From: Dex Dexter <dexterlabs@xxxxxxxxxxx>
Subject: Re: [TCML] Toroid question
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Date: Thursday, June 4, 2009, 2:57 PM
Overvolting NST by 25% means usually a serious core
saturation.That's not a healthy operation mode for any
transformer.Also,NST can eat a lot of power itself then.I
bet that your Tesla coil circuit powered by overvolted NST
does not get more than 500 W out 620 W supplied.I don't know
what to say about dr. R's paper either.It is more surprising
that he found small coils so inefficient than large coils
efficient.My only scrappy coil is a 3" coil,with static
gaps.340 kHz resonant,with virtually no topload.Power input
100 VA.It gives 11 inch sparks (so the spark factor is
1.1).I'm positive that many list members can make 100 VA
coil with at least 1.4 factor.Which is much better than
according to pro's experience!
:)
Dex
--- futuret@xxxxxxx
wrote:
From: futuret@xxxxxxx
To: tesla@xxxxxxxxxx
Cc:
Subject: Re: [TCML] Toroid question
Date: Tue, 02 Jun 2009 19:23:11 -0400
Dex,
Yes, the spark lengths decreased for equal power input as I
increased
the PPS rate.
I agree that large bang size is very important. Yes,
larger coils have
lower losses,
and that may account for the better efficiencies of the
larger coils.
My old research coil using a regular 12/30 NST, drew about
620 watts,
and gave 42" sparks.
That's how much power they draw when the system is set up
as mine was.
I fed
the NST with 140 volts input... that's part of the key to
the excess
power draw. Probably
some saturation going on at that voltage. Not
many folks realize they can draw that much power. My
TT-42 coil is not
as efficient
because it was built for portability.
The coils you mentioned for which the factor varied from
1.5 to 2....
I see that as still being
close to the formula, since the formula is a rough
guide. I've
mentioned over
the years that the factor can be changed for certain coils,
etc. I
just used
1.7 as a sort of average for various coils. I've seen
even rather
small coils
show a factor of 2.0, such as the solid state DRSSTC
types.
Regarding the diameter of the secondary, I don't have a lot
of faith in
that
concept. I think smaller diameter coils may often use
smaller toroids,
or have
too few turns of wire, etc. I'd like to do the
comparison tests
myself, but
I haven't gotten around to it. It's true that a
larger diameter coil
has
more inductance for a given number of turns, and will show
lower
losses, etc.
But I don't think it should make a great difference for
spark length.
I'm sure it will make some.
Of course an extremely tall narrow coil would be bad, since
it would be
hard to
couple, and might not have enough inductance, etc. I
like to think of
the
diameter as increasing as the overall coil size increases,
just to keep
everything
in proportion, electrically and all.
Cheers,
John
-----Original Message-----
From: Dex Dexter <dexterlabs@xxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Tue, 2 Jun 2009 7:42 am
Subject: Re: [TCML] Toroid question
John,
Thanks for clearing up these doubts.
I understand it is an empirical formula for how a well
constructed
spark gap
coil should perform aproxinately.You gave an example of 12
kv/ 30 mA
NST coil
with SRG and 120 PPS delivering 38" sparks.I know one can
even squeeze
out
little more juice than 360 W from such NST ,but not
much.Therefore the
coil
outperforms the formula prediction and factor b=1.7 in
spark lenght =
b*SQRT(P)
should be replaced by b=2.
I'm wondering if you observed a gradual spark lenght
decrease in your
tests as
you changed sync PPS rate from 120 PPS to 240 PPS,and then
to 480 PPS
keeping
the input power same all the time?The efficiency of power
source unit
matters
,but not much for bigger coils.Also power factors are high
enough for
SRG
systems and folks are right when plugging VA instead of
W.Speaking of
larger
coils,I don't know much data either.Here's what I've found
out so far:
K.Eldridge's big Oklahoma coil:
Power input:30 kW
Break rate:120 PPS SRG
Bang size:~250 J
Spark lenght:26-27 ft
M.Denicolai's "Thor":
Power input:5 kW
Break rate: 250 PPS,DC charger realisation
Bang size:~20 J
Spark lenght:10 ft
G.Leyh's Electrum :
Power input: 95 kW
Break rate: 360 PPS,DC charger realisation
Bang size:266 J
Spark lenght:~40 ft
Dr. Resonance's Australia coil:
Power input:~150 kW
Break rate:120 PPS SRG
Bang size: ~ 1250 J
Spark lenght: 78 ft
The only system here which follows well the formula is Thor
with
b=1.7.The
Oklahoma coil has b~1.85 while Electrum has b~1.5.I noticed
that
despite much
higher power level Electrum use aprox the same bang size as
the
Oklahoma
coil,but works at 3x higher PPS rate.Contoversal
Dr.Resonance's coil
uses even
more power,but what differs drastically is a huge
bang size of it.If
the data
is correct that coil has b=2.4.I think bang size means a
lot.Also it is
known
fact that bigger coils with larger diameters tolerate
higher couplings
and
larger bang sizes.I'm not sure if the smaller aspect ratios
and larger
diameters
give the only advantage due to possibilty of higher
coupling and larger
bang
sizes or there's something more to it (unknown to
me).Here's
interesting paper
of Dr. Resonance regarding the role of secondary diameter
in Tesla
coil's spark
performances:
http://www.classictesla.com/download/resonance_tips.pdf
Dex
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