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EMI CHOKE QUESTION

Discussion in 'Electronic Design' started by Yzordderrex, May 19, 2005.

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  1. Yzordderrex

    Yzordderrex Guest

    I have recently been given responsibility for EMI choke design. The
    company I work for makes motor controls.

    I am looking at a 12amp servo drive (single phase 230v input) that will
    pull about 150 amps peak on the input side when balls to the walls 300%
    output.

    The EMI filter choke is wound like any other single phase unit you
    would see on a toroid. Winding A on one side, and winding B on the
    other side of the ring. Each winding taking up about 160 degrees of
    ring so that there is some voltage creepage distance.

    I have wound a 10 turn tertiary winding on the core that I use to
    measure inductance. I jam my 30v bench supply into the tertiary
    winding an watch the rate of rise of current to measure the inductance.

    When I excite the core with 150 amps not all of the flux is cancelled
    so that the inductance goes to nearly zero. I'm assuming that the
    filter is probably useless at the peaks of the line currents.

    Would I be better off using an insulated wire and wind each coil say
    330 degrees and interleave the coils - bifilar?

    We have gear to measure and I will probably proceed on this path for
    today. Just soliciting your thoughts.

    regards,
    Bob
     
  2. Paul Mathews

    Paul Mathews Guest

    Yes. And, for extreme cases, you can consider using coaxial cable
    instead of individual wires.
    Paul Mathews
     
  3. Yzordderrex

    Yzordderrex Guest

    Ok, thanks Paul.

    I just finished winding a choke bifilar and the inductance stayed
    constant up to 50amps.

    Unfortunately my supply only goes to 50amps. I would like to get
    flavor at 150amps.

    I may look at a Rubadue style wire to wind units.

    regards,
    Bob
     
  4. colin

    colin Guest

    dont forget that although the flux on each side of the toroid cancel
    eachother out so there is no circular flow around the core, they do however
    add up to cuase a net flux across the core, wich if high enough wil cuase
    enough flow through the air to saturate the whole core.

    Colin =^.^=
     
  5. Paul Mathews

    Paul Mathews Guest

    Good point. Cross-winding midway around takes care of that problem.
    Paul Mathews
     
  6. Yzordderrex

    Yzordderrex Guest

    Colin, Paul,

    Seems you two have lost me. Not sure what a net flux across the core
    is, and cross-winding is a term I'm not so familiar with.

    One thing I did realize is that winding bifilar will tend to decrease
    the differential mode inductance - So differential noise components
    might then actually be worse.

    regards,
    bob
     
  7. Yzordderrex

    Yzordderrex Guest

    Colin, Paul,

    Seems you two have lost me. Not sure what a net flux across the core
    is, and cross-winding is a term I'm not so familiar with.

    One thing I did realize is that winding bifilar will tend to decrease
    the differential mode inductance - So differential noise components
    might then actually be worse.

    regards,
    bob
     
  8. Yzordderrex

    Yzordderrex Guest

    Colin, Paul,

    Seems you two have lost me. Not sure what a net flux across the core
    is, and cross-winding is a term I'm not so familiar with.

    One thing I did realize is that winding bifilar will tend to decrease
    the differential mode inductance - So differential noise components
    might then actually be worse.

    regards,
    bob
     
  9. Yzordderrex

    Yzordderrex Guest

    Colin, Paul,

    Seems you two have lost me. Not sure what a net flux across the core
    is, and cross-winding is a term I'm not so familiar with.

    One thing I did realize is that winding bifilar will tend to decrease
    the differential mode inductance - So differential noise components
    might then actually be worse.

    regards,
    bob
     
  10. Paul Mathews

    Paul Mathews Guest

    The differential mode component you mention is just leakage inductance
    between the common mode windings. Most of this flux is 'in the air',
    rather than 'in the core'. If you absolutely must minimize the number
    of components in your design, then it may be worthwhile to depend on
    leakage inductance for DM benefits. However, on the down side, winding
    methods that increase leakage inductance also increase the likelihood
    of imbalances that lead to core saturation. At the point when the core
    saturates, the CM properties of the component pretty much disappear.
    When you place windings around a core, proceeding uniformly in the same
    direction, there is a general flow of current in the direction of those
    windings. For a toroid, this has the unintended effect of one or more
    'turns' effectively following the core and producing a field through
    the core axis rather than within the core material. You can cancel
    this effect by alternating the direction that the turns advance around
    the core. 'Cross-winding' of single-layer toroids involves winding ~
    half way around the core, 'jumping across the core center to the
    opposite side, and winding an equal number of turns advancing in the
    opposite direction around the core. All turns have the same direction
    with respect to the core itself. Some mfgrs of toroidal inductors
    always follow this practice. For a horizontally mounted toroid, it's
    also quite easy to specify 2 windings wound in such a way that they can
    be series connected to achieve the cross-winding effect. If done
    properly, cross-winding also reduces the distributed capacitance of the
    inductor, making it effective at higher frequencies.
    Paul Mathews
     
  11. Terry Given

    Terry Given Guest

    dont use a supply, use a monster cap. Charge the cap up, and "splat" it
    across the choke. Easy to get 1,000A that way :)

    just choose Ecap >> Echoke at Idesired

    Cheers
    Terry
     
  12. JeffM

    JeffM Guest

    [Yzordderrex reposted his response]

    The new beta of Google Groups has a much lower latency than the old
    iteration.

    If you get a Server Error message,
    wait a minute or 2 and refresh the thread page.
    Usually your post has gone thru,
    it's just that the ACK page hasn't come back.

    BTDTGTTS
     
  13. Mark

    Mark Guest

    does your system need common mode or differential filtering (or both)
    to solve the EMI problem?

    Mark
     
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