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Re: Tesla Coil Power Factor

Hi Terry,

> Original Poster: Terry Fritz <terryf-at-verinet-dot-com>
> 
> At 10:33 AM 9/21/98 +1200, you wrote:
> 
> >Original Poster: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
> >Hi Terry,
> >           A quick comment on one point:
> >
> SNIP...........>> 
> >> John02.jpg and john03.jpg show this situation.  John02.jpg is to a 1 foot
> >> arc and john03.jpg is to the grounded target.  The bottom trace in both
> >> pictures is the output voltage of the secondary at 200kV/div.  the top
> >> trace is 10kV/div in john02.jpg and 20kV/div in john03.jpg.  I worry that
> >> the grounded target case may not be realistic.  The arc occurs before the
> >> secondary is fully charged.  In fact the coil has not quenched before the
> >> arc starts.  This is not very realistic of how most people run their
coils.
> >
> >I submit that it is. If a coil can't start launching an arc by the 
> >time the secondary has fully rung up, it is unlikely to do so, quench 
> >or not. In fact, there is a hint of a suggestion from some tests that 
> >allowing more than one beat can actually assist in this process as 
> >amplitude can peak a second time and be a bit higher than a straight 
> >ringdown a bit further down the track if the primary is good. One can 
> >see this by superimposing quenched over non-quenched waveforms on the 
> >scope. Certainly, my best coil/s run like this. 
> 
> In john03.jpg it is apparent that the system is loosing energy before the
> quench.  However, I believe this is due to the high corona loss between the
> top terminal and the target.  The actual strike discharges the system
> instantly but the loss before that point seems due to corona.  Thus I
> wonder if this is a good test to use.  Of course, a streamer has early
> losses too so maybe it is valid.

In my case, I took all measurements first without a rod in place, then 
positioned the rod to get the spark measurement. There was no 
breakout of any kind during the first part of the test.

> >     Further expts with good quenching gaps show me at least that the 
> >quench comes at the expense of increased primary loss.
> >     I tried two ways: loosening coupling which reduced beats before 
> >quench. I also tried more gaps in series. Initial amplitude with more 
> >gaps was down on what it was with fewer. I was able to superimpose 
> >previously captured waveforms with those taken subsequently with 
> >different ks, gaps etc and there were definitely additional losses 
> >occurring. Output spark also showed a drop which corresponded exactly 
> >with losses the scope was showing. Since the tests were done under no 
> >breakout conditions, spark was measured bu encouraging strikes to a 
> >ground rod positioned such that strikes were consistent with 
> >different coil settings.
> 
> A two notch firing does allow a slightly higher maximum voltage since the
> system is able to transfer maximum energy.  However, I find that the high
> losses during the second notch reduces streamer energy.  High quenching
> gaps do burn a lot of power but if the time they are active is minimal, it
> is better overall.  I still think first notch quench is the way to go.
> 
> I have heard that there are some "sweet spots" for the coupling
> coefficient.  Perhaps a carefully tuned coupling would reduce the energy
> loss I am seeing.  I will try to play with it some to see if I can reduce
> the loss.

Two notes on this: the sweet spots are signalled on the scope by a 
deep null between beats signalling complete transfer (minus circuit 
losses). The second is that coupling can be adjusted to take 
advantage of whatever gap one is using. Loose coupling works well 
with otherwise poorly quenching gaps as it lengthens the null period.
Unfortunately the gap has longer to add to the losses as the 
transfer period also increases.

      The sweet spots in descending order are 0.6, 0.385, 0.28, 0.18, 
0.15 0.12.......   These are the math values for a lossless system. 
As Bert pointed out once, the fact that the system is losing energy 
while effecting transfer means that the practical values are somewhat 
higher than these and exact values for a particular system are 
dependent on losses for that system (e.g. a lower Q primary will 
require higher k than one with a higher surge impedance to hit the 
sweet spot).

Malcolm