Snubber for triac light switch?
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From: pawihte on 3 Feb 2010 13:20 If I use a triac as a simple on-off switch to control a lamp at mains voltage, do I need a snubber across the triac? Say the lamp is 10 meters away from the triac, mains-rated LED or 100W incandescent (not CFL, mercury, neon, etc.), and the switchig is via an optoisolator without zero-cross sensing. Thanks in advance.
From: whit3rd on 3 Feb 2010 16:36 On Feb 3, 10:20 am, "pawihte" <pawi...(a)fake.invalid> wrote: > If I use a triac as a simple on-off switch to control a lamp at > mains voltage, do I need a snubber across the triac? Say the lamp > is 10 meters away from the triac, mains-rated LED or 100W > incandescent (not CFL, mercury, neon, etc.), and the switchig is > via an optoisolator without zero-cross sensing. If your LED lamps use any kind of transformer, the triac switch can be a DC source under some trigger conditions, which will blow fuses or expensive LEDs. In the incandescent lamp case, the snubber would mainly be of use to prevent RF emissions.
From: Phil Allison on 3 Feb 2010 21:02 "whit3rd" "pawihte" > If I use a triac as a simple on-off switch to control a lamp at > mains voltage, do I need a snubber across the triac? Say the lamp > is 10 meters away from the triac, mains-rated LED or 100W > incandescent (not CFL, mercury, neon, etc.), and the switchig is > via an optoisolator without zero-cross sensing. If your LED lamps use any kind of transformer, the triac switch can be a DC source under some trigger conditions, ** Only in the case of phase control and ONLY if the gate is *pulse fired* at a 100/120 Hz rate. Which is not what the OP is doing. which will blow fuses or expensive LEDs. ** DC in a transformer primary burns out the transformer. In the incandescent lamp case, the snubber would mainly be of use to prevent RF emissions. ** Only a single current spike when the lamp comes on and none as it goes off - cos the current then is close to zero. So any RFI is much less than regularly generated by ordinary light switches. ...... Phil
From: pawihte on 4 Feb 2010 00:45 Phil Allison wrote: > "whit3rd" > "pawihte" >> If I use a triac as a simple on-off switch to control a lamp >> at >> mains voltage, do I need a snubber across the triac? Say the >> lamp >> is 10 meters away from the triac, mains-rated LED or 100W >> incandescent (not CFL, mercury, neon, etc.), and the switchig >> is >> via an optoisolator without zero-cross sensing. > > If your LED lamps use any kind of transformer, the triac switch > can be a DC source under some trigger conditions, > > ** Only in the case of phase control and ONLY if the gate is > *pulse > fired* at a 100/120 Hz rate. > > Which is not what the OP is doing. No. No phase control. Just a simple on-off function. > > which will blow fuses or expensive LEDs. > > ** DC in a transformer primary burns out the transformer. But that won't happen with a full-cycle on-off function, will it? The switching cycle wil be at least several seconds. > > In the incandescent lamp case, the snubber would mainly be of > use to > prevent RF emissions. > > > ** Only a single current spike when the lamp comes on and none > as it > goes off - cos the current then is close to zero. > > So any RFI is much less than regularly generated by ordinary > light > switches. > > ..... Phil Thanks.
From: Jasen Betts on 4 Feb 2010 05:28
On 2010-02-03, pawihte <pawihte(a)fake.invalid> wrote: > If I use a triac as a simple on-off switch to control a lamp at > mains voltage, do I need a snubber across the triac? Say the lamp > is 10 meters away from the triac, mains-rated LED or 100W > incandescent (not CFL, mercury, neon, etc.), and the switchig is > via an optoisolator without zero-cross sensing. Thanks in > advance. If your mains leds are just a series string with no transformer or other inductor then yeah, you can use a triac for on-off control. incandescant lamps are fine too, NE2 indicator lamps also. --- news://freenews.netfront.net/ - complaints: news(a)netfront.net --- |