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Re: Neon murder

Subject:  Re: Neon murder
  Date:   Mon, 26 May 1997 21:14:06 +0000
  From:   "John H. Couture" <couturejh-at-worldnet.att-dot-net>
    To:   Tesla List <tesla-at-pupman-dot-com>


At 03:39 AM 5/26/97 +0000, you wrote:
>Subject:      Re: Neon murder
>       Date:  Mon, 26 May 1997 13:09:31 +1200
>       From:  "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
>Organization:  Wellington Polytechnic, NZ
>         To:   tesla-at-pupman-dot-com
>
>
>Hi all,
>         Just like to make a comment about "filtering chokes" with 
>only a few 10's of uH of inductance. That value is comparable with or 
>less than the inductance af most TC primaries. Surely you should be 
>using at least a milliHenry or more???
>
>Malcolm
>
>> >  The problem is that the spark in the operating gap produces transient
>> >voltages that can easily puncture the insulation in a neon. These
>> >transients
>> >are in the nanosecond range and are partially blocked by a choke of
>> >about 30
>> >microhenrys. Most coilers believe the chokes are for the peaks of the
>> >operating dampened wave voltage which would require millihenry chokes
>> >and
>> >are not a problem. These peaks are usually less than twice the rated RMS
>> >secondary voltage which the neon windings can handle. 
>> >
>> >  
>> 
>> John, how do you suggest building a 30uH choke? What works best, flat or
>> cylinderical spiral, and does it get hot? Wire size?
>> 
>> Thanks in advance for any help.
>> Tristan Stewart
>> 
>>-------------------------------------------------------

  Tristan, Malcolm and All -

  A 30 uh choke can be easily made with 50 turns spaced on a 2" dia x 8"
long PVC tube. The wire can be #12 AWG type TW or equal. Paint overall
with
varnish. Protective spark gaps should also be used on the neon secondary
connections. The RF choke will not get hot because the neon secondary
currents are not large enough and the impedance is low. 

Some coilers say they do not use RF chokes but this is for pole and not
neon
transformers. Also, large TC systems have enough inductance in the
primary
circuit wiring to attenuate the transients without RF chokes.

  This RF choke will attenuate nanosecond voltage transients to at least
50%
which appears to work well with typical classical Tesla coils up to
about 3
KW. Note that if the choke inductance is too large (millihenries) and
the
connections too close together the voltage drop of the transient across
the
choke can be large enough to cause the transient to spark across the
choke
and negate the protection of the neon transformer. There are reasons why
the
protective spark gaps do not cause these problems.

  The transients ride on the top of the operating dampened wave voltage.
This problem also occurs on electric power company high voltage
transmission
lines. When these lines are disconnected (like TC operating spark gap)
an
arc occurs at the switch which causes voltage transients along the line.
Utility power transformers are protected from these transients (and
lightning) by surge suppressors. These suppressors could be used to
protect
TC neon and pole transformers but the cost is prohibitive.

  Note that the above RF chokes are used for a different reason than the
RF
Filters on the low voltage primary side of the neon. The RF Filters
(millihenries) help prevent the RF operating frequencies from going out
on
the utility power lines. The design of these filters are a different
problem.

  If you have other RF choke questions, let me know and I will try to
answer
them. 

  John Couture