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Second Generation Tesla Coil
 

    For my second generation Tesla coil, I decided to go for broke and get everything as big as I could (within reason of course).  For my primary, I use 1/4 in copper tubing (which is the same as before, everything else is differant). 

     For my secondary I am using a 6in. diameter PVC pipe wound tightly with 22 AWG magnet wire, about 1192 turns or 31in. (A little over actually) the height to width ratio is 5/1, which is optimum for a small coil, but will due nicely for a medium sized one like this (large Tesla coils have huge 18+in. diameter secondaries).  Below is the new secondary in two stages of development, early winding on a jig, and complete, waiting for installation.  The secondary is disattachable; I made it this way so that I could more easily transport everything.  the Rf connection is a piece of copper sheeting tied the the last urn of secondary, which is clamped onto a ground wire.  The 6-in secondary sits in a 6-in PVC pipe cap, which is "L" bracketed down to a piece of wood.

    

     My power supply consists of 4 microwave oven transformers, with their primaries on one side in parallel, and the opposite in anti-parallel. The MOTs have the secondaries in complete series with opposite orientation on either side, with a center tapped ground, this orientation is important as it keeps both outputs at 4000+/- volts in respect to the ground, instead of a ground and then a 8+ Kv output, which would really badly overrate the insulation on the MOTs (4kV is twice the rated value, 8 kV is 4 times). 

     My capacitor is a professional Maxwell Pulse Cap rated for 75nf and 40kV, which is nearly half the optimum larger than resonant value capacitor for my transformer array (I got a great deal on it from a fellow Tesla coil enthusiast, who sold it to me for $100, it's worth up to $800 elsewhere).  Yes, ther is a piece of grass in from of the images, that is becasue I run this coil in the yard.

    

     For my spark gap I am "currently" using an synchronous rotary spark gap, propeller style.  The center thoriated tungsten electrode rotates between 4 brass bolt electrodes at 1800 RPM. 

    

     I use 10 AWG wire for low current conncetions, but I used 2 parallel strands of 6 AWG wire for the tank circuit (where peak current is over 600 AMPs).  The formula for arc length in inches is 1.78*sqrt(transformer wattage) and for my power level I should get around 8ft arcs (assuming 1000 watts per transformer, with losses, this gives an 8 ft output as an estimate!  In reality it is limited to a much lower power level, so 54 inches of spark isn't all that bad.)

    It is important to note, I cannot safely just plug this thing in the wall, it will flip breakers like a dolphin at sea world (or grandma making pancakes, whichever analogy you prefer).  So, an inductive ballast is being used along with power factor correction capacitors.  For my ballast, I use a quick and easy single MOT with shorted secondary, and my PFC caps are motor run capacitors.

 For optimum coupling my primary coil is adjustable up and down (around a stationary secondary) which is an option I never could exercise with my last coil.  This allows me to get maximum inductance (for best performance) and just keep it under the point where it begins having secondary breakdown (racing arcs etc., which are mui malo senior! nicht guten, very bad.)  I can also adjust the height of my topload from the top winding of my secondary, which also makes a differance in performance.
    Some other goodies I have this time are a variac, and EMI filters.  The variac allows me to adjust the voltage put into my MOTs, allowing me to adjust the voltage put out of my MOTs.  This allows me to start up the coil slowly, reducing stress on all of the parts.  I also have some EMI filters, which filter out a lot of the RF "noise" transmitted back teh AC power line, into my breaker box, where I do not want it.
     Here are some half decent pictures of my coil in operation, I will have much better-updated ones soon, but for referance the arcs in the pictures below are about 30-40 inchers.  I now get 40-55 on a bad day!  I will have movies soon as well.

Home, Hobbies, Tesla coil.

Scott Bogard. 2007