Re: El Supremo

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Ken,

At 05:49 PM 9/12/2002 -0700, you wrote:
>Terry (& all)-

>> 
>> The big thing "I" see here is that with only a minor rearrangement, 
>> you
>> have 2400 volts instead of 600 driving the secondary in sort of a 
>> Marx
>> configuration.  That allows higher frequencies (far less secondary 
>> loss),
>> and lower loss in the primary!!!  Just what my OLTC needs!!!! 
>> :-))))
>
>You lose me here.  Do you mean, charge each of the 4 sections to 600 V
>instead of 150?  No problem there, conceptually.  But how does that allow
>for higher frequency?

You still have the same number of caps storing the same number of Joules.
But instead of ten all in parallel you put 2 each in series in say 5
sections.  That would give 5X the voltage (3000 volts) and 1/5 the primary
capacitance.  So, instead of 47uF at 600V you have 9.6uF at 3000V.  Same
primary energy but 1/5 the capacitance and SQRT(5) times the frequency
(2.2X).  With the higher primary voltage, the primary currents go way down
and so do the losses!  The higher secondary frequency allows a dramatic
increase in secondary Q!  It is far more like a MOT coil now but no MOTs
;-))  I am pretty sure this is the direction OLTC-2 will go now.  This
method seems to fix all the problems!!

>> 
>> "I" don't see the great need to switch two circuits at the Fo 
>> frequency for
>> my OLTC type of coil.
>
>I assume here you mean, switching actively for each half-cycle rather
>than passively, thru the diode, as you currently do.  No, you wouldn't do
>that for the OLTC-type--but El Supremo would have to incorporate that
>since there's no primary resonance to set up the cycling.  The capacitors
>are just discharging dc-wise.

Yes.  This is were our two coils differ.  Mine is just a plain disruptive
coil where your's has all this fancy control going on.

>> 
>> That does work very well!!  The IGBT reverse diodes work perfectly!
>
>Yes, if they're built in, so much the better...

Built in is the only way to go. ;-)

>
>Since both my coil and someone else's spark-gap coil are "disruptive",
>and they sit side-by-side, so to speak, and draw much the same power from
>the mains, and yet--the other guy's sparks are 30% longer...I have to
>conclude that that has something to do with the shape of the power
>impulse put into the secondary.  That's why I conclude it's best to
>emulate a spark-gap coil, in putting by far the most of the power of each
>spark into the first few cycles of that spark's excitation.

Yes.  This subject is all new.  We have much to learn about pumping arcs as
a function of formation time and all that...

>> 
>> I worry a little about using caps as a primary inductor element 
>> directly.
>> Not sure what kinds of odd electrostatics goes on there.  Streamer 
>> hits to
>> a primary cap (optimistic ;-)) would be a bad thing.
>
>Oh, I wouldn't worry about that at all.  Nothing but good old C, L & R
>inside those capacitors!  And as to streamer-hits, with the cap's on the
>outside of the primary conductors, the hits will go to the copper rather
>than to the capacitors.

Ok.  OLTC-2 may use that ;-))

>
>> 
>> >I envision two
>> >1/2"-diameter copper pipes for each segment, spaced vertically 
>> perhaps
>> >1/4" apart and with the capacitors' leads soldered to their outer
>> >peripheries.  Easy to assemble, easy to change the capacitors.
>
>Now, I think more like 1": substantially lower inductance.

Multiple parallel primary loops spaced apart sure can get that inductance down!

>> 
>> They can be "one" supply :-)))  Think Marx generator.  Simple 
>> resistors can
>> isolate the section during firing since say 5 ohms is trivial to a 
>> 0.01 ohm
>> primary loop.  All the current will ignore the 5 ohms...
>
>That's right.

I may have to think about that on more since on firing the resistors may
see very high voltage.  Inductors may indeed be needed.  But one supply is
sure nice!

>> 
>> >A
>> >very small emitter resistor developing perhaps 0.2V at peak 
>> emitter
>> >current should suffice to steer current away from the stronger
>> >transistors into the paralleled weaker ones.  
>> 
>> Yips!!  No!!  That 0.2 ohms is an enormous power drain for a 
>> disruptive
>> coil!  Think of what it does to the primary Q.  If you have say 0.5 
>> ohms of
>> primary resistance in a 20Arms primary circuit that is 200 watts of 
>> real
>> power!!  I would never consider adding any resistance in the 
>> primary!
>
>No!, no!  Not 0.2 ohms but 0.2 volts: that's all you'd need to persuade
>the other paralleled transistors to take up the load, with their
>conducting Vc-e's of maybe 3 V or so. 

Oh!  Ok...  0.2V will not hurt.  In my case an IGBT running 500 amps peak
(I know, that's a little 'high' ;-)) would need a resistance of 400uOhm...
That is the resistance of my entire 10 caps in parallel.  But if the added
resistance is somewhat less than the IGBTs it won't matter.  Remember Q = 2
x pi 2 F x L / R  that Q and R relation was a big factor for OLTC-1...  R
too big, Q to small.  Q=27 for the bare secondary :-((  Too much little wire...

But the peak power is still 100 Watts so it needs to be a good tiny bit of
wire so as not to degrade and fail before the IGBT wire bonds do :o))
Probably just the package resistance would do it.  

You may not be able to use the caps like I do but you probably are not
running the super high currents either.  I am going to try to get the
current down in OLTC-2 since running 500 peak amps per IGBT is just not
"healthy".
 
>> TVS transorbes are wonderful things too just to be really sure!!
>
>Try it first without?...

I always like to try it first 'with' :o)))  They are cheap and you can just
snip them out of the scope says they are not doing anything.  However, your
design may really not need them.  Think about streamer strikes and unusual
situations (like a FET failure).  They are cheap and may help prevent
multiple damaged parts in case something goes haywire.

>I'll interpose comments (and I wish that my received emails did not
>include a whole lot of superfluous "carriage returns"; does everyone
>suffer that?)...

I think it is the mail program doing "word wrap" at 80 characters.  A
setting somewhere may turn that off.

Cheers,

	Terry