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Tesla Coil primary part help

Discussion in 'High Voltage' started by TheStyle1, Nov 6, 2011.

  1. TheStyle1

    TheStyle1 New Member

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    Hi everyone
    i am building a 1.8KW tesla tower and i have a problem
    i couldn't make the primery part round because the wire was too strong,
    plus my HV Hawg capacitor is 21.6 nF instead of 21.2 nF ,,
    does that effect my design and will it work ?

    thanks in advance for your help



    [​IMG]
     
  2. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Hi TheStyle1. Welcome to AAC!

    It's actually very difficult to get the primary to be perfect. Trust me, I've tried :D
    I looks like it might be round enough to work, but it won't operate at its full potential. Make sure none of the primary windings are significantly close to each other. It appears in the photo that the second, third, and fourth turns (viewed from the angle the camera is at) are kind of close. I would suggest trying to separate them a bit.
    A method you could use to make the primary more round would be to add more supports. It appears you only have three there. If you add one in between each one (for a total of 6) it will help a lot, I'm sure.

    Also, this is going a bit off-topic from your question, but it looks like the secondary is a bit short. How long is it? How many turns? From this angle, it looks to only be 12-14 inches, which probably isn't the best match for your primary. And I'm not so sure about the topload, either, but the larger capacitance may balance out the lower inductance of the secondary....
    Sorry, I'm just typing out my thoughts as they come. I would highly recommend at least adding a strike rail just above the primary. If this coil works normally, it will strike the primary a lot, sending high voltage, high frequency spikes into the tank circuit. That could be very dangerous, not only for the cap and transformer, but also for you. A grounded strike rail is highly recommended to ground any arcs that stray in that direction.

    Keep us posted on your progress. I am always interested to see a Tesla coil build! And as always, please be careful ;)

    Best regards,
    Der Strom
     
  3. TheStyle1

    TheStyle1 New Member

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    well first let me thank you very much for you help,, you made me happy ^_^
    for the time being i just want to see the sparks as its my first project and i had an idea that will separate them a bit i will use a piece of wood for that.

    regarding my seconday, thanks for askin again, its 22.5 inch long around 1100 turn ,

    [​IMG]

    i just designed the table to make it movable so that i can change the inductance and make sure that i will be able to make changes during the test,
    another issue i have, is that i don't know how to connect the seconday to ground,in our power system we have to ground wire, should i connect it to a rod and bury it in the gound? how deep? and the spark gap is 3 or 4 inchs will do
    BTW this is the structure i am using, not the same value but same elements orders

    [​IMG]



    and thanks for mentioning the strike rail i will make sure to have one close to the topload
    sorry for this many questions cuz if it didnt work i will be so depressed ^_^
     
    Last edited: Nov 6, 2011
  4. dave

    Dave New Member

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  5. Boncuk

    Boncuk New Member

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    Hi TheStyle1,

    you will certainly admit if I say your primary winding looks pretty messed up other than the secondery coil.

    I suppose you used copper pipe of 6mm outer diamater for the coil.

    If the material is too hard to bend you might heat the entire coil in a camp fire until the copper turns red hot.

    Take it out of the fire and allow cooling at ambient temperature. After that treatment the copper gets as soft as butter.

    Stretch out the entire coil evenly on the ground to polish the surface (for a better appeareance, using steel wool) and start winding inside out using 6 clamps to hold the pipe. Use clamps to hold the work you've done so far. The windings should have equi-distance horizontally and vertically.

    (I saw several possible dead shorts in your coil.)

    I have wound copper pipes around huge fans of 2.85m diameter to measure air speed. The finished circle was perfect and so you should look your coil.

    Boncuk
     
  6. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Ah, thank you for posting the other picture! The secondary looks about right there :D I guess the angle just wasn't the best in the first one.

    Anyway, to start with, a 3 or 4 inch spark gap is much to large for the TC, unless you have a 150kV neon sign transformer. It should be more like half an inch, though you'll need to adjust it for best performance.

    NEVER ground your secondary to your household ground. It should be completely independent from the rest of the circuits. Take the wire at the bottom of the secondary and attach some insulated wire to it. connect the insulation to a 3-4 foot rod and pound it 2-3 feet into the ground. Generally, the deeper the better. This ties the "negative" side of your secondary winding to earth, and will allow the secondary and the topload to create an LC circuit that will oscillate at a certain frequency. This is the frequency you'll want to match with your primary tank circuit.

    You seem to be on the right track. Let us know if you have any other questions :)

    Der Strom
     
  7. TheStyle1

    TheStyle1 New Member

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    Thank you very much Boncuk for your suggestions, i thought of using fire at first but then i realized that it gonna cost for tolerable problem, i will have to use it if the arrangement will not get my coil functional. before using the fire, i intend to drill horizontal holes in a piece of wood then stick it to my primary and its force should be able to hold them apart for a while, after i have the system working i will see the primary again and might buy a new smaller one.

    BTW my friend Der Strom it wasn't the angle problem, i took the pic before i finished the table so it was all the way down ^_^
    i will test it soon and by that i mean next Tuesday cuz we are in a vacation right now
    i will report my lunching
     
  8. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Ah, that makes more sense :D

    I am looking forward to hearing how it goes. Perhaps you could take a video, as well? ;)
    Enjoy the rest of your vacation!

    Der Strom
     
  9. TheStyle1

    TheStyle1 New Member

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    Video! sure ! absolutely! mean while i am thinking of the next project ! a power one cuz i want to be a power engineer ^_^
    thank u very much
     
  10. duffy

    duffy New Member

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    Instead of wire, try copper tubing. At these voltages and frequencies, the wire has a "skin" effect where most of the current travels on the surface anyway. For making perfect-looking round bobbinless coils, I wind them around a cylinder that's smaller than what I want, then they "spring back" to the larger diameter. With this you would probably want to find a cone shape to wind them around.


    Won't affect it, this design is a relaxation oscillator that will find its natural resonance.

    It often helps to make the tunable primary, though. Wind an extra turn on it, and instead of having that outside lead head back to the supply, use a small battery clamp or something like this -
    image005.jpg
    - so that you can adjust it for peak resonance with the secondary.
     
  11. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Agreed, on both accounts. Tubing is probably the most popular among tesla coils enthusiasts nowadays. As for the capacitor, a larger capacitance simply means you'll need less inductance in the primary. That is where the tuneable primary comes in handy--you can simply clip the cable on to any part of the primary to "tap" it and produce the correct resonant frequency. You may even want to consider building a Tesla Coil tuner, as found on this site. It will help you tune the tesla coil primary so that it resonates properly with the secondary. It is a very useful tool that will help you a lot.

    Good luck!
    Der Strom
     
  12. RCinFLA

    RCinFLA Well-Known Member

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    I think you guys are getting way overboard on the use of large copper tubing for primary. While it is true that the primary tank circuit Q is important, when you factor in the loading of the secondary leakage there will not be much improvement in Q compared to reasonable gauge wire.

    I believe you want to go for resonance of primary in the 75 kHz to 150 kHz range. Lower freq. gets you higher voltage but higher freq. is more fun to physically play with. You can check by lightly coupling into primary with function generator and AC voltmeter through 1 pF coupling in series with each. (obviously not excited by neon transformer). Voltmeter will peak at resonance. You can also measure Q by 3 db bandwidth but you will likely get a higher number then actual operation due to length of spark gap conduction and secondary corona leakage reducing operating Q.

    I don't know what you guys are using for resonating cap but I had problems with blowing holes through 1/8" plate glass insulation. I was driving with 12kV neon sign transformer. Went up to 3/16" glass and did not blow holes. I used parallel resonant primary with spark gap in series with neon transformer. It was about 3/4" gap if I remember correctly. Too close and just sizzles at 50/60 Hz. Too great and doesn't spark. When gap is correct it makes a hell of a racket. Neon transformer secondary was center taped which is where I hooked secondary bottom return. My primary was about 20 turns of spark plug wire (non-resistive type). With your copper tubing with so few turns your cap has to be high value which is tougher for getting high voltage rating.

    The 0.4 mH chokes are not going to do much for you. Their reactance at operating frequency it much more then several hundred ohms.
     
    Last edited: Nov 16, 2011
  13. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    RC, I am simply saying that relatively large-diameter tubing is ideal (depending on the size of the overall coil) because the losses are very low, as well as the resistance. A coil with a higher resistance means less-efficient energy transfer to the secondary, which leads to a poor output.

    The frequency range depends on the size of the coil itself. There are ways to calculate everything, but I would just use a Tesla Coil tuner, the plans for which are readily available on the internet.

    The value of the tank capacitor is crucial, and must be made to match the transformer as well as possible. Again, you can calculate the necessary value on a site like this one.

    The width of the dielectric in the tank cap (if you're using homemade ones) is very important. The thicker it is, the less likely it will be to be burnt through, but it will also reduce the capacitance. With most medium-sized tesla coils, the necessary capacitance is around 10nF, though it greatly depends on the size of the transformer and coil. Usually it's tough to get enough capacitance. That is why beer bottle caps are fairly popular with the beginners--the glass is thick enough that it won't burn through, but thin enough to provide about 1nF of capacitance. It doesn't take many of them to make up a decent tank cap.

    Also, RC, I definitely would not recommend grounding the secondary to your transformer ground. In fact, I would highly recommend AGAINST it. That provides an easy path for high voltage RF spikes to get into the mains system and damage any electronics plugged in elsewhere in your house. It definitely was not a very good idea, TBH.

    The size of the OP's primary tubing is reasonable for the size of this coil. It should work fine with the matching tank cap for the transformer. However, this is judged simply by looking at it, so I can't be completely sure. I strongly recommend you work out the calculations on that site I posted earlier and see what you come up with.

    Regards,
    Der Strom
     
    Last edited: Nov 16, 2011
  14. RCinFLA

    RCinFLA Well-Known Member

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    That was suppose to be primary in my first sentence. I might have returned secondary to non-spark gap side of primary. It was 50 years ago and just going by memory. (no, I did not know Tesla personally) Resonating cap was about 3.5 nF, but I had more primary turns. Secondary was 6" diameter about 33" long of #28 gauge Formvar wire, about 2600 turns.
     
    Last edited: Nov 16, 2011
  15. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Oh, okay, I have heard of that design. However, it still poses the problem I described earlier of high-voltage spikes in the transformer, and thus in the mains. It's not recommended, but yes, it works. Perhaps experimentation and understanding has increased within 50 years regarding the best way to ground the secondary. I always learned, and discovered for myself, that it is safest and more effective to ground it through a large stake pounded into the earth.

    I sure wish I had met Tesla in person, though. That would have been a meeting that would never have been forgotten! :D
     

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