Reason of frequently triac failure in the dimmer

[spec]

Theres no factory made light dimmers for sale in Nepal?

It is a question of funds and access.

spec

 

[tcmtech]

I see. That doesn't justify much given the cost of the correct parts to build his own will be more than buying a properly made one.

So unless he already has a good triac with a 6 - 10+ amp 600+ volt rating laying around plus all the other parts needed to make a stable firing circuit there's nothing financially to gain from the DIY approach as it has already shown.

 

[MrAl]

I saw 'NTC' in a thermistor (used in series of mains of a computer SMPS)

100 meter far, my neighbour have a big 3 phase motor. When they turn ON and OFF, I can feel the effect in my home in mains. Do they generate spikes and can affect to my triac of my home?

Hi,

Yes, absolutely. You could try to measure it with a meter but you need a fast meter. I use an analog meter for that so it can catch the ups and downs. A scope would be even better.

600v triacs are usually not that much more expensive than 400v ones. A snubber may help also for the really fast stuff.

 

[Willen]

So why not just buy a heavy duty rated dimmer and be done with it? Why reinvent the wheel and do it poorly?

Hi tchtech,
As a hobbyist, I like to do things myself. I like poor, hard and DIY way. And I like to poke engineers.

Theres no factory made light dimmers for sale in Nepal?

If the devices is not related to VERY common 'consumer' electronics then the device is not accessible for me. Once I had seen a factory made small fan controller (dimmer) and that had BT134, DB3, some resistor and some capacitor and a pot; almost same as my circuit of #1.

 

[spec]

I see. That doesn't justify much given the cost of the correct parts to build his own will be more than buying a properly made one.

So unless he already has a good triac with a 6 - 10+ amp 600+ volt rating laying around plus all the other parts needed to make a stable firing circuit there's nothing financially to gain from the DIY approach as it has already shown.

No 'justification' is required. The OP wishes to build his own circuit. On the basis of your logic most of the projects on ETO would be 'non-justified'.

spec

 

[Willen]

OK, now I made a conclusion circuit from the suggestion of yours. Learned some critical points of triac too. Any comments still?

One question: look at the R1, it's connected to the right side of the load here. I found in some circuit, R1 is connected to the left side (mains) of the load directly. What would be the difference?

 

[spec]

OK, now I made a conclusion circuit from the suggestion of yours. Learned some critical points of triac too. Any comments still?

One question: look at the R1, it's connected to the right side of the load here. I found in some circuit, R1 is connected to the left side (mains) of the load directly. What would be the difference?

Wow, that is the best dimmer circuit of that type I have seen- full belt and braces military design.

spec

 

[Les Jones]

I would still add a suitably rated varistor in parallel with C-X. This should clamp transients to a level thet the SCR can withstand.

Les.

 

[spec]

One question: look at the R1, it's connected to the right side of the load here. I found in some circuit, R1 is connected to the left side (mains) of the load directly. What would be the difference?

Interesting question. If R1 were connected to the left side of the load, the DIAC trigger phase angle may be a touch erratic, because after the DIAC fires, the capacitor will start charging again and will have some voltage across it when the mains changes from one polarity to another.

spec

 

[MrAl]

OK, now I made a conclusion circuit from the suggestion of yours. Learned some critical points of triac too. Any comments still?

One question: look at the R1, it's connected to the right side of the load here. I found in some circuit, R1 is connected to the left side (mains) of the load directly. What would be the difference?

Hello again,

That circuit looks a lot better now.

The connection to R1 affects the current into the gate, limiting the current once the triac turns 'on'. The peak current is still higher, but the average current is a critical design point of most triac designs...it can not be too high or the gate gets too much power. In a more modern circuit the average current (and thus average power) is limited by using a pulse instead of a constant 'on' signal.

That brings us to the question, why are you not using a more modern circuit? Modern circuits eliminate the requirement for a diac which is another design point for some applications. With a diac the 'lamp' may not be able to be dimmed all the way down to near dark, but with a modern design the triac conduction angle is adjustable over the full range from nearly zero to nearly full on.
A modern design syncs the gate drive pulse to the line zero crossing, creating a pulse after a short time delay set by the user control. It fires once every half cycle. That maintains a steady conduction angle that determines the total power output, but it can be adjusted to nearly zero output.

 

[Willen]

That brings us to the question, why are you not using a more modern circuit?

Light was not totally dark with sensitive gate 2N6073 but I got totally dark with BT136. However PWM driver seems safe and good controller as your saying.

Maybe I can use a 555 chip to generate PWM and can drive the triac. The controller would need little more parts. And I think I need to protect the gate because it's connected to critical PWM chip. Maybe need an isolator.

 

[tcmtech]

Maybe I can use a 555 chip to generate PWM and can drive the triac. The controller would need little more parts. And I think I need to protect the gate because it's connected to critical PWM chip. Maybe need an isolator.

Easier said than done when you have any inductive component in the load.

https://www.electro-tech-online.com/threads/ac-control-circuit-question.147790/