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transformer secondary coupling

Discussion in 'Electronic Design' started by Jamie M, May 5, 2012.

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  1. Jamie M

    Jamie M Guest

    Hi,

    If the secondary of a push-pull ferrite transformer requires significant
    HV clearance from the ferrite core will there still be enough coupling
    for it to operate efficiently assuming the primary is wrapped right
    onto the core? Also is it possible to use a simple ferrite rod as a
    transformer at least somewhat efficiently? For making a secondary with
    high clearance a ferrite rod is a lot easier than using a toroid or
    core. I was thinking of a 1" diameter, 6" long ferrite rod, with a
    single layer secondary 3" diameter and 6" long.

    cheers,
    Jamie
     
  2. Tim Williams

    Tim Williams Guest

    EXACTLY what you're asking. The chart shows EFFECTIVE permeability of
    a rod versus length/diameter ratios [plus rod's permeability, which
    once more than a certain amount has little impact]


    Not exactly; OP is talking about a transformer. Rods make poor transformers
    due to the low inductivity and k. If you put another rod on the other side,
    and some flat pieces to bridge across them and make a connected magnetic
    path, you'll do alright. Such construction looks very much like the average
    flyback transformer core.

    The page you're thinking of may very well be,
    http://myweb.msoe.edu/williamstm/Images/Rod_Core_Pressman_Billings_Morey.png
    I snipped it from a book online by Pressman, Billings and Morey; evidently
    they got it from Micrometals, but I don't recall finding it on their website
    (it's probably buried in their literature somewhere).

    Note also that the inductivity (uH/t^2) varies with position, so that turns
    towards the center have the highest, and turns at the exact end have about
    half the inductivity. These figures are the average over a winding covering
    the entire core. The turns on the end contribute little, so they are often
    omitted (which likewise raises the apparent average), as can be seen in most
    commercial parts. Those turns probably have higher eddy current losses,
    too, further lowering the Q.

    Tim
     
  3. Tim Williams

    Tim Williams Guest

    Has reasonable efficiency if you're doing a resonant converter. You may
    even need to add leakage inductance (assuming you start with a closed loop
    core, like a flyback transformer core). Tricky part is calculating how
    much.

    An open rod makes a terrible transformer, but it can still be usable.
    Before deflection was integrated, the oldest prototype TV sets used a (air
    cored) Tesla coil, or rod-cored construction, to generate HV from an
    oscillator. Later on, the whole deal (HV, focus, deflection, isolated
    filament voltages, auxiliary power and sync signals) was integrated, and the
    flyback transformer we know today has changed little since.

    Tim
     
  4. Jamie M

    Jamie M Guest

    Hi,

    It is probably 50kV and 50mA max DC load.

    cheers,
    Jamie
     
  5. Phil Allison

    Phil Allison Guest

    "Jamie Moron "


    ** You musty be utterly INSANE !!!

    Piss off imbecile.
     
  6. Wimpie

    Wimpie Guest

    El 05-05-12 23:10, Jamie M escribió:
    increasing the diameter of the secundary winding does reduce the
    coupling, but doesn't reduce the sec to sec coupling (for you push
    pull stage).

    Try to figure out whether the prim or sec leakage inductance can be of
    use (for example current limiting).

    You will very likely run into partial discharge and/or corona
    discharge problems.

    What type of circuit are you using (current type or voltage type push
    pull)?

    Regarding the output is at 50kV at 50 mA, or 50kV no load, 50mA short
    circuit?
     
  7. Fred Abse

    Fred Abse Guest


    Sounds like a six inch air gap, and a field that'll couple to anything
    that happens to be passing.
     
  8. Jamie M

    Jamie M Guest

    Hi,

    I don't know the exact required current, 50kV at 50mA is an upper
    rough estimate of the power required.

    cheers,
    Jamie
     
  9. Jasen Betts

    Jasen Betts Guest

    as long as it gets close enough pass through the hole it should work
    as a transformer.
    for very low values of "somewhat"
    look at the high voltage transformers used in old CRT displays,
    it's a square ring with HV winding on one side ans LV on the other.
     
  10. Jamie M

    Jamie M Guest

    Another project worthy of the "Phil Allison seal of approval"
     
  11. Jamie M

    Jamie M Guest

    Hi,

    For a custom ferrite core prototype, how well would packed ferrite
    powder work compared to a solid ferrite core? I guess the inductance
    would be lower due to the larger distributed air gap. I was thinking
    of making a wood or plastic form to hold the ferrite powder and also
    act as the primary to secondary insulation.

    cheers,
    Jamie
     
  12. Phil Allison

    Phil Allison Guest

    "Jon Elson"
    Jamie Moron :
    Phil Allison

    ** That was not my reasoning.

    The OP is clearly a clueless, trolling idiot with a death wish.

    His motives for wanting such a supply are deeply suspicious and he has not
    one tiny clue of the safety or design issues involved in such high voltages.

    Shame here on anyone who assists his lunacy.


    ..... Phil
     
  13. Jamie M

    Jamie M Guest

    Hi Phil,

    I've made a handwound tesla coil before so try to be careful around
    HV. The purpose of the power supply is for an electron beam
    melter/welder.

    cheers,
    Jamie
     
  14. Jamie M

    Jamie M Guest

    Hi,

    Thanks that is interesting and could allow using smaller standard
    ferrite cores instead of a custom large toroid core. How would the
    efficiency of five stacked autotransformers compare to a single
    transformer? I'm not sure about driving the autotransformers though, I
    guess there would need to be extra floating HV supplies to drive them.

    cheers,
    Jamie
     
  15. Phil Allison

    Phil Allison Guest

    Jamie Moron :

    ** Thought you must be one of THOSE NUT CASES !!


    ** You must be utterly INSANE !!!

    Piss off - bloody imbecile !!!!!!!!!!!!!!!!!!
     
  16. Jamie M

    Jamie M Guest


    Hi,

    Thanks, would vacuum tube diodes work at 10kHz+ and 50kV/50mA?

    I am using a vacuum chamber so maybe could put thermionic diodes
    in a full bridge configuration right in it?! :)

    cheers,
    Jamie
     
  17. Fred Abse

    Fred Abse Guest

    Early color TVs used a thermionic diode as a half-wave rectifier with
    half-sine pulses >25kV, about 20 microseconds wide at a PRF of 15.75kHz.
    About a milliamp DC out. Directly heated filament, supplied from a
    well-insulated few turns loosely around a flyback transformer limb.

    I doubt anybody makes them, now. Somebody like Perkin Elmer might still
    make similar diodes to special order, at megabux.

    If you only want a few, swap meets might be the best bet. I can't recall
    the tube number, but I bet Mike (Terrell) can.
     
  18. Tauno Voipio

    Tauno Voipio Guest

    How are you thinking to avoid being grilled by X-rays? Even the tube
    rectifiers generate an appreciable amount of X-rays at those voltage
    and power levels.
     
  19. In the old color TV sets, the diodes were in a metal box, both to keep
    the 30kV away and to contain the X-rays.
     
  20. amdx

    amdx Guest

    How about taking the easy route and get some *old style neon sign
    transformers. I think a standard rating was 15kv at 30ma, so it may take
    series/parallel combo to get to 50kv at 50ma. I'll let you pick the
    rectifiers.
    I ran a couple in series one time and had sparks coming out of the
    ground, yikes!
    Mikek
     
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