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Spike!

Discussion in 'Electronic Basics' started by Randy Gross, Nov 11, 2004.

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  1. Randy Gross

    Randy Gross Guest

    Greetings,

    I read an article on a transformer test recently where the term
    "spike" was used. I didn't give it much thought then but, It stuck in
    my mind because the last few words in the article contained: "Be
    careful when you turn it off, there's a huge spike..."

    I recall discussions on Inductors and how they release thier energy
    back toward the source but, in this case, once the circuit is broken,
    how do the coil/coils discharge? Is the spike fired back into the
    mains or into other circuits in the panel? Is this a source of
    "Noise"?

    Randy
     
  2. Any inductance has the following relationship between current and
    voltage:

    V=L*(di/dt) Or the voltage (volts) across the inductor is
    proportional to the time rate of change of the current through it
    (amps per second). The inductance (in henries is the constant of
    proportionality. If a transformer or other inductor is connected to
    an AC source, and happens to be switched off (I goes toward zero very
    fast) at the moment when the current happened to be quite large, the
    voltage produces can be very high. This is the spike they are talking
    about. This is the same process used to produce sparks from an
    ignition coil.

    If you measure the resistance of a transformer with an ohm meter and
    disconnect it while your fingers touch both sides of circuit break,
    the transformer may produce enough voltage that the small current
    built up by the ohm meter may be pushed through your fingers and give
    you a small shock.
     
  3. Randy Gross

    Randy Gross Guest

    These are sobering statements. From knowledge gathered from this group
    and books on basic electricity, I have reconfigured and tested many
    transformers and overlooked one basic fact about them, they are
    inductors and capable of delivering a vicious bite when they are
    turned off. I've been lucky!!

    I try to conduct all of my experiments safely, for myself and those
    around me. What safeguards can I institute to guard against an
    accidental encounter?
     
  4. peterken

    peterken Guest

    an acidental encounter is an accident, cannot always be avoided when
    experimenting...
    ..... unless you begin building protetion circuits before experimenting, but
    i wonder what real techie always does that
    at least i've never seen one do it in over 24 years



    These are sobering statements. From knowledge gathered from this group
    and books on basic electricity, I have reconfigured and tested many
    transformers and overlooked one basic fact about them, they are
    inductors and capable of delivering a vicious bite when they are
    turned off. I've been lucky!!

    I try to conduct all of my experiments safely, for myself and those
    around me. What safeguards can I institute to guard against an
    accidental encounter?
     
  5. Steve Evans

    Steve Evans Guest

    don't work drunk; don't work tired. Keep one hand in your back pocket
    at all times; eclectricy and water don't mix; don't stand in puddles;
    low voltages at *high* currents are just as dangerous; remove all
    metallic jewelry.... And more? I'm sure there are! Bring'em on...
     
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