Snubber for triac light switch?

[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. Thanks in
advance.

 

[whit3rd]

On Feb 3, 10:20 am, "pawihte" <pawi...@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.

 

[Phil Allison]

"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

 

[pawihte]

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.

 

[Jasen Betts]

On 2010-02-03, pawihte <pawihte@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.


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