What I learnt this year.

Discussion in 'Electronic Design' started by Syd Rumpo, Jan 9, 2014.

  1. Syd Rumpo

    Syd Rumpo Guest

    Ferrite cores conduct electricity! Ouch! Not brilliantly, but a
    measured 10k or so over a cm or so.

    I've never been much involved in the black arts of coils, but for the
    past half century I've believed/assumed ferrite to be an insulator.
    Don't know why.

    For some reason, the RM12 cores I'm using have the type printed on one
    half of the core only, so mixing up types could happen if you were
    careless. I have been. But it seems that the two types I'm using have
    quite different resistivities, so I can match up the two halves again.

    Cheers
     
    Syd Rumpo, Jan 9, 2014
    #1
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  2. Syd Rumpo

    JW Guest

    I didn't think it conducts either, or at least had a very high resistance.
    <http://www.google.com/url?sa=t&rct=...4ID4Cw&usg=AFQjCNHg99f2du1HUw8liN7kWd1GQlS33g>

    Apparently some are and some aren't. I just grabbed a random core I have
    lying around, and it's resistance is >100 Megohms which is the limit of my
    DMM.
     
    JW, Jan 9, 2014
    #2
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  3. Syd Rumpo

    Bill Sloman Guest

    past half century I've believed/assumed ferrite to be an insulator.
    I've been aware that ferrites were conductive since I first played with them in the late 1960's, and furthermore I knew - from the start - that manganese-zinc ferrites were a lot more conductive - but had higher permeability - than nickel-zinc ferrites.

    The old Mullard ferrite data books were horrible in many respects, but theydid spell this out.
     
    Bill Sloman, Jan 9, 2014
    #3
  4. I've never seen it spelled out, but I knew it was true (didn't know it
    varied that much). Perhaps that's at least partly why some are coated
    with epoxy.


    Best regards,
    Spehro Pefhany
     
    Spehro Pefhany, Jan 9, 2014
    #4
  5. Syd Rumpo

    Guest

    I knew it, but got reminded recently when I got a 32kV tingle
    from touching a supposedly insulated core!

    Cheers,

    James arthur
     
    , Jan 9, 2014
    #5
  6. Syd Rumpo

    Syd Rumpo Guest

    Oh, just meter probes, good enough for a comparison. These are RM12
    cores, so a better way might be to clip them together and use the spring
    clips as terminals.
    ..
    ..
    ..
    No, not really better - I get about 2k between clips on the RM12 N41
    1000nH cores I'm using, and about 7k on an N87 160nH set, but all rather
    sensitive to pressure. Still, a clear difference.

    I guess conductive epoxy would make a good contact, but I'm not *that*
    interested.

    Cheers
     
    Syd Rumpo, Jan 9, 2014
    #6
  7. A four-terminal measurement would eliminate contat resistance from the
    measurement - if you ever wanted to go to that much trouble to get a
    definitive answer.
     
    Adrian Tuddenham, Jan 9, 2014
    #7
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