PSN-L Email List Message

Subject: Re: The coil has been wound!
From: John Popelish jpopelish@........
Date: Sat, 19 Mar 2005 21:40:43 -0500

> ChrisAtUpw@....... wrote:
> In a message dated 20/03/2005, jpopelish@........ writes:
> > Next step is to add the support rods that hold it up
> > inside the magnet structure and seal the whole thing 
> > in a protective layer of wax.
> Can you not use it dry as wound?

Sure.  But I am afraid it might bump the wire while assembling the
magnet structure or while aligning the pendulum.  This wire is so
fragile that a bump could easily nick or break the wire.

> Try hot candle wax?

That is what the phrase, "protective layer of wax" refers to.  I will
probably dunk the whole thing in a cup of melted paraffin and wipe all
of it off, except for over the coils.  The wire is supposed rated for
140 C.

> It is the linear motion output which is of interest. I use much
> smaller ready wound coils with flat quad magnets. What is the self
> resonant frequency of your coils in their magnet housing?

I haven't tried to predict this but will measure the characteristics
(both electrical resonance of the coil inductance with its and the
cable capacitance and the pendulum resonance after the magnets are
mounted on the pendulum and aligned around the coil.

> I use a small coil winder with a five figure digital counter - a
> magnet and a reed relay. The very large coils that I used to use
> were made by dipping a wood former in hot wax, turning it off in a
> lathe and then adding a paper layer and cloth layers + polyester
> resin. I then turned off the cloth to give a slotted coil with a ~10
> thou substrate. After winding the coil, I warmed the whole thing
> with a hair dryer to soften the wax and slid the coil off the wood
> former. It was a bit fiddly, but satisfactory. The largest coil that
> I wound was about 80,000 turns and took a week to finish. It was
> used to measure paramagnetic susceptability at a low magetic field.

Sounds like a gem.  

Mine took my wife and me about 4 hours to wind, but a half hour was
used up making the splice.  If I was going to make many more, I would
build a much better winder and counter.  This time I had a Rube
Goldberg arrangement of a variable DC supply driving a small DC motor
that turned the coil and a worm drive that turned a gear once avery
100 turns.  I glued a small brass flag under that gear and had that
pass over two wires to complete a circuit with a piezo speaker and a
signal generator.  This gave a ray gun blast once every 100 turns, and
my wife ticked those off for me (320 of them for each half of the
coil).  I had to rig up a ball bearing shaft to hold the 1 pound spool
or the wire would break before moving the spool.  

I had to move the spool 6 feet away from the winder so that the wire
could absorb the bumps and surges without exceeding its elastic
limit.  Found that out with 4 attempts that got to only a few hundred
turns and two that almost made it to 3000 turns.  I found that a wet
or dry vacuum cleaner made a nice sucker gun to pull the wire off
while the spool was run backwards at high speed to prepare for another

I sat and guided the wire back and forth with two fingers (wrapped in
teflon thread tape, at my wife's suggestion, because the friction of a
finger tip slowed the winding and added more tension to the wire),
using a bright reflection off the top of the build to see whether
things were flat and even or not.  An automatic lay down mechanism
would have been nice.  But I am satisfied that I broke that red hair
only once in 4 miles.

John Popelish

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