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RE: AC grill primary



Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 10:57 AM 12/30/2003 -0700, you wrote:
>Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com>
>Re. octagonal vs. circular:  If you enjoy challenges, you could try
>winding it with one hand tied behind your back.  But there is certainly
>no functional advantage to any non-circular shape, and quite likely
>you'll have problems with corona off the corners, and certainly it will
>be a lot more effort to make it look half-way decent.
>
>Re. stranded wire - this is definitely a bad thing.  Unless you have
>true Litz wire, losses in stranded wire are much higher than solid
>conductors.  See my experimental results at
>http://www.laushaus-dot-com/tesla/primary_resistance.htm.  Also, one wants
>the primary conductor to be rigid so that the windings stay in place,
>and a stranded conductor would tend to be a bit floppy.
>
>A 14 or 12 gauge solid primary will work for a 15/60 NST.  The losses
>would be lower if you used copper tubing, but I can't say exactly how
>much that would affect performance.

If you want to wind with smaller gauge wire (to make the mechanical process 
easier), one could wind multiple parallel strands, making a sort of flat 
ribbon.  Say you made a little jig to wind on.  It would be easy to wind, 
say, 4 strands of bare AWG12, along with something suitable as a spacer.

By the way, there are a lot of clever ways to make winding a spiral a LOT 
easier, especially with relatively stiff stuff (like the aforementioned AWG 
6 solid).  Mostly, it relies on having really sturdy forms that can take a 
lot of load when you're winding. this usually means solid wood.

One can buy precut circles of 3/4" plywood and make a very thin spool with 
stiff, sturdy flanges. You stack, say, a 24" (3/4" thick), a 6" (1/4" thick 
- for 1/4" OD tubing)) and a 24" circle(3/4" thick) with a good sized bolt 
through the middle. A hole drilled through one flange, or a slot in the 6" 
spacer, provides a place to anchor the start of the winding.  You can screw 
some 1x2 or 2x2 strips on the outside of the flanges to make it stiffer, or 
to give yourself a handhold.

You can either wind tight, and then expand the coils after dismantling the 
form, or, wind with a spacer. If you're making a bipolar coil, for 
instance, you'll need a pair of primaries, so wind two pieces of tubing 
together.  The spacer needs to be fairly stiff and sturdy (vinyl hose does 
NOT work, for instance.. tried and failed) Nice solid rope might work, as 
would steel cable.