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Also, be very aware that a TC will kill electronics. The bigger the coil, the longer the reach. They operate anywhere from 150Khz up through about 500KHz for the smaller ones.
A word on grounding the coil. The bottom of the secondary is attached to an earth ground. Drive a decent grounding rod into your soil, and use that. Failing to do this will result in poor performance of your coil, as well as increased radiation of noise, and possible destructon of your coil and anything electronic in your home.
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Ok, so you've decided you want to build a coil. First off, you need to find a transformer to power your beast. Most people start off with a neon sign transformer(NST), I would recommend something like a 12KV 60ma unit if you can find it, though 12KV 30ma will work just fine for a first coil. While 15KV transformers are available, it gets a lot harder to build a decent capacitor for that kind of voltage. What you see here is what is referred to as a 'Pole Pig', or line distribution transformer. This particular unit is rated at 5KVA, with 240V in and 14.4KV out. The insulators are about 14" long, and the tranny itself is about 30" tall. Weighs in at just over 200lbs, and contains about 14 gallons of mineral oil. Set me back about $200. While a NST will make you swear and curse if you are stupid enough to get in the way (I speak from experience) a Pole Pig will kill you. Dead. You have been warned. Your transformer decides the remainder of your coil, so you should really get that before you bother with anything else. |
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You'll see a lot of these things in coil pics. This is called a safety gap. When you get high frequency, high voltage kickbacks from your primary, this will be the only thing that keeps your transformer from going to the great junkyard in the sky. Construct it from rounded materials, either carriage bolts, or as I have here, brass balls. The center conductor is connected to your earth ground NOT your electrical ground. |
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Ok, this is the thing that will eat much of your time. The secondary coil is wound on a non-conducting form. For smaller coils, 3" PVC can be used. You want to have a winding/diameter ratio of 4-5 at 3". This means your winding should be between 12" and 15". Use a relatively small gauge wire, but not too small. 24AWG works well, as does 26. This coil is somewhat larger and is wound using 22AWG wire. Some of the tesla coil programs you can find from Bill's site above will give you an idea of how much wire you will need. If you use PVC, it is recommended that you dry it (use a very low oven) and then seal with polyurethane prior winding your wire. Start between 1.5 and 2" from the bottom and close wind the wire. Make certain there are no overlaps, or kinks. Do not in any case punch holes in your secondary form. This can lead to flashovers inside the coil, which will ruin your form (and your day). After you finish winding, coat the coil with a few layers of polyurethane, both to hold the coil togther, and to protect the windings from little dings and such. BTW: Make sure you use oil based polyurethane.. water based conducts too much at high frequency. |
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This is some additional protection, though the coiling community is split on the value of it. This is supposed to be a high frequency choke. The idea is that the inductance is high enough to block the RF energy from getting into your transformer and killing it. Since this is an air-core choke, the resistor is there to kill off the Q of the circuit. Else I'd have a mini coil here. Not sure if I recommend these anymore or not, but the construction is wind 6" of #26 wire on a 2" form. (or, if you can get them, use a toriod ) |
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This is part of your primary circuit. 1/4" refridgerator tubing makes a great primary coil. Space it 1/4". Ideally you want to use plastic for your coilform, but you can get by with wood, if you seal it correctly. THis form is wood, but has 6 coats of urethane. You want between 1 and 2 inches between the inner turn of your primary and the secondary, when it is in place. |
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Here are my capacitors. I've constructed them using polyethylene plastic and foil, sunk in mineral oil. Detailed construction directions for these caps can be found here Note the use of very wide, low impeadance connectors, and the safety gap across the capacitor as well. For those that are looking for quick and dirty, see the directions on bill's site for making beer-bottle (saltwater) caps. |
| When I get a pic of my old ones, I'll have the SW caps here | Directions to follow |
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Next you need a spark gap. This particular gap is pattered after the TCBOR (Tesla Coil Builders Of Richmond), and popularized by one Richard Quick. As a result it is also known as the RQ gap. It consists of 3/4" to 1" hard copper pipe placed inside a larger PVC pipe. Each pipe is between 2" and 6" long, depending on your power level (a small NST powered coil should use 2"). Gapping is set at about 0.025" between each pipe, and the HV is connected across this. |
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One requirement of a RQ gap is getting enough air flow. In this case I am using the "vacuum gap" modification to the standard gap. This is a small vacuum motor that draws air in through the slots on the side of the gap, passing it between the pipes. This helps quench the spark, as well as cool the pipes. |
| Toriod Picture | I'll get to this in a bit, but having a torid Greatly increases your spark size. |
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Here is my coil, fully assembled. |
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And a time-lapse exposure of the coil in action (this was about 2 seconds in total dark) That streamer you see actually went up out of sight to my garage door opener. About 62". This was the run that got me kicked out of the garage. |