# Re: double wound secondary (fwd)

```---------- Forwarded message ----------
Date: Sun, 30 Sep 2007 11:06:50 -0300
From: Antonio Carlos M. de Queiroz <acmdq@xxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: double wound secondary (fwd)

Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Sat, 29 Sep 2007 18:24:54 -0400
> From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
> To: tesla@xxxxxxxxxx
> Subject: double wound secondary
>
>
> Hey everybody,
>      I know, this topic has been covered an awful lot in the archives, I
> looked; but there seems to be some disagreement, weather it is good or
> bad.  It seems lately, everybody now thinks it is not such a bad idea, as
> it decreases the resistance, therefore increasing output.  But, from what
> I know of formulas and such, two inductors (since a coil is essentially an
> inductor) in parallel decreases the inductance, which should decrease
> voltage out?  Does this situation not apply with a transformer, or does
> the resistance decrease make that much of a difference to make up for it?
> Or, does nobody actually know why it works so well?  Just curious (and
> considering double winding my 6-in secondary). Scott Bogard.
>
> _________________________________________________________________
Two coupled inductors in parallel, with bifilar winding and high coupling
(M=sqrt(L1*L2)), act as a single inductor with L=L1=L2=M. The proof is
easy.
It remains to be seen if the loss is smaller than when using a single wire
with the same area of the two wires used in the bifilar winding.
You can probably use a simulator as Javatc, that calculates wire losses,
considering a single coil with the total number of turns with the two wires,
and then divide the resulting resistance by 4 to obtain the resistance of
the bifilar coil. Compare then with what happens with a wire with doubled
area and single winding. In principle, I would expect similar results, or
advantage for the single wire winding because there would be space between
the turns, reducing the proximity effect, if the winding length is kept.
Note that using the same winding length you can use a wire with twice the
diameter, and so four times the area. The losses must be smaller in this
case.

Antonio Carlos M. de Queiroz

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