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Re: mains filters attenuation range.
>
> Original Poster: Finn Hammer <f-hammer-at-post5.tele.dk>
> Since I am running between two phases, to get 380 volts in, I would have
> to get a 3-phase filter = expensive.
No you don't... You have two hot leads and the safety ground. From a
filtering standpoint this is no different than the standard Line/Neutral
that is common in the US. Either way, you need to filter both wires.
> Looking at EMC filters in the farnell catalogue, one thing that struck
> me was, that the attenuation at 100 KHz is typically only 20 dB, not
> rising to 60-90 dB before well into the megahertz range.
Not surprising.. Filtering the lower frequencies requires bigger (e.g. more
expensive) inductors and capacitors.
> Is this really not a "bad" way to use a filter.?
> Then there are motor drive filters, they come in 100 and 150 and 300
> KHz, and attenuate better than 85 dB common mode, but they are equally
> expensive.
They also have other peculiar properties unique to their application,
however, they wouldn't be a bad start, if you found some cheap (good luck!)