Re: OLTC update - Coupling figured out :-)

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

Original poster: "K. C. Herrick by way of Terry Fritz <twftesla-at-qwest-dot-net>" <kchdlh-at-juno-dot-com>

Terry (& all)-

Figure -25 appears to show the secondary voltage reaching max. at the 2nd
half-cycle and that is, indeed, extremely good.  I should think you'd be
able to see that directly on the scope by just laying your probe out as a
little antenna, as I do.

If my pet theory, as to voltage rate-of-rise vs. spark-progression time,
is true, however, that high rate may not do you much good in increasing
spark length, at just 30-odd KHz.  Getting up there in 1 cycle at 140 KHz
would be a different thing entirely.

As to why my system takes its 30 cycles to ring up--don't know yet.  My
secondary sits directly on the primary, with spacing of perhaps 1" from
the top of the primary bundle to the first secondary turn and having the
same nominal 12" diameter.  Certainly, if I could drive it with a sine
wave with all else being equal, I suppose I would.  But the MOSFETs have
to turn on hard, of course.  Also, it strikes me that the harmonic
content of my voltage square wave will not elicit a lot of primary
current because the impedance of the primary is a lot higher for those
components.  So...let it be square, as far as I can see.

And as to harmonics "fighting" each other...say what?  Does such a thing
happen??  Not per anything I learned 50 years ago...but then one forgets,
or never learned in the first place, a lot.

I'd made a rough measurement many months ago that seemed to show that I
got the best coupling to the secondary with a (larger diameter) primary
located about 6" up (on a ~36" coil).  Once I get my system up & running
again (after the current irksome task of changing out 8 MOSFET-driver
transistors for huskier ones), perhaps I'll make such a coil.

And by the way, what is the mechanism that will cause your losses to
decrease with increased input current?  

Ken

On Sun, 25 Aug 2002 12:26:20 -0600 "Tesla list" <tesla-at-pupman-dot-com>
writes:
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> 
> Hi Ken,
> 
> I am using only about a 75 volt firing voltage right now (starting 
> out real
> slow).  But perhaps at these low levels the losses are higher and 
> loosing
> power to the primary coil which just "looks" like very high 
> coupling.  From
> the scope trace at:
> 
> http://hot-streamer-dot-com/temp/OLTC08-24-01.gif
> 
> The secondary losses are fine, but not sure about the primary.  I 
> will
> check into this.  I may just have to keep cranking it up and the 
> problem
> will go away ;-)
> 
> YEP!  Your right!  I ran MicroSim with more realistic "low power" 
> losses
> and got:
> 
> http://hot-streamer-dot-com/temp/OLTC08-25-01.gif
> 
> That is indeed what I am seeing.  The coupling is fine after all.  
> There is
> NO problem.  I just need to keep cranking the power up and the 
> losses will
> reduce naturally.
> 
> Thanks for the insight here!!  It would have taken "me" a long time 
> to
> figure this one out ;-))
> 
> I am surprised your coil has such a long ring up.  Unless the 
> coupling is
> very low, which a I doubt, Perhaps the square waves don't couple as 
> well.
> Only the Fo sine component may be doing the coupling while the 
> higher order
> harmonics of the square wave are either not coupling or "fighting" 
> each
> other.  An interesting and unknown problem, exciting a two coil 
> system with
> square waves instead of sine waves...  Maybe Paul's program could 
> analyze
> such a case since the harmonics in the secondary may easily come 
> into play
> in such a case.  Simple MicroSim models may not see the true action 
> there.
> 
> I will try to run some models on this and see if I can figure 
> anything out.
> 
> BTW - I think I know of a very easy way to measure the primary 
> current.
> Just a loop of wire under the primary (or near it) to a scope probe. 
>  The
> voltage on the loop should be proportional to the current (or maybe 
> it
> needs a load resistor?).  A simple and very useful instrument whose 
> details
> will have to wait for another day...
> 
> Cheers,
> 
>         Terry
> 
> 
> At 09:31 AM 8/25/2002 -0700, you wrote:
> >Terry (& all)-
> >
> >I've been following the OLTC saga off & on.  But it's just occurred 
> to me
> >that you may find yourself up against the situation I've found with 
> my
> >s.s. coil:  As you may recall, I apply a ~1200 V pp square-wave 
> burst, of
> >up to ~6 ms duration, to a 3-turn (untuned) primary circuit for 
> each
> >spark.  With a 140 KHz secondary Fr and a 6" x 24" smooth 
> (Landergren)
> >toroid, it takes ~30 cycles of constant (not exponentially 
> declining!)
> >excitation to bring the toroid potential up to the spark break-out 
> level.
> >
> >You are applying, I believe, ~680 x 2.8  = ~1900 V pp, initially, 
> to a
> >3-turn primary circuit--incorporating much less resistance, 
> admittedly,
> >than mine--but your excitation must (necessarily) 
> exponentially-decline
> >quite rapidly.  I'd think you might require more or less those 30 
> cycles
> >to pump up the voltage & I fear that the decline of your primary 
> voltage
> >may preclude that.
> >
> >Were you able to do any simulations on that?
> >
> >Ken Herrick
> >
> >On Sat, 24 Aug 2002 23:02:13 -0600 "Tesla list" <tesla-at-pupman-dot-com>
> >writes:
> >> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> >> 
> >> Hi All,
> >> 
> >> Today I set up the coil for action:
> >> 
> >> http://hot-streamer-dot-com/temp/OLTC08-24-02.jpg
> >> 
> >> I powered up the coil...
> >
> >[snipped]
> >
> > 
> >
> 
> 
> 
>