# Re: neon vs. potential transformer

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From: 	Rodney Davies[SMTP:rgd872-at-anu.edu.au]
Sent: 	Thursday, July 17, 1997 8:01 PM
To: 	Tesla List
Subject: 	Re: neon vs. potential transformer

Hi John and Peter,

On Tue, 15 Jul 1997, Tesla List wrote:

> From: 	FutureT-at-aol-dot-com[SMTP:FutureT-at-aol-dot-com]
> Sent: 	Tuesday, July 15, 1997 4:14 AM
> To: 	tesla-at-pupman-dot-com
> Subject: 	Re: neon vs. potential transformer
>
> In a message dated 97-07-15 01:36:44 EDT, you write:
>
> Yes, normal neon transformers can draw double or more their rated
> wattage, it all depends on the size of the tank capacitor.  Certain
> capacitance values will result in an equal but opposite reactance
> to the leakage reactance of the transformer.  The result is that a
> 60 Hz low frequency resonant condition is created.  Effectively,
> the current limiting feature of the transformer is "neutralized",
> allowing the transformer to draw more current.  The use of this
> "resonant charging" effect is one of the secrets of neon TC
> performance.
>
> I forget the formula for calculating the proper capacitor size offhand,
> but someone will probably post it again.   A .007uF capacitor works
> well with a 12kV, 30ma trans, and a .014uF works well with a 15kV,
> 60 ma trans.

1
C = ------------
2*Pi*F*R

Where C is capacitance if Farads
Pi = 3.14159....
F is line frequency 50/60Hz
R is impedance of transformer (Volts/Amps)

> A potential transformer is a type of transformer used by the electric
> ulitility companies for measuring the voltage on their high voltage
> power lines.  These transformers are very well made, very robust,
> and have low losses.  Two of these transformers used together can
> approach the performance of a pole or distribution transformer.
> Unfortunately, they can be hard to obtain.

If you like Peter, you can use my SWER...

> I use a special "series-rotary" synchronous spark gap on my TCs,
> which might just help their performance a little.  I suspect however
> that a well made, multiple static gap with air or vacuum quench may
> equal or come close to the sync-gap in performance, but I can't be
> sure about that.  There's been a lot of postings on the list cautioning
> coilers not to open up their gaps too wide to prevent transformer
> destruction.  To obtain maximum spark output however, it is necessary
> to use a maximum gap setting.  I have not destroyed any neon
> transformers since I've been using safety gaps, but still, the possibility
> of destruction is there.

if you're going to use a rotary, it is highly advisable that it *is* a
synchronous rotary (Peter, for us it's 1500 rpm, or multiples of that..)
Asynchronous gaps + neon transformers (eventually) = dead neons.
I built a series air-quenched gap for my Neice's coil in Brisbane and
works quite well...
Jason Judd and myself were playing with his coil this evening using a
static 7-point gap (self-quenched) and were getting a good 19-20 inches
from 2 15KV 30mA neons in parallel.
The coil is a 13.5" winding length on a 4" (I think) diam pvc pipe using
0.25mm space wound copper wire. Roughly 550 turns.
We built a rolled capacitor for it tonight which measured around 12.73 -
12.79nF. This is the best performance to date... mind you, it's was about
midnight and -3 degrees C in his garage, so we left early...

> I also like to use more than the usual number of turns in both the
> primary and secondary coils.  I use from 25 to 35 turns in the primary
> and about 1500 turns in the secondary.  But many coilers have
> obtained very good results using far fewer turns, so I can't say for
> sure how important this is either.  In general, it would seem that more
> turns would raise the surge impedance of the tank, and lower the
> percentage of power lost in the spark gap.

Exactly the theory Jason and I came up with. Those winding dimensions are
typically unusual, however, the idea of not loosing energy across the
spark gap was what sparked of an interesting thought pattern. I must
commend you John on your output with this type of coil...very impressive!

> It is important to use the correct sized toroid.  A toroid that is too
> small will produce numerous simultaneous spark streamers but they
> will all be short.  A toroid that is too large will not allow the spark to
> reach it's full length.