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Re: [TCML] Isolating Transformer

>From my personal experience, Dave is correct. Although there is no way in the real 
world to stop all EMI feedback from the harmonics rich RFs generated in the pri-
mary circuit, you can stop "some" of it. When I run my big SGTC, ~40 ft. outside
my garage on the driveway, one set of the florescent ligths in my shop always goes
"haywire", inspite of the incorporated filtering inside my control panel. However,
adding small EMI filters at the input of my RSG motor and the fan motor does 
seem to prevent premature death of the said motors, as opposed to running
them with no EMI filtering at the input.

From: dave pierson <dave_p@xxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx> 
Sent: Friday, April 26, 2013 1:08 PM
Subject: Re: [TCML] Isolating Transformer

> My knowledge about electronics and frequency filters is limited to
> basic stuff, so is it valid if I'm wondering if an off-the-shelf
> line filter does do anything usefull in the first place?
  it varies.  depends on the filter.

> Especially for larger coils with a resonant frequency around or below
> the 100kHz, since I think most filters start to be effective from the low
> Mhz range. Doesn't anyone happen know usefull schematics for a DIY high
> current, low-pass filter, which has an effective cutoff above mains
> frequency?

> As far as I've learned, an iron core in a transformer, is effective at
> mains -low- frequencies and therefore shouldn't pass the higher
> frequencies.
  Sort of: Transformers, as all components, have lots of
  stray effects.  Notably, in this case, there is stray capacitance
  primary-secondary, primary-core-secondary.  This stray capcitance
  can pass higher freqs nicely.  Special transformers, as i mentioned
  earlier have internal shields.

  Another stray effect: highish freqs can radiate AROUND a filter,
  coupling coil side to line side by capacitance, inductance, emi.
  to be Really Effective the filter must be 'in' a 'shield wall',
  aka a Faraday Cage. 

> But I've read higher frequencies are still passed, because of
> inductive coupling between windings, which leaves me a bit confused.
  And capacitive.  There are the ideal components, existing in
  textooks, and the real ones, with lotsa stray effects.

>A bit of explanation would shed some light on this matter.
  bESIDES A BIT OF tESLA coil tinkering, i have worked in
  pro grade EMI/RFI.  One of my 'mentors' learnt his on
  1500VDC, 2000A locomotives...

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