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My first ever tesla coil build

Discussion in 'General Electronics Discussion' started by elpechos, Feb 21, 2017.

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  1. elpechos

    elpechos

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    Feb 21, 2017
  2. AnalogEL

    AnalogEL

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    Feb 21, 2017
    This is more of a question than a suggestion,,, I've built spark generators out of car ignition coils but never wound one like in your pictures. Didn't take any time to google it either. :)

    It seems like you need good magnetic coupling between the primary and secondary of your coil, and as pictured it looks like your primary is only really well coupled to the first few secondary windings.

    I do see what looks like a skinny aluminum rod in one of the pictures, does that run down the center of the secondary and help couple ALL of the windings together?

    Would making this rod out of something more magnetic like iron or steel (like a piece of re-bar), or ferrite improve things? It seems like the frequency would go way down, but the losses may go way up.

    This has probably already been dealt with in the design, you just can't see it in the pictures.
     
  3. elpechos

    elpechos

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    Feb 21, 2017
    With a Tesla coil you usually try to get a weak coupling between the primary and secondary.

    A Tesla coil is different than a regular transformer in that it's a resonant transformer. A standing wave goes up and down the secondary, bouncing off the top and bottom of the coil.

    The primary adds more power at each peak causing the voltage to get higher and higher. (think like pushing someone on a swing until they get higher and higher) This means unlike a regular transformer the increase in voltage can be much higher than the ratio of windings.

    Edit:
    As to the core; there is no core in the secondary. Tesla coils are generally air-cored.

    Because of the resonance. Tesla coils ring at a single frequency (mine is about 1.5mhz) at high voltage, this makes them very good radio transmitters, the transmitted radio can be used to transfer power at a distance. See
    Thanks
    Matt
     
    Last edited: Feb 23, 2017
  4. AnalogEL

    AnalogEL

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    Feb 21, 2017
    Wow, fascinating and non-intuitive. :)
     
  5. elpechos

    elpechos

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    Feb 21, 2017
    I believe my explanation isn't exactly correct. I don't fully understand how the tesla coil operates myself. The standing wave 'bouncing' off the top and bottom isn't entirely accurate. I believe capacitance between the secondary windings and also the top load and the secondary windings comes into play. Because you have capacitance and inductance it acts like an LC circuit. The overall effect is similar to a wave bouncing up and down the secondary though.
     
  6. elpechos

    elpechos

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    Feb 21, 2017
  7. 32Vwasbetteronboats

    32Vwasbetteronboats

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    Feb 18, 2017
    I built a Tesla coil in 1991 before the internet using this book.

    [​IMG]


    My capacitor was two glass shower doors aluminum foil then some glass from storm windows for the top layer of glass. It glowed blue on the edges.

    Spark gap was a music CD screws set on edges on circle saw motor with variac for speed control. Also used regular spark gaps I fashioned from things.

    The coil that I got best results was a concrete form tube shellacked , I forget the size but lawn mower wheels fit in the ends and I mounted it to spin so I could wind on the 800 feet of magnet wire I got.

    The arks when I ran the thing would skip winding so I unwound the whole thing and rewound it with fishing mono filament between the winding.


    My PVC coil, with the heavy rubber covered wire worked well too, or more consistently. 10 gauge solid core of course.

    Power was oil burner ignition transformers 23ma 10,000v alone 2 or 3 in parallel see what happens.

    I got a brass ball from those things used in a fireplace

    [​IMG]


    I think at one point I started running 220 through the ignition transformers and it worked better. Try 220 I know I did.


    This was the early 90s and the good ignition transformers were getting phased out, replaced with these light cheesy ones. I guess today you just type "pole pig" into google and click shopping. Wanted one of those !

    Anyway looking at your photo your magnet wire secondary may need a spacer between windings as I said it likes to skip winding when its close arks up the side. Fishing line then the shellac the whole thing.

    And power the crap out of it, power in = power out. Play with a rotary and adjustable gap that's the variable for me that made up for math mistakes.

    And make BIG capacitor, made one from that pile of storm windows I found that kicked butt till the electric started finding its was though and the foil was to close to the edges and would crack the panes.

    Its so fun, my coil was nothing, got 10 inch sparks would be a YouTube embarrassment today but a running Tesla coil in real life is so much more impressive then watching on YouTube. Vent that ozone.

    Have fun, don't get zapped that part sucks.
     
    Last edited: Feb 25, 2017
  8. 32Vwasbetteronboats

    32Vwasbetteronboats

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    Feb 18, 2017
    [​IMG]

    That secondary looks to close, I got best results like this

    [​IMG]

    Make this shape for your primary.

    What you do is connect one wire to base of the primary then connect the other with an alligator clip at different levels, number of turns till you get maximum result.

    All about screwing with variables till it really fires off. You can hear it getting better as you get closer. It gets a sharper crackle that sounds tuned.
     
    davenn likes this.
  9. 32Vwasbetteronboats

    32Vwasbetteronboats

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    Feb 18, 2017
    My primary was copper tubing

    [​IMG]
     
  10. 32Vwasbetteronboats

    32Vwasbetteronboats

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    Feb 18, 2017
    Now I read the rest of your page instead of just looking at the pictures,they looked alot like my first tries and I just started typing.

    Slayer Version transistors
    ... Not so sure how to do this.

    Thanks for the thread though and getting the Idea of building another coil back in my head. I have 2 30ma 15,000 volt neon sign transformers a buddy was throwing out for building another one I just never seem to do it.
     
  11. elpechos

    elpechos

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    Feb 21, 2017
    I've been meaning to experiment with different primaries.

    The Slayer Exciter though doesn't need fine tuning the resonance of the primary as the transistor circuit automatically tunes itself to the resonance of the secondary
     
  12. 32Vwasbetteronboats

    32Vwasbetteronboats

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    Feb 18, 2017
    "This simplicity does come with a downside, as you increase the supply voltage your transistor will die suddenly, and without any warning. Seriously, I’m not joking, this circuit is where transistors come to die. It’s the transistor god of death in your favorite religion."

    Maybe you need that choke coil part ??

    [​IMG]

    [​IMG]



    Those fields building and collapsing maybe its some kind of feedback fry ?
     
  13. 32Vwasbetteronboats

    32Vwasbetteronboats

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    Feb 18, 2017
    "automatically tunes itself"

    I am trying to get it. Been a wile for me.
     
  14. elpechos

    elpechos

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    Feb 21, 2017
    A choke is a pretty good idea; I'll probably try that if I ever revisit this circuit.

    The flyback is definitely not the only reason why this circuit tends to kill transistors though. They also spend a lot of time in a half-on state, so they dissipate a hell of a lot of a heat,

    The LED diode there is meant to help prevent a high negative emitter/base voltage on the transistor. Replacing as I mention in the article. An LED doesn't always seem fast enough to do this, though; replacing it with a shottky helps a lot.

    Thanks
    Matt
     
  15. elpechos

    elpechos

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    Feb 21, 2017
    The slayer circuit tunes itself because it's locked/synced to the secondary. Low voltage on the secondary turns off the transistor. It also doesn't have a tuned primary circuit. So there's nothing about the primary to 'tune' as such. The LC circuit on the primary of a traditional tesla coil is replaced with a transistor oscillator in the slayer circuit.
     
  16. 32Vwasbetteronboats

    32Vwasbetteronboats

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    Feb 18, 2017
    I just remember being facinated with that whole lenth of the wire divided by the speed of light thing doing the math and it landing on the AM radio band.

    186,000 x 5280 / the lenth of my wire.

    Then the quarter wavelength part.
    I think the primary does have to be tuned, you can force a bell to ring at a different tune but it likes its natural spot.
     
  17. elpechos

    elpechos

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    Feb 21, 2017
    In a traditional Tesla coil, yes, the primary needs to be tuned as the primary LC oscillator needs to resonate at the same frequency as the secondary.

    The slayer exciter tesla coil has no such capacitor and the primary isn't configured as a resonant/LC circuit, so there's nothing to tune. Instead the oscillations are provided by the transistor at whatever frequency the secondary happens to be, this is achieved by feedback from the secondary to the transistor oscillator. A regular tesla coil has no feedback mechanism to automatically match the secondary, so you need to tune it by hand.
     
  18. 32Vwasbetteronboats

    32Vwasbetteronboats

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    Feb 18, 2017
    I think I might be getting it, still stuck on the idea it need to ring together but it is together.
     
  19. elpechos

    elpechos

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    Feb 21, 2017
    In a traditional tesla coil there is two oscillators the primary, and the secondary, which are both inductor/capacitor resonators
    In the slayer circuit. There is only the secondary LC resonator, the primary LC resonator is replaced by a transistor oscillator, which doesn't need tuning because it has feedback from the secondary.
     
  20. elpechos

    elpechos

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    Feb 21, 2017
    I'll add to my blog a better description of how the traditional spark-gap tesla coil and slayer exciter circuit are different. There seems to be a lot of confusion on that point :)

    Thanks, Matt
     
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