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Thread: Identifying Toroidal Cores

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  1. #1

    Question Identifying Toroidal Cores

    I need to wind some toroids for a project that I'm working on and have a few cores laying around.
    Is there any way to identify what the ferrite mix is (ie. 43, 63, etc)?

  2. #2
    Join Date
    Jul 2008
    Location
    Richmond, VA
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    121

    Default

    Not easily, no. About the best you can do is wind a known number of turns on it and accurately measure the inductance. That will get you in the ballpark. If you can measure the inductance across a range of excitation frequencies, so much the better.

  3. #3

    Default

    Quote Originally Posted by KE7AQL View Post
    I need to wind some toroids for a project that I'm working on and have a few cores laying around.
    Is there any way to identify what the ferrite mix is (ie. 43, 63, etc)?
    ::Cores are often color coded to help you identify the mix; unfortunately, many aren't and even with those that are, you'd have to know the manufacturer of the core to trace back exactly what the color means.

    When I "buy" cores (thankfully, they're pretty cheap!) I buy them according to the mix, diameter and thickness and once I get them I always "color code" them myself to remind me later what the heck I have. I use small dots of colored paint. Mix 43 would be yellow-orange, two dots side by side. Mix 75 would be violet-green, two dots side by side, etc. That way, even many years later, I know what I have.

    WB2WIK/6

  4. #4
    Join Date
    Nov 2005
    Location
    New Jersey
    Posts
    3,236

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    A few years ago, I read a web page that explained how to the identify ferrite mix with a MFJ antenna analyzer. Of course I didn't bookmark it. When I bought an analyzer, I wanted to ID the ferrites in my junk box, and now I can't find the web site.

    Not helpful, I know. But maybe someone out there knows of that web page and can provide a link.
    73, Ron KR2D

  5. #5

    Default

    Quote Originally Posted by n2jso View Post
    A few years ago, I read a web page that explained how to the identify ferrite mix with a MFJ antenna analyzer. Of course I didn't bookmark it. When I bought an analyzer, I wanted to ID the ferrites in my junk box, and now I can't find the web site.

    Not helpful, I know. But maybe someone out there knows of that web page and can provide a link.
    Here ya go, from my old stomping grounds.

    http://www.w8pgw.org/node/303

  6. #6
    Join Date
    Dec 2004
    Location
    Shropshire, UK, SY10. Locator IO82LS
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    673

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    http://www.alan.melia.btinternet.co.uk/toroids.htm

    Have a look at this site. It is important to distinguish between iron-dust and ferrite cores, if you're using any kind of power the ferrite will probably saturate easily, produce non-linearity and harmonics, become hot and even disintegrate.

    Typical manufacturers are Amidon, Ferroxcube, Fair Rite and Micrometals. Amidon use colour codes for their dust toroids and the same code is emulated by some lesser manufacturers. In the case of unmarked, colourless toroids, as contributors have already said, try a few turns at various frequencies and see what happens. Bear in mind that some materials are deliberately lossy and designed for EMC reduction, still quite useful though on power leads for that purpose.

  7. #7

    Default

    Once you get a core of known mix, use the MFJ unit, measure it and record what found for future reference. The color coding is good too.

    I have had good results ID'ng cores by measuring their physical dimensions with a caliper and then using a low freq LC bridge (the common 1 kHz types, not sure if the cheap multimeter types would be of any use) with some turns applied to the core, measure the inductance and calculate the AsubL (inductance factor) (from the number of turns and inductance measured). Then go to the catalogs and match the AsubL you calculated against the core size you measured. The initial perms are determined at low freqs so using 1 KHz works very well.

    73,
    Pete

  8. #8
    Join Date
    Feb 2006
    Location
    San Leanna, Texas
    Posts
    107

    Default

    Am I correct in assuming that the ones i have that are magnetic are powdered iron and the non-magnetic ones ferrite?

  9. #9
    Join Date
    Mar 2007
    Location
    Christchurch, New Zealand
    Posts
    737

    Default non magnetic toroids

    No.

    Ferrites, and iron powder are both ferromagnetic.

    Non-magnetic toroids might be "grade 0", made of phenolic, to be used as a former when you need a toroidal coil with a core mu of 0.

  10. Default

    I've been looking through things before I throw them away and taking the cores and a few other odd parts here and there and storing them.

    I have a whole bin full of 'em that I really want to identify.

    Of course, purchasing them from Diz (The Toroid King) also works.....

    I also picked up the little kit from "QRPMe". Rex sells a plastic handle that is wicked nice for when you have to wind them small suckers. If I ever lose or break this thing.... it will be a sad day. Makes winding them a whole lot easier.

    Jonathan
    Wow, disappear for a couple years and you find how dated a signature can be!


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