# Re: SPICE, Solid State Suk's, and Slugs (fwd)

From: 	Scott Stephens[SMTP:stephens-at-enteract-dot-com]
Sent: 	Tuesday, December 23, 1997 1:22 PM
To: 	Tesla List
Subject: 	Re: SPICE, Solid State Suk's, and Slugs (fwd)

At 08:15 AM 12/22/97 -0600, you wrote:

>My maximum spark is 14 inches from Solid State electronics - the
>details are on my web site.
>
>  http://ourworld-dot-compuserve-dot-com/homepages/AlanSharp
>

usefull for anyone interested in solid state design.

>The bottom feeding magnifier arrangement means the energy can be
>put in over say 10mS.

Realy? wouldn't your Q (assuming Fr=100KHz, and the 63% time constant =
Tc= [2Q/(2 PI Fr)] or (2 R/L); so your coil, which IIRC, uses .4mm
non-litz wire, would need to have a Q of > (10mS 2 PI 100KHz)/2 or 3000!

After approximately the first time constant period, 63% if the applied
energy has gone to heating the coil's copper loss and capacitance loss. So
if I fig'r right, You need to put 2x the desired output energy within 1 time
constant to see your target power available. Is my math wrong?

>
>>1) Building a switch-mode inverter to turn 120VAC to 20KV+, since the size
>>of the primary discharge capacitance decreases with the square of the
>>voltage, and it's dielectric thickness increases linearly with voltage,
>why
>>not use 100KV+ in spark gaps? This would make for a very compact and
>>effiecent supply, that could be shut down after the gap fires, for rapid
>>quenching
>
>But the Ferrite cores commonly available are physicaly small with very
>limited
>winding areas - how will you fit in the amount of insulation that will be
>reduced
>for 20KV+ - or even 10KV. You'll also need a big step up ratio on the
>transformer
>but then interwinding capacitance becomes a problem.

These are factors I'll be investigating. I've taken apart an auto ignition
coil (now stop laughing, I know, it's hardly good for 50W) and will
investigate replacing its Si-steel core with ferrite, after enlarging its
core  area by removing windings.

>>3) This option I am pursuing now. Slug my secondary with ferrite. Bring
>its
>>resonance down to 25KHz. Increase it's time constant to 10milli-seconds.
>Now
>>I have time to put 50J of energy into it using semi's. My problem will be
>>dielectric heating and loss of all the poly I'll be using around the
>slugs.
>>Hopefully, the slugs I have (giant beads, 2"x2"dia with 3/4"hole) won't
>>saturate in a 5"dia coil, bring its inductance up from around 45mH to over
>>1H, and not have horrible core loss. My Q better be 750+. More simulations
>>to do.

>I found a big improvement on increasing the inductance of my coil. But this
>means that coils have to be physicaly bigger or have more turns of
>thinner wire - more resistance.

Exactly, It the Q, the L/R ratio, which is the limiting factor in
integrating the slow and constant (or even impulsed) power from semi's

>Slugging the coil with Ferrite is very attractive but the snags are the
>ones
>you mention plus internal sparking to the slug.

My greatest concern now.

>We may just trade one set
>of losses for another.

No doubt. But at low frequency (HF and lower) dielectrics like poly-ethylene
have very high Q's, I consider the reciprocal of the loss tangent Q, then
poly has a Q of around 10,000. Beats the hell out of copper! Oils loss
tangent reciprocal, IIRC, is only around 1000. But that's enough if you
count on loss. And it lends itself to convection cooling, forced air &
heatsinks. Is my thinking flawed? I know, plastic can't stand the thermal
abuse copper will. I can see corona-blackened poly running out of my plastic
fusor after 30 seconds. But this is where thermal, and E-field simulations
come in. I found some neet FEA (finite element analysis) freeware for such
simulation available in the form of "Q-field".

>It maybe that a modest bit of slugging at the
>bottom of the core could be helpful.

If you don't try to keep the Mu0 (permiability) gradient of the core even,
hot zones may develop wich could lead to arcing between the sections of the
coil. If 90% of your L is at the bottom, 90% of the voltage drops there too.

>>4'+ sparks, and quite a show. Its low frequency skin depth will probably
>>blow the surface layers clean off anything it zaps.
>>Has anyone made a study of exploding fruit/veggies?
>
>Or exploding fingers - even 6 feet away from my 500W coil - I can get
>sparks jumping from my fingers to the metal.

I would prefer a safer high-frequency coil. But it occured to me, which I
posted on the other tesla list, that a coil could be operated in higher than
the Fr, 1/4 wave mode. My former mentioned gradient breakdown accounted for,
a 10uS pulse (100KHz) might be propagated and integrated over the Q-limited
time constant of a 25KHz resonant coil. With the right chirp/impulse signal,
dispertion from the ferrite could even be compensated for.

I've just gotten my feet wet with PS-Spice, and I'll need Aplac, or NEC or
some decent code to do the type of non-linear transmission line simulation
to evaluate the efficacy of such a design. And in the end, I'll just have to
deal with the junk I've torn out of TV's and found at the Hamfest.

So maybe I'll just try it and see how hard it bites :)

>Not yet but I think the way to do it is to build two identical coils and
>drivers - out of
>phase.

I thought of a couple of designs (well, I remember my college prof's lecture
on TC's) of designs that increase the inductance by using ferrite 'flux
concentrators' (realy, just flux plugs) at the coils ends, and multi-segment
coils shaped in 'D''s and 'V's geometry to increase inductance, K-coupling
and HV isolation.

I can imagine some truly evil contrivances, with incredible Q's, that would
be created from ferrites and piezo-ceramics. Mu and E values in the 1000's,
the size of baseballs, that could store > 10's of KW's. These are
acoustic-vibration devices, and have more in common with fly-wheels than TC's.

But if/when I get around to seriously evaluating them, acousticy, I'll
probably find thermal or material stress factors will limit their potential.
Just like these semi's. I looked at power dissipation, and frequency
responce, and AC-steady state analysis, and got excited. But when I
considered the systems from a transient analysis or time-domain, things
don't look so good!