I've been designing some wireless modules and finally got them to work and now I have a network of them and want to use them for home automation purposes. Controlling stuff like chandeliers, heating, and even simple lamps and so on. The load voltage is 220VAC and the current is normally up to 1 or 2 or in some cases 3 Amps I guess.

Now I'm wondering what is the best way to control those stuff? Electromechanical Relays or Semiconductor solutions like SSR, Triac, MOSFDET, ... ?

I'm not sure which solution is the best. The thing is Since I want to install this system into other peoples homes I want it to be safe, very reliable, perfect and without any problems or dangerous in long term uses. You see I don't want to blow their homes! That's why I'm asking you guys.

On the other hand I sort of have a limitation for space considering I have to implement this system into a wall switch or the top of a chandelier somehow (for now I'm not sure which one to go). As always there is other limitation as well, Money!

Now what I think is that electromechanical relays do not generate too much heat in the load side. They are also simple to use. Although there is the contact sound.

But the thing about using relay is since I have 5V or even less trigger signal with not too much current I have to use small signal relays (right?). The latched version of these relays does not draw much current in the control side considering it latches its state. But unfortunately they don't switch high currents. Apparently up to 2.2A which maybe enough for me in some cases. But about the long term use that I mentioned, I'm not sure electromechanical relays take care of that.

Now there is semiconductor solutions like SSR, Triac, MOSFET, and ... They don't generate sound as opposed to electromechanical relay. I don't know about the size considering I've never used a SSR before and a discrete opto-triac and Triac (and probably a heat sink) may take too much space. Plus I know SSR probably costs too much as opposed to other methods.

So with all the stories I just said what do you think would be my best option?

1-Simple Electromechanical Relays

2-Small Signal Relays


4-Opto-triac + Triac


or something I'm not aware of.

  • \$\begingroup\$ SSR == Optotriac + Triac, Small signal relays is no go, Mosfet SSR still new, remains SSR and Relay. If there will be a short circuit, then your SSR will blow before any fuse can save it, also special fuses with silver wire are more exensive than SSR, so.. \$\endgroup\$ Sep 11, 2015 at 18:31
  • \$\begingroup\$ I know SSR == Optotriac + Triac in functionality but they are different things when it comes to cost, space, implementation and safety. I'm sorry I'm not sure I got your conclusion at the end. Are you saying that I have to go with electromechanical Relay? What's wrong with Small Signal Relays? Please explain more for future references. Thank you anyway \$\endgroup\$
    – mostafanfs
    Sep 11, 2015 at 19:36
  • \$\begingroup\$ Small signal relay, like I am in mind, they are to be used for switching signals, not to drive loads. Anyway I would just buy the rady made components, a base for rail mount with interchangable relay/SSR - width 6 or 8mm. findernet.com/en/products/families/10/series/39 \$\endgroup\$ Sep 12, 2015 at 18:59
  • \$\begingroup\$ Well if there is ever a short circuit then there is a chance that relay contacts will stick together or even get melt. Plus a relay has not too long life cycle after all. I mean how many times can you switch a relay before it goes crazy? SSRs are kind of expensive on the other hand. That modules you mentioned I'm not quite sure what they are. I think Optotriac + Triac is the way to go. Considering the load is not inductive, load current is not high and after all they are electronic switches in fact and therefore they have a long life cycle. Much longer that relays. Right? \$\endgroup\$
    – mostafanfs
    Sep 13, 2015 at 10:14

1 Answer 1


Im a noob in electronics, but i think you can use a electromechanical relay and a transistor together

Principle of use is 1. Amplify your 5v signal using a transistor (idk maybe a enhancement mode mosfet, ask a pro. You need one that will output 12v? When your base is supplied with 5v (n-p-n maybe))

  1. After your signal is amplified, feed it into the relay

Again, im a noob at electronics. But this should give you an idea

*electronechanical relay isolates the main line from your signal (i think)

*you will end up having a 12v line using this though

  • \$\begingroup\$ Thank you. Yeah I know about using transistors with this. Otherwise relay coil wouldn't work at all. For now I'm not sure about using relays. And there is no 12V. Only 5V. If I ever had to use a relay I should use the one with 5V coil voltage. \$\endgroup\$
    – mostafanfs
    Sep 11, 2015 at 20:55

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