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Re: [TCML] VTTC geometries, opinions needed

John,
Thanks for this info as it applies to me as well (good timing). I was sort of planning on winding square #8 magnet wire on the acrylic itself. Sounds like a potential problem depending on heat and something I can now divert around. 

Thanks,
Bart

Dr. John W. Gudenas wrote:

Jim
You are going to have a huge current in your primary. With my dual 833A VTTC and a 12awg primary that was initially on a .125 acrylic form, I developed a problem. I melted the primary acrylic form. Now, I did have long runs of 5 minutes or longer while I took a lot of discharge pictures. Just be aware that many acrylics have a very low melting temperature and your primary can get hot. Obviously heavier gauge wire will not get as hot, but it really wasn't "that" hot. The acrylic just melted easy.
I did not run staccato but the 60 Hz continuous duty cycle and this certainly will cause greater heat. I finally had a high temp. phenolic form with a .5" wall fabricated for my primary to accommodate my long runs and duty cycle.
I don't know what type of acrylic you have, but just be aware it can have a very low melting point and your primary can get hot. I really don't know if this is a problem for you, but it can't hurt to keep it in mind. 
John


John W. Gudenas, Ph.D.
Professor of Computer Science


On Sep 7, 2009, at 2:12 AM, Jim Mora wrote:


Hello Coilers,

I am planning a quad 833C @ 4KW and have most of the goodies now (I have
been rat holing for several years). For the secondary former I have a 36" .125" wall 6 inch acrylic tube. I want to wind it with 32 inches of # 21awg 200c wire. That amounts to 755 turns at 23.6 turns per inch. The coil should 
have a self resonance of 367.35hz. For a top load and more for shielding
there will be a 7" .25" (rounded edge) plate which gives a total resonance 328khz using -20% with Javatc 9.1. Is that an error? I want to stay near the 
coveted 350khz resonance point.
I have a few concerns: is 755 turns enough? I chose the wire to keep Fo up 
there and still have some coil height.

The primary will be an eight inch acrylic .125 tube with a sliding grid
feedback coil. The secondary (the unwound part) will go through the deck to 
be able to adjust the coupling on s screw of some type.
I am under the impression the primary to secondary coupling should be close 
to k=.22 what is the max?
There will be 1" vertical HDPE wind standoffs around the primary former and the winding will be 3/16 soft copper tubing spaced .2". So the primary is 
actually 10". The feed back coil will be above the primary and be 8" in
diameter.
I plan to use a total of .004uf mica cap array that gives about 15 turns of the primary. This gives a mutual inductance of about 220 and an inductance 
of ~59uh.
The primary will be cool if it doesn't are over (which I think is unlikely) 
as it can be tapped the classic way.

Any concerns or critics welcome. I will start the project this winter.
Dr Spark, you are using a 2awg primary, yes? That is counter intuitive to me 
as I think we want higher impedances to match the high impedances of the
tubes. What am I missing there? Having (4) in parallel surely helps this.
My test transformer can deliver 10KVA at various voltages with a target FW @ 
4500v but weighs in about 200lbs. Good for setup and testing though!

Thanks
Jim Mora

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