RE: SSSSSSSSSSSSSSSSSSSSSSTTC Coil questions for Mr. Steve

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Steven Ward" <srward16-at-hotmail-dot-com> 

Okay okay, too many S's in the SSSSTC.  How about we thing of a better 
name?  Like the SWSSHVITTC (Steve Ward Solid State High Voltage Inverter 
Topology Tesla Coil)... ahh, much easier to remember now...maybe not.

Answers (to the best of my abilities) within:


>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: SSSSSSSSSSSSSSSSSSSSSSTTC Coil questions for Mr. Steve
>Date: Fri, 16 Jan 2004 18:03:50 -0700
>
>Original poster: "Mccauley, Daniel H" <daniel.h.mccauley-at-lmco-dot-com>
>
>
>
>Hey Steve,
>
>I was wondering if you had some more information on your
>SSSSSSSSSSSSSSSSSTTC coil.  For example, I'm curious to
>see an overall schematic plus what kind of parts you were using for
>various components within your design.

Okay, when i get some time i will start adding more schematics and things.
Basically for the mosfets im using IXYS80N50 and 48N50s (4 of each per 
inverter bridge thingy).  Yes, its terrifically overrated.  The caps across 
the power rails of each half-bridge section are 5uF at 400VDC rated.  They 
are probably more than needed but i have lots of them.  The ultrafast 
diodes and supply rail diodes are all fairchild 30A 600V stealth diodes (i 
forget the actual part number).  And thats really it for the power stuff.

For the controller im using my same old antenna based feedback design (see 
the SSTC2 page for some details on that).

My gate driver (and what a driver at that!) is pretty overbuilt.  Basically 
i buffer the outputs of my controller board through a 74hc14 hex inverter.
That sends an inverted and non-inverted output to a pair of TC4420s IIRC.
That drives a mini gate drive transformer.  This in turn drives 2 IRF044 
60V 50A mosfets in a half-bridge configuration.  The input to the 
half-bridge is 30V at 2A.  This in turn drives ALL 16 mosfets.  I have a 
1/4 ohm resistance on the output of the driver to kill the aweful ringing i 
had (it was the only way! trust me... i went insane with this part of the 
project).



>Also, you said you had a PSPICE simulation of this circuit.  I was
>wondering if you got the simulation to work and
>possibly if you could share your simulation.

Okay, i can get around to that as well.  Last time i played with the 
simulation it worked, but i was getting extremely high current predictions.
Im not sure where my mistake was, but i will find the old pspice files and 
upload the good ones.  I also tried to simulate the whole coil (feedback 
driver too!) but i ended up having convergence errors non stop (just too 
much going on???).  Anyway, i will work on getting some clean simulations 
posted.  Busy busy...


>Your videos and pics look great and as Sue stated already, the
>appearance of the arcs look to be a cross between
>a disruptive coil (with the branching and curving) and a typical SSTC
>(which is a somewhat fat arc with minimal
>branching).

The output really seems like most of my other SSTCs.  They all tend to 
branch quite a bit, but my coils use really thin wire for low frequency 
operation.  I speculate that a lot of the sparks apperance has to do with 
the coils parameters.  But the arcs are indeed awesome, hehe.  I just need 
to get this thing cranking out 4 footers ;D



>I'm also wondering if the size of your secondary (high inductance) is
>contributing to the longer arcs you are
>getting.  I'd be curious to see what kind of output you get when running
>on one of your smaller coils.

I was also getting good results with a smaller coil.

In a test, i tried the larger 6" coil with my older SSTC driver.  I managed 
to blow a bunch of fets (for the first time really!).  Im not sure why, but 
my driver did not like the 6" coil.  The SSSSTC seems to have no problems 
with either coil.  But i too agree that the higher inductance could be 
helping a lot.  I really havent pushed this new system far enough to see 
the REAL results.


>Also Steve,  since you've been doing lots of work with SSTCs lately,
>have you found any correlation between different
>sized toploads and the length of the arcs.

Somewhat, yes.  My systems will not work with large toroids though.  I 
usually choose a toroid whose capacitance matches (or is close) to that of 
the coils self capacitance.  This for some reason seems to work the best.
On an older system i had a larger toroid.  The sparks were only 17".  I 
then went for a "matched" toroid and viola, 21" sparks.  This is not really 
enough evidence to conclude that matched toroids are better though.  If my 
driver didnt mind the larger toroids so much, i would be able to do more 
tests, but for now im just going with what works well.

  Since a sharp-break-out
>point is typically used with SSTCs, this relationship
>might have more to do with the amount of capacitance on the topload than
>the break-out voltage characteristic of
>the topload toroid.

Oh yeah, exactly.  Ive also run some of my SSTCs without breakout points.
They do eventually breakout with a super loud cracking spark!  I usually 
needed full wave rectification (120pps) to keep a steady breakout.  60pps 
seemed to have stressed the system as it needed to achieve a new breakout 
on every pulse. Its really awesome to bring a screwdriver near the toroid 
in this situation, talk about St. Elmo's fire!  Everything nearby is 
extremely charged... including the metal frames on my glasses (i could feel 
it arcing to my skin!).  Thats when i got spooked and left it alone.

Give me a few days and i will get those files up on my site.

Steve


>Thanks
>
>Dan