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Re: Windings vs. Diameter - errors

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

At 07:05 PM 6/30/2006, you wrote:
To get my turns estimate, I usually place a piece of paper on the coil and run a pencil over it. This gives a tracing of each turn and makes it easy to place flat on a table in good light with a ruler to count turns per inch, to whatever precision you want. eg 19G wire is .0335 in diameter by my micrometer. Over 2 inches on my 4 inch coil there are 58 turns ie .0345 inches /turn. Gives a wiring percentage of 97% which is "better" than machine wound 19G of 95% by your table.

Neat idea!! I have also put marked tape on coils and taken high res digital photos. Blow them up on the computer in a graphics program to mark off the turns... But easier still just to count them in the first place ;-))

The new little coil measures 17.41mH.

It measures:

985 turns (exact)

2.992 inches in diameter of the form but not with the wire diameter added (#30 at 0.0116 inches in diameter via a new Starrett 436 micrometer.)

11.50? long

That works out to....  r = 1.4989...   16.965mH by Medhurst.

So the wound coil is 2.6% over Medhurst predicted. That is vastly better than I have ever guessed before ;-))

If we assume I made an error in the diameter, it would work out to 3.042 inches which is far inside what I can measure. So I might be seeing the Medhurst formula's error now ;-))

MandK gives 17.06422mH which is only 2% low. But the "other" meter (I don't normally trust it) "matches" that at 17.06mH... So probably all down in the measurement noise errors now... I have "standard" caps somewhere...

But I think "I know the details" for such things now ;-)) Coils that have their turns "packed or not packed" is a big deal.