why triac blows by non-dimmable CFL even when its off?

"ravi"

** Bad idea - unless the triac is a "snubberless" type and is continuously triggered rather than pulse fired. ** Very dimly - right ?

** The current flowing through a snubber cap will faintly light most CFLs or tern them into slow strobe lights. ** The CFL has a filter electro inside that comes right after the bridge rectifier - when AC is first applied the cap charges very rapidly to the peak value - hence the current spike.

The triac must be rated to take this spike current and with multiple CFLs on the same circuit it can build up to hundreds of amps.

** See above.

Best keep CFLs away from all triacs.

.... Phil

"ravi"

** BTW:

How did you measure that current spike ?

That ain't so trivial to do safely and accurately.

I use a specially made interface with a Hall Effect current transducer for such jobs - mine has 100kHz bandwidth Hall transducer followed by a DC to true RMS converter IC and a 3.5 digit LED display.

The most used feature though is a BNC output of the current wave that goes straight to my scope.

.... Phil

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I used simple 1ohm resistor and connected in in line to CFL to measure with my scope. While CFL lamp was in socket properly i saw hardly any current flowing, but as i was unscrewing the lamp from socket, i measured upward of 20A current spike and if I repeat it few times it blows BTA16 (16A) snuberless triac easily.

"ravi" "Phil Allison"

I used simple 1ohm resistor and connected in in line to CFL to measure with my scope.

** That ain't so safe - unless your scope is a plastic case portable.

While CFL lamp was in socket properly i saw hardly any current flowing, but as i was unscrewing the lamp from socket, i measured upward of 20A current spike and if I repeat it few times it blows BTA16 (16A) snuberless triac easily.

** The BTA16 is a standard triac with a short pulse current rating in the hundreds of amps.

The BTA16-600BW or BTA16-600CW are the only snubberless versions

Must be something fishy about your triggering arrangement ( or the lack of a suitable snubber) for the triac to be damaged by a 20 amp current pulse that lasts only 50 uS or so.

Possibly at the instant of connection, the dv/dt rating of the triac is being exceeded and so it tries to commutate "on" under the extreme load presented by the CFLs rectifier and internal electro cap.

That could kill it.

.... Phil

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Yes, I am using CW version. It could be lack of suitable snubber as you pointed out. This dimmer was designed years ago when there were no CFLs. Current pulse lasts for over 200usec. Next I will try to measure dv/dt and try to compare with maximum rating of datasheet. Thanks

"ravi"

Yes, I am using CW version. It could be lack of suitable snubber as you pointed out. This dimmer was designed years ago when there were no CFLs. Current pulse lasts for over 200usec. Next I will try to measure dv/dt and try to compare with maximum rating of datasheet.

** And when you have done all that experimenting - you might just wake up to how much simpler it would be to use a relay instead.

BTW

Have you considered the issue of the triac's holding current yet ?

A CFL draws zero current up to 80% of the time it is on.

.... Phil

ake up

I know relay would be nice, but let's just say its out of control. At this point everything is on the table. I can probably add 35mA worth of resistive load parallel to CFL and measure the effect if it solve the problem.. Thanks

"ravi" "Phil Allison" "ravi"

I know relay would be nice, but let's just say its out of control. At this point everything is on the table. I can probably add 35mA worth of resistive load parallel to CFL and measure the effect if it solve the problem..

** You need to post your schematic somewhere for me or anyne to give any real help.

I fear you have a drive circuit that draws its power via the lamp load - and that is a disaster with CFLs.

.... Phil