Relay or triac?

Thread Starter

crankler

Joined Dec 14, 2010
19
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..
 

Thread Starter

crankler

Joined Dec 14, 2010
19
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.
 

thatoneguy

Joined Feb 19, 2009
6,359
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.
 

Tahmid

Joined Jul 2, 2008
343
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.
 

R!f@@

Joined Apr 2, 2009
9,734
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
 

Thread Starter

crankler

Joined Dec 14, 2010
19
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.
 

R!f@@

Joined Apr 2, 2009
9,734
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.
 

Thread Starter

crankler

Joined Dec 14, 2010
19
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?
 

R!f@@

Joined Apr 2, 2009
9,734
Load current handling depends on the Triac or relay capacity.

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

Wendy

Joined Mar 24, 2008
22,170
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.
 
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