Path: utzoo!attcan!uunet!fernwood!apple!olivea!mintaka!bloom-beacon!daemon
From: chuck@mitlns.mit.edu
Newsgroups: sci.electronics
Subject: Re: How to reduce noise from light dimmers?
Message-ID: <1990Nov6.133221.7556@athena.mit.edu>
Date: 6 Nov 90 16:25:06 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: M.I.T. Lab for Nuclear Science
Lines: 17

-Message-Text-Follows-
In article <35639@cup.portal.com>, Nandu@cup.portal.com (Narendra J Kulkarni) writes...

>Most of the cheap dimmers chop the sine wave using triac and do not use
>zero crossing and this generate lot of RFI, AM stations are more sensitive
>to this, you can try to reduce the noise by shielding the dimmer with a metal
>wire mesh / or solid metal case, using toroid ferrite bead in the line, these

  Won't most of the RF be coming from the wires in the wall downstream of
the light switch? If so you might do a lot better putting the dimmer on
the neutral return from the light instead of the hot lead, so as to minimize
the ammount of wiring "antenna" that has the high dV/dt. Having said that,
please forget it!! You don't want to have wiring left hot when the 
switch is off. Maybe they ought to make a dimmer that switches both
lines off so the triac could be put on the neutral with some amount
of saftey

				Chuck@mitlns.mit.edu