would be grounded.

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