Re: NST/OBIT current limiting (fwd)

---------- Forwarded message ----------
Date: Thu, 18 Dec 1997 17:22:38 -0700
From: terryf-at-verinet-dot-com
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: NST/OBIT current limiting (fwd)


>From: Adam <absmith-at-tiac-dot-net>
>To: tesla list <tesla-at-pupman-dot-com>
>Subject: NST/OBIT current limiting
>Does anybody know how the current limiting on an NST or OBIT varies with 
>output voltage?  For example, when I crank the variac to 140V, does the 
>current increase from the rated value also? What happens at saturation of 
>the core?
>I am quite curious as to the nature of the limiting mechanism, since I've 
>never seen any curves for the output.

The output current is normally proportional to input voltage.  Ie.  A 60 ma
xfmr at 120 volts will become a 30mA xfmr with 60 volts in.  When you hook a
capacitor accross the output things change dramatically.

>From: Adam <absmith-at-tiac-dot-net>
>To: tesla list <tesla-at-pupman-dot-com>
>Subject: Resonant  rise in my obit.

>I knew that matching the cap to the transformer caused a resonant rise, 
>but I was unaware of exactly how great it could be.  I did a little test:

>I hooked up my variac, with voltmeter, to my Webster OBIT.  I then 
>connected the obit's HV outputs directly across 5 0.030" gaps in my 
>cylinder static unit.  The gaps arc'd at a variac setting of exactly 121 
>VAC.  Next, I connected my 0.006uF rolled cap across the gap, and it now 
>begins to fire at 21 VAC input.  Almost a factor of 6 in voltage rise! 
>That is pretty extreme.
>Adam Smith

That's why we blow them up all the time :-)  The rise you see is typical.  A
15000 volt neon could get up to 100KV+ with a good capacitor match.  Of
course, it would fail very quickly.  The current output also has a similar
resonant rise if you want to place an ammeter accros the secondary and
repeat your test.

The other big neon killer is insufficent protection of the neon output
terminals from high frequency RF.  The neon can take 15000 volts at 60 HZ
but hit it with 15000 volts at 200 KHz and it will fry.