Connect with us

Determining number of turns of a coil?

Discussion in 'Electronic Repair' started by N_Cook, Aug 19, 2012.

  1. N_Cook

    N_Cook Guest

    Is there an online calculator anywhere ? or failing that what sort of
    "packing factor" for 0.08mm (+/- .005mm ) winding on a relay coil.
    I have a good idea of the weight , subtracting an estimate of the plastic
    former and this would give the length from the density of copper but number
    ot turns ?.
    Impregnated coil so cannot count-off turns
    Rectangular section to coil , on the inside anyway, 14x 16.4mm , 16.8mm
    width, outer layer is curved at "corners" and bulging (from the winding not
    abuse) so more scatterwound than precise regular lay-up .
    Outer dimensions of 21.4mm bulge / 20.3mm , or so, at outer edges one way
    and 23.4/22.2mm , the other, a bit of geometry would give a good idea of the
    volume of this space but what ratio of that volume would be copper and what
    air+varnish, then what sort of weight would be contributed by the varnish?
     
  2. mike

    mike Guest

    Wind more turns. As many as you can fit in your attention span.
    2 is a lot better than 1.
    Measure the inductance of each winding.
    Or apply volts and measure the ratio.
    Accuracy of the result is proportional to the number of
    turns you add and the precision of your measurements.
    Most anything electrical you do will give more accuracy than weighing stuff.

    Curiosity killed the cat...but I gotta ask, "why do you care?"
    Sometimes people ask complicated questions when the solution
    to their problem is very much simpler.
     
  3. N_Cook

    N_Cook Guest

    I forgot to say this coil has a burnt/sputtered patch
     
  4. Simple approach... Find an ohmeter that can read very low resistances with
    high resolution. You can then duplicate the coil by winding a coil with the
    same resistance using the same wire on an identical form.

    Right?
     
  5. mike

    mike Guest

    Yet you still refuse to disclose why you care.
    Is the number of turns really the defining parameter for this winding?

    Cut the winding off the core.
    Take a high res picture of the face of the cut.
    Calculate the area. Count the turns in a smaller area, multiply.
     
  6. N_Cook

    N_Cook Guest

  7. N_Cook

    N_Cook Guest

    The copper filling factor would be the ratio of copper as weighed to the
    weight if that volume was totally filled with copper. The volume is easy
    enough to calculate, but how to get an estimate of the number of turns from
    the filling factor. The length is calculatable from the coil weight,
    ignoring weight of the impregnation
     
  8. As others have pointed out (including myself, on many occasions), this is
    the sort of question or problem that shows up all-too-often in UseNet groups
    (and elsewhere!).

    There's a story (probably apochryphal) that Edison asked a new employee to
    calculate the volume of a light bulb. The young man sat for some time with
    calipers and a slide rule, making little progress. Edison finally
    interrupted his work, poured water into the bulb, then emptied the water
    into a graduate. (The graduate's name is not recorded.)

    On the assumption Mr Cook wants to wind a replacement, why should he not
    simply get a form and wind wire of the appropriate thickness, then //test//
    the coil * to see if it works the way he wants it to? He could have done
    that by now!

    I am a //great// believer in theory. You never //really// understand
    something until you grasp the principles involved. BUT...! There are some
    things you simply go and do, without worrying about theory, because "doing
    it" involves a lot less time and trouble.

    * Not to be confused with Tesla coil.
     
  9. N_Cook

    N_Cook Guest

    Perhaps a bit of integral calculus. In a coil winding manual I have a table
    of wire gauge v the minimum excess advance per turn to avoid upsetting of
    wound layers. Then sum the layers in terms of the number of turns per width
    and this excess , including in a notional paper layer per turn (p), out to
    the outer layer set an average value . Including p being negative (layers
    settling into the gaps of the previous layer) and determine what value of p
    gives the right length of wire to fill that volume, then that gives the
    number of turns. At the first approximation ignoring curvature at the
    "corners".
     
  10. You don't need integral calculus to calculate this, any more than you need
    calculus to determine the number of "layers" in a recording-tape "pancake".
    The approximation assuming the "discreteness" of each layer is good enough.
     
  11. N_Cook

    N_Cook Guest

    Glad to see a contribution pertaining to the thread subject heading ,
    typical Usenet , most of the thread ,so far , is off-beam.

    I doubt the increase in "layer length" of wire per layer goes up lineally
    with each layer but again first approximation could assume so and so simple
    arithmetic series summation should be all that is required. I just measured
    the outer layer "circumference" ie rounded rectangle and not as much
    difference as I thought, 77mm around the centre bulge and 74mm at the edges
    ..

    Hopefully I can now do the maths and then if I mess-up grinding across a
    section of the original coil ,
    so unable to count wire endings, then will at least I will have something to
    go with . I don't know how the impregnation will react to a cutting disk ie
    smearing.
     
  12. N_Cook

    N_Cook Guest

    I found that tables from wire suppliers are a great guideline. But,
    nothing beats having to fight 'stacking factor' on your own.

    I use 0.5 for wrapping 36 Awg enameled wire. I know I should be able
    toget better than 0.7.

    So take the winding area multiply by SF and divide by wire cross
    section area and you'll get very close..

    And, from experience, if there are a few layers, don't count on nice
    neat, high density layering and stacking, doesn't work that way.

    Oh, also watch out for stretching the wire, making it slightly thinner
    and 'appear' to be able to put on more turns, you'vve actually reduced
    the wire size instead.

    ++++

    By stacking factor do you mean the ratio of copper volume to the volume
    occupied by the copper ? ie the last layers always need squahsing into the
    available (calculated) space between former and iron core etc.

    I will try that , also calculation via derivation of a formula for such
    situations , and also try cutting through the coil mass and counting
    directly , hopefully . For future reference as to accuracy of each method
    (in one instance anyway)
     
  13. There's a story (probably apochryphal) that Edison asked
    I might have misquoted it. Edison might have said "find".

    Regardless, one of the points of this anecdote is that you should look for a
    good solution -- not necessarily the solution you were asked for.
     
  14. N_Cook

    N_Cook Guest

    I found that tables from wire suppliers are a great guideline. But,
    nothing beats having to fight 'stacking factor' on your own.

    I use 0.5 for wrapping 36 Awg enameled wire. I know I should be able
    toget better than 0.7.

    So take the winding area multiply by SF and divide by wire cross
    section area and you'll get very close..

    And, from experience, if there are a few layers, don't count on nice
    neat, high density layering and stacking, doesn't work that way.

    Oh, also watch out for stretching the wire, making it slightly thinner
    and 'appear' to be able to put on more turns, you'vve actually reduced
    the wire size instead.



    ++++

    By stacking factor do you mean the ratio of copper volume to the volume
    occupied by the copper ? ie the last layers always need squahsing into the
    available (calculated) space between former and iron core etc.

    Or do you mean 1 is the mathematical theoretical ideal packing of first
    layer n, next n-1, next n etc
    all precisely registered over the previous layer , within the hollows, that
    in itself a fraction of the total volume occupied by the coil , again some
    preciese mathematical value for a given wire gauge.
    Then 0.7 is the real world ratio of copper for a machine wound coil plus
    skilled worker ratio of actual to this ideal.
    Then .5 is the likely ratio value for anyone else doing layup of fine wire
    with hand cranked coil winder.
     
  15. N_Cook

    N_Cook Guest

    My formula uses the assumption that the length per turn increases, layer to
    layer, linearly by 2 wire diameters per "corner" so 8 x .08mm per turn. For
    44SWG .08mm wire I assumed the manual coil winder excess turn advance of 8
    percent. From the weight of wire then the length. Then using my formula ,
    came to 30 layers and a p value of -.013 mm
    That gave 5790 turns

    I disc ground through the coil and because I can weigh to 0.01 gm counted
    off a sample of 952 turns and then ratioed by weight to 6420 turns .
    Perhaps for machine wound coil can drop the 8 percent to 7 percent for 44
    swg to give a better result.

    So now know the inductance as well as the DC impedance (plus a useful
    formula for the future , for 44 swg anyway)
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-