Nigel does not know, he has only theories based on his experience as a small appliance repair tech. It is much more likely that when the filament breaks initially the coiled coil filament falls down to make connection at say half the filament length, drawing considerably more power until it finishes vaporizing.

The result is obviously not a direct short. Every one familiar with the old C7 Christmas tree bulbs can think back to clipping an out bulb and having it come back for a while brighter than the rest.
I will stand by my statement that improper design and application cause the triacs to be susceptible to the aforementioned effect.

 

I'm going to jump in here, and say that you both (Nigel & Uber) are right.

While I was stationed in Germany (U.S. Army), I was technical director for the local Moral Support Activities branch. My job entailed maintenance and repair of all of the electronic equipment. Among all the varied types were several triac controlled light boards. The lights used most often with these boards were par 36, par 38 and par 64.

Like Nigel, I replaced many triacs in the control boxes, and most failures happened when a bulb blew, but NOT ALWAYS. I'm guessing about 30% of the time it was due to overloading of the channel, and probably 45% due to bulb failure. The rest could be attributed to other causes, such as power spikes and drop-outs.

However, the failure rate was actually quite low, I replaced maybe 10 triacs during the three years I held that post, out of a possible 100 units.

 

Discrete semiconductors is certainly not my strong point, here's my opinion on the whole matter.

Triacs cost less than £1 each, so wouldn't mounting them into a socket instead of fixing them in place be a much better idea? So when it does break, you could just yank it out and throw another one in.

__________________
when you post that reply, im just kidding.

 

They do not generally blow. It is just much more common to be either overloaded or not heat sunk properly.

Now if it is an inductive load it is an entirely different story... but still the failure is non destructive, it simply does not turn off at the end of the cycle.

 

Thanks but this circuit without any isolat

 

You don't need isolation unless you like to touch live circuits

__________________
"There is no way to peace, peace is the way!"

 

i like your project. thanks

 

Sorry I missed this before. I stand by my statement: only an over stressed triac will blow and the chances are they are not properly heat sunk.

These testosterone laden color organs hopefully use at least 15A triacs in them. The fact of the matter is that triacs typically handle 10x their rated current for an entire power line half cycle safely and that much current readily vaporizes what is left of the failing bulb.

Dan

 

you can not socket them. 10-20A and the high temeratures that are developed in even a properly applied power component lead to the failure of the connector.

Dan

 

i like this project.

 

Updated schematic for this thread:
Shaded text reads:" original design used a 27K resistor for R2, circuit worked as low as -35C windchill. Lamp outputs are fused for personal safety."

Attached Thumbnails