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120V-20Kac Transformer source

Discussion in 'Electronic Design' started by John Larkin, Sep 13, 2004.

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  1. John Larkin

    John Larkin Guest

    Sounds like a neon sign transformer to me.

  2. Jamie

    Jamie Guest

    like the header said.
    i am looking for a source to get
    120V in 20K AC out transformers at
    60 Hz. to generate no more than 20 Ma
    NON-Auto Type both leads available
    at the secondary.

    we are going to be building some
    hi-pot units and would like these
    transformers .
    would be nice if they would have a low
    voltage tape from the secondary for a
    voltage level monitoring circuit but
    need absolutely needed.
  3. John Fields

    John Fields Guest

  4. John Fields

    John Fields Guest

    Have you never heard of Google?

    will get you something like 185,000 hits.
  5. Jamie

    Jamie Guest

    well maybe a neon sign transformer could be used but
    its needs to be put in a Hi-pot unit.
  6. John Larkin

    John Larkin Guest

    Then put an autotransformer ahead of it. They run hot anyhow.

  7. John Fields

    John Fields Guest

  8. Rich Grise

    Rich Grise Guest

    If you're making a hipot, you don't want any more
    than maybe .1 mA, and preferably more like 5 uA, full-
    scale. This is also called a megohmmeter or megger.
    Is it possible to make an adjustable flyback from,
    say, < 100V to 20 KV?

    20 KV at 20 mA will kill you right now. I've heard
    that it's so fast that it even beats your reflexes -
    you're dead before you can flinch.

    Do not ever under any circumstances have allow
    equipment capable of voltages/currents like that
    that people will be holding in their hand while it's
    in use.

    I'd say, adapt a TV flyback, and be sure to use at
    least 1M series resistance.

    Good Luck!
  9. Rich Grise

    Rich Grise Guest

    They run hot at 15 mA. If you're running that kind of
    current out of a hipot, you're running a death trap.
    Put a 10M resistor in series to limit the current to
    1.5 uA, and then I'd consider it usable by a competent
    tech. And I'd imagine that when they pot the thing,
    the primary gets just as much insulation as the secondary,
    so it probably wouldn't mind running overvoltage at all,
    as long as the core doesn't saturate, and you keep the
    VA down.

    Good Luck!
  10. John Fields

    John Fields Guest

    1. You can't get 15mA out of a 20mA NST at 15kV,
    you can only get it with 0V out. I.e.,shorted secondary.

    2. 15000V/10000000 ohms = 1.5mA

    3. You imagine?

    4. It probably?

    5. Any more guesses?
  11. Jamie

    Jamie Guest

    i wasn't planing on allowing the full load to the
    test fixture, i just want that load factor to
    prevent over load on the transformer because
    there are 2 things are taking place, one is
    the material passing through the beed box covers
    a large area and thus large amounts of capacitance
    is a problem which loads its and the material is
    passing at a high rate of speed.
    the units we have now simply turn the voltage off
    as soon as a short is detected and an alarm is sounded.
    as far as 20 Ma being a problem , i can see it could be a
    problem if it was constant but if what you are saying is true
    then we would have had a good many people dead by now from operators
    not discharging a high capacitance real of wire with lots
    of footage on it after a test. some times they don't allow for the
    crow bar to operate.
    most of our older units have a simple current fold back using a
    incandescent lamp.
    Like i said, i don't plain on delivering that amount of current
    at that voltage, i would just looking for a transformer that could
    coast. in the units i am designing there will be current limited already
    in place and what i am doing measuring the output voltage to slowly
    apply the needed current which will bring the required voltage needed
    to the set point. this way on low drain applications the current will be
    very low..
    and upper apps will be increase as needed to a max set point which would
    constitute a a short out in any case. the circuit actually uses a choke
    on the return side for the ground on the output and the sensor pulse
    is used there to fire off an alarm because most of the time a pin hole
    will generate the short spike you need., the 60 Hz will be shunted by
    the choke.
  12. legg

    legg Guest

    There is no telling what actual voltage is stored on the wire reel's
    capacitance, at the time it is disharged accidentally by the operator
    (anywhere from zero to +/- AC test peak). Depending on the
    capacitance, this could represent a serious hazard.

    I think you would find that one injury was sufficient proof of
    supervisory incompetence.

    How does the operator bypass the crowbar, and why haven't you
    corrected the safety feature so that it cannot be bypassed?

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