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Re: Smoking the Neons!
>Date: Mon, 21 Oct 1996 22:25:30 -0600
>From: Tesla List <tesla-at-poodle.pupman-dot-com>
>To: Tesla-list-subscribers-at-poodle.pupman-dot-com
>Subject: Re: Smoking the Neons!
>Reply-to: tesla-at-pupman-dot-com
>
>> Subject: Smoking the Neons!
>>From bert.hickman-at-aquila-dot-comMon Oct 21 21:21:29 1996
>Date: Mon, 21 Oct 1996 00:27:02 -0700
>From: Bert Hickman <bert.hickman-at-aquila-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: Smoking the Neons!
>Tesla List 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
>> -=*< If your not shooting in 3D then your not getting the whole picture >*=-
>
>Jerry,
>
>Jim Fosse had a recent post that concisely described the problem. If the
>rotary gap is not synchronized to the 60 Hz power coming in, there will
>be times when the voltage stress on the neons exceeds their insulation
>capability. This is especially true if you've sized your cap to be about
>the maximum for your neon's current rating.
>
>If you still want to use the rotary, put a single static gap across your
>transformers. With everything else disconnected from the neons, set the
>gap spacing to be just a little bit wider than the arcover distance. Now
>hook up the rest of the system. If the rotary "misfires" the static gap
>will fire, preventing severe overvoltage getting to the neons.
>
>You also should add series inductors, caps to ground, and safety gaps to
>ground for reducing RF coupling to the transformers, and to provide a
>path to ground for any secondary "hits" that may couple into the primary
>circuit.
>
>Safe coilin' to ya!
>-- Bert --
Bert,
I do not concur with the advice to use RF bypass capacitors to
ground from the terminals of a small shunted transformeer such as a
neon. Any capacitor large enough to be a good RF bypass (low
reactance) at a few hundred kilohertz will also be so large as to compete bigtime
with the system capacitor for the meagre charging power available
from the high impedance secondary winding of the transformer.. My experience
using merely measly 500 pF doorknobs on a 10kV -at- 23 mA funace transformer
is a failed transformer in about 45 seconds of operation into nothing else but
the bypass caps! I did this twice, the first time with 500 pF an they
second time with only 250 pF. Both times I heard sizzling inside as they
failed. This has been discussed on the list before. It seems that
the voltage does not distribute itself evenly along the secondary
winding and resonant effects caused by external capacitance loads can
cause crest points within the winding space and a hot spot followed
by insulation failure.
rwstephens