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Experimenting with Magnetic Components - Calculate your own Inductor

jancumps

A little bonus blog for the Experimenting with Magnetic Components contest: check calculations.

 

 

I want to make a toroidal inductor, with this NiZn ferrite core:

Laird 28B0375-400 ferrite cylindrical core, 81 ohm, 4.83 mm length, 5.08 mm inner diameter, 9.53 mm outer diameter

The inductor should be 60 µH.

 

 

I'm using an online calculator to get the right number of windings.

L is given. d is an attribute of the enameled wire you're using.

 

Most info (the green values) comes from the core's datasheet.

The µ comes from another document of Laird, their catalog of ferrite cores.

 

When calculating, the expected number of turns is 12:

 

I made this 12 windings inductor:

 

Result:

At 10 kHz, the meter reports 60 µH, at 100 kHz it's 57 µH

 

 

Close to the requested value.

 

If you're looking for the formulas: https://coil32.net/ferrite-toroid-core.html

 

 

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Anonymous
  • in reply to javagoza

    Exactly as Jan says, just wind a few turns, ideally fairly separated evenly, and then measure : ) Then, knowing the dimensions, you can compare with typical types. If the inductance is very low for the core, then it could be iron powder instead of ferrite, so that narrows it down slightly. Also, if you know what topology and operating frequency it came from, that might help too.

    If the core is the very unusual colour of brown/pink-ish, then thats a trick one - it is neither ferrite nor iron powder : ) but instead an almost benign material. It's used just to have a shape to wind on, and it is (almost) effectively an air core.

  • I got the "chopstick technique" to wind toroid inductors from w2aew:

     

  • in reply to javagoza

      wrote:

    ...Do you know if there is any way to determine what type of ferrite you are using?

    I have a lot of ferrite cores salvaged from devices I pick up on the street, I can't resist

    I know the core type because I ordered it at element14 - it was in one of my project14 baskets.

     

    One way of finding the µ value is to wind (say) 10 or 20 windings on a core and measure the inductance.

    Because you can measure the other values with a caliper, the only remaining parameter is the µ.

    You could use the calculator I used. Set the parameters you know or can measure, then play with the µ until the inductance and winding count matches your design.

    Then look up on the internet what particular Ferrite composition the µ value corresponds to.

  • in reply to javagoza

    I remember doing an experiment similar to this to calculate relative magnetic permeability in one of the electromagnetics labs many years ago:

     

    Observations of Magnetic Permeability of Different Materials – Science Projects

  • Really cool, Jan. Thanks.

    Do you know if there is any way to determine what type of ferrite you are using?

    I have a lot of ferrite cores salvaged from devices I pick up on the street, I can't resist