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Re: [TCML] Toroid question
Dex,
The NST is rated for 120 Volts, and I supplied it with 140 volts,
so it's 17% over-voltaged. Yes, they'll be some saturation.
My goal was not to avoid saturation. My goal was to see what
results I could obtain. Since I'm using power drawn from the
wallplug in my formula, it doesn't much matter how much power
is wasted. The results still agreed with my formula. Yes, if
the transformer was more efficient at that voltage, etc., then
the system would have outperformed the formula. I designed
the formula with some leeway to account for some inefficiencies
in a coil. Still, a small coil like that has to be pretty good to meet
the formula's "prediction". The formula was necessarily a
compromise to accomodate a wide spectrum of different coils.
In one test I powered my research coil using an efficient
potential transformer, and indeed it only required about 550
watts wallplug power to produce the 42" sparks.
I agree with your other comments. I think some rather small
coils are actually purposely designed to be rather inefficient to make
them
more reliable, or to use a higher pulse rate for a certain sound effect,
etc.
John
-----Original Message-----
From: Dex Dexter <dexterlabs@xxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Thu, 4 Jun 2009 3:57 pm
Subject: Re: [TCML] Toroid question
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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