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Re: A new mini-coil competition winner!



Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Karl,

The resonant capacitor value for the modified transformer is:

Cres = 0.038 / (2 x pi x 60 x 4000)  =  25.2nF

so the 25nF capacitor in the coil is right at resonance. Just like an NST system, the voltage at the gap can be pretty high and well over the rated voltage with a resonant size cap. So instead of the firing voltage being 5524V it might be much higher. I suspect it is closer to 15kV!

There is an easy way to check. Disconnect the cap and primary coil so "only" the transformer and gap are in circuit. With just the gap as the load for the transformer, it should put out its rated voltage. Then see if the gap fires. If it does, then the gap is set to 5524. However, if the gap does not fire and the electrodes need to be moved closer, then the gap was set for a higher voltage. Once the gap is set for 5524V I think the spark length will go way down :-( Like 7 to 10 inches. So set the gap back to where it was :-))

Cheers,

        Terry


At 07:01 AM 6/6/2006, you wrote:
Hi Terry, everyone:

Perhaps I am missing something here, but I do not see how my new mini-coil could be charging to a firing voltage of 15.6 kV as suggested. I built this coil expressly to enter in Gary Laus' competition here: http://www.laushaus.com/tesla/minicoilcontest/ using the same equipment as the other entries. As Gary mentioned in his earlier post, the only real difference between my coil and the others is the much larger and longer secondary, and matching higher inductance primary. The gap is similar to the other entries in design and spacing. This coil begins to fire smoothly at an input voltage of only 26 VAC and output scales nicely as the variac is turned up to 100% The smooth sphere reduces all of the energy wasting small streamers that typically come off of a rougher topload. I use a 1/4" rounded acorn nut to direct the streamers and prevent breakout from the top winding of my secondary. (Yes, I know spheres do not shield the secondary as well as toroids, but it was easier and cheaper this way.)

I got the 47 watt coil figure from ScanTesla, which also said I could only expect 6.4" streamers. Obviously there is something funny going on here as I measured 18 1/8" streamer hits to a metal frame around a cork board which was not directly grounded. Could you (or anyone else) look over my coils specs found here: http://www.laushaus.com/tesla/minicoilcontest/karllindheimer_cat1.htm. and see why my ScanTesla calculations are so off?

Here is the ScanTesla output for my coil:

ScanTesla  V-7.50  May 31, 2006  Terry Fritz
Goal =        0.058516730  maximum Load Energy
Model Number = 641
Goal Number = 111
Cprimary (nF) =   25.000
Lprimary (uH) =   14.600
Rprimary (Ohm) =  3.000
Coupling = 0.100
Csecondary (pF) =  18.0
Lsecondary (mH) =   18.750
Rsecondary (Ohm) =  300.0
Cload (pF) =   1.8
Rload (kOhm) =  220.0
BPS =  120.000
Dwell (T1) Time (uSec) = 1000000.0
Ilprimay Maximum (A) =  -211.2
ICprimary RMS (Arms) =   3.6   ILsecondary RMS (Arms) = 0.07252
VCprimary Maximum (kV) =   5.524
VCsecondary Maximum (kV) =    73.494
Coil Power (W) =      47.0   Primary Bang Energy (J) =   0.392
Load Power (W) =       7.0   Load Bang Energy (J) =   0.059
Leader Length (in) =    6.4
Primary F0 (Hz) = 263435.1   Secondary F0 (Hz) = 273957.5
Load Energy Rise Time (uSec) =   16.5
648/648 Goal
Models Tested = 648 / 648

Thanks,

Karl

ScanTesla input data:

* ScanTesla Parameter Input File  V-7.50
*
* This file should be in the same directory as the program.
*
* Lines starting with "*" are ignored.
*
* The program expects these input parameters in order and as shown.
*
* These parameters define the coil values to be scanned.
*
* Cprimary (Farads) - start, stop, Inc
25.0e-009
25.0e-009
1.5e-009
* Rprimary (Ohms) - Start, Stop, Inc
3.0
3.0
1.0
* Lprimary (Heneries) - Start, Stop, Inc - If Inc < 0 then automatic Lprimary tuning is used
1.80e-006
16.00e-006
0.20e-006
* Lsecondary (Heneries) - Start, Stop, Inc
18.75e-3
18.75e-3
1.0e-4
* Coupling - Start, Stop, Inc
0.10
0.10
0.01
* Rsecondary (Ohms) - Start, Stop, Inc
300.0
300.0
1.0
* Csecondary (Farads) - Start, Stop, Inc
18.0e-12
18.0e-12
1.0e-13
* Cload (Farads) - Start, Stop, Inc - If Inc < 0 then automatic streamer load is used
1.0e-12
1.8e-12
0.1e-12
* Rload (Ohms) - Start, Stop, Inc
220.0e3
220.0e3
1.0e3
* Time (sec) - Start, Stop, Inc - If Inc < 0 then automatic timing is used
0.0e-6
750e-6
1.0e-7
* Vrail - DRSSTC Buss Rail Voltage (volts) - 0.0 for a conventional coil.
0.0
* VCprimary Initial Value (volts) - Primary capacitor voltage for a conventional coil. 0.0 for a DRSSTC.
5600.0
* BPS - Coil Breaks Per Second
120
*Dwell Time (sec) start, stop, inc - DRSSTC T1 time. Ignored for conventional coil.
1
1
10.0e-6
* DRSSTC Current Limit (Amps) - Set very high for conventional coil.
10000.0
* Coil Power Limit (Watts)
1000
* Goal Type - 0=find maximum VCsecondary 1=find maximum streamer power 2=find all
1
*


On Jun 5, 2006, at 9:59 PM, Tesla list wrote:

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

This length of streamer seems high for a 47 watt coil!!

1.7 x SQRT(47) = 11.65 inches.

ScanTesla7.62 matches 18.125 inch streamers to:

===============
ScanTesla  V-7.62  June 4, 2006  Terry Fritz
Goal = 1.811882e+001  Maximum Leader Length
Model Number = 33
Goal Number = 32
Cprimary = 2.500000e-008
Lprimary = 1.520000e-005
Rprimary = 3.000000e+000
Coupling = 0.100000
Csecondary = 1.786000e-011
Lsecondary = 1.903000e-002
Rsecondary = 2.200000e+002
Cload = 3.019803e-012
Rload = 2.200000e+005
BPS = 120.000000
Dwell (T1) Time = 4.000000e-004
Ilprimay Maximum = -586.024560
ICprimary RMS (Arms) = 10.143320   ILsecondary RMS (Arms) = 0.198816
VCprimary Maximum = 15637.864770
VCsecondary Maximum = 206184.112188
Coil Power = 376.596037   Primary Bang Energy = 3.138300
Load Power = 61.741797   Load Bang Energy = 0.514515
Leader Length (in) = 18.118816  Streamer
Primary F0 = 258183.410484   Secondary F0 = 272998.342486
Load Energy Rise Time (uSec) = 15.700000
==============

But the firing voltage is 15.6kV and the coil power is 377W!

The gap is burning up most of the power (308 watts) and I assume the breakout was with a needle point.

Since the 25nF cap value is "resonant" with the modified transformer, I think the primary firing voltage might be pretty high. In that case, an SISG would need many more sections than expected!! So don't "blame me" if an SISG firing at a true 5400V does not works so good :o))

If you put in a 5400V SISG the streamer length is 11.1 inches.
If you put in a 15300V SISG the streamer length is 31.8 inches!!!!
due to the massive reduction in gap losses:

=====================
ScanTesla  V-7.62  June 4, 2006  Terry Fritz
Goal = 3.184172e+001  Maximum Leader Length
Model Number = 27
Goal Number = 26
Cprimary = 2.500000e-008
Lprimary = 1.460000e-005
Rprimary = 3.400000e-001
Coupling = 0.100000
Csecondary = 1.786000e-011
Lsecondary = 1.903000e-002
Rsecondary = 2.200000e+002
Cload = 5.306954e-012
Rload = 2.200000e+005
BPS = 120.000000
Dwell (T1) Time = 4.000000e-004
Ilprimay Maximum = -625.298745
ICprimary RMS (Arms) = 16.286988   ILsecondary RMS (Arms) = 0.384995
VCprimary Maximum = 15090.010213
VCsecondary Maximum = 343993.817664
Coil Power = 351.135000   Primary Bang Energy = 2.926125
Load Power = 230.765294   Load Bang Energy = 1.923044
Leader Length (in) = 31.841721  Streamer
Primary F0 = 263435.136206   Secondary F0 = 272998.342486
Load Energy Rise Time (uSec) = 35.700000
==================

So I think the firing voltage is super high but the transformer seems to live :-))) Beware that a precise firing voltage SISG gap might not work so good unless it is made to fire at super high voltages, too in which case it might double the streamer length to 32 inches :-))))

I did not scan for the best "quench time", but ScanTesla "can" do that now too :-)))

Karl's secondary only has about 220 ohms of Rac loss too ;-)) If we take the secondary RMS current squared times that we get: 220 x 0.198816^2 = 8.7 watts. Very nice ;-)) That goes to 32 watts in the high voltage SISG case. Still "ok", but the secondary might get warmed up.

If you are going to make an SISG for it, think about 17 sections!!
and 32 inch streamers!!  Hope that little transformer lives ;-))

Cheers,

        Terry


At 06:48 PM 6/5/2006, you wrote:
I'm pleased to report a new entry and performance record in the
mini-coil competition, using a 4kV/20mA NST.  Karl Lindheimer has topped
my coil's performance by a very substantial margin, achieving a record
18.125" streamer length.  See
http://www.laushaus.com/tesla/minicoilcontest for contest details.
Karl's coil details are at
http://www.laushaus.com/tesla/minicoilcontest/karllindheimer_cat1.htm.

Karl uses the same NST as I do, similar gap, and same capacitor value.
He uses an 8" spherical top load while I use a 3.5"x10.75" toroid.
Wintesla calculates that Karl's Ctop is just slightly less than mine, by
less than 1pF, so I don't know that this is significant.

Where Karl's coil departs from mine is in a much larger secondary coil -
diameter, length, aspect ratio, and inductance, and a comparably higher
inductance primary.  Perhaps the "secret" to superior performance lies
in the higher primary inductance, lowering gap losses.

It's too bad that both Karl's and my experience shows that ultimately,
size matters.  The 3.5"x10.75" toroid I use is aesthetically much larger
than I would like.  I was hoping that the best performing mini coil
would be something I could keep on a shelf with no disassembly needed.

Congratulation Karl - and I look forward to you blowing away this record
with an SISG!  Maybe there, "gap" losses will be less sensitive to
primary inductance and overall size.

Regards, Gary Lau
MA, USA