Relay or triac?

Discussion in 'The Projects Forum' started by crankler, Jan 6, 2011.

  1. crankler

    Thread Starter New Member

    Dec 14, 2010
    19
    0
    I have a project in which i will control the speed of the electric fan (220Vac, 60W, 5A max.) through the microcontroller automatically depending on the temperature. I was planning to replace the fan's switch with either a relay or triac. Min. time interval between switchings is 10seconds.

    Which do you think is better suited for the application: RELAY or TRIAC? why?

    Thanks..
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    With a triac you can control the speed too.

    With a relay, you can either ON or OFF the fan.
     
    crankler likes this.
  3. crankler

    Thread Starter New Member

    Dec 14, 2010
    19
    0
    This electric fan has a switch for speed control (1,2,3). I can replace the rotary switch with relays or triacs, one for each speed level. Forget about phase control with triac, etc. All i need to do is switching.
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    A Triac would still be better, relays aren't often rated for that many cycles of breaking higher current loads. Arcing would shorten the relay's life span.

    An opto-isolated Triac package is perfect for what you are trying to do, and would allow for full speed control from the uC as well if you decide to add that in the future, without changing the hardware.
     
    crankler likes this.
  5. Tahmid

    Active Member

    Jul 2, 2008
    344
    25
    Hi,
    I would still choose the triac because it is solid-state and no mechanical parts are involved. No matter how many times the switching will be, triacs will last longer and will also take less space on the board.

    Hope this helps.
    Tahmid.
     
    crankler likes this.
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    If triac is difficult to get, relay is an option if properly rated, and easier to integrate into a typical toggle controller. (If it is a house hold fan, load is rarely a problem for 10A contacts).

    Using a triac requires to play with mains more than a relay, As the relay circuit can be tested without mains to see if they switch.After that you can connect the relay contacts to the speed limiting inductor appropriately without a hassle.

    But you will need a relay for each speed. So cost wise it is expensive. But will be somewhat more reliable
     
    crankler likes this.
  7. crankler

    Thread Starter New Member

    Dec 14, 2010
    19
    0
    so triac has more pros. My problem with triac is i think it's more complicated. how to turn it on and off, with the microcontroller dc and the driven load ac.
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    It is driven at zero crossing and should use opto's to isolate the DC from AC mains side.

    It's not difficult to use triac as an on/off switch. It's the speed control part that a bit complicated.
     
    crankler likes this.
  9. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    Here's the way I did it for 117 vac at 2 amps. I didn't use a zero crossing optocoupler, but you could substitute one if you think it's required.
     
    Asad ahmed1 and crankler like this.
  10. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    Yes, I forgot that the OP's load was a fan. I use it to control a resistance heater.
     
  11. crankler

    Thread Starter New Member

    Dec 14, 2010
    19
    0
    so in case of that optocoupler, i don't need a zero crossing detector for this application?
    Would it work well with greater load current, probably a max. of 5 A?
     
  12. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Load current handling depends on the Triac or relay capacity.

    Zero crossing can be achieved through such opto's or through certain circuitry
     
  13. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    There is an AC device that uses a triac called a solid state relay (SSR). It uses an LED/resistor (which takes between 3 to 10V many cases) to turn on an optically coupled triac. You can buy them off the shelf in any size you need, but a small digital circuit with a 3 to 9V battery can turn them on.

    That is my recommendation.
     
Loading...