[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Tesla coil Parts and plans

Original poster: "Paul B. Brodie" <pbbrodie@xxxxxxxxxxxxx>

I have been scrounging parts to build a SGTC and so far I have: 15 kv 30 mA NST, 3 lbs. of 26 AWG and 9 lbs. of 25 AWG magnet wire, a 8 ft x 4 inch piece of thin wall white PVC (not foam core), a 0 - 140 v 20 A variac, a length of 3 inch diameter flexible dryer duct formed into a toroid with 2 pie plates forming the center, 50 ft. of .25 inch soft copper tubing, 50 .003 mF 35 kv film caps, two .03 mF 35 kv pulse discharge caps, 4 680 pF 20 kv door knob caps, 2 .01 mF 40 kv poly caps, eight 5 kv 2 A diodes, an 8 ft copper clad ground rod, and a 4 series gap made with 1.5 inch hard copper pipe inside a 5 inch piece of PVC with a cap that allows me to connect the shop vac to the top and suck fresh air through the spark gap.

I also have Wintesla, Walt Noon's designer software, and JavaTC 9.1. They all give very similar results, which is reassuring. I still have 1001 questions. My knowledge of electronics is virtually all self taught and I worry that I am guilty of some misconceptions. Also, I am extremely conservative and I want to build in as many protective features, both for safety and protection of the coil itself.

Before describing my plans for the controls, tank circuit, and primary, I'd like to get the secondary out of the way. I have cut off 21 inch length of 4 inch diameter PVC and sanded off all imperfections and ink. I then sealed it with multiple coats of polyurethane, inside and out. The following may have been a mistake. I covered all the area to be wound with wire with double sided carpet tape to help hold the winds as I apply them. I want to use the 26 AWG magnet wire and wind 18 inches. I have calculated that I can get approximately 1000 winds. I also plan to seal both the top and bottom of the secondary and provide a small hole in the bottom to equalize pressure. I plan to leave 1 inch of PVC uncovered by wire at the bottom and 2 inches at the top. How much space between the top of the secondary coil and my toroid?

Starting at the wall plug, I want to put an EMI filter between the wall outlet and the variac. My first stupid question. My variac says that one side is common to line and load. Does this mean that the variac is NOT acting as an isolation transformer? Do I ground the variac case to my house ground? From the variac, I plan to go to the NST. Where do I ground the NST, house ground or to the RF ground? From the NST, I want to wire to a safety gap with the center grounded to my RF ground. Should I provide a bypass cap between the NST and safety gap? Which caps are suitable for this? Do I want to put in RF chokes between the safety gap and main capacitor? Any recommendations on which of the caps to use that I already have? The software recommends approximately .006 mF cap for the primary. The Java software recommends using a larger cap than is recommended by the program. Here is where I think I am a little fuzzy. How is the value of the primary cap determined? What is the impact of using a larger than necessary cap? Does the size of the cap, the distance between gaps in the spark gap, the inductance of the primary coil and the size of the toroid all impact this calculation? Won't any of these factors change the resonant frequency?

Next, I want to wire to the series spark gap. How do I determine the width of each individual gap? At what total gap should I start at? Will too wide of a spark gap cause excessive load on the NST? I had trouble getting this NST and I paid too much for it. I want to do everything I can, within reason, to protect it!!!

What type of wire should I be using to wire from the NST to the bypass cap to the safety gap to the cap to the series SG and then to the primary coil? I was planning to form the primary with a 6 inch diameter. One inch between the inner winding and the base of the secondary coil. Is this sufficient spacing? I plan to space .25 inch between windings. I calculate that I will get between 13 and 15 windings. To attach to the primary, I plan to solder my wire to an ATC fuse holder and then snap the fuse holder onto the copper tubing wherever I like.

I am going to great lengths to build a substantial RF ground completely separate from my electrical service and water pipes. The ground here is very good for grounding, red clay with a high iron content. I plan to sink at least 5 eight foot ground rods with 4 of them forming a square 5 feet to the side and cabled to each other and then cabled each to a central rod which will be my attachment point for RF ground. This attachment point will be approximately 10 feet from the TC location in the front of the garage. I plan to use two 4 AWG car jumper cables, 4 strands total to attach the coil to ground.

I plan to attach the NST case, the safety spark gap, and the base of the secondary all to RF ground. Can someone please explain to me everything I need to know and am afraid to ask about a counterpoise ground?

Any and all comments will be most gratefully accepted. If I seem to be particularly off base in any area, please point it out. I am striving to learn as much as I possibly can while doing this, instead of just following someone's recipe. Oh yes, I almost forgot. I was contemplating using the HV diodes I have to rectify the NST output to pulsed DC. Would this help to ease the burden on the primary cap?

If anyone would like to communicate with me offline about this, please do. My email is pbbrodie@xxxxxxxxxxxxx
Think positive!