Using Triac to control solenoid

Question

I have to design a 4 relay or 4 triac switch.

First would control a 12V solenoid for water flow. Second would control 230V for a complete device which contains a small boiler as well.

After reading this: Triac versus Relay

It is still not clear to me if triac circuit like this:

http://www.instructables.com/id/Small-Triac-Switch/

are safe to use here. I read that triacs can break then let current flow (which would be catastrofic in my case at controlling the solenoid). This can never happen to relays, if the relay broke then that only means it wont turn the device on.

So can I rely on triacs for long time period (years)?

Even a relay can remain with a contact stick together. – Marko Buršič Mar 09 '16 at 16:00 — Marko Buršič, Mar 09 '16 at 16:00

score 2 · Answer 1 · answered Mar 09 '16 at 13:19

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Whether you use a relay or a TRIAC, there's a chance the relay contacts could fail closed (welded together) or the TRIAC could fail shorted. The way to avert a potential catastrophe - if either of those happens - is to use a non-resettable thermal fuse which will break the mains connection to the device in case the device should overheat.

answered Mar 09 '16 at 13:19

EM Fields

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The relay or triac (TIC 206) would be normally open and only operate for a short period (30 seconds) a day. As I understand the triac is never fully open, its just acting like a large resistance while a relay needs no effort to be open. – Defiler Mar 09 '16 at 13:27
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If you're looking for someone to share the liability in making your choice for you, it ain't me babe. The advice I gave you will let you sleep nights without worrying about whether someone burned to death because you made a mistake, so either take it or don't... It's up to you. – EM Fields Mar 09 '16 at 14:01

score 1 · Answer 2 · answered Mar 09 '16 at 19:08

schematic

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Triac controled load with thermal trip and fault indicator.

The triac option has no moving parts and could provide a good solution to your problem. The SSR (solid-state relay) versions include the opto-isolated trigger circuit which keeps mains away from your control circuit and many incorporate a zero-cross switch on which minimises transients and noise from the wiring.

Best practice would be to have a separate thermal trip on the boiler. Figure 1 shows one configuration with a trip indicator.

Using Triac to control solenoid

2 Answers2

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