Well, it totally depends upon the type of failure of BT139. If there is leakage from gate .... it will blow up 4017 in worst case. However I haven't seen such kind of failure.
To avoid triac failure, never connect load beyond its rated capacity.

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And never use them to feed bulbs, because when the bulb fails it almost always takes out the triac at the same time.

Bit difficult for a light sequencer though?.

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The 4017 would quickly self-destruct. I built a similar circuit using MCT2 optos and T106 triacs to control Christmas lights ( up to 200 per triac, fused). A smaller version using 2N3904s alone turned on LEDs as a mini name-in-lights project, with 6 recipients.

 

I doubt if that would happen ! When bulb fails, it becomes open circuit ! How will that affect the TRIAC ??
I have been using this circuit for years now with quite a lot bulb failures, never had to replace a TRIAC or 4017 yet!
Can you explain ?

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I’m away of this BT series TRIACs. For running lights its ok but when it comes to sensitive light dimming (Phase Controlling) this series acts poor.

I’m using TIC216 or BTA16-600B because they don't seem to suffer from any dv/dt problems.

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As bulbs fail they commonly go S/C before they go O/C, this kills the TRIAC's - it's a VERY, VERY common fault on light units. I've made a lot of money over the years repairing light units damaged in this way

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May I suggest a safer circuit, built 20 years ago and still functions.

Attached Thumbnails

 

 

Thats pretty dang cool! Its next on my boredom list.

 

Hi folks,
First time poster. I'm looking for help on a light sequencer. But since I'm electronically inept, I was hoping someone could point me in the direction of where to purchase one.

I am setting up my lighting effects for Halloween and have several lights (light bulbs and floods) I need to manage.

Thanks!

 

You undoubtedly have properly rated triacs in your own circuit. Nigel is a repair shop guy who sees primarily consumer crap that undoubtedly has under rated triacs.

Another way to look at it would be that you have a military type of design and what Nigel sees is cut rate crap manufactured in China.

While the bulbs do tend to short before they open, triacs have a tremendous surge rating that handles it fine. Were it not so there would be no market for triac lamp dimmers.

 

Certainly not military grade, but certainly professional and semi-professional grade, used for light shows in clubs and disco's. You don't really get anything similar in consumer electronics?.

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I have never heard of one blow.

It is more likely in that case to be frayed wires shorting out or under rated triacs in that case. Clubs are likely to be moving things around or putting in over size bulbs bulbs for effect.

 

I don't know where you're from?, but you've obviously never been involved in disco or clubs, or in any service work

This is an EXTREMELY common and well known problem, with fuse manufacturers even bringing out special highly expensive fuses to try and reduce the problem.

Do you have MCB's rather than fuses at home?, it's commonplace for the MCB to trip out if a bulb blows, same thing - high current surge takes it out.

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US ... Almost everything here is circuit breakers, but they don't blow either. How often do you hear of wall lamp dimmers blowing out? That would be the real difference between an overloaded or crappilly designed triac circuit blowing and what you are seeing.

If it was that properly designed and rated triac circuits were blowing out all the time you would be hearing of people replacing their wall dimmers all the time.

 

So you've no experience of light effect units at all, and you're basing your idea on domestic light dimmers

Completely different things, and the lamp failure rate is massively different.

Incidently, if it's of any help to you?, TRIAC's used are generally TO220 rated at 8A continuous, with a maximum 4A load per channel (1000W per channel) for a 3 channel unit, correspondingly less as you get more channels (as there's a 3000W total capability).

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