Re: [TCML] Corcom EMI filter

[Gary Lau <glau1024@xxxxxxxxx>]

I don't think there's a simple answer here, or a simple way to find out.
For the damage to the irrigation system, it's not clear if the offending
spikes originated from the Tesla coil power cord.  I think it's at least as
likely that cables coming out of the irrigation unit were capacitively
coupled to the streamers and topload, and the irrigation unit power cord
provided the return path to ground for the coupled transients.  If this was
the failure mode, adding any amount of AC line filtering wouldn't have
helped.

Alternately, maybe the RF ground was poor for any number of reasons.  Maybe
the RF ground cable was too long, had excessive inductance, etc.  A poor RF
ground would result in some portion of the ground current seeking an
alternate path to earth, the only alternative being the AC mains wires.  A
better RF ground would be the better way to reduce the RF voltage developed
on the mains leads, but it's possible that an EMI filter may help as well.
But one should bear in mind that EMI filters are designed to attenuate
frequencies far higher than the resonant frequencies typically encountered
in most of our coils.

I used the words "if, maybe, or, alternately" a lot above.  The truth is, I
don't know what the exact nature of the beast is that kills appliances, or
how to go about finding out.  I use a Corcom EMI filter in my coil, just
because it's cheap and won't hurt.  I have a ferrite EMI thingie on the AC
cord to my coil for the same reason.  And I have MOV's on the hot & neutral
lines to ground in my Variac.  I can't prove that any of this helps, but it
seems reasonable.  But most importantly, I disconnect all cables going to my
garage door opener when running a coil in the garage.

As far as the Terry filter being a low-pass filter, this is true.  But, it
is not meant to do a lot of attenuating at the coil's resonant frequency.
Additionally, the RF ground, which is actually extremely active, RF-wise, is
connected to the NST's core, and does not go through the Terry filter.  The
Terry filter is only designed to prevent damage to the NST.  Reducing EMI to
the mains was never it's intent.

Regards, Gary Lau
MA, USA

On Tue, Nov 9, 2010 at 6:19 PM, Brandon Hendershot <
brandonhendershot@xxxxxxxxx> wrote:

> Hi Gary, Steve,
> These EMI Filters, would they eliminate all the bad transients coming from
> the coil via the power cord? Or would they simply limit it a lot more?
> Filtration is definitely something I think we all should all be more
> concerned with as potential victims of serious collateral damage.
> Brandon
>
> On Tue, Nov 9, 2010 at 3:01 PM, Gary Lau <glau1024@xxxxxxxxx> wrote:
>
> > The filter case should be connected to the mains green-wire ground.  I've
> > written a web page on this very non-intuitive topic:
> > http://www.laushaus.com/tesla/emifilter.htm
> >
> > Regards, Gary Lau
> > MA, USA
> >
> > On Tue, Nov 9, 2010 at 4:01 PM, Steve Vance <steve_vance@xxxxxxxxxxxxx
> > >wrote:
> >
> > > Hello List,
> > >  After reading about all the stuff other people have fried with their
> > Tesla
> > > Coils I think I will add some more protection to my current build. I
> have
> > a
> > > few Corcom 30VSK6 30 amp EMI filters laying around. I think I will put
> > one
> > > on the supply line of my 12/30 NST powered coil. The question I have
> is,
> > > would it be better to connect the case ground of the filter to the
> mains
> > or
> > > the rf ground?
> > > Any input would be appreciated.
> > > Steve
>
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