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Re: Smoking the Neons!

At 10:25 PM 10/20/96 -0600, you wrote:
>>From jgore-at-cyberramp-dot-netSun Oct 20 21:34:20 1996
>Date: Sun, 20 Oct 1996 01:48:51 +0000
>From: jgore-at-cyberramp-dot-net
>To: Tesla List <tesla-at-poodle.pupman-dot-com>
>Subject: Smoking the Neons!
>
>>Determine if you actually need a rotary. If you're only going to drive
>>from neons, a rotary won't improve your performance. - it'll only
>>smoke the neons!  Don't try to go cheap and dirty on a rotary. 
>
>Could someone explain this statement? How does using a rotary hurt my 
>neon sign transformers, and or my caps? I'm not being critical here, I really
>just don't know!
>I've designed my coil to use two 9KV neons, to make about 3 foot 
>arcs. Is a rotary really going to blow it? what could I do to make a 
>rotary work with a small coil like this?
>Thanks for any info...........................Jerry



Jerry,

I asked that same question just a couple of days ago.
I asked :

4. The message I get from the list archives is that rotary gaps are not
>>    for neons. The message is loud and clear that using a rotary on a neon
>>    is inviting transformer failure. Why? What is it that promotes a failure?
>>    I'm not likely to build a rotary anytime soon but would like to know just
>>    the same.



And then Robert Stevens said:

>Re your rotary gap and neons question.  Because of the inherently 
>high secondary inductance of a typical neon xfmer when used with 
>power matched capacitor sizes for tesla coils the resultant circuit often 
>operates at some level of 60 Hz resonant charging.  It is not 
>uncommon to see over 20 kilovolts appear across the output of a much 
>lower nameplate rated neon.  When you use a static gap system it inherently
>acts as a safety clamp, limiting the overvoltage on the transformer because
the 
>static gap is always physically present across the transformer.  When 
>one exchanges the static gap for a rotary, now you have a gap system 
>that may not have its contacts anywhere near closed at the same time 
>that the 60 Hz waveform on the neon secondary is experiencing a 
>voltage peak.  In this case the neon becomes grossly overvoltaged and 
>the smoke that is bottled up inside which it needs to work properly, escapes.





And then Jim Fosse said:

>Mike,
>Think about a static gap: it's just sitting there waiting for
>the voltage to rise above it's breakdown voltage (10KV - 15KV) ... The
>voltage across the neon will not exceed this value.
>
>NOW think about a rotary gap. It is NOT just sitting there waiting for
>the voltage to rise above it's breakdown voltage........ No, it's
>rotating; and changing it's breakdown voltage, to many hundreds of KV
>at max spacing. So the voltage across the neon will rise, to the
>neon's output voltage times the "Q" of the neon's leakage inductance/
>primary cap, to the breakdown voltage (100KV??) of the rotary gap.
>Eventually, the phase of the "resonant voltage" and the rotary's
>breakdown voltage will max ( at several hundred KV) and the poor neon
>will blow.


And then Richard Hull said:

>The rotary forces a break rate!!!!  Most beginners run the things at 
>countless billions of breaks per second!  Somehow or other, they find the 
>20,000 rpm motors and put 24 studs on a 6" diameter wheel and hum the 
>thing up.  This shortens the lifetime of a neon sign by about 10,000% 
>over just shorting the ouputs together, plugging it in and walking away.
>
>The series static gap allows the, naturally weak, neon transformer to 
>supply energy and quench the spark in its own good time and at levels 
>relatively comfortable to its natural desire to squelch the output 
>voltage.  This avoids any ill timed interupts and reflections from the 
>tank.  Still, the transformer is doomed!
>
>R. Hull, TCBOR
>


Three different answers all saying the same thing. Convinced me.
Build a vacuum gap - your neons will thank you.



Mike Hammer
mhammer-at-midwest-dot-net