+ Post New Thread
Results 1 to 14 of 14
  1. #1
    Junior Member level 3
    Points: 189, Level: 2

    Join Date
    Mar 2017
    Location
    India
    Posts
    26
    Helped
    0 / 0
    Points
    189
    Level
    2

    Dimmer AC Circuit Resistor burns

    Hi,I'm doing a dimmer which is connected to a relay to work as a switch to Turn ON/OFF.
    Now the circuit which I implemented is this

    Click image for larger version. 

Name:	Dimmer.jpg 
Views:	13 
Size:	14.8 KB 
ID:	138852

    where I'm using MOC3021 & BT138-800E(TRIAC)

    and according to the MOC3021 Datasheet its written as for a sensitive gate use this Fig.2

    Click image for larger version. 

Name:	MOC3021.jpg 
Views:	14 
Size:	50.5 KB 
ID:	138853

    Now my real doubt is where to connect Load ? whether to MT2 or MT1?
    because both the figures shows different connections
    and I think there will be no much difference if we change the terminals
    and when I start dimming then the resistor connected to MT2 is getting burnt whether its 1k,10k,10k1/2W anything
    and for 2-3 times the dimming worked after that the resistor starts burning?
    is it because any other device like MOC3021 got burnt within this 2-3times or any other reasons?

    please help me through this
    Thanks in Advance

  2. #2
    Super Moderator
    Points: 24,477, Level: 38
    andre_teprom's Avatar
    Join Date
    Nov 2006
    Location
    Portugal
    Posts
    7,352
    Helped
    917 / 917
    Points
    24,477
    Level
    38
    Blog Entries
    5

    Re: Dimmer AC Circuit Resistor burns

    if we change the terminals and when I start dimming then the resistor connected to MT2 is getting burnt whether its 1k,10k,10k1/2W anything
    Are you using any strongly reactive load, such as a motor ?
    If yes, it is missing a snubber on your circuit.
    --------------------------------------------------------------------------------------------------
    Part of the world that you live in, You are the part that you're giving ( Renaissance )



    •   Alt19th May 2017, 14:56

      advertising

        
       

  3. #3
    Junior Member level 3
    Points: 189, Level: 2

    Join Date
    Mar 2017
    Location
    India
    Posts
    26
    Helped
    0 / 0
    Points
    189
    Level
    2

    Re: Dimmer AC Circuit Resistor burns

    Quote Originally Posted by andre_teprom View Post
    Are you using any strongly reactive load, such as a motor ?
    If yes, it is missing a snubber on your circuit.
    The load is Incandescent bulb, and I've a snubber circuit too.

    Click image for larger version. 

Name:	IMG_20170519_174646.jpg 
Views:	10 
Size:	485.2 KB 
ID:	138859


    This is the circuit which I'm working on where relay is also a part of the circuit :)



  4. #4
    Super Moderator
    Points: 236,364, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    40,881
    Helped
    12493 / 12493
    Points
    236,364
    Level
    100

    Re: Dimmer AC Circuit Resistor burns

    Resistors > 2k will probably been overloaded and shouldn't been used. If 1k resistor burns, you have either a problem with non-triggering triac (defective or different type than BT138 with high trigger threshold) or a shorted capacitor. The capacitor must be rated for 250 VAC or at least 630 VDC.



  5. #5
    Super Moderator
    Points: 51,995, Level: 55
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster

    Join Date
    Apr 2014
    Posts
    10,442
    Helped
    2485 / 2485
    Points
    51,995
    Level
    55

    Re: Dimmer AC Circuit Resistor burns

    Hi,

    We don't see how you drive the MOC's LED.
    According datasheet the max current to trigger the MOC is 15mA. I doubt there are 15mA.
    But I don't know what happens when LED current is too low.

    To be at the safe side: follow the datasheet recommendations.

    Klaus



  6. #6
    Junior Member level 3
    Points: 189, Level: 2

    Join Date
    Mar 2017
    Location
    India
    Posts
    26
    Helped
    0 / 0
    Points
    189
    Level
    2

    Re: Dimmer AC Circuit Resistor burns

    Quote Originally Posted by FvM View Post
    Resistors > 2k will probably been overloaded and shouldn't been used. If 1k resistor burns, you have either a problem with non-triggering triac (defective or different type than BT138 with high trigger threshold) or a shorted capacitor. The capacitor must be rated for 250 VAC or at least 630 VDC.
    Thanks @FvM
    can you please elaborate this ?

    - - - Updated - - -

    Quote Originally Posted by KlausST View Post
    We don't see how you drive the MOC's LED.
    Thanks @Klaus
    MOCs LED is driven from the controller using program
    int AC_LOAD = 3; // Output to Opto Triac pin
    int dimming = 128; // Dimming level (0-128) 0 = ON, 128 = OFF
    void setup()
    {
    Serial.begin(9600);
    pinMode(AC_LOAD, OUTPUT); // Set the AC Load as output
    attachInterrupt(digitalPinToInterrupt(2), zero_crosss_int, RISING); // Choose the zero cross interrupt
    }
    void zero_crosss_int() // function to be fired at the zero crossing to dim the light
    {
    // Firing angle calculation :: 50Hz-> 10ms (1/2 Cycle)
    // (10000us - 10us) / 128 = 75 (Approx)
    int dimtime = (75*dimming);
    delayMicroseconds(dimtime); // Off cycle
    digitalWrite(AC_LOAD, HIGH); // triac firing
    delayMicroseconds(10); // triac On propogation delay
    digitalWrite(AC_LOAD, LOW); // triac Off
    }
    void loop()
    {
    dimming = 90;
    delay(7000);
    dimming = 50;
    delay(7000);
    dimming = 20;
    delay(7000);
    }



    •   Alt22nd May 2017, 07:13

      advertising

        
       

  7. #7
    Super Moderator
    Points: 51,995, Level: 55
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster

    Join Date
    Apr 2014
    Posts
    10,442
    Helped
    2485 / 2485
    Points
    51,995
    Level
    55

    Re: Dimmer AC Circuit Resistor burns

    Hi,

    MOCs LED is driven from the controller using program
    I am referring to currents (and/or voltages)

    Klaus



  8. #8
    Junior Member level 3
    Points: 189, Level: 2

    Join Date
    Mar 2017
    Location
    India
    Posts
    26
    Helped
    0 / 0
    Points
    189
    Level
    2

    Re: Dimmer AC Circuit Resistor burns

    Voltage @ MOC 1,2 pin is 12.7mV



  9. #9
    Super Moderator
    Points: 51,995, Level: 55
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster

    Join Date
    Apr 2014
    Posts
    10,442
    Helped
    2485 / 2485
    Points
    51,995
    Level
    55

    Re: Dimmer AC Circuit Resistor burns

    Hi,

    this is a useless value.

    If you compare the 12.7mV with the values given in the datasheet you may see it canīt work.

    I donīt like guessing, but with your given informations we need to.
    So I assume you measured the voltage with a DVM .. and the control signal is PWMīd.
    We canīt know if your DVM reading is the average value or the RMS value. We canīt know the drive voltage, we canīt know duty cycle. --> Impossible to verify your circuit.


    Klaus



  10. #10
    Junior Member level 3
    Points: 189, Level: 2

    Join Date
    Mar 2017
    Location
    India
    Posts
    26
    Helped
    0 / 0
    Points
    189
    Level
    2

    Re: Dimmer AC Circuit Resistor burns

    Sorry, even I'm unable to understand because now its showing as 0.53V but mostly its showing 0.0V (its always been varying)
    but dimming is happening
    so what may be the issue ?



  11. #11
    Super Moderator
    Points: 51,995, Level: 55
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster

    Join Date
    Apr 2014
    Posts
    10,442
    Helped
    2485 / 2485
    Points
    51,995
    Level
    55

    Re: Dimmer AC Circuit Resistor burns

    Hi,

    --> use a scope.
    In cas eyou donīt have one, then buy one or lend one.


    Klaus



  12. #12
    Junior Member level 3
    Points: 189, Level: 2

    Join Date
    Mar 2017
    Location
    India
    Posts
    26
    Helped
    0 / 0
    Points
    189
    Level
    2

    Re: Dimmer AC Circuit Resistor burns

    any idea why it is not showing any voltage @ MOC?
    and what are the cases where MOC & BT138 could be damaged?
    hey @FvM, the cap 0.1uF should be 275VAC one?



  13. #13
    Junior Member level 3
    Points: 189, Level: 2

    Join Date
    Mar 2017
    Location
    India
    Posts
    26
    Helped
    0 / 0
    Points
    189
    Level
    2

    Re: Dimmer AC Circuit Resistor burns

    Quote Originally Posted by KlausST View Post
    Hi,

    --> use a scope.
    In cas eyou donīt have one, then buy one or lend one.


    Klaus
    is 0.53V is also wrong voltage @ MOC?
    what are the cases where MOC & BT138 could be damaged?



    •   Alt24th May 2017, 07:00

      advertising

        
       

  14. #14
    Junior Member level 3
    Points: 189, Level: 2

    Join Date
    Mar 2017
    Location
    India
    Posts
    26
    Helped
    0 / 0
    Points
    189
    Level
    2

    Re: Dimmer AC Circuit Resistor burns

    Hi,now my dimming is working without any fault or damage of resistors when I replaced 0.1uF cap by 0.1uF/275VAC

    But I'm still getting 0.4V @MOC3021 and 1.09V @4N35

    And guys help me with the circuit I've attached where relay is also connected,the problem is when I send some instruction even without the relay being ON the dimming is happening instead it should only dim when relay is ON and according to the instruction given the dim should change
    Thanks in advance
    Click image for larger version. 

Name:	IMG_20170519_174646.jpg 
Views:	3 
Size:	485.2 KB 
ID:	138938



--[[ ]]--