ferrite core coil winding by hand

Discussion in 'The Projects Forum' started by franky_acc, May 6, 2014.

  1. franky_acc

    Thread Starter New Member

    Jan 23, 2014
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    Hi All,
    I hope this is the correct forum to post this.
    I am trying to create a custom inductor. For me to get going, I have a ferrite core that needs wire winded on it. The ferrite core I have is square. I don't know if that makes a difference. I hand winded the coil. I winded a 22 gauge wire around it 20 turns. I was able to get 2 rows of 8 turns and the last row has 4. Between each row, I put duct tape to keep the wires in position. I tried to make the wires in each turn as tight and as close as possible. Once I was done, I tried measuring the inductance using an LCR meter but no luck. The meter shows OL.
    This was my second attempt and I reused the wire. It is okay to reuse the wire?

    Any help would be appreciated.

    Thanks,
    Frank
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,093
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    There is some danger you nicked the insulation and have a shorted coil. Check the DC resistance of your coil against the expected value for the length of wire you used.

    You can also calculate the expected inductance with the Wheeler formula.
     
  3. #12

    Expert

    Nov 30, 2010
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    6,759
    Wrap the core with a piece of thick paper to keep the corners from nicking the wire.
    Masking tape works very well and it's thinner than Duct tape.
     
  4. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Did you measure the inductance with the ferrite core assembled?

    20 turns of wire is not going to have much inductance, many multimeter LCR ranges etc don't go down to small inductors. The meter will just read OL.

    Why did you choose 20 turns? How much inductance did you expect?
     
  5. franky_acc

    Thread Starter New Member

    Jan 23, 2014
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    Hi All,
    Thanks. I now read some inductance. I think the issue was the wires getting shorted at the corners like some of you mentioned.

    @RB: I was just testing to see if I can get inductance. I wasn't trying to reach any particular value.

    Here is another question:
    If I put two windings on a ferrite rod seperated about 1inch to 3 inch, what effects to the 2 windings have on each other if any? If I place another metal on one end of the rod, I expect the inductance to change. But will the further winding have much change compared to the closer one?

    Sorry, I'm a noob on inductors.
     
  6. wayneh

    Expert

    Sep 9, 2010
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    If the other coil has no load on it, I don't believe it will have much impact on the first coil. An EMF will be generated in the 2nd coil by current flowing in the 1st, but no current will move in the 2nd and therefore it will not generate a back-wmf.

    No offense, but why are you playing with inductors before studying how they work? You must have a plan to use one?
     
  7. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Are you using enameled wire?
     
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    What is the "square core"?

    Maybe it is not an inductor core but a lossy core, designed for suppression? People pull these from PSUs or PCs and try to wind inductors on them, which don't work very well.
     
  9. franky_acc

    Thread Starter New Member

    Jan 23, 2014
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    Hi Wayneh,
    Both will be attached to a different load/circuit. I know very basic of how inductors work. But beyond that I don't know? Where can I find more info?
    Yes, I do plan to use one.
    I did read some of the inductor material on this site but again they are basic and don't answer my question. Maybe I overlooked something?
    Some questions are when putting another metal to the top of the core the Voltage will change. Keeping the same uH on a core how can I vary the voltage change (stronger or weaker) when placing a metal infront of the core? Will having more rows or longer/shorter core have variability in the change in voltage? Will the shape of the core have affect (i.e. cylindrical or rectangular or custom shape)?
     
  10. franky_acc

    Thread Starter New Member

    Jan 23, 2014
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    It is more rectangular.
     
  11. wayneh

    Expert

    Sep 9, 2010
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    Coil geometry affects inductance. Common shapes have been studied in detail and you can find models to help predict inductance with a given coil design.

    Voltage across an inductor depends on the circuit it is in and what you're doing with it.
     
  12. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    A photo would be good! :)

    The point I was making is that some people take the bare suppression ferrite cores out of old PSUs and try to wind coils on them, but they don't make good inductors.

    We still don't know anything about your core.
     
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