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Re: A new mini-coil competition winner!
Original poster: "Karl L." <karl@xxxxxxxxxxxxxxxxx>
Hi Gary, Terry, all...
I've gotten so many excellent suggestions and replies regarding my
mini-coil performance "mystery." I think we may be getting close to
a solution - Karl
Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
Based on Karl's stated .06" gap separation, which is pretty close to
what I also have on my mini coil (I have closer to .07"), I can confirm
that his gap width has been properly set for a 4kVRMS NST. If it was
breaking down at 15+kV, it would have to be much wider.
Regards, Gary Lau
MA, USA
Yes. My gap is set for 0.06" and fires nicely with just the xfrmr
attached at ~108 VAC input to NST. - Karl
Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
Hi Karl,
Wow!!!
The coil power is:
1/2 x 25nF x 5090^2 x 120BPS = 38.86W
If 18.125 = F x SQRT(38.86) Then F = 2.91!!
But if we do the regular Freau equation:
1.7 x SQRT (0.038 x 5090) = 23.64 inches...
So something is going on "I" don't understand. Let me think on it %:-)
Cheers,
Terry
OK Terry. So streamer length still falls short of theoretical
maximum. I believe that smaller coils never reach the Freau limit
anyway. - Karl
Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
Hi Karl,
I see what is going on 8-)
If we model your coil with MicroSim:
http://hot-streamer.com/temp/Karl1.gif
We get this:
http://hot-streamer.com/temp/Karl2.gif
If the component values are shifted a tiny bit we basically get the
coil firing twice on each peak of the sine wave from the transformer.
So it fires at both 5.5 and 8.3mS That doubles the streamer power.
So you are closer to 78W in.
If it were 120BPS the new ScanTesla gives 9.7 inch streamers. So
your double firing almost double the spark length!!!! Normally I
would expect it to increase SQRT(2) or 13.7 inches with doubling power.
ScanTesla does not do double firing so we have to guess a bit and I
am not sure the function of double firing to streamer length is well
understood (a DRSSTC thing).
This brings the Freau number down to 2.06 which makes more sense :-))
It is hard to know what Rprimary is for your coil since it is
significantly different that what we are used to. But I am sure an
SISG even with double firing will further increase the arc distance
significantly. I am not sure how much though.
Cheers,
Terry
Terry, now this idea is starting to make a lot of sense. Since my
gap is not too wide, and set for ~ 5kV I could see how resonant
charging could quickly replenish the charge in the caps leading to
those extra firings per each 1/2 wave cycle. - Karl
Original poster: FutureT@xxxxxxx
In a message dated 6/6/06 7:45:43 PM Eastern Daylight Time,
tesla@xxxxxxxxxx writes:
Also, did you see any reason ScanTesla predicted only 6.4" streamers?
>My earlier post contained the input and and output files I used in
>the program.
Karl,
Congratulations on your results. It's a great looking coil
too. I think the coil may be drawing more than 47 watts.
If the output voltage is figured at 4.4kv rms, that comes
to 155VA output. Figuring 155 watts wallplug, and
using my formula of
spark length inches = 1.7*sqrt input power watts
gives 21" as a spark length. So it seems
to me that your coil is working well. Most
small coils fall somewhat short of my formula.
Your break rate must be higher than 120 bps because
of the use of a resonant value
capacitor. Maybe the firing voltage is a little higher
than expected for some reason. The large radius of
curvature of your topload
may be helping the results also, even with the breakout
point. Also I agree with Gary that the high primary
inductance is probably reducing the gap losses and
helping the results. Your spark length at 18" is
close to the value of 21" which my formula "predicts"
If the power input is as I suggested.
The higher breakrate is probably reducing the efficiency
some also, but apparently not much. Regarding gap
losses, I think that the initial energy transfer to the
secondary is what contributes most to the spark length.
The initial transfer tends to involve rather low gap losses
especially when using a high inductance primary.
I once built a coil which was similar in physical size.
It used a 3" diameter by 15" tall secondary with a 3"
x 10" toroid. It was the TT-32 coil. It used a 7.5/30
NST and drew about 270 watts I think. So the predicted
spark length was 28" but it only gave about 25" sparks.
I used a 120 bps rotary gap however.
John
Thanks John. I have a kill a watt meter, and during initial testing
of the primary I found a variac'd firing range of ~150 - 185 VA. No
caps or coils were connected, only the xfrmr and gap. Curiously, the
PF was 0.26 and it indicated a draw of around 40 watts. The kill a
watt doesn't work when the coil is actually firing (too much RF hash
on line.) - Karl
Original poster: FutureT@xxxxxxx
In a message dated 6/6/06 9:20:14 PM Eastern Daylight Time,
tesla@xxxxxxxxxx writes:
If the component values are shifted a tiny bit we basically get the
coil firing twice on each peak of the sine wave from the
transformer. So it fires at both 5.5 and 8.3mS That doubles the
streamer power. So you are closer to 78W in.
Terry, Karl,
I wouldn't be surprised if Karl's coil is firing 3 or even 4 times
per 60Hz half cycle. A resonant value cap can cause the
cap to charge very quickly. Either that, or the firing voltage
is higher than we suspect for some reason. In any case
I think the input wallplug power is probably 150 watts or so.
This would put the "Freau" number at around 1.5 which is
what I think it should be for this coil. Even though Karl
built a very nice efficient coil, I doubt it's showing
unexpectedly high efficiency. But if by some magic it *is* showing
unexpected efficiency, then it must be due to the large spherical
topload because no other factor could explain the
performance IMO. ( My best guess is there's nothing
special about large spherical toploads either.) Again, my
guess is that the Freau factor is actually about 1.5, and
that the efficiency is as expected.
I'll do some speculating;
I suspect the coil probably runs with a smooth hissing sound.
This would be because of a high break rate. The coil may be
producing a thick long bright single coalesced streamer with
a fuzzy end, (tendril-like streamer). These may require a high
break rate to form. It would be good if Karl could measure the
input power using a wattmeter, and measure the breakrate
somehow.
John
Hi John. I'm beginning to lean toward your theory more. I do not
think there is any "breakthrough" in efficiency with this coil. I do
think the larger secondary and corresponding primary allow for
greater and more efficient energy transfer from primary to
secondary. Richard Hull's design notes specified a 6:1 aspect for
smaller coils. I also think the large, smooth sphere is helping
too. This is the smoothest topload I've ever used, and it produces
none of the small streamers that usually come off a toroid. The
firing voltage would have to be set around ~5 kV due to the spacing
on my gap, and having multiple firings per 1/2 cycle seems very
plausible. You are right about the single, bright streamer. It has
a few "tendrils" at the very end of it, until it connects with
something. I'll work on trying to measure bps somehow. -Karl
Original poster: "dest" <dest@xxxxxxxxxxx>
> Original poster: FutureT@xxxxxxx
>
> Again, my guess is that the Freau factor is actually about 1.5,
> and that the efficiency is as expected.
>
> It would be good if Karl could measure the input power using a
> wattmeter
"Hi John, All,
That has got to be the most succinct suggestion and reasonable
way to wrap up a discussion that I've seen in a long time. Well Done !!"
i think here is exactly right place for these very wise words of Matt D.
: )))
What?? I need to know what is going on here with my coil. I've
gotten so many great responses so far. Any ideas yourself? - Karl