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Re: Tesla Coil Power Factor

Hi Terry, all,
                Thought I'd mention something that's been bubbling 
around in my mind since this discussion started:

> Original Poster: Terry Fritz <terryf-at-verinet-dot-com>
> 
> Hi Malcolm,
> 
>     Thanks for the "sweet spots".  I knew someone would have them.  I was
> trying different couplings this afternoon but it didn't make much
> difference in my case.  There is still some considerable charge left on the
> primary after quench.  I'll test this more.
> 
>     Unfortunately, during the last test, the voltage probe measuring the cap
> voltages blew the resistor string to bits (there is a certain visceral
> thrill when one is turning up the old variac about to max and suddenly a
> loud and sickly, bang!...arc...fizz sound is heard :-)).  An old design
> flaw in the thing finally caught up with me.  Of course, the 30 feet of
> fiber-optic cable protected the scope and such but the $30 voltage probe is
> trashed.  I won't be able to take direct voltage measurements for at least
> a week or so :-(.  Perhaps I can continue with my other measuring
> instruments in the mean time.  Some times the bleeding edge of technical
> research is painful....  But that what makes it so much fun :-))
> 
> All the best,
> 
>     Terry

Sorry to hear about the resistors.

     There is a thread on the Tesla-2 list about safety gap firing 
and what causes it. One guy who was having such problems found that 
reducing k all but got rid of the problem. Not unexpectedly, his coil 
output dropped a bit as well. However, the thought that occurred to 
me (yes, I will test this at risk of my own transformers) was that a 
gap which does quench rather better than others *might* be 
extinguishing at a time when there is somewhat more energy in the 
primary circuit than a poorly quenching one and this energy *might* 
have something to do with the safety gap firing. Your observation of 
good quench (correct me if I'm wrong) leaving a reasonable voltage 
still on the cap seems to fit with this thought. I do feel that it is 
time this nuisance was quantified and eliminated properly.

     The chap kindly tried a raft of things including changing 
terminal size, adjusting k, leaving filter chokes out etc. Of all the 
things he tried, this was the only one that solved the problem. 
Investigation is ongoing. The clear picture I was left with after 
seeing his results is:

- running with no filter is a bad idea if the coupling is too tight
(and that could well relate to gap quenching ability). I personally 
stand corrected on that idea :(  However, it appears to be on if a
safety gap doesn't fire. I also suspect that the filter cap in my DC 
chargers (not huge) has been acting as a transient absorber.

- some filters may be better than others but are better than none at 
all if this is a problem

- reducing k is a great idea if one strikes this problem (the 
tradeoff being some output for a long lasting NST)

I think the trick now would be to monitor the transformer terminals
and gap with the scope and see whether the problem occurs during zero 
crossing in the gap or when the gap finally ceases to conduct (judging 
by his results it is the latter)

It won't be too long before I put a transformer of mine at risk to 
find this out.

Cheers,
Malcolm
<snip>