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Re: Help!(with wire size) Please!!




From: 	Geoff Schecht[SMTP:geoffs-at-onr-dot-com]
Sent: 	Friday, September 05, 1997 10:29 PM
To: 	Tesla List
Subject: 	Re: Help!(with wire size) Please!!

I use Litz wire quite a bit in switching supply transformers that I design;
I figured that if its good there, it would be cosmic in a Tesla coil. The
whole point behind using it in an SMPS at frequencies between 50kHz and
about 500kHz is to reduce the copper losses by increasing the utilization
of the wire at HF. Interestingly, at SMPS frequencies over 500kHz or so,
Litz starts losing ground due to the high interelement capacitance between
all of those little strands of insulated wire. Litz wire's also frequently
used in IF transformers (at 455kHz), loopstick antennas and those old high
Q, Pi-wound RF chokes that you can't get anymore (i.e. stuff that operates
with mostly sinusoids below 2MHz).

Evidently, a 2x or so unloaded Q inprovement isn't a major consideration in
TC secondaries if the ground impedances are generally that bad. I never
really thought about that aspect. So I guess that the moral is to keep it
simple (and cheap) with good ol' single-stranded magnet wire. Thanks for
saving me the trouble of finding out the hard way.

This information will not, however, please Dr. Litz :( 

Geoff Schecht
> 
> 
> From: 	Edward V. Phillips[SMTP:ed-at-alumni.caltech.edu]
> Sent: 	Thursday, September 04, 1997 12:39 PM
> To: 	tesla-at-pupman-dot-com
> Subject: 	Re: Help!(with wire size) Please!!
> 
> "This discussion brings up the interesting question of skin
effect.....has
> anybody experimented with winding a secondary using Litz wire?"
> 	I have.  Wound a 5-1/4" by 18" coil with litz wire which had
> the same outside diameter as #24 (would have to find the spool to
> remember what the actual litz designation was, but think it had about
> 50 strands).  Performance was definitely poorer than smaller coils
> I have wound with solid wire.  Not sure what conclusion you can reach
> from that, but for TC work I wouldn't go to the expense of litz.
> In my opinion the UNLOADED Q doesn't matter very much , just the
> coupled power during discharge.  I'm sure there are those who
> will disagree......................
> 	For VLF antenna loading coils litz gives about 50% more
> Q than solid wire, in my experience which is limited to a couple
> of coils.  However, in actual use the unloaded Q is unimportant,
> but for a different reason.  The resistance of a typical ground
> circuit is much larger than the effective resistance of the loading
> coil.
> Ed
> 
> 
>