Issues with AC Phase control

Discussion in 'General Electronics Chat' started by SPE, Mar 7, 2017.

  1. SPE

    Thread Starter New Member

    Mar 7, 2017
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    At the moment I am in the process of making an AC Phase control circuit but am having some issues. Currently it will dim a light bulb but when connecting it to a higher load such as a single phase shaded pole motor it will only turn the motor slowly and make an audible humming noise. If you have any insight to what could be causing this issue would greatly appreciate it thanks!
     
  2. vrainom

    Active Member

    Sep 8, 2011
    126
    20
    Those are induction motors and unlike dc or universal motors don't work well with phase-angle control. Also inductive loads create electrical noise which depending on your circuit could be having an effect on it. Are you just testing it with the motor or is it your target load?
     
  3. SPE

    Thread Starter New Member

    Mar 7, 2017
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    The motor is the target load. I tested the motor plug directly into AC with a light dimmer and it was able to control the speed. The current circuit we have is a zero cross detector and an opto isolated triac to power the load.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Most of the ceiling fan motors etc are shaded pole and a ordinary light dimmer will control them, I have a couple installed here.
    The motors that have a problem are usually 1ph cap start.
    Is the one in the OP μp controlled?
    Max.
     
  5. SPE

    Thread Starter New Member

    Mar 7, 2017
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    I'm honestly not sure but a light dimmer did control it no problem. The issue is that I need to be able to control the speed with a microcontroller.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Which circuit and code are you using?
    You also need to add some kind of snubber when moving over to motor control.
    Max.
     
  7. vrainom

    Active Member

    Sep 8, 2011
    126
    20
    Could you draw or describe your zero crossing detector circuit and the circuit from the opto to the triac? The whole schematic would be much better.
     
  8. SPE

    Thread Starter New Member

    Mar 7, 2017
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    Code (Text):
    1. const int triacPin = 7;
    2. const int zeroPin = 2;
    3. const int potPin = A0;
    4. const int sw = 3;
    5. int triacDelay = 13500;
    6. //int triacInt = 200;
    7.  
    8.  
    9. void setup() {
    10.   pinMode(zeroPin, INPUT_PULLUP);
    11.   pinMode(triacPin, OUTPUT);
    12.   pinMode(sw, INPUT_PULLUP);
    13.   attachInterrupt(0, zero, RISING);
    14.   Serial.begin(9600);
    15.  
    16. }
    17.  
    18. void loop() {
    19.   //Serial.println(digitalRead(zeroPin));
    20.   if(digitalRead(sw) == LOW){
    21.     triacDelay = 5250;
    22.   }else{
    23.     triacDelay = 7144;
    24.     //9750
    25.   }
    26.  
    27.  
    28. }
    29.  
    30. void zero(){
    31.   delayMicroseconds(triacDelay );
    32.   digitalWrite(triacPin, HIGH);
    33.   delayMicroseconds(200);
    34.   digitalWrite(triacPin, LOW);
    35. }
    36.  
    This is the code we are using, these settings will give use two different brightness on a light but neither will turn the motor except at very very low speed.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I would use the bridge and H11L1 method shown in Fairchild AN-3006 for detecting the zero cross point, the result is a .8ms pulse every crossing point.
    Q1 is not needed.
    Max.
     
  10. vrainom

    Active Member

    Sep 8, 2011
    126
    20
    I'm gona blame the caps you're using as voltage droppers for the zero crossing detector, they're like a highway for noise. Plus, the detector would produce a pulse once the zero crossing has already passed.

    Check out Max's suggestion so you could implement something similar with what you already have. I like that it has an 11v zener in series to make the detector immune to noise instead of cleaning up the signal with an rc filter.

    I'll attach the schematic Max is talking about in case you're having trouble finding the file.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The only reason for Q1 in the detector is to invert the signal for the 555, if using a micro then it can be used direct for a positive going pulse.
    Max.
     
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