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Secondary with thin wire
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From: Antonio Carlos M. de Queiroz [SMTP:acmq-at-compuland-dot-com.br]
Sent: Friday, February 20, 1998 12:27 AM
To: Tesla List
Subject: Re: Secondary with thin wire
Malcolm, Bert, all:
> I would expect the Q to come in at no more than 150 with that wire
> and probably less. Skin and proximity effects mean a very great deal
> when it comes to quality. I have noted the odd experience with
> extreme experiments in the past, one of which should be in the
> archives from last year. The coil was literally a throwaway.
I am afraid that you are right. I wound the coil today anyway. I used
an adaptation in my lathe to wind the coil, but had to turn the lathe
by hand, because with power I didn't have the necessary control to avoid
overlaps and spaces. Otherwise, it was no problem to use the thin wire.
The coil ended with 1152 turns covering 12.6" of the 3.5" PVC tube.
Before varnishing the coil, I took some measurements. It shows an
inductance of 33 mH and a DC resistance of 142 Ohms (that wire was a bit
thicker than #32). I found no sure way to measure the self-resonance
frequency with the instruments that I have at home. The theoretical
value is 402 kHz. I saw clear signs of the series resistance increasing
dramatically with frequency, apparently reaching 400 Ohms at 50 kHz and
1600 Ohms at 100 kHz (Q=42!) (I have to verify this with better instruments).
>For a small coil, the fine wire should work quite well! The only problem
>I'd have is trying to see the blasted stuff to close-wind it! I'd still
>coat the tube, since it will otherwise be a source of additional loss
>that's easily preventable at this stage.
Just a question of adjusting the wire feed in the winding machine to be
0.5 mm ahead of the coil end and pressing the wire against the previous turns
with a finger nail. Slow, but works. I varnished the tube before winding.
Antonio Carlos M. de Queiroz
mailto:acmq-at-compuland-dot-com.br
http://www.coe.ufrj.br/~acmq