RE: Why do TC's use line filters wired in reverse

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

Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Gary.Lau-at-compaq-dot-com>

Hi Terry:

I hadn't seen the dual-stage filters before as all of the surplus/ham-fest
ones I've come across are single-stage.  But I think even the dual-stage
units are not truly symmetrical and would matter as to which way they are
connected.  There are two stages of inductors - one for common-mode and one
for single-ended noise.  In Bill's filter (and in general I suspect) the
common-mode chokes are a much higher inductance value and probably form a
better filter for what we're trying to eliminate.  I would want this to be
the first line of defense and nearest to the NST, as anything that gets past
it is coupled into the case ground.

There is also more to consider when tying things to the RF ground in the
hope of protecting them in the event of a streamer-hit.  I had at one point
tied everything metal and within striking distance to RF ground.  Fan
housings, motor cases, PFC cap cases, etc.  However, I recently burned out a
motor speed control dimmer, I believe by subjecting it to the high voltage
transients present between the AC neutral (ultimately tied to 3rd wire
ground) and RF ground that the dimmer case was tied to.  The narrow
clearance between the circuit traces and the case arced and took out the
circuit.  I can easily see a similar thing happening between a fan or RSG
motor housing and the windings or PFC cap case and outer plate, so I no
longer RF-ground things that have narrow clearance to AC wiring.  I've not
done so yet but it may be wiser to set up a decoy strike-shield *around*
things we don't want to get hit.  Of course we all know how unpredictable
streamers are...

Regards, Gary Lau
Waltham, MA USA


>Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
>
>Hi Gary, All,
>
>It looks like this is much more messy than I thought.  I always used "dual
>stage" filters and mine happened to be more or less symmetric.  However, I
>see Bill has found a non-symmetric one :-) 
>
>http://www.geocities-dot-com/billvanyo/emifilter.jpg
>
>Single stage filters are probably mostly non-symmetric too (as I say that,
>someone will probably find a symmetric one :-))
>
>Example schematics are at:
>
>http://hot-streamer-dot-com/temp/LineFilters.gif
>
>I think there are three factors:
>
>1. Is the filter symmetric or non-symmetric.
>
>2. Does the filter have a "dirty AC" and "clean AC" side.
>
>3. Is the filter AC or RF grounded.
>
>There is another factor to consider if the streamer should hit the grounded
>case...  I always RF grounded due to that.  I also use MOVs on my filters
>which only adds to the fun.
>
>So, depending on exactly what filter a person has, the hookups could be
>very different.
>
>Much to ponder...
>
>Cheers,
>
>	Terry

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