Re: OLTC update - Coupling figured out :-)

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Terry, Ken et all,
                       I've been following the OLTC development with 
much interest.

On 25 Aug 2002, at 12:26, Tesla list wrote:

> 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

That is very probable. k after all is a geometry thing. Have you yet 
calculated your primary Q from its ringing down alone? I expect that 
will fill a big gap in the story. If it only rings for a few cycles, 
you know the losses are big. I agree that the proportional losses 
will be higher at low primary voltages. Your situation is totally 
different from a CW-driven coil. The cap rings down to empty whereas 
the CW coil feeds in a constant amount of energy per cycle as long as 
the primary is ringing (at constant amplitude).
 
> 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 ;-)

What is you unloaded secondary Q?
 
> 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.  

That is to be expected since the primary doesn't decrement. No 
surprise there. The coils are running under different conditions.

Regards,
malcolm


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]
> >
> > 
> >
> 
> 
>