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RE: [TCML] Toroid question

To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Subject: RE: [TCML] Toroid question
From: "Lau, Gary" <Gary.Lau@xxxxxx>
Date: Fri, 5 Jun 2009 13:26:44 +0000
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Thread-topic: [TCML] Toroid question

Well, just know that it's extremely common to boost power to NST's to 140V with a Variac and I'm unaware of any fallout due to that.  The usual failure mode of an NST is one of the HV windings developing a low impedance short to ground due to carbon tracking.  When using a static spark gap, the NST secondary voltage is unaffected by the boost in primary voltage; you'd just get higher current and a higher BPS.  The NST is likely to run hotter if you run for an extended time, so I don't do that.  If you were really serious about not running an NST outside of it's intended limits, you probably shouldn't be using them in a TC at all ;-)

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: Dex Dexter [mailto:dexterlabs@xxxxxxxxxxx]
> Sent: Friday, June 05, 2009 7:16 AM
> To: Tesla Coil Mailing List
> Subject: RE: [TCML] Toroid question
> 
> 
> Adam ,
> You calculate better then I do :-)
> 
> Gary,
> I wouldn't take a chances even with 15%  higher voltage on primary side of my
> NST.
> Who wants to do it  that's OK.I  don't want to damage  NST.
> For more power,I'd rather take more powerful NST or put 2 NSTs  in parallel.
> 
> 
> Dex
> 
> 
> --- Gary.Lau@xxxxxx wrote:
> 
> From: "Lau, Gary" <Gary.Lau@xxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Cc:
> Subject: RE: [TCML] Toroid question
> Date: Thu, 4 Jun 2009 22:33:44 +0000
> 
> 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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> > > Tesla@xxxxxxxxxxxxxx
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> > >
> > >
> > >
> > >
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References:
- RE: [TCML] Toroid question
  - From: Dex Dexter

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