lsls00@iliad.Berkeley.EDU (Ilia Levi) (11/06/90)
Is there an easy way to reduce noise from the light dimmer? When I listen to an AM radio at the same time that the dimmer is on, I get a very bad hum. I know that you can buy 'noise free' dimmers, but this one is embedded in the light fixture, and I don't want to replace it.
Nandu@cup.portal.com (Narendra J Kulkarni) (11/06/90)
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 will help only to a limited case, also try orienting the AM radio antenna if all fails then buy a new dimmer
chuck@mitlns.mit.edu (11/07/90)
-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
karn@envy..bellcore.com (Phil Karn) (11/09/90)
In article <3987@osc.COM> jgk@osc.COM (Joe Keane) writes: >The problem is that they use a triac to cut off the current in the middle of a >cycle. No, Triacs are just AC versions of SCRs, and both always keep conducting until the load current through them goes to zero at the end of an AC cycle. Noise is generated in lamp dimmers because the triacs are turned *on* in the middle of a cycle. You may note that the noise decreases somewhat when the dimmer is turned all the way up. That's because the triac is being triggered at the beginning of the cycle, when the load current is still small. Midrange is worst because the triac is triggered halfway through the cycle, at the peak. The best way to filter lamp dimmers is with self-contained RFI filters as close as possible to the dimmer. Corcom, Cornell Dublier and others make such filters, and they are very common at amateur radio hamfests. Phil
wb8foz@mthvax.cs.miami.edu (David Lesher,,255RTFM,255rtfm) (11/09/90)
Others said: >The problem is that they use a triac to cut off the current in the middle of a >cycle. As it is the current shuts off very quickly, generating all sorts of >RF noise. Ahemmm....... Unless they are using GTO [Gate Turn Off] devices, dimmer triacs can only turn off at the zero-crossing. They work by delaying turn on until later in the cycle half. That's where the noise comes from. -- A host is a host from coast to coast.....wb8foz@mthvax.cs.miami.edu & no one will talk to a host that's close............(305) 255-RTFM Unless the host (that isn't close)......................pob 570-335 is busy, hung or dead....................................33257-0335
jgk@osc.COM (Joe Keane) (11/13/90)
In article <3987@osc.COM> i write: >The problem is that they use a triac to cut off the current in the middle of >a cycle. As it is the current shuts off very quickly, generating all sorts >of RF noise. Sorry folks, i was thinking of something else. As we all know, a triac turns _on_ in the middle of a cycle. So the right way to filter the output is with a series choke.