Re: Cap Location (fwd)

---------- Forwarded message ----------
Date: Mon, 12 Jan 1998 19:44:01 +0000
From: "John H. Couture" <couturejh-at-worldnet.att-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Cap Location

At 05:38 AM 1/12/98 +0000, you wrote:
>From: 	terryf-at-verinet-dot-com[SMTP:terryf-at-verinet-dot-com]
>Sent: 	Sunday, January 11, 1998 10:16 PM
>To: 	Tesla List
>Subject: 	Re: Cap Location
>        Put the gap across the transformer, and the high voltages induced by
>the primary coil may hurt the transformer (especially if it miss fires).
>Put the cap across the transformer, and the high frequency high voltage
>signal is place directly across the neon burning the secondary winding.  An
>interesting dilemma.  
>        My thoughts are:
>                If the cap is across the transformer, the high-frequency /
>high-voltage signal will kill the neon for the following reason.  The neon's
>output terminals are basically very large value inductors.  The
>high-frequency voltage will be distributed very unevenly across the outer
>windings of the neon's secondary coils.  At 60Hz the voltage is evenly
>distributed throughout the winding but at say 200KHz the voltage will be
>mostly blocked by the inductance of the neon's secondary winding resulting
>in most of the voltage drop on the last few turns of the secondary winding.
>Then pop!...neon's got burnt windings.
>                With the gap across the transformer, if the gap opens under
>a high current condition (rather unlikely but....), the voltage induced by
>the TC's primary inductance my go very high and also blow the insulation.  
>        This is why we play with inductors, resistors, MOV networks, etc. to
>try and block these nasty signals from the neon.
>        With the gap across the transformer, a spark gap should be able to
>save the neon from the spikes and you should be OK.  With the cap across the
>transformer, you will need inductors, resistors, and other messy to design
>parts.  Can't make any mistakes with these or the neon gets fried.  
>        You must also be cautious of the output of the neon and the primary
>capacitor resonating and producing higher voltages than you want.  My 15KV
>60mA neon and 0.01725uF primary cap can reach 15KV at only 40 volts AC in
>due to this.  If I were to put 120VAC into the neon it would hit about 45KV
>and the cap or the neon would blow.  
>        To make a long story short, go with the gap across the transformer
>and use a good spark gap across the transformer to catch any induced spikes
>during the break.
>        In a related note, my real-time fiber-optic voltage and current
>probe is now working properly after many months of dealing with bandwidth,
>noise, finding parts, etc.  It can easily measure the situations we have
>here.  I have been trying it in a number of situations and I will soon have
>it hooked to a full power primary circuit which will easily show the
>differences between the two situations described above.  I will report the
>results as available.  I will try the circuits without the secondary in
>place for now since I have calculators, laptop, digital scope, etc. laying
>all over the place.  Not ready for any 4 foot arcs right now :-) I may need
>to build a new spark gap first.  According to the probe, my present gap
>really sucks!  Works for a few pulses then just acts like a continous short.
>You can easily hear the transition from proper arcing to poor shorting once
>you can see it on the scope as it is happening.  Very interesting stuff!!
>        Terry


   Terry -

  We will all  be waiting anxiously to hear how your research turns out.

  One note of caution on the rise in destructive voltages. There is a big
difference in whether the voltage wave is a sine wave or a nanosecond pulse
wave. The type of waveform (RMS or Peak or pulse width) should be indicated
for the voltage. The sine wave requires much greater energy than the pulse
type. A gain in sine wave voltage could require a gain in input energy. This
is not true of pulse type waveforms.  However, either waveform can destroy a
transformer or other electrical equipment.

  What is the load on the neon with the 15 KV at 40 volts? 

  John Couture