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Simple AC Filters

Posted By: Scott35

Simple AC Filters - 02/24/02 11:20 AM

These Schematics have been duplicated from the "Theory Area", for your convenience.

[Linked Image]

Topic: AC line filter - simplest form
posted 06-18-2001 08:59 PM

Here's a drawing of a simple AC line filter, which can be used to either drain excessive Harmonics, or to try to get rid
of noise [EMI/RFI,etc.].
It's kind of like two "PI" filters stacked on each other

This one has a bandwidth of 48 to 440 Hz - where it should crossover. I'll figure the Fc and Fres for it, then post later.

The 465 microHenry Inductors [chokes, or coils "L"], can pass upto 6 amps before entering the point of no return
[AKA getting close to letting the smoke out].

The input section of Capacitors creates the first part of the Low Pass filter, by allowing higher frequencies to pass
through the Capacitor [the Resonance of the Capacitor as compared to the Resonance of the Inductors will pass
higher frequencies easier - the Inductors will allow lower frequencies to pass easier].
The final section of Capacitors will allow any high frequencies that passed thru the Inductors, to be "Shunted to
Ground" via the ground center tap point between the two Capacitors in the output section.
This can help to drive Harmonic currents to ground, rather than backfeed thru the AC power system - which is why a
Dedicated and Isolated grounding conductor should be used [to keep the shunted currents from flowing all around the
AC power system's grounding conductors, conduits, etc.]
Dedicated IGs should be terminated at the grounding electrode's connection to the grounded conductor for the system
feeding it [main service, or if SDS, the transformer].

Scott SET

[This message has been edited by Webmaster (edited 06-18-2001).]

[Linked Image]

Topic: AC line filter - "Just A Little Beefy'er"
posted 06-18-2001 09:15 PM

Here's one more AC line filter - this one is more selective than the other one.
It has a set bandpass area of +/- 50-60 Hz, but from figuring the Resonant Frequency of the RLC network at the
input, it looks like the Fres is somewhere around 100.65 Hz, and the Harmonic drain filter portion at the output might
be somewhere around >240 Hz - I'll double check these numbers and repost [unless someone else wants to... hint,
hint, hint ...]

Anyhow, this one uses the same consepts as the first one does. The Resistor at the input does a dual purpose thing:
Drains the Capacitors and helps drain the "Midrange" frequencies.

BTW: These filters are nearly the same as Passive Crossovers used for Speakers in Audio Systems. Differences are
there's normally only one line used when placing any series connected elements [in this case, the Inductors]; also,
there's normally no center tapped Capacitor banks [or other type of elements].
Bypassing a speaker lead to ground would be done with a Capacitor of small value [in the 10 pF ranges] connected
from each speaker lead to a grounded conductor - which is not an active circuit conductor! only runs from a star
grounding point to a speaker. It can be driven to earth ground, or just connected to the enclosure of the power
amplifier. All depends on the system, components and the interference.

Scott SET

[This message has been edited by Webmaster (edited 06-18-2001).]
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