Electromechanical Relay for VAC switching

Question

I'm looking at PID devices for coffee machines. There's a tendency to use SSRs (for the regular reasons) but at the current levels (12 amps 120VAC) required these tend to be large (60mm longest dimension).

Even with my own SSRs using opto-isolators and triacs I still need a large heat sink area - especially inside a coffee machine which gets warm and won't dissipate the heat.

I'm looking at controlling 4 AC items in the coffee machine (2 boilers, pump, solenoid) and trying to stuff 4 SSRs into that space will be a challenge.

So here are my questions:

• Am I right in concluding that 4 x EMRs can fit into a smaller space given the largish current?
• Also if I go the EMR path, how can I extend the life of the relays?
• Is it possible to use a zero crossover to switch the relay? Or is the switching delay too slow?
• What other traps should I watch out for?

Answer 1

You can use an Opto-Triac as a cheap SSR. There are many posts here that discuss that. One of them is here.

Here is where @stevenvh builds an equivalent of a SSR.

Here is another discussion related to yours.

Another good post answered by @Anindo.

Below is one of the classic image used in most of the SSR discussions:

Opto-triac solution will save you space over EMR.
Opto-triacs do come in zero-cross flavors.
For a coffee machine switching delay is negligible.
"Moving parts" are the traps to avoid.

Answer 2

EMR's produce heat too so dispating heat is the issue. A PID controller with a temperature senser inside the cabinet will be able to adjust the output accordingly.