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Help modifying inductor from .55mH to .5

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  • Help modifying inductor from .55mH to .5

    I need a .50mH air core inductor for a speaker build and have a .55mH that I am trying to modify instead of buying a new one:

    https://www.parts-express.com/pedocs...al-drawing.pdf

  • #2
    It's not worth the trouble.
    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

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    • #3
      You should measure, but baring that I estimated striping off about 29 inches
      John H

      Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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      • #4
        Originally posted by billfitzmaurice View Post
        It's not worth the trouble.
        We agree. Just use it and you will never hear the difference
        craigk

        " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

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        • #5
          If you can figure out how many wraps per diameter, width, and gauge of the inductor are required to reach your goal you just need to see how many more are required to reach the inductors curent value. That would be the amount you need to unwrap.
          An ex. For simplicity lets say you need 50 wraps to make a .50mh inductor and need 55 wraps to make a .55mh inductor. That would be 5 more wraps to make the .55mh inductor. To reach .50mh you would simply subtract 5 wraps.
          Hope this makes sense. I agree with Bill though. .05mh probably won't make much difference.

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          • #6
            The DCR of a coil is proportional to the length of wire, but Le isn't, so that scenario doesn't work. In any event you'll never hear the difference within +/- 10% from spec.

            www.billfitzmaurice.com
            www.billfitzmaurice.info/forum

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            • #7
              I don't understand how that wouldn't work? I mean if I can figure out how many turns it takes to get my value (say .50mh) with a online calculator and then using the same calculator figure out how many more turns it would take to get the value I have (.55mh) why couldn't I just take away the amount more of turns it took to grt to the value I have? I understand how this wouldn't be the most precise method as it would be hard to accurately measure an existing inductors size and gauge but it should get you close.
              Are you saying I should be using length instead of turns? I have never tried making an inductor so I don't know.

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              • #8
                Originally posted by cpconner View Post
                I need a .50mH air core inductor for a speaker build and have a .55mH that I am trying to modify instead of buying a new one:

                https://www.parts-express.com/pedocs...al-drawing.pdf

                I found an equation for creating new inductors from scratch but haven’t been able to figure out how many times I should unravel the .55mH to reach .5mH. Is it even worth it? Any advice is appreciated!
                Just take off three or four turns.

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                • #9

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                  • #10
                    Originally posted by killa View Post
                    I don't understand how that wouldn't work? I mean if I can figure out how many turns it takes to get my value (say .50mh) with a online calculator and then using the same calculator figure out how many more turns it would take to get the value I have (.55mh) why couldn't I just take away the amount more of turns it took to grt to the value I have? I understand how this wouldn't be the most precise method as it would be hard to accurately measure an existing inductors size and gauge but it should get you close.
                    Are you saying I should be using length instead of turns? I have never tried making an inductor so I don't know.

                    The online calculators are OK but not real world accurate. There is variability in the wire and the wrapping. Because PE specifies the dimension of the coil, we can get close to figuring out the wire length with the calculators, so you can make a estimate of the wire to remove. I don't trust wraps as the mH is not the same value with each turn.
                    John H

                    Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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                    • #11
                      2 turns will be about .06, and you will certainly not hear or measure the difference, I have the same choke and a sencore Z meter,
                      I had to make a .5 from a .8 and counted the turns.
                      Guess xmax's age.

                      My guess: 15. His grammar is passable. His trolling is good.

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                      • #12
                        You could look up the weight for the two sizes and subtract the corresponding wire/weight from the larger, .55 mH coil to get to approx. the same weight as the .50 mH coil.

                        I did it just for fun:

                        The .55 mH (AC20-55) weighs .064 Kg, and the .50 mH (AC20-50) weighs .061 Kg.... that's a .03 Kg difference, and both are 20 ga. and both have 2 zip ties according to the pic, so the main difference should be the magnet wire weight.

                        If you have a small digital scale, you could snip off pieces and throw them on the scale until you arrive at 3 Kg.

                        Could be fun just to try, but I agree, it probably won't matter to anyone's ears.

                        TomZ
                        *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                        *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                        *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

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