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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
--- futuret@xxxxxxx wrote:
From: futuret@xxxxxxx
To: tesla@xxxxxxxxxx
Cc:
Subject: Re: [TCML] Toroid question
Date: Sat, 30 May 2009 21:25:22 -0400
Dex,
In my formula, I use the total power drawn from the mains. But
the formula is only a rough guide anyway. Many folks use the formula
in different ways for example they might use the input kVA instead
of watts, etc. The formula still tends to work reasonably well and is
only intended for rather efficient coils. Inefficient coils will tend
to
produce much shorter sparks. Small static gap coils with small
tank caps often produce much shorter sparks than the formula
would suggest.
It's not true that I developed the formula based on SRSG, 120 PPS,
equal bangs, although that is a popular myth. I actually based it on
a variety of coils both 120 PPS and higher async break-rates such
as 280, 340, 420 PPS, but not specifically those break-rates, but
similar
break-rates. Apparently, larger coils tend to be more efficient so
they
have less trouble meeting the "prediction" given by the formula. Small
coils have trouble reaching such efficiencies at times. Because of
this,
small coils seem to require 120 bps SRSG operation to fit the formula.
Larger coils seem to get by well at higher breakrates at least up to
some (unknown) PPS point. I don't have space to run large coils,
so I had to depend on reports by others regarding their coil's
efficiencies,
when analyzing the larger coils.
Cheers,
John
-----Original Message-----
From: Dex Dexter <dexterlabs@xxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Sat, 30 May 2009 3:12 pm
Subject: Re: [TCML] Toroid question
John,in your formula
Spark lenght = 1.7*SQRT(P)
is P in watts power delivered to Tesla coil circuit or total power
drawn from
the mains?
Also,I heard that you developed the formula on the basis of SRSG , 120
PPS,and
equal bang sizes coils.
Does that mean it is not so accurate for static gap coils,ARSG
coils,and higher
PPS coils.
Dex
--- futuret@xxxxxxx wrote:
From: futuret@xxxxxxx
To: tesla@xxxxxxxxxx
Cc:
Subject: Re: [TCML] Toroid question
Date: Fri, 29 May 2009 18:18:23 -0400
Andrew,
at my website, I show my TT-42 coil with a 4" x 13" spun toroid. The
coil
produces 42" sparks using a robust 12/30 NST. An ordinary 12/30 gives
about 38" sparks.
http://futuret.110mb.com
Cheers,
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