Inductor Advice

Discussion in 'General Electronics Chat' started by R!f@@, Jul 24, 2014.

  1. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    I am meddling with a CRT display Controller.

    An inductor used in a 12V to 40V boost controller is burned.
    I managed to break the ferrite core. And yet struggling to find proper gauge wire for it.

    Question is will the core be OK if I glued it?

    Does the size of the wire gauge is critical ?

    Can I use another inductor ?
    The later one I think inductance is important, right ?
     
  2. MrChips

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    Oct 2, 2009
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    No, it wouldn't be same if you glued it.
    The number of turns is more important than the wire gauge. Make sure the wire gauge can handle the current.

    A photo might help.
    Also make and model of the CRT or what part of the circuit is the inductor?
     
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  3. R!f@@

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    So I need a good core eh !

    It's part of a crane. The CRT display shows all the sensor gauges they say. I checked and the CRT uses 40V to power up. The controller uses a boost supply to create the 40V needed. The controller is separate from the CRT.

    Do you still need a picture ?

    Turns is 74 or 75
     
    Last edited: Jul 24, 2014
  4. ronv

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    There may be a shorted FET to go with the inductor.
     
  5. R!f@@

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    FET is OK. I always check all the power components.
    Here is a photo of the inductor.

    Why is there a gap in the center.
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Do I see cracks in the core?

    [​IMG]

    Bertus
     
  7. R!f@@

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    That's the points Bertus.

    What are my options?
     
  8. bertus

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    Hello,

    If there are cracks, there will be airgaps, that will change the property of the core.

    Bertus
     
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  9. R!f@@

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    Would a slightly bigger core do ?
    or what about a toroid ?
     
  10. praondevou

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    Ideally, yes I would not reuse this core. However, there are also airgaps on the two outer branches of the E-core.
    Since there are different core materials I would prefer to reuse it instead of using an unknown core material of different size. I would glue it together minimizing the resulting air gap of the crack.

    The wire gauge should be approximately the same , it was chosen for a certain current.

    If you want to replace the inductor as a whole you would need to know the inductance.

    I hope you counted the turns before disassembling the coil??

    What's the controller chip? Does it have current limiting of some sort?
     
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  11. wayneh

    Expert

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    You can likely buy what you need IF you can specify it. Or build it, if that's the last resort. But either way you need to know the specs of what's needed; inductance, frequency, current. Pretty tough to guess those just by visual inspection, although the core material and shape is a hint about frequency and function.
     
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  12. debe

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    Sep 21, 2010
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    I salvage SMPS transformers from old TV VCRs & computer powersuplies for rewinding for 12V SMPS. I use an old microwave to cook the T/F to soften the glue holding them together. May take several 2minute goes to soften the glue, have a mug of water in the oven aswell. This is hard on the microwave, but I have plenty of salvaged magnetrons to use up. Ive probably dismantled 30 transformers before the magnetron died. I find most of these SMPS seem to run on a fairly similar frequency. You will be surprised at what you can getaway with when there are no easy options.
     
    Last edited: Jul 24, 2014
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  13. THE_RB

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    I think given the extreme size of that centre air-gap, the tiny difference from glueing the cracks on the core won't make that much difference.

    Don't put glue IN the crack, hold or clamp it together dry first (so there is nothing in the crack) then apply an epoxy glue to the outside. That will reduce the chance of making the crack have a "gap".

    I would just glue it, add the 75 turns and see how it goes. You'd probably have your answer by now. :)
     
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  14. wayneh

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    In my experience, super glue on a non-porous surface like this, with a light clamp applied, gives a VERY thin layer of adhesive. And a very strong bond, although I'm not sure about heat stability.

    The effect of an air gap is proportional to its size, so I agree with RB - it's worth a try.
     
    Last edited: Jul 25, 2014
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  15. R!f@@

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    I got the wire today.
    Let's see what I can do.
     
  16. R!f@@

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    I got the wire. They measure 0.8mm in diameter. Same size wire originally used.
    I got the wire from a passive speaker network.

    I wound the bobbin as I recall the way I unwound it ( I think ).
    Wound to 74 Turn.

    Crappy cam for closeup...sorry.

    [​IMG]

    Soldered it and checked. The Output showed a whopping 60V. EGAD !!! :eek:

    Here is the picture of that area

    [​IMG]

    The IC data is attached.

    There is a VR below the smoothing cap next to the blue cap. It is labelled 40V.

    I am showing some additional pictures of the Monitor.
    [​IMG]

    [​IMG]


    Questions.

    Will the turn direction effect the Voltage?
    Do I need to reduce the turns to reduce voltage or use the VR ?
    Is the cores air gap creating a higher voltage?

    I used a cable tie to hold the core in place for now.
     
    Last edited: Jul 25, 2014
  17. ian field

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    With a core gap that big, the cracks probably aren't going to make a lot of difference.
     
  18. debe

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    I would see what VR does first, but suspect you may have to reduce the number of turns.
     
  19. praondevou

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    On an inductor with a single coil the winding direction won't make a difference.

    An additional air gap would lower the inductance (with the same number of turns). I don't know why that would cause the voltage to be so much higher. The IC has a voltage feedback loop and a current limit. Try to find out where the feedback loop is. Maybe there is something wrong in that circuit too.
     
  20. THE_RB

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    Possibly dried out electro caps in the feedback loop. That often causes the regulated voltage to go high.
     
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