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Re: NST Filter
Original poster: "Jason Petrou by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jasonp-at-btinternet-dot-com>
Terry, Jonathon, Michael, all,
Thanks for the help with the MOVs... i now see how they work - very clever
invention!!! Im assuming that the capacitors / capacitor are high impendence
for low freq. AC and low impendence for high freq ac, therefore shorting out
all high frequencies that will otherwise go to the xfmr... is the value of
the capacitor critical? for example could I use a 500pF 40KV cap for this,
instead of lotsa dinky ones? Also is it neccecary to connect the whole thing
symetrically to RF ground - ca you just put the whole thing between the two
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
Sent: Friday, June 08, 2001 3:36 AM
Subject: Re: NST Filter
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> Hi Johnathon,
> At 09:48 PM 6/7/2001 -0400, you wrote:
> >In a message dated 6/7/01 09:43:23 PM Eastern Daylight Time,
> >Woa! Does that sound like another switch I know of... - Spark Gap??? The
> >problem I see with using a MOV instead of a SG is that maybe there is too
> >much current to be switched by a MOV. I think...
> >Jonathon Reinhart
> There is a big problem...
> When a spark gap arcs it will turn on and stay one no matter what the
> voltage. Only when the current reaches zero will it stop conducting.
> will stop conducting once the voltage goes less than 1800 (for the ones I
> use). So a gap made with them will simply quit once the voltage gets
> than the threshold to turn them on.
> So, the primary cap charges to 18000 volts, the string of 10 MOVs turns
> and the cap discharges back to 17900 volts and the MOVs turn off...
> Another way to look at it is the power dissipated is 1800 volts multiplied
> by the RMS current of the primary (~10 amps) so each one would dissipate
> 18000 watts!! :-)) Of course, that is assuming they were working, which
> they will not...
> For protection, this is great since they will only clip the peaks of a
> voltage spike thus reducing their internal power dissipation and allowing
> them to take a lot of abuse as in Ed's post today.