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:
>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
> 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!!
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?