RE: Re-configuring X-Ray Transformers

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Thomson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>

Hi Godfrey,

Your advice is sound and much appreciated.  I won't run this transformer on
a standard Tesla coil as you are correct, most of the energy will be wasted
on corona discharge.  If I decide to use the X-ray transformer, I will build
a special coil completely submerged in transformer oil.  I have plans for
building one of Tesla's oil filled spark gaps as this is so far the best
design I have seen for reducing electrostatic leakage.  I'm first trying to
figure a way to use modern materials and parts to save lots of milling and
casting time.

I would like to point out an observation I have made concerning flat spiral
secondaries.  I have built several configurations of these coils and every
one of them runs a very quiet and cool spark gap.  Also, the transformer and
caps never heat up, regardless of whether the system is in tune or not or
whether the spark gap is wide or narrow.  I believe there is still corona
leakage, but not as much as with a cylindrical secondary coil.  So far,
however, I have only been able to get 5" sparks with a 15KV 60mA NST.  There
is much that needs to be explored concerning flat spiral secondaries.

I have just setup a new list just for working on this type of coil.  It's at
http://groups.yahoo-dot-com/group/spiralcoils/

Dave

David Thomson
dave-at-volantis-dot-org <mailto:dave-at-volantis-dot-org>


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, January 31, 2002 8:17 AM
To: tesla-at-pupman-dot-com
Subject: RE: Re-configuring X-Ray Transformers


Original poster: "Loudner, Godfrey by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <gloudner-at-SINTE.EDU>

Hello David

I think you said that your x-ray transformer was 110kV at 3mA. This is not
necessarily the true rating of the transformer. It means that with the
proper x-ray tube in place, the transformer will deliver a steady 110kV at
3mA. The design of an x-ray transformer is done with the load of the x-ray
tube very much in mind. You transformer is probably for 120 volt input. With
no load on the transformer, the voltage might be very much in excess of
110kV. The amount of excess will depend upon the quality of the transformer.
With a load like a tesla coil, the current output could be much more than
3mA. Since your transformer is small, it is unlikely that it can delivery
high currents for sustained periods of time without burning the primary or
secondary. Because there is much room for heat sinking, the huge x-ray
transformers can delivery currents substantially over those needed for x-ray
tubes. I don't know if your transformer is rectified or not. Your probably
better off if the output is DC, but will the rectifier system withstand the
extra current that is sure to be above the x-ray tube application? Even if
the rectifier system could handle the current, RF currents, caused by arcing
the secondary, will eventually destroy the rectifier. Even if the output is
AC, you will still have to operate at very high voltage to get a current of
3mA or higher. In the case of AC output, I would employ a LTR (larger than
resonant) cap. Actually running at about 110kV is uncharted territory. There
will be certainly severe corona problems at the primary and spark gap. I
would go for a static gap. You might have to put the tesla coil under oil to
control the voltage stress. I once read about someone who ran a tesla coil
from a 150kV/1000mA x-ray transformer, with the production of huge
streamers. I did not believe a word of this fish story. Considering all the
problems, I would not try to run a tesla coil with your transformer. But if
you really like to experiment in uncharted territory, don't let my opinion
stop you.

Godfrey Loudner

> -----Original Message-----
> From:	Tesla list [SMTP:tesla-at-pupman-dot-com]
> Sent:	Wednesday, January 30, 2002 1:23 PM
> To:	tesla-at-pupman-dot-com
> Subject:	RE: Re-configuring X-Ray Transformers
>
> Original poster: "David Thomson by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>
>
> Hi Dave,
>
> >	Others have tried HV (typically x ray) transformers.	I believe
> the catch
> has been that a distinctly different spark gap approach is needed...
> >	And the choice (or construction....) of caps becomes
> challenging...
>
> Thanks, I would like to connect this X-ray transformer to a spark gap.  I
> can easily make capacitors to handle the voltage.  Plexiglas and aluminum
> capacitors I make work well and are rated well over 150KV.  Am I right
> that
> the higher the input voltage, the smaller the caps should be?  I have a
> 100
> to 300pF variable capacitor rated at over 150KV I could use if it will
> match
> the transformer.  I could make a larger capacitor if necessary.
>
> Would a standard air gap work or do I need something with less losses?
>
> Dave
>
> David Thomson
> dave-at-volantis-dot-org <mailto:dave-at-volantis-dot-org>
>
>