Re: DRSSTC Primary Circuit Feedback Control

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jimmy Hynes <jphynes@xxxxxxxxx>

Hi,

On Mon, 06 Dec 2004 23:14:57 -0700, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi Jimmy,
>
> "Zero current crossing" is a game...  You might have to "predict" the
> "when" and "time" things since the circuits to detect it in real time are
> too slow...  The dI/dT is really unforgiving there...  Microprocessors ;-)))
>
> But once you hit the magic mark.  All is happy!!!

I don't really see it as that big of a deal. As long as you get close,
most of the current is gone. Mine works fine open loop...
>
> BTW...  Can an 80 amp peak primary circuit produce nice
> sparks?...  "probably"...  In a conventional, say 15/60 NST LTR system with
> a 25nF cap and 21kV firing voltage, we have 5.5 joules "per spark"...  But
> that's it!!  No more...
>
> In a DRSSTC system, the 15.75nF primary cap may store up only 9 kV for just
> 0.64 Joule... 80 amps in a 250uH primary inductor is like 0.8 Joule...  But
> the key is that the primary system energy is not "fixed" like in a regular
> coil.  In a DRSSTC, we are constantly pumping power into the resonant
> system all through the cycle!!  Hahaha  Terry sounds like he knows all
> about this stuff when telling "Jimmy" about DRSSTCSs :o))))))  But I think
> I am on one of my infamous "rolls" ;-))  But it is like a tube coil on
> super steroids and run like a conventional coil!!!  The actual Tesla coil
> needs to be low loss in this case with the big primary conductors and all...

But... With only 80 amps, the impedance is so high that any streamer
load will pull it down, and you can't grow streamers. "Normal" SSTCs
keep pumping energy into sparks, but they don't have huge sparks

>
> "Spark length" is very dependant on getting a very high voltage on
> something and then "turning it off!"...  This is demonstrated by tube coils
> and  John's staccato coils.  My solid state coil makes only six inch spark
> till it switch it off at just the right time to bump a long spark out of
> it...  Tesla coils arcs need to be "pulsed"...  Charge up the space
> capacitance and then disrupt it to smash some ions out there...  Once the
> arc is started, pump power into it....
>
> The models say I am pumping 640 watts of "real" power into the
> primary/secondary system which is far higher than other models...  So
> something is gonna blow!!!  Nice secondary arcs!!  Hope, hope ;-)))
>
> Cheers,
>
>         Terry
>
>
>
>
> At 10:27 PM 12/6/2004, you wrote:
> >Hi,
> >
> >
> >
> >
> > > > > The models (not real confident in the numbers..) say the IGBTs 
will do
> > > > > about 40 watts of heat as is.  But with "perfect" zero cross 
switching,
> > > > > that goes down to 1.2 watts!!
> > > >
> > > >Huh? What frequency and switching times? My simulations showed about a
> > > >factor of 2 increase in loss when hard switching about 80% of peak
> > > >current. A factor of 30 is hard to believe.
> > >
> > > Looses at "zero current" are real low.  Just the primary RMS current
> > > then...  But not sure I trust then numbers.  IGBTs are not really 
linear so
> > > switching losses get pretty high if the current is high.  That mJ loss
> > > stuff on the data sheets adds up...  Also worrisome having 20,000 volts
> > > behind it!!!
> >
> >Oh, that's where you got the switching loss numbers. I wouldn't trust
> >those too much either. What I did is use Pspice to simulate the
> >circuit, and integrate the instantaneous product of voltage across the
> >IGBT and the current through it. I'm not sure how accurate the models
> >are when it's way out of spec, but I'd trust this way a little more
>
>