Messing up voice coil winding

Discussion in 'General Electronics Chat' started by R!f@@, Apr 24, 2010.

  1. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    Hi there my fellow geeks.
    I have a little predicament. You see the pics, one show a metallic drum, another with kapton around it and one with a finished voice coil.
    But I did not wind it....heee heee heeee. :D
    I am just showing them so you guys can get the picture on what I am talking about.

    I have been winding these and always had one hell of a time with it.
    The wire is wound on a kapton bobbin. These voice coils are 300W RMS power handling 15" woofer. These things have been with me for like months, the only seller here sells them at USD200.00 per basket :eek:.
    See the price tag of these suckers. There is no way I am going to spend 800 bucks to get 4 of these fixed.
    So naturally I always wind them and every time I have to make a new drum to get the right diameter.
    I am fixing these for the second time, at first I bought new voice coils on ebay and they ended up unwinded inside the air gap,. and the cone was rock solid.:eek:.
    This time I ain't buying but I had to buy the cone and the spiders.
    I have kapton film and just recently got the wires.
    Since repairing a woofer for the second time will damage the cone and the rest too much, i have to rebuild the whole thing.
    And still I got everything half the price.

    Now like I said, I am going to have a hard time with this, so I am asking you guys to do this for me.....Kidding :D
    See the Pic with the voice coil (ready made) next to the drum.
    I like to know how I can yank the voice coil after winding it without denting it.
    After the winding is complete the kapton will be pretty tight and I cannot remove it without damaging it and to remove it I have to wind loosely, which is not a good thing for these woofers.
    I cannot seem to figure out a way to wind it tightly and remove the voice coil easily. The drum is only 0.5mm larger than the magnet so I have to wind it tightly, and there will be two layers of coil, so loose winding cannot be used.
    Before what I do is use paper between the kapton and drum, after finishing I can slide the paper out but this too works half the time and the drum should be smaller than the magnet diameter.
    And making a bobbin is really hard thing here and expensive. I have to go to a machine shop to lath it.
    So guys, tell me how I can accomplish this thing. How should the winding drum be made so I can take the coil with just two fingers.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Can you take a section of inner tube and use it to put opposing pressure inside the winding form? The fixture to do that and allow lathe winding crosses my eyes, but you could release the air pressure and allow the coil to slide off the form.

    If you were in Alaska, you could just use ice and melt it free.
     
  3. retched

    AAC Fanatic!

    Dec 5, 2009
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    Or wrap some film around the winding drum and wind on the film. Then slide the finished coil onto the next one by pulling the film not the coil.

    Like moving a refrigerator with a throw rug. :)

    I like the temperature change Idea.. the drum would stay cold, and you could heat the coil with a 9v batt to heat a little then slide it off.
     
  4. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    Sorry guys. Temperature won't be enuf. these are not bearing on a shaft.
    But retched's idea will seem to work, I wonder why I did not thought of that.
    Use an extra layer of kapton inside but half way in will do the trick nicely, I can yank it any way I want and yet I won't be touching the coil.
    Thanks fella's.
    I'll post the result or rather a tut on remaking a woofer. :D
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Kapton insulation itself may be the reason why your woofers are failing.

    The US Navy banned the use of Kapton insulation in aircraft in the mid-1980's, after discovering some very unpleasant properties of the material.

    If you damage the Kapton insulation in any way (a minor scratch on the surface that you wouldn't be able to see) it will tend to separate (break), and resume it's as-manufactured shape. Usually, this is not the desired shape. Once the integrity of the Kapton insulation has been breached, it is subject to flashover and carbon tracking. Static electricity can be enough to cause the 1st flashover. After that, you can wind up with catastrophic failure - even a fire. Fires in aircraft = very bad news.

    Manufacturers of civilian aircraft are still using Kapton insulation. There was an incident in a Boeing 747 regarding the fuel tank catching on fire. It was later speculated that the Kapton insulation used was a likely cause of the failure.

    I don't know offhand what else to suggest as a replacement for Kapton. However, you should know that if you make even the slightest scratch in the Kapton tape, you will wind up having dead woofers in another few months.
     
  6. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    But Sgt, the original voice coil was also made of kapton, that is why I bought a reel of kapton.
    I have seen metal bobbin though.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Maybe that is why you are repairing them for the 2nd time.

    How many more times do you want to repair them?

    If you use corona dope, you won't have that problem again.
     
  8. R!f@@

    Thread Starter AAC Fanatic!

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    corona dope
    hmmmmmmmmmm!

    does this have glue properties, or is it just an insulator.
    I want a high strength adhesive that can hold the coil in place
     
    Last edited: Apr 25, 2010
  9. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    I am repairing for the second time cause I used crappy voice coils.
    This time it will done by hand, and got to find some high strength bonding material that could withstand the abuse of Bass pumping at high power
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    Corona dope is a high-voltage moderately high-temp insulation material that you mix up and paint on with a brush.

    Never tried using it as an adhesive. Don't know why it wouldn't work though.
     
  11. rjenkins

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    Nov 6, 2005
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  12. retched

    AAC Fanatic!

    Dec 5, 2009
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    Duh, because im smrtr than U.

    BTW- the new keyboard works great -- thanks Sarge. ;)
     
  13. R!f@@

    Thread Starter AAC Fanatic!

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    aaaaaH! :cool:

    Smarty pants....:D
     
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