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transformer core

Discussion in 'General Electronics' started by Kevin Weddle, Feb 25, 2004.

  1. Kevin Weddle

    Kevin Weddle Guest

    What I can I use for a transformer core? I think I need a piece of
    steel with a large area. The example core that I have seen has a large
    area as opposed to just length. Do I have to find a steel shop to get
    a core?
     
  2. ron doctors

    ron doctors Guest

    This is a very open question.
    Lets have some answers and we can help!

    1. Function? What are you going to do with the transformer. The ans.
    to this will lead to more ? but without knowing the end use it is far
    too open a ?
    Did you know that tfr. cores can be made of .. silicon steel, cobalt
    steel, nickel steel, ferrite , even air! ..?

    2. Why? You can buy transformers for almost every function for less
    than it will cost for the parts! ( BTW see my trasnformers listed in
    http://www.members.cox.net/rdoctors/clearall.html

    3. What technical skills do you have?

    4. Do you understand basic transformer design?


    Hoping to help ...
    ron
     
  3. Kevin Weddle

    Kevin Weddle Guest

    This is going to be a power autotransformer. I need the voltage to be
    right,so I need to wind my own. I have been told to use iron instead
    of steel, but I don't want to glue a core together and I don't want to
    strip a transformer. I can't measure the inductance but I can
    calculate it. The question is how good will the transformer be.
     
  4. Bill Vajk

    Bill Vajk Guest

    A solid core will have significant eddy currents and will
    be inefficient. How well your application deals with that
    sort of inefficiency is more to the point.

    Bear in mind that transformer manufacturers go to the trouble
    of laminated cores even for small wattage applications.
     
  5. Robert Baer

    Robert Baer Guest

    Since you clearly do not know what you are doing, the "transformer"
    will not be too sucessful.
    Iron or steel could "work" but neither is ideal, and a solid block
    will result in gross heating and/or fire.
    Get a surplus transformer, damnit, and strip the secondary, and wind
    the desired new secondary to be connected in series with the primary:
    aiding or opposing, depending on needs.
    Or get a variac = variable auto-transformer.
     
  6. Kevin Weddle

    Kevin Weddle Guest

    I imagine that the core material is small. For a stepup
    autotransformer, the entire winding has to be on the core. This means
    I would have to physically combine several cores together to make
    this. Also, the magnet wire is going to be difficult to wrap on many
    cores.
     
  7. Robert Baer

    Robert Baer Guest

    Not really.
    Look at any non-toroid power transformer and note that the windings
    are put on a cardboard (or plastic) slip-on form.
    So when one gets a power transformer and removes the silicon-iron
    laminations, then one sees that base and can remove the secondary togive
    space for a new secondary.
    If one makes a larger transformer from same-sized laminations "stolen"
    fromtwo or three transformers, then one makes a winding form for use.
     
  8. Kevin Weddle

    Kevin Weddle Guest

    Okay. So you suggest laminating several cores together, then winding
    the magnet wire around a form made of cardboard. It sounds a little
    bit like a ball of junk. But I think you have convinced me. You know
    that a large transformer can be a little expensive to tear apart.
     
  9. Robert Baer

    Robert Baer Guest

    I doubt that you need a transformer rated more than 1000 watts.
    First you must determine the power that the new transformer is going
    to handle.
    There are many surplus transformers available, and the chances are
    good that you can find one with a similar rating, which would mean that
    you would not have to make your own winding form.
    For E-I laminations, the total cross-sectional area = square root of
    the power Times 0.290 .
    If you only measure the center cross-section area, then double that
    for the total.
    And for cost, it pays to shop around; wierd voltage transformers at
    times go for far less than standard voltages, as nobody can use the
    wierdos.
    Grab one and plunk it downatthe cash register and ask how much for
    this hunk of metal.
    If too much, leave it there and walk away...you may be called back and
    given a better price.
    Add in other stuff, maybe even really junky crap and call it a pile of
    metal..
     
  10. Kevin Weddle

    Kevin Weddle Guest

    There exists a chart for the power flux density. I have found that a
    few square inches of cross-sectional area should cover most
    applications. Also, I have found out that the core is square in shape
    and the magnet wire can be wrapped around it. I had a different idea
    for the electrical characteristics too. I am using the value of the
    inductive reactance rather than the number of turns for my
    calculations.
     
  11. Robert Baer

    Robert Baer Guest

    I have never seen inductive reactance used with the dwesign of (sine
    wave) transformers.
    There are equations relating cross-sectional area, power ratine and
    turns per volt to each other, given the core (material and shape) and
    frequency.
    I gave one part of that recently; i have used the formulas from a
    booklet printed in the mid 1940s many times and never had to re-do any
    of the hundreds of hand-wound power transformers (from 5 watts to 1000
    watts at 50-60Hz).
    The formulas do not mention flux density, but (obviously) the
    relationships are based on the flux density (for the silicon steel used
    then - but still work well for the more modern alloys that are more
    efficent).
     
  12. Kevin Weddle

    Kevin Weddle Guest

    You know that there is a formula for transformers incorporating
    inductance. I don't have my book on it. This is, however, an
    autotransformer. This means that it will obey the laws of the voltage
    dividing. I would suspect that an ordinary transformer would be the
    same. The number of turns is just not real enough to calculate the
    voltage.
     
  13. Robert Baer

    Robert Baer Guest

    Incorrect.
    Knowing the core area (as i mentioned) and use of a simple formula
    will enable one to calculate TURNS PER VOLT.
     
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