Microcontroller-based: Electric fan switching- relay or triac?

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Do you mean if i remove the gate voltage, the triac will turn off in the next current zero crossing?

About the RC snubber, what is its purpose? does it look like this:
 

Do you mean if i remove the gate voltage, the triac will turn off in the next current zero crossing?
Click to expand...
Yes, exactly.
About the RC snubber, what is its purpose? does it look like this:
Click to expand...
Yes. It's purpose is to limit the voltage slew rate (dV/dt) and also reducing overvoltages. Triacs can be self-triggered (without gate voltage) in case of a too high dV/dt, the said opto triacs are particularly sensitive to it. They often are used in a special circuit as shown in this thread:
https://www.edaboard.com/threads/162207/
 
Thanks for the link.. i'll try to study about rc snubber
 

Hi,

Suppose฀ we฀ have ฀an฀ inductive฀ load,฀ such฀as motor.฀The฀ current ฀and฀ voltage ฀through ฀the฀ triac and ฀the ฀load฀ are ฀no ฀longer ฀in฀ phase.฀ At ฀the ฀time฀ the฀ triac ฀snaps ฀into฀ non-conductive ฀mode, ฀the฀ voltage฀ across฀ the฀ triac ฀is, ฀in the ฀worst ฀case฀ (for ฀a฀ phase฀ angle ฀of ฀90° ฀between V฀ and ฀I)฀ the฀ peak฀ line฀ voltage.฀ And,฀ the triac’s ฀switching ฀speed฀ may฀be ฀on ฀the ฀order ฀of ฀a฀ few฀ microseconds ฀or ฀less. ฀Hence,฀ dV/dt฀ can ฀easily reach฀ hundreds ฀of฀ volts/microsecond.฀ The฀ actual dV/dt฀ depends฀ on฀ the ฀load,฀stray ฀inductance฀ and฀ capacitance and ฀the฀ triac’s ฀parameters.

A฀ common฀ solution฀ to ฀dV/dt฀ problems฀ is ฀to฀ add฀ an ฀RC-snubber฀ network฀ across฀ the฀ triac,฀ as฀ shown฀ in฀ your diagram. The ฀RC ฀network ฀slows ฀the ฀rate ฀of฀ change฀ in฀ applied฀ voltage฀ and ฀thus฀ drops ฀the ฀dV/dt below ฀the฀ triac’s ฀rating.

Hope this helps.
Tahmid.
 
hi friends
1.using triac as switch than a relay will a better option.
2. it does not need zero cross detector , bcos it need only when you are controlling the phase.
3.snubber circuit is necessary when using a inductive load is using with a triac.
4.use a optoisolator moc3021 to couple the triac with your control circuit(see the data sheet you will confirm how to use moc 3021). the triac will conduct untill the control ckt provide supply to opto isolator.
5.for fan use BT138 triac , sufficient for 60 watt load generally used in fan speed regulator.
 
i have a question about the rc snubber, will it consume power even if the triac is turned off? Looks like it will...
 

Yes, in 100 mW order of magnitude, depending on the dimensioning.
 
Whatever you tell, be very sure that it does not work. But I'm basically satisfied, if we can agree, that the Microchip circuit is working correctly and should be suggested.

P.S.: Sometimes schematics don't represent the actual circuit. Someone may have corrected them silently when assembling the circuit.

Ignoring zero crossings mean, turn the output on or off at will. The triac (or SCR) will immediately turn on, but turn off delayed after the next load current zero crossing (which is not exactly identical to voltage zero crossing with inductive loads). A RC snubber would be needed at least with MOC302x to prevent dV/dt self triggering, but doesn't harm with triacs in general for
ceiling fan.
 

My question is late I know, subject quite well covered.
What surprised me was the apparent collective wisdom that a relay solution was probably the best.
Bearing in mind the application & likelihood that the poster would probably prefer to accomodate his circuit mods within the body of the fan speed switching module which is quite large large on most Chinese made domestic 3 speed fans for example; I would have suggested that three relays was both relatively expensive & space consuming.
It's possible there are really small relays of adequate capacity, but here we are switching mains AC & I know of no such relays.
Further comment on the economics etc please?
 


i'm doing the same project. Can you please give me your circuit,design and program ASAP???????
 

I built up using a TRIAC to control the phase angle to control the speed of a fan. I have added snubber circuit also. But its giving "hum" when its in low speed(Speeds 1 to 6 out of 10). This hum is getting reduced to wards high speeds. I have tried some controllers that I bought out side, technically they are also operating with the same principle of controling the phase angel. So, I shifted to relay control by switching capacitors. Now its fine, no hum at all at any speed. But, yes, with relays its looks more bulkier and little bit more power consumer than TRAIC controller.

Most of the people are suggesting to use TRIAC, that means they have not faced this "hum" issue or the level of "hum" is not concerned for them? If everybody suggests to use TRIAC, it would be helpful if I can get some suggestions for resolving this "hum" issue.
 

I've done something like this.

Code: 
/******************************************************************************
Program for Duel AC Fan controll.
Program written by Engr. Mithun K. Das
MCU: PIC12F675, X-Tal: 4MHz(internal)
Date: 15-Oct-2012. cell: +8801722448270.
*******************************************************************************/
unsigned int speed1, speed2,zero1,zero2;
int cnt1,cnt2,cross1,cross2;

void main()
{
CMCON=0x07;
ANSEL=0x07;// gp0 & gp1 &gp4 analog in
OSCCAL = 0xFF;
TRISIO=0b00001111; // gp2 and gp5 output
GPIO=0x00;
while(1)

{


      // get speed1
      ADCON0=0b00000000;
      speed1 = ADC_Read(0);
      cross1 = speed1*10/1023;
      // get speed2
      ADCON0=0b00000100;
      speed2 = ADC_Read(1);
      cross2 = speed2*10/1023;
      // sense
      ADCON0=0b00001000;
      zero1 = ADC_Read(2);

      if(zero1<=5)
      {
        GP4_bit = 0;
        GP5_bit = 0;
        cnt1 = 0;
        cnt2 = 0;
      }
      else
      {
       cnt1++;
       cnt2++;
       if(cnt1>cross1)
       {
        GP4_bit = 1;
        Delay_ms(1);
       }
       else
       {
         GP4_bit = 0;
       }

       if(cnt2>cross2)
       {
        GP5_bit = 1;
        Delay_ms(1);
       }
       else
       {
        GP5_bit = 0;
       }

      }

}// while
}// void main

It works fine in simulation, but in real hardware the circuit don't work as follows. Sometimes, lamps flicker.

here is my circuit:

 

can u post details?
how can i make NEC ir switch & control fan speed by pic12f629 or 675 ?
 

The control mechanism is very simple. If you want to use a IR, then increase/decrease the value of a variable with EEPROM enabled. Then the variable will be compared with each cycle of the input sine wave. In this way you can control fan speed.
 
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