# Determining number of turns of a coil?

• posted

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?

• posted

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.

• posted

plastic

number

not

way

the

what

varnish?

stuff.

I forgot to say this coil has a burnt/sputtered patch

• posted

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?

• posted

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.

• posted

with distortion of the maths though

• posted

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

• posted

This is what makes trying to help people so frustrating. If the coil is open or shorted and precludes normal diagnostic measures, why not just say so?

Burnt/sputtered is useless info. Sure, we can all guess what that means, but it's better if you just say what you mean in terms relevant to the solution.

If you wanna rewind the coil, just say so. It's not rocket science. If you know the diameter of the wire and the width of the winding, you know the number of turns per layer. If you know the height of the winding, you can calculate the number of layers. Multiply the two.

Now comes the unknown part. Is there anything between the layers? If you have precision winding equipment, can you increase the number of layers by shifting each layer? I'm sure there's math to determine this. I'd just draw some circles on paper and measure the ratio when they're closest packed. If you don't have precision winding equipment, you probably can't get nearly as many turns as the calculations suggest.

If you wanna know, cut off the winding and make some actual measurements.

If it's a rely, you'll probably find that filling up the space works.

If it's some other problem, try being less abstruse.

I was gonna say, "sorry about the rant"...but I'd do it again... so sorry isn't the right word.

• posted

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.
• posted

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".

• posted

table

width

p

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.

• posted

of

to

(layers

of

"pancake".

enough.

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.

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Wait, His boss said 'calculate' the volume, not 'measure' the volume, nor 'find' the volume. The employee was doing as asked. Why ridicule him? Or, is the original anecdote contain a misquote?

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?

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.

• posted

number

not

the

what

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)

• posted

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.

• posted

factor" for 0.08mm (+/- .005mm ) winding on a relay coil.

If you have a dead unknown coil, easiest is to remove the wire (unwind some, cut if you have to) and (1) find its gauge with ohmmeter or microscope-and-ruler, (2) weigh the copper after it's removed.

Get new wire, same gage and weight, and wind all of it onto the form.

• posted

number

not

the

what

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.

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I don't know the 'exact' definition of SF, but I always thought it meant the ratio of copper cross sectional area vs available window cross sectional area

I drew out a round wire WITH insulation and stacked it into a cross sectional area and quite frankly was shocked at how poorly that works out. At least that result is the BEST that can be done, since it relates to the physical geometry of laying wires down. One other thing to watch for is the insulation thikcness. For enaled wire there is single, double, and tirple coating.

• posted

table

width

p

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)

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