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RE: [TCML] Toroid question



Yep.

But the really interesting part is that something mysterious and wonderful happens when NST's are operated above their nominal voltage.  The current limiting due to the shunts appears to diminish, allowing WAY more than the faceplate-rated power or VA to be drawn.  I think that NST brand, and degree of LTR cap sizing may affect the effect.  Unfortunately this non-linear behavior is not well understood and we're unable to model it.

Regards, Gary Lau
MA, US

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Yurtle Turtle
> Sent: Thursday, June 04, 2009 5:42 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Toroid question
> 
> 
> 140 volts into a 120 volt transformer is not a 25% overvolting. 140/120 = 1.167 or
> 16.7%. Most of us have variacs that do this, so we do.
> 
> Adam
> 
> --- On Thu, 6/4/09, Dex Dexter <dexterlabs@xxxxxxxxxxx> wrote:
> 
> > 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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> >
> >
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> 
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