DRSSTC, OLTC, OL-DRSSTC, M.I.C.,K.E.Y M.O.U.S.E. TC... Re: ALF: why not DRSSTC?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Greg,

At 04:35 PM 9/24/2005, you wrote:
> Hi Jimmy, Steve, Terry,
>
>
> Part of the problem I have had in grasping the OLTC and DRSSTC 
> concepts is that I haven't found a concise one-sentence description 
> for either of them.  For instance, I had thought that OLTC addressed 
> the techniques for 'Off-Line' operation of a Tesla Coil.  Does the 
> term also refer to the general case where a single solid-state 
> device replaces the spark-gap in a classic impulse-type Tesla Coil?

When originally made, the OLTC had these distinctions:

1.  The primary firing voltage was just the rectified AC line 
voltage.  The AC line and a rectifier charged the primary capacitor 
"directly" to say 340 volts.  That "was" the firing voltage!!  Later, 
a resonant inductor helped to almost double that voltage.  But there 
is NO high voltage transformer used to charge the primary cap.  The 
primary voltage "never goes higher" than the primary cap voltage.  It 
works right "off the line" voltage, but can still produce "big" coil" 
outputs.  Unlike say a tube or transistor coil, the OLTC was still a 
full powered disruptive coil.

2.  Since the primary voltage is low, "enormous" primary currents are 
used to impart the power on the secondary.  Mine was designed for 
7000 peak primary amps!!  Thus, a very large primary capacitance and 
a very low primary inductance was needed.  The OLTC operates in the 
many thousands of primary amps range.  The "Key" that started it all 
was modeling with Mark's MandK program that showed a "single turn" 
(low inductance) primary would still have "enough" coupling.  That 
meant the high currents at low voltage could be used to duplicate a 
standard high voltage primary coil's magnetic field and deliver it to 
the secondary.

3.  IGBTs allowed for relatively low loss switching of low voltages 
but at super high currents.  Now that the voltage was "low", standard 
big IGBTS could be used.  With the primary voltage in the 700V peak 
range, just "off-the-self" power electronics could now be used.  By 
over driving the gate voltage to the 20 to 25 volt range, the IGBTS 
could be hit with up to three times their rated peak current (and 
they liked it ;-)).  A reverse diode allowed for reverse current flow 
and the IGBT could hold the system back until the time was just right 
to begin (also a major idea!!)).  The low duty cycle kept device 
heating low.  The "spark gap" was now silent and dark...

4.  The OLTC was the first big coil that had very high power with 
precise timing and quenching "electronically" controlled.  Without a 
spark gap, it could fire time after time with almost perfect repeatability.

From afar, the OLTC stood out as a "big coil" that had an 
"electronic spark gap" and "no high voltage transformers".  The 
"whole thing" weighed 40 pounds...  In England, where HV transformers 
are much harder to get, they really went to town!!!

Steve Conner took the OLTC to it finest form in his OLTC-II:

http://www.scopeboy.com/tesla/ol2derby/pics2.html

Derek has also done great work on them!

http://www.roffesoft.co.uk/tesla/oltc/oltc4.htm

Finn just made one, but I don't have the link handy.

The OLTC is nice where not too giant sparks are needed but a reliable 
"big" "solid state" coil is...


Then came "Jimmy and the DRSSTC"  :-)))  Coiling will just never be 
the same...  Jimmy took all the tricks of the OLTC, and used them to 
"change everything!!"  He gets the current "Nobel prize in Coiling" ;-))

1.  The line voltage now charges a big buss capacitor for virtually 
"unlimited available energy" "during a bang".  Still an "off-line" 
machine with no transformer, but now we can draw as much power as we 
want inside the firing cycle.  All the old rules about "limited" bang 
energy get thrown out...

2.  The primary coil and capacitor voltage is now "resonated" to far 
higher voltages by an "H-bridge" of IGBTs.  The push-pull H-bridge 
forces current into the primary circuit.  That current builds up high 
voltages on the primary through resonance, but those voltage are 
still safely far away from the IGBTs and other 
"electronics"!  Suddenly, we have our high voltage primary back with 
far lower losses than the OLTC primary.  We no longer need giant 
primary currents eating vast amounts of power in losses.  Of course, 
we "still can" run giant primary currents to get like "12 foot arcs" 
from a "solid state coil" :-))))    BTW - Steve still is not using 
his "BIG" IGBTs :o))))

3.  The DRSSTC actually reuses un-needed power buy restoring energy 
back into the buss caps when the coil is quenched.  We usually don't 
give that much thought, but you should (as you have!) for a giant machine...

The OLTC broke a lot of ground and introduced a lot of new technology 
and options.  But, it never was a "perfect" machine.  They are 
frightening monsters that pack a lot of power and electronics (no one 
goes near them ;-)), but they could not "beat" a conventional 
coil.  The low primary voltage and high currents just are too lossy 
in the primary...   They are remarkably reliable.  Aside from fried 
secondaries, I am not sure if the primary drive side has "ever" been 
reported to fail???

BUT, the DRSSTC can beat any machine out there!!!  It directly solved 
the two problems of the OLTC!!  The technology is much like any high 
power switching power supply and so are the electronics.  For many 
power electronics engineering types, coiling just got easy 
;-))   There is an ever growing number of them.  They even have their 
own website :O)):

www.drsstc.com

Right now, DRSSTCs are where all the action is at!!!

But, there is "still a problem" with DRSSTCs.  They are not "simple 
and easy"...  PC boards, ICs, digital scopes, current probes, EE 
degrees (or in the process of getting them), and MONEY...  DRSSTCs 
ARE a complex business!!  And not cheap...  I spent about $1600 on 
mine (http://drsstc.com/~terrell/) but I went all out...  Maybe I 
have the record of most dollars spent on one :O))  But mine has 
microprocessors, fiber optics, optical gate drive, multiple 
selectable software modes...  Dan wrote "The Book!!".  Steve has "the 
big one".  Jimmy is the "god"...

I think Steve is the driver master ;-)

http://www.scopeboy.com/tesla/drsstc/dr3_1.gif

And the other two sheets!!

http://www.scopeboy.com/tesla/drsstc/dr3_2.gif

http://www.scopeboy.com/tesla/drsstc/dr3_3.gif

:-))))

So, these days, "I" am trying to make them "dirt simple"...  COTS 
parts...  No ICs...  VERY cheap ;-)))  Maybe "any noobie kid" will 
soon be able to make one ;-))

Cheers,

        Terry