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Re: NST Max Ratings and Mains Resonance (fwd)
---------- Forwarded message ----------
Date: Fri, 13 Feb 98 09:05:13 EST
From: Gary Lau 13-Feb-1998 0847 <lau-at-hdecad.ENET.dec-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re: NST Max Ratings and Mains Resonance
>From: Thomas McGahee <tom_mcgahee-at-sigmais-dot-com>
>
>Bill, Malcolm, and other interested coilers,
>Besides the resonant rise that Malcolm mentions, there is also
>the fact that when the main cap and the transformer are set to
>resonate at the mains frequency, the transformer is capable
>of providing current levels that are several times the usual
>'current-limited' value. If the wire in the secondary is too
>thin, then you can actually burn out the secondary winding
>under these mains-resonant conditions.
>
>Thus, with the proper resonant conditions a 15KV 60 MA
>NST can charge the mains cap up to voltages in excess of
>40KV, and at a rate that is much greater than the 60 MA
>rating would suggest. Note that both the extra voltage and
>extra current can contribute to the NST failing prematurely.
Since changing from an RQ static gap to a sync rotary gap, I believe
my 15kv/60mA NST is delivering enormous secondary currents, due to the
choke series resistors (500 Ohms/75 Watts) smoking. This implies currents
of ~400 mA. While using a sync gap guarantees that the cap voltage won't
ring up on multiple cycles, I am concerned about toasting my NST's delicate
windings. Is there a way to calculate what the maximum secondary current
from my NST is, knowing that it is resonant with my .01 uF cap? Is there any
way to de-tune this resonance, short of changing cap value or different NST's?
Gary Lau
Waltham, MA USA