Re: neon vs. potential transformer
Sent: Tuesday, July 15, 1997 4:14 AM
Subject: Re: neon vs. potential transformer
In a message dated 97-07-15 01:36:44 EDT, you write:
><< > I also had tried using a 15 kV, 60ma neon trans, which gave a 65"
> > spark and drew 2600 watts. Yesterday, I installed the potential
> > trans into the same TC and with 6.7millihenries of ballasting, it
> > produced a 65" spark and drew 2100 watts. Toroid size is 6" x 26".
> I wonder if you could enlighten me about your Xformers. I have a 30mA
> 12Kv neon and the wattage on the nameplate says 360W. Do these
>tranformers really draw almost double the nameplate rating?
> Also I have been running a TC with 2 30Ma 15Kv Neons and I only get 30"
> sparks and I am sure they do not draw 2.5 Kw!(they would have blown my 8
> amp fuse) Are these modified neons you are using? If not, please tell me
> the secret of how do you get such long spark lengths from such low
> Also, what is a potential xformer?
> Cheers and some confusion from down under,
> Peter E. >>
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
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.
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.
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.
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.
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.
Finally the coupling between the primary and secondary should be
adjusted for best performance. I obtain the best performance with
my systems using a k value of about .12 or so.
Good luck with your projects,