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What's the "danger zone" for tesla coils?

Discussion in 'General Electronics Discussion' started by Apocaloptigon, Jun 29, 2018.

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  1. Apocaloptigon

    Apocaloptigon

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    Jun 23, 2018
    First off, I know that tesla coils (at least as far as I know) operate at frequencies too high to pierce the body and go through the heart etc. But if somehow you got shocked by one with a much lower frequency, I'm asking how dangerous that would be.
    If 2 tesla coils had a transformer ratio of 1000 (higher voltage, lower current) and the other 100 (lower voltage, higher current), which one would be more "dangerous?"
     
  2. hevans1944

    hevans1944 Hop - AC8NS

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    For you, either one would be extremely dangerous because clearly you don't have a clue how a Tesla coil works. Turns ratio is mostly irrelevant because the primary AND the secondary of a Tesla coil are operated as resonant tuned circuits. To remedy your lack of knowledge and understanding visit some of the many Tesla coil forums to see what people are building and how they treat their creations.

    Why would anyone deliberately subject themselves to arcs from an operating Tesla coil? You will find videos on the Internet of people protected by conductive mesh "Faraday shield" clothing who deliberately subject themselves to high-voltage arcs before a paying audience. Some people will do almost anything for money, but we have to assume, sans reported fatalities, that they know what they are doing. You should stay at least twice the distance of the longest arc from an operational Tesla coil. For many coils, this would be a distance of at least twice the height of the secondary coil. Tesla coil arcs give a whole new meaning to the phrase "reach out and touch someone."

    The photographs you may have seen of Tesla sitting unperturbed while lightnings flash all around him were double exposures. Tesla may have been theatrical in his presentations, but he was no fool.
     
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  3. Apocaloptigon

    Apocaloptigon

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    Jun 23, 2018
    Ok obviously I need some extra information about what really makes it a tesla coil. What would a plasma globe circuit be called? Because that's the only at-home example of a "tesla coil" I can think of, and it's obviously safe to touch directly (without the glass dome).
     
  4. Hopup

    Hopup

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    Even the low power ones are dangerous, your body is not able to detect the high frequency and voltage as pain but it can still hurt especially your nervous system.
     
  5. K9WG

    K9WG

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  6. WHONOES

    WHONOES

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    It's current that kills not voltage. The resistance of the human body varies from about 1KΩ to around 100KΩ depending on conditions. 100mA is generally regarded as enough current to kill instantly. A tesla arc can easily be in the mega volt region and cause enough current to flow through the body to kill immediately.
    If you have not understood anything that has been said on this forum, abandon any thoughts about Tesla coils and take up knitting fog instead.
     
  7. Apocaloptigon

    Apocaloptigon

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    Jun 23, 2018
    Really? I didn't know the body wasn't able to detect it; I just assumed that the charge couldn't get through the skin. Well it still hurts like a shock to touch a plasma globe circuit, but that's some very nice information.
    No, I've actually made a van de graaff before. I know a lot about electricity, but not nearly enough about tesla coils and transformers.
     
  8. Hopup

    Hopup

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    Jul 5, 2015
    "a Tesla coil's streamers can be very harmful. If you are shocked by the streamers, you will not feel pain, but your circulatory and nervous system can sustain severe damage."

    I'm sure you would actually still feel something if you would be grounded by being wet etc, before you would likely die. If you are poorly grounded it will not hurt at all but can still do bad stuff.
     
  9. Apocaloptigon

    Apocaloptigon

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    Jun 23, 2018
    Man I always assumed tesla coils, at least the weak single-transistor ones were just compact transformers. Had no idea they got this dangerous
    And to make things clearer, I was talking about one powered by a 9v, a transistor, and a resistor. Though I didn't think that was a real tesla coil.
     
    Last edited: Jun 29, 2018
  10. Apocaloptigon

    Apocaloptigon

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    Jun 23, 2018
    AHA! I did some research and discovered it was a slayer exciter circuit, not a tesla coil. If anybody still cares:
    Is a slayer exciter circuit harmful at all?
     
  11. Hopup

    Hopup

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    If you don't know 100% you should assume it can kill you and work accordingly. Its not as dangerous as Tesla coil if you run it with that 9V battery.
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It's certainly possible to get burns from these. And the magic thing is that they don't tend to hurt while they happen.

    As an example, I presume you've seen those battery powered plasma globes that emit streamers inside a plastic globe. You can move the streamers by placing your hand or fingers on the bulb. For a bit of amusement, try holding an axial capacitor between your thumb and second finger, place the far lead on the globe then draw an arc to your index finger from the other end. It looks really cool. Then look at the tip of your finger. You'll see a spot of charred flesh. It's only tiny -- which is a good think because I don't like cooking human, especially when that human is me!
     
  13. hevans1944

    hevans1944 Hop - AC8NS

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    Here is an anecdotal story. Your mileage (or kilometers) may differ of course...

    Near the middle of the last century I was serving a four-year term of enlistment in the U.S. Air Force. Life was boring for a single airman stationed at a snowy, isolated, post in the northern peninsula of Michigan. When I was offered an opportunity by my first sergeant to join the local base amateur radio club and study for a Novice-class amateur radio license, I eagerly accepted. A few weeks later, while "practicing" receiving Morse code in a class held at the clubhouse, I was surprised to be informed that I had passed the 5 word-per-minute Morse code test! I didn't even know I was being tested... nor did any of the other students in the class know when they were being "tested," lest they fill up with dread and fail to copy the code. So we all passed our code tests, and we all passed the written "theory" test, and the volunteer examiner sent the results off to the FCC. Some time later (probably no longer than a month but it seemed like forever) we received our "tickets," a printed paper license authorizing each of us to own and operate a radio station in the amateur radio service. We were now Hams!

    I had a LOT of time on my hands during off-duty hours, and I was anxious to get started in amateur radio. I couldn't afford a Collins "rig" which was the "top-of-the-line" equipment in 1966, so I settled for an almost "look alike" Heathkit SB-300 receiver kit:

    [​IMG]

    I was barely able to afford this kit on my A2C monthly salary. And there was no money left over to purchase a transmitter. So, after putting the receiver kit together, and with the help of a few friends (and permission from the first sergeant) we erected an 80m dipole antenna about ten feet above and parallel with the gravel-and-tar roof of our barracks. I found a spool of "practically new" coaxial cable tucked away in a corner of our Armament and Electronics (A&E) maintenance shop. Using an oscilloscope and a pulse generator, along with a variable 100 ohm potentiometer connected across one end of the coax, I determined that the coaxial cable characteristic impedance was 50Ω. Voila! My first sergeant determined that the spool of coax was "surplus" to our shop's current needs and allowed me to remove it to the barracks and install it between my ground-floor room and the roof antenna some three stories higher. So after a few months of labor I was now "on the air" as a short-wave listener (SWL) and could practice receiving CW transmissions by real amateur radio operators while I built a Novice transmitter.

    I devoured the only issue of The Radio Amateur's Handbook (an ARRL yearly publication) that I had, reading it from cover-to-cover while drawing up schematics of various transmitter options. Back in those days, Novice class licenses were limited to transmitting with only 75 watts of input power to the "final" output tube. And the dipole antenna I had erected was useful only on the 80m amateur radio band, where a small slice of spectrum was allocated for Novice operators. Allocated, not reserved: any other amateur could use the same slice of spectrum but Novice operators could only operate in "their" slice. Still, it was enough to make contacts with other amateurs, including some novices, and become proficient in receiving and transmitting Morse code. Now all I needed was a transmitter and a telegraph key. And maybe some earphones. And an SWR bridge. And maybe a grid-dip meter for pruning the dipole to the proper length for resonance in the 80m NOVICE band... Geez, this is becoming an expensive hobby.

    Besides spectrum (band) limitations and power limitations, Novice-class operators were also "rock-bound" to fixed frequencies, selected by whatever quartz crystals one could afford to buy. I could live with that, transmitting on one frequency while listening on another slightly different frequency, changing crystals if necessary to avoid QRM (interference) from more powerful stations who wanted to park their transmissions at or near the frequency I was using. I was able to purchase, scrounge, or otherwise acquire about a half dozen quartz crystals for the 80m Novice band (3.525 to 3.600 MHz) and by the winter of 1966 had finished construction of my very own Novice transmitter and a separate power supply for it. I wish I had taken and preserved pictures of this "rig" because I was really proud of my work. The RF power section was fully enclosed inside a mesh cage salvaged from the high voltage section of a junk TV. I used an RCA 6146B beam-power pentode biased for Class C operation driving a pi-network load. A separate RF oscillator tube and full break-in (QSK) keyer with envelope-shaping network, to eliminate key "chirps" or "clicks" drove the "final" to 75 watts input power. I spent all my free time that whole winter "on the air" practicing Morse code and "rag chewing" with those Hams who enjoyed it.

    The dipole was not oriented in a very favorable direction. IIRC, the wire ran east and west along the top of the barracks, meaning the antenna lobes were oriented north and south. Not much was north of Kincheloe AFB, MI and very few stations were directly south either. Still, I managed to obtain contacts and held conversations (QSOs) with many stations until my enlistment expired in May 1967. During the time I was operating "on the air" I learned a few "tricks and tips" from other Hams. One of these seemed novel and simple to apply: use an ordinary, wood-encased, sharpened #2 lead pencil to test your RF "tank circuit" for the presence of RF, drawing a short, hissy, arc from the tank coil to the pencil point while holding the body of the pencil between thumb and forefinger. Worked like a charm on my little transmitter, although I still used a small neon lamp connected to a single loop of wire as a visual indicator.

    After leaving the Air Force, I managed to get a job as an electronics technician at a local university. Lots of opportunities to discover new things electronical as well as optical, chemical, and other branches of science. One day I was asked to help out with troubleshooting an RF induction heater. This little beastie operated at about 450 kHz, which is near the frequencies that Tesla coils generally resonante. It used a water-cooled power triode as an RF oscillator to drive ten turns or so of copper tubing wound around a hollow nickel "susceptor." The copper tubing had cooling water flowing through it because the nickel susceptor became white hot (Incandescent) during induction heater operation. Except this day it wasn't doing that. I suspected the power oscillator had quit oscillating and so I pulled out a #2 lead pencil to test that theory, a 'la amateur radio practice.

    I was still pretty new at working around high-powered electronics, so I gingerly held the pencil at one end with the metal ferrule holding the eraser grasped between my thumb and forefinger. I carefully approached the tank circuit, attempting to draw a small arc if it were operating. When the pencil point came within about a half-inch of the tank coil a fat, sizzling, arc jumped across the gap. Another arc formed between my fingers, thumb, and pencil. All this happened very quickly and the result was I immediately dropped the pencil. Unfortunately the damage had already been done. I pin-point sized wound pierced my thumb and charred the flesh around the area where the arc occurred. It was quite painful, but more importantly, it took almost a month to heal.
    Apparently the flesh was cauterized internally as well as externally, prolonging the healing process.

    I learned a valuable lesson from this (non-fatal) experience: use proper test equipment instead of my valuable body to test electronics. I do remember when I was just a kid that a neighborhood radio-tv repairman, who also happened to be a licensed radio amateur, showed me how he tested for the presence of AC in his basement workshop, cum ham-shack, with knob-and-post wiring by carefully bridging two bare wires with thumb and forefinger. Seemed to me like a dumb thing to do, standing on a dirt floor in a damp basement, but the idea must have stuck in my head somewhere for me to try a similar stunt with a 50 kW RF induction heater.

    Do be careful messin' aroun' with Tesla coils, even if they are built with so-called slayer exciters and operate from 9V dry cell batteries instead of from mains power. Believe me, you are NOT ready for a mains powered Tesla coil yet.
     
    Last edited: Jun 30, 2018
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  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You win :D
     
  15. K9WG

    K9WG

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    Mar 8, 2018
    BTDT with 800V at 28MHz....

    No amount of ice and cold water can quench the pain
     
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  16. Apocaloptigon

    Apocaloptigon

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    Jun 23, 2018
    I definitely agree that I'm not ready for a real tesla coil yet, that's mainly why I'm doing extensive research on them. Right now I'm focused on that slayer exciter, hoping to make one just for fun and also knowing that it can't harm me once I eventually make it. Before I joined any forum or used any circuit simulator etc, I did tons of research on what's harmful and what's not, especially the "why" part out of curiosity. This also includes every type of electronic device that seemed fun (including things like leyden jars) out of curiosity.
    I'm fine though I promise
     
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