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[TCML] Sec design trade-offs and considerations





Chris raises an interesting point here. This is much like a catch-22 analogy.

A lower inductance would mean faster charging of the magnetic field, however, max output potential favors a higher inductance and large dia sec coilform.

Also, the IGBTs used in solid state coils like to switch at or below 50 kHz which usually again requires larger inductance and either large dia coilform or lots of sec turns. Too many turns and you begin to run into the tradeoff points between getting large inductance vs. too much resistance.

Some experimenters use as many as 2,600 turns on the sec to keep the switching freq low while other experimenters prefer to use large dia sec coilforms. With solid state coil designs, I prefer around 1,800 sec turns and the largest dia. sec coilform possible. The balance here, of course, it the size of the sec toroid which increases with large dia sec coilforms --- and the cost rises with the larger toroid sizes.

I use k value of 0.17 to 0.18 for most designs. You can do a lot of "what-ifs" in JAVATC to check the coupling values for different inner and outer pri coil radii.

Certainly a lot of trade-offs to consider for optimum performance at reasonable cost.

Bart Anderson's JAVATC program enables experimenters to try many different configurations to achieve desired performance, and then a cost analysis is conducted for each different configuration.

My personal preference is to "best guesstimate" the cap size and then use the "auto-tune" feature in JAVATC to determine best pri number of turns to match. In most solid state coils values between 0.6 uF and 1.5 uF are common with pri sizes of around 4 turns. You can use less but then tuning points on the primary become very critical. Use 4-5 turns with a 0.6 to 1.5 uF pri cap and see what JAVATC tells you to use for the primary. I like around 1.0 to 1.5 uF with 3.5 to 4.5 turns on the pri tap. Then, I check the calculated JAVATC coeff. of coupling (k value) to see if it is in the 0.17 to 0.18 range. I make inner and outer radii adjustments as necessary to get the k value in this critical range. The idea is to couple as tight as possible but definitely to not "overcouple" and get into the "racing sparks" range --- usually a value of 0.2 or above.

16 inch dia. sec coilform with 34 x 8.5 toroid atop a 24 x 6 inch toroid. These can be spun toroids or, if cost is a major consideration, the good old aluminum tape dryer duct type toroids work fine. Sonotubes coilforms or fiberglass work equally well.

BTW, if anyone is working on a solid state design I have developed some "datasheets" that can be helpful to setup of over design and also a separate datasheet for pri-sec geometry. Filling in these sheets first with dimensions helps transfer the data into JAVATC for the test runs. Contact me off-list if you want them emailed to you. Also, if anyone needs help with JAVATC initial run contact me off-list for assistance.

Many happy sparks,

Dr. Resonance


Resonance Research Corp.
www.resonanceresearch.com


----- Original Message ----- From: <FutureT@xxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Thursday, November 22, 2007 11:39 AM
Subject: Re: [TCML] quench times again



In a message dated 11/22/2007 11:47:26 A.M. US Eastern Standard Time,
list@xxxxxxxxxxxxxxxxxxxxxxxxx writes:

I am also trying to work out, that other than coupling and frequency which
effect the tank "transfer speed" to secondary... can the secondary  itself
become "easier to drive" to make the transfer quicker ?   this is why I
thought that a lower inductance would take less time to  "charge" and the
energy transfer would be quicker than a lower  inductance.... though this
could just be down to a higher  frequency...


cheers,
Chris



Chris,

I'll ignore the arc-to-ground case which is a special case.   Most
folks like to see mostly air streamers I think. The transfer speed to the
secondary is not the problem preventing fast quenching.  The real  problem
is streamer (actually leader) impedance.  If the streamers were  somehow
of a lower impedance, this would drain the energy faster from the secondary.
Low impedance results in a heavier loading effect by the streamers.
If the streamers were of low enough impedance, then there would be no
energy left to go back into the primary and prevent quenching. The effect
of streamer loading reflects back through the system to affect the  quench
time.  In the case of the arc-to-ground, the streamer impedance  becomes
very low, and drains the energy quickly.  If the energy transfers  to the
secondary quickly, but can't
get out quickly via the streamers, then there's a bottle-neck, a  traffic
jam.  It's as if many cars are streaming onto a highway from  various
feeder roads, but up ahead a couple of lanes are shut down for  repair.
Now the traffic backs up.  If the cars speed quickly to that  bottle-neck,
it won't do them a lick of good.  They'll still have to slow down or  stop
until the traffic ahead makes its way through the constriction.   Souping
up the engines of the cars, or reducing the friction of the car's
powertrain, etc. won't help.  The only thing that will help is  to
remove the constriction, to open the lanes of the highway which are
closed for repair.  This opening of the lanes, would be analogous  to
reducing the impedance of the streamers of the TC.

John



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