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    Step Cieling fan regulator using Triac

    Am trying to build a solid state, mcu controlled fan regulator, not by triac pwm but, the one which uses capacitors as step fan regulator which does not make hum, attaching circuit. as you can see, it is replication of mechanical regulator, however uses triacs to switch on off capacitors, so that, higher capacitance total means higher speed, lowest is speed 1.
    Problem am facing is, triac are burning, a little click like sound and triac burns, i mean internally, no visible mark.whenever fan changes speed, or turned off, some triac will burn. something i must be doing wrong, looking for help.
    At one test Q3 failed, while doing a turn off, of triac Q1 and Q2, so it was not even on while failing.

    thank you

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    Phase is 230V AC 50hz, triac are used as switch only no pwm

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    Re: Step Cieling fan regulator using Triac

    What is your control sequence: 1= low, 2= medium, 3= high, 4= full?
    Do you open one Triac first before closing the other Triac?

    I am sure that you already checked them, but for our benefit: What is your line voltage and the Triac's rated voltage? What is the Triac rated current and the load current?

    Without knowing more details, perhaps a brute force approach could work: NTC inrush-limiter thermistors in series with each Triac. They should be sized such that its cold resistance only allows a current lower than the Triac's maximum non-repetitive current rating.
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    Re: Step Cieling fan regulator using Triac

    At one test Q3 failed, while doing a turn off, of triac Q1 and Q2, so it was not even on while failing.
    Suggest you get self-triggering of opto triac or main triac by high dv/dt. That's likely to happen with inductive load, RC filters for the opto triacs are suggested. Refer to application circuits for triac switching of inductive loads.

    High peak currents can be theoretically avoided if only one triac is turned on at a time (and dv/dt self triggering is avoided). I would however opt for a fail safe circuit with series resistors for each capacitor, e.g. a few ohms. Calculation reveals that power dissipation isn't high, hence you don't need NTCs, just small pulse stable power resistors.


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    Re: Step Cieling fan regulator using Triac

    Hi, yes am switching on a triac before closing other. so switching speeds, has not been a problem, when i turn the fan off, the triac burns. always the q3, triac are rated to 600v, 8A, so well within limits. current is 1A but not sure how much is inrush, however turning on is not the problem, I have move the capacitors to high side, and it was worse, (looking at some other circuit) gate resistors burned with a spark. they are 0805 1k. smd. So am thinking to get a snubber circuit if that helps although am using snubberless triac. Opto never failed , so have to do something with triac



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    Re: Step Cieling fan regulator using Triac

    What's the opto triac type?

    I suggest an RCR filter/snubber circuit like below to prevent parasitic triggering. R2 can be reduced to 50 to 200 ohm to make the circuit work as a snubber for the main triac.

    Click image for larger version. 

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    The other suggestion is a series resistor for each capacitor.



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    Re: Step Cieling fan regulator using Triac

    Its moc3021 , shall try snubber, then a series resistor. shall let you know



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    Re: Step Cieling fan regulator using Triac

    Thank you Schmitt, and FVM, seems like, you both are right, it's high current i think is frying the Triac while operating in parallel , followed the suggestion of FVM to have a series resistor with Capacitor, and it looks more stable at initial tests so far, shall need to do extended test in some combinations, to know the stability, I have kept a 10 ohm resistor, 1/4 watt, it was the nearest available in my spares. I guess a 0.5 watt should be good for long run. I tried snubber first with a 0.01uf 2kv, that did not work. Thank you for your help, and let you know if something else shows up.



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