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Re: Safety gaps destroyed my Neon ?
Two replies in one,
At 09:01 AM 5/28/98 -0700, rwstephens-at-hurontario-dot-net wrote:
>Tesla List wrote:
snip....
>
>Viv,
>
>I have been arguing against using a grounded center tapped NST safety
>gap for years because I feel this is asking for trouble as you pointed
>out. You just cannot guarantee that both gaps will light simultaneously
>to stop the voltage surge with such a gap system. One half going into
>the conductive state might well reduce the overall surge sufficiently to
>prevent the second from lighting at all. At the same time, a healthy
>surge then becomes directed to where it can do damage. Just my opinion.
>
>Robert W. Stephens
>
I have seven 1800 volt 2500 amp MOVs across each leg my neon output. They
are DigiKey # P7215-ND or Panasonic ERZ-V10D182. I also use safety gaps
but these MOVs have just sit there quietly working away. They cost about
$20 for all of them. Since I do so much testing, I figured they would be a
good investment. I have never had a problem with them and they seem to
work fine. Although, I don't know if they have ever had to really work or not.
Viv wrote,
>No I don't have any resistors only two 3mH chokes. After
>these problems I intend filters, resistors etc etc. I
>need to SEE whats going on, so getting a high voltage
>probe to try scope this stuff is a new objective..
I would definitely get resistors. Inductors and capacitors don't have a
way of dissipating energy so they simply store it and oscillate. No
telling where the energy eventually may end up. I no longer use inductors
in protection circuits because they just like to ring too much.
I would also be cautious of having gaps directly across capacitors because
they may damage the caps due to high current, they may not stop the voltage
surge with so much current, or they may cause high dV/dt which could damage
the neon's high inductance windings. I put safety gaps basically in
parallel with the main sync rotary so as to fire if/when the sync gap misses.
Also, In resonant systems, the currents from the neon "can" me much higher
than it's ratings. There may be a problem there but we usually consider
neons to be pretty tough current wise given that we run them at room
temperature and for brief periods. Also they supply near their ratings the
vast majority of time in their normal neon sign uses.
Cheers,
Terry
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