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Re: EMI Filter Hookup? -- Internal House Wiring Popping And Crackling



>Original Poster: "William Parn" <parn-at-fgm-dot-com>
>
>I need help in how and where to hookup a EMI filter?
>
>Many Thanks,
>Bill Parn
>
Ok Bill,

I was a little short in my first reply, let me correct that.
(but on the list this time, because it could be interesting to more people,
and yes I made a joke).

EMI filters normally have the following configuration:

2 cap's from Line and Nul to Earth (4.7 - 10 nF)
1 cap between Line and Nul (0,25 - 0,47 uF)
1 resistance between Line and Nul (220 - 1.500 kOhm)
2 coils with ferrite core in series with Line and Nul (1,5 - 4 mH)

The values are just for indication. They are values I have seen and measured
on commercial EMI filters. Basically they are low-pass filters (50/60 Hz AC
resistance is low for the coils, but high for the capacitors, but for RF of
course this will be the other way around).
The resistance is probably to unload the capacitor, because it could hold a
dangerous voltage when the fuse is gone. I can really see no reason why the
direction could be important. I've seen all kind of configurations in
commercial filters. Some of them were opposite connected compared to others.
Maybe Dr. Resonance could explain why the direction is important.

The only value that's important for us, is the maximum RMS current.
Big copiers does have nice rated EMI filters (10 - 16A).

But the EMI filter is just the 'thin piece of rubber' I ment. The real work
has to be done between NST/MOT/PIG and fire gap. If you don't filter
there you will eventuelly blow your power supply! And because of the High
Voltage over there, you must make your own filter.  Normally this means 2
capacitors to earth and 2 resistance's serial, because coils here seems to
introduce unwanted ringing (you could look into the www.pupman-dot-com archives
for details).

To overcome this kind of filter problems (behind the power supply I mean)
I'am thinking about a DC supply in combination with a special RSG with load
and unload segments on it, but it could take some time before I can report
results. I'm a family man with a demanding job, so building a decent TC is
not done overnight.

Ruud de Graaf
Greetings from lovely and 'spring is in the air' Holland