10 Channel Light Bulb Sequencer

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Phasor said:
Why would it need isolation? :?:
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What happens when the power line gets hit by lightning?

I used to work on SM power supplies, and every single model that was designed to be connected to the mains had to pass a Hipot test. > 2kV between the AC input and the DC output/case. If the triacs weren't driven by an opto coupler, then the circuit would surely fail this test. The test was designed to ensure that if the power line was hit with lightning, and you were touching the unit at the time, you would be somewhat protected from a good zapping.
 

All down to cost - they generally fit TRIAC's rated at least double the maximum load rating, I've seen then fitted with five times the rating, and they still blow (but probably slightly less?).


No idea what the mechanism is, it's just a well known commen occurance, presumably it's either the filament shorting out the contacts, or some kind of arc as it fails.

Perhaps it's a characteristic of PAR36 bulbs (and similar), although normal bulbs cause it as well, but not so often - but you generally get far more PAR38's than normal bulbs fed from light systems, so it's not a fair comparison.


No, the TRIAC's fail immediately the bulb goes - generally (always?) you have multiple bulbs per channel - you will see one bulb on that channel go out (sometimes with a brighter flash), and the rest go permanently ON. If the fuse fails as well, all bulbs obviously go out, but this is less common, the fuse usually survives.
 

I've repaired (a few) and examined (a lot) of lightning damaged equipment, 2KV insulation is nothing to lightning - it's presumably just the standard test voltage used for insulation testing.

Incidently, the old saying 'lightning never strikes twice in the same place' is completely untrue, we had the exact same houses struck almost exactly a year apart - bad luck or what?.
 
Ive experienced that too, first time the lightning struck my house - it blew my computer up (dead power pack, although the rest of it survived), a year and 2 days later the house was struck again (we were in the garden watching this wall of rain come up the street - was really freaky) and our 3 day old 52" plasma screen got zapped good and proper - never to work again, and left a big 'Y' shaped scorched mark etched into the screen.

After reading this thread, i think I need to go through all my old disco gear and I have loads of effects that are no longer working - need to check the triacs on them.
 

My younger brothers house was struck the other year, it blew a big hole in his roof (through his £22 each handmade tiles ) and vapourised a number of rafters. Not a single electrical item in his house survived, and he had a LOT of gear - included FOUR - yes FOUR - surround sound systems.

After reading this thread, i think I need to go through all my old disco gear and I have loads of effects that are no longer working - need to check the triacs on them.
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All my old mates who used to run disco's seem to have retired from it now, so I don't get loads of repair work any more
 
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.
 
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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.
 
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.
 
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
 
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."
 

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