Re: NST Filter

["Tesla list" <tesla-at-pupman-dot-com>]

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, tesla-at-pupman-dot-com 
>writes: 
>
>Woa! Does that sound like another switch I know of... - Spark Gap??? The only 
>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 
>hometown.aol-dot-com/kidd6488/tesla
>

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.  MOVs
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 lower
than the threshold to turn them on.

So, the primary cap charges to 18000 volts, the string of 10 MOVs turns on,
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 high
voltage spike thus reducing their internal power dissipation and allowing
them to take a lot of abuse as in Ed's post today.

Cheers,

	Terry