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# Re: [TCML] Tesla Coil parameters list like Tesla Map software (i.e. spark length, secondary height, # of NSTs)?

John,

I see what you mean with the formula 1.7 * sqrt NST power. I'm only getting
about 50-65% of that meaning at 1850W I get 3-4' sparks and should get
closer to 6'

I am using a 20A 0-130vac variac that actual gives up to 145 vac measured.
It is when I turn this up bast 120vac on the dial I get closer to 4' sparks
- BUT then I'm blowing 20A fuses in the variac.

toroid diameter (inches) = 0.5*sqrt input power (watts)

means with 1850W I should only use 21.5" and I have 6"x25" so that's close.
However, If I move up to an 8" diameter aluminum dryer ducting (with 17.75"
center) that will be almost 34". I keep reading Bigger is best but it
sounds like it may not be here.

Thoughts?

Tim

On Mon, Apr 6, 2015 at 8:45 PM, Futuret via Tesla <tesla@xxxxxxxxxx> wrote:

> I use the formula:
>
>  spark length (inches) = 1.7*sqrt input power (watts)
>
> For example a coil that uses 1000 watts should
> produce a 53.7" spark.  However this formula only
> works for very efficient coils.  To get this sort of
> efficiency it's usually necessary to use a synch
> rotary spark gap at 120 bps, and a suitable LTR
> sized capacitor (for NST systems).  Such a coil
> would work well with a 16" toroid.  Toroid size tracks
> with spark length as given by the formula.
> Figure the toroid diameter should
> be about 0.3 times the calculated spark
> length.  Or use the formula:
>
>  toroid diameter (inches) = 0.5*sqrt input power (watts)
>
> Note that my formula uses a square rule for
> spark length vs. power input.  The older idea
> of using a more linear relationship probably
> came about because many small old coils
> tended to be inefficient and therefore gave a
> false impression.  The toroid formula will
> also only work right for an efficient coil.
>
> For example my TT-42 coil produces a
> 42" spark from an old "robust" 12/30 NST.
> The system draws about 800 Watts.  The
> formula suggests 48" sparks, but I only
> get 42".  However I have to crank up
> the input power using a 140V output
> variac to get the 42" spark, so the NST
> is probably saturating some at that point,
> and becoming less efficient.  NST's can
> draw a lot more than their rated power
> in a Tesla coil running at 120bps.
> Over-volting them also makes them
> draw more power.
>
> Your 6" x 25" toroid should be able to
> produce 80" sparks (assuming a
> suitable Tesla coil design and power
> input.  I don't think going to an 8"
> There must be something else
>
> John
>
>
>
>
>
>
>
> -----Original Message-----
> From: Timothy Gilmore <tdg8934@xxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Sent: Mon, Apr 6, 2015 8:09 pm
> Subject: Re: [TCML] Tesla Coil parameters list like Tesla Map software
> (i.e. spark length, secondary height, # of NSTs)?
>
>
> I found Jeff Pennoyer's
> site:
>
> http://www.webring.org/l/rd?ring=teslaring;id=107;url=http%3A%2F%2Fhome%2Ecomcast%2Enet%2F%7Epennoyer%2FJeffPage%2Ehtml
>
> At
> the bottom there is this list which falls in line with what I was
> looking for
> on spark length:
>
> APPROXIMATE SPARK LENGTH VRS POWER INPUT CHART
> SPARK LENGTH
> POWER INPUT
> 6 - 8 INCHES 300 W
> 8 - 12 INCHES 500 W
> 12 - 18 INCHES 700 W
> 15 -
> 20 INCHES 1000 W
> 18 - 24 INCHES 1200 W
> 24 - 30 INCHES 1500 W
> 30 - 36 INCHES
> 2000 W
> 36 - 45 INCHES 2500 W
> 45 - 56 INCHES 3000 W
> 56 - 64 INCHES 3500 W
> 64
> - 72 INCHES 4000 W
> 72 - 80 INCHES 4500 W
> 80 - 90 INCHES 5000 W
>
> So using (2)
> 15kv 60mA NST provides about 1850 W. I am getting at least 36
> inches and many
> times 48 inches or more of sparks from my 6"x25" toroid:
>
>
>
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
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