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

From: 	Jim Lux[SMTP:jimlux-at-earthlink-dot-net]
Sent: 	Monday, December 22, 1997 10:35 AM
To: 	Tesla List
Subject: 	Re: SPICE, Solid State Suk's, and Slugs (fwd)

> The big problem is an order-of-magnitude gap between the impulse power
> ability of cheap transistors, and the Q of the 2ndary coil.
> My goal is to build a solid state, effiecient TC that can put 25J, 1MV
> across a 50pf torroid-coil load.
> My coil has a Q of 100-at-100KHz, and with a time constant of around 250uS,
> their is no way, short of an array of 25 40A/400V pulsed FET's, or 5
> (which will cost $100 EZ) I can deliver that much impulse power in that
> short of time.
> I've seen pulsed SCR data showing 100+ amp performance, but I'm don't
> their viable either.
The SCR's don't turn on or off very quickly, so your di/dt is low
> 3) This option I am pursuing now. Slug my secondary with ferrite. Bring
> resonance down to 25KHz. Increase it's time constant to 10milli-seconds.
> 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
> 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
> 1H, and not have horrible core loss. My Q better be 750+. More
> to do.
> I know, its not a Tesla Coil, its probably a Oudin coil. But it will make
> 4'+ sparks, and quite a show. Its low frequency skin depth will probably
> blow the surface layers clean off anything it zaps.

Actually, it is a Pulse Transformer. The most common variety is the one in
your car for the ignition, and probably the second most common would be the
trigger transformer for a xenon strobe. They work, they are reliable, the
problem is the weight of the core. The core has to hold the energy of the
pulse. And, of course, the insulation issue.  Fruengel in "high speed pulse
technology" has a few pages on designing these units, and I understand that
there was an article in "the Bell Jar" about a 250 kV impulse transformer. 

I have been pursing the same approach, although at a somewhat higher energy
level: 40 kJ to produce a 3 MV pulse lasting many microseconds to allow the
spark to propagate many meters. My problem is insulation and mechanical

Pulse transformers are used a lot in the Capacitor discharge spot welding
business. Imagine a machine to weld an 8 foot wide section of steel
reinforcing mesh, i.e. 48 welds simultaneously at several kAmps each.
Charge a cap up to a few kilovolts, run it through a 100:1 step down, and
there is your megaamp discharge.

> Has anyone made a study of exploding fruit/veggies?
Check out Bill Beatty's web page (www.eskimo-dot-com/~billb) and look for the
stuff on capacitor discharge.
> On the bright side, with such high L, a tiny little primary directly on
> core will result in a massive step-up / Z-match. No giant end-match
> transformer. No flux-loss out the ends of the coil to eddy-heat terminaly
> and supports. 
For the impulse transformers, they typically use a bar core, because the
pulse lasts such a short time, the magnetic field doesn't have time to
propagate out the end of the bar, before it collapses due to the load