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Re: NST Max Ratings and Mains Resonance (fwd)
---------- Forwarded message ----------
Date: Sat, 14 Feb 1998 09:08:54 -0500
From: Thomas McGahee <tom_mcgahee-at-sigmais-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Cc: lau-at-hdecad.ENET.dec-dot-com
Subject: Re: NST Max Ratings and Mains Resonance (fwd)
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: NST Max Ratings and Mains Resonance (fwd)
> Date: Friday, February 13, 1998 11:15 PM
>
>
>
> ---------- 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
Gary,
Steal an idea from the pole pig crowd. Add a series inductance with the
the NST primary. Several coilers have had reasonable success using
microwave transformers. You disconnect the secondary wire that goes to the
core, and connect the two secondary wires together. Dead short, but this is
a current limited transformer, so it takes the abuse. You may have to use
more than one microwave transformer. You connect the primaries in series with
the NST primary. You might want to add a resistance in parallel with the
microwave primaries to smooth things out a bit. You will have to
experiment, but that is where half the fun is anyhow :)
The added inductance should 'spoil' the 60Hz resonance effects enough to
help your NST survive longer.
Hope this helps.
Fr. Tom McGahee