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What is the minimum amount of current that can be fatal at around 20KV?

  1. Sep 1, 2010 #1

    i probably dont need to give you all this information, but i will anyway :)

    i have a flyback transformer from a TV connected to a 30V 1A power supply via a transistor from a TV (a high power line output transistor), and the signal on the base of the transistor is around 100KHZ alternating dc sine-wave at around 5-10V, the flyback transformer produces a spark at a maximum length of around 2.5 cm, which i assume is a maximum of 20KV, and i always assumed that if i touched it i would get a nasty shock (though i have never got a shock from it, it would atleast burn me as i can light toilet paper with it), but it would be harmless, but today i calculated that as the current drawn from the power supply is around a third of an amp, the maximum current from the flyback transformer's high voltage (around 20KV) output (not accounting for any losses) would be .49MA, the transistor gets very hot within a few seconds of operation, and has to be immersed in water to keep it cool (atleast thats the easiest way to do it), could this current and voltage combination be fatal? could you please give me a rough way to calculate the LD 50 of some current and voltage combinations?

    thank-you for enlightening me as there is little information on the WWW about it.

    thanks in advance, alf.
  2. jcsd
  3. Sep 1, 2010 #2


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    I can't help with any formulae, but I will say this: Until you get very positive responses from a professional electrical or electronics engineer or technician... Don't touch it!
    'Nuff said.
  4. Sep 1, 2010 #3
    This is unconfirmed, and are simply values I remember seeing somewhere. It should provide you with a good estimate though.
    1. Voltage does not play a role as long as it pierces the skin.
    2. Lethal current is about 60-80 mA on skin contact, or as low as 2mA straight through the heart. For DC, on skin contact its 5-6 times higher lethal limit, still ~2mA if there's a direct conduit to the heart though.
  5. Sep 1, 2010 #4
    Danger is right. Even after you have training, always put one had behind your back in your pocket, and wear insulating shoes. I know of one summer student at a national laboratory who was knocked unconscious (with fibrillations) by poking around inside a TV set with the power on.

    You need to distinguish between a dc current and pulsed current (or Joules). I have many times been shocked by automobile ignition circuits (condenser-coil variety) with a 0.25 uF capacitor charged to ~300 volts = ~0.01 Joules. Tasers are higher (~0.3 Joules).

    [I assume no liability for this advice]

    Bob S
  6. Sep 2, 2010 #5
    My understanding is that your body chemistry determines how many amps will flow through your heart, provided the source is capable of providing enough sustained current at atleast 40v. Even a 9v battery could injure you if you stuck it in an open chest wound. Each person responds differently, so it is important to be careful with any amount of electricity. Like others have said i wouldn't stick my finger in there regardless of the calculations done.
    I don't think AC/DC should play a big role though.

    This article explains it well:
    Last edited: Sep 2, 2010
  7. Sep 2, 2010 #6
    Edison and Tesla had a big "War of Currents" to determine whether the other's choice of current, AC or DC, was more lethal. Public executions of stray cats, stray dogs, cattle, horses, and even an elephant were carried out to determine which form of electricity was more lethal.



    Bob S
  8. Sep 2, 2010 #7
    Uhh... remember that permanent burns can be a bummer for yourself almost as much as "fatality" can be to your loved ones.
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