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Get shock from a standard transformer?

Discussion in 'Electronic Basics' started by [email protected], Feb 10, 2006.

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  1. Guest

    Hello.
    I see on many transformers (of home application like chargers, scanners
    etc.) that they're capable of delivering upto 1000ma, or even 1500ma.
    As I know, an amount of over 0.24ampre can kill someone.
    So how come when I touch both ends of the output (which is about 12v)
    nothing happens, I dont get any feeling at all, let alone get zapped to
    the next life?
     
  2. Pooh Bear

    Pooh Bear Guest

    Less than that in fact.
    The voltage is to low to do any harm. You're probably drawing microamps.

    Graham
     
  3. Guest

    The voltage is to low to do any harm. You're probably drawing microamps.

    Can you explain this to me?
    Because I know that its the current which counts, like, for instance in
    those transparent balls that when you touch them you draw a small
    lightning - they contain something like thousands of volts, right? and
    they don't electrify you.
    Also, where I work they use 24vDC rt amplifiers that go up to 1000w, so
    they use 20-30A, and they _can_ shock you, despite the relatively low
    24v, right?
    so how does it work?
     
  4. GotCoffee

    GotCoffee Guest

    Try wetting your fingers first. If that doesn't work, wet your fingers
    with salt water (lick them). Remember to use the same hand for both
    leads. You don't want any current running thru your heart.

    The 12V is enough voltage. It's the amps that kill. We tell the
    people just starting into electronics that 100mA is enough to kill you
    if it goes across your heart.
     
  5. Guest

    Are you saying that if I do that on my transformer I _will_ get zapped?
     
  6. Rich Grise

    Rich Grise Guest

    The 1000mA or 1500 mA is what the power supply is _capable_ of providing.
    Since it's a constant voltage supply, the current drawn by the load (in
    this case, you) is _inversely_ proportional to the resistance of the load,
    and the resistance of dry skin is in the tens to hundreds of thousands of
    ohms.

    Hope this Helps!
    Rich
     
  7. Guest

    oh ok...
    thanx!
     
  8. Ralph Mowery

    Ralph Mowery Guest

    While small ammounts of current (anything over about .05 amps , or 50 ma) is
    very dangerous through the outside of the body, it has to do with the
    resistance of your skin. Normal dry skin resistance is a few 100, 000s ohms
    or more. The 12 volts from the transformer can not force much current
    through that resistance. Plug it into the I=e/r equation. That is the most
    current that can be drawn from the transformer will be atleast 100,000 ohms
    devided by 12 volts. That is way below the .001 amp that it takes for most
    people to feel on the outside of the skin. If you apply 12 volts directly
    to the heart or brain where it is wet and a short distance apart, then it
    may be dangerous. If you take a 9 volt battery and touch it to your mouth
    where it is wet and the resistance is much less than 100,000 ohms then
    enough current will be drawn to be felt.

    You have to understand that no mater how much current a power source can
    supply, it is the resistance in the circuit that limiates the current drawn.
     
  9. Your 12v transformer can deliver up to 1000ma into a load. If you hook
    a 12 ohm resistor across the transformer output, the voltage across the
    resistor would be 12v and 1000ma would be flowing through it.

    Luckily for you, your skin resistance is much, much higher than 12 ohms
    so if you touch the terminals only a tiny fraction of 1000ma flows
    through your body. As others have suggested, you can increase the
    current flow by wetting your hands with water or salt water to reduce
    your skin resistance. If you are unlucky enough to break the skin with
    the terminals, you would present an even lower resistance.
     
  10. Guest

    The voltage is to low to do any harm. You're probably drawing microamps.

    Can you explain this to me?
    Because I know that its the current which counts, like, for instance in
    those transparent balls that when you touch them you draw a small
    lightning - they contain something like thousands of volts, right? and
    they don't electrify you.
    Also, where I work they use 24vDC rt amplifiers that go up to 1000w, so
    they use 20-30A, and they _can_ shock you, despite the relatively low
    24v, right?
    so how does it work?
     
  11. Guest

    pls ignore this message... I sent it about an hour ago :-b
     
  12. Bob Masta

    Bob Masta Guest

    In addition to what others have posted, note that at RF
    frequencies there may be a greater ability to punch through
    the dead skin cells at the surface which are causing the
    skin resistance to be so high. So don't mess around with
    this!


    Bob Masta
    dqatechATdaqartaDOTcom

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Home of DaqGen, the FREEWARE signal generator
     
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