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Re: secondary wire length
> Hi all,
>
> I just saw a formula on the web for calculating the length of wire would on
> a secondary coil-form:
>
> [pi]DNH
> L= --------- where,
> 12
>
> L=length of wire in feet
> D=outside diameter of coil form
> N=number of turns per inch
> H=height of coil winding itself
>
> Basically, this formula states that "the circumference of a single turn,
> multiplied by the number of turns, will give the length of the wire."
>
> What I'm thinking is, that a single turn doesn't meet its beginning, but
> overlaps itself, and so, is slightly (*very slightly* in a close-wound coil
> ;) longer than what the calculation yeilds for a single turn.
>
> In a close-wound coil it's probably no big deal, and truthfully, I don't
> calculate wire-length anyway (unless I'm researching).
>
<snip, see original post for lengthy details>
Yes, this has come up before. The first equation (the simplified one) is
indeed a valid approximation for close-wound coils only. In a close-wound
magnet wire secondary, we're talking an error in approximation of less than
3 feet per thousand. In otherwords, over 1000 or so turns on a 12"
secondary, you may be off by roughly the height of the windings, or
approximately 1 turn.
In the real world, there are other sources of error that are equally bad
(probably worse) than the approximations made by this calculation. These
include: Form irregularities, poor winding technique, and differences in
magnet wire turns-per-inch (by brand and insulation build) vs. table t-p-i
values.
For space-wound coils, you are very right that this formula breaks down.
-Adam
adamsmith-at-mediaone-dot-net