Hey I'm working on a home automation system where I can replace one of my 2 way switches to an Arduino Or node MCU controlled one but I want to avoid normal relays because as of what I know they can be unreliable and tend to fail. So is there any way I can replace my switch with an Arduino controlled switch and also I cannot use solid state relay as it has only two terminals and it cannot replace my two way switch.
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I think you are calling what is called a three way switch a two way switch. A three way switch SPDT has three terminals and the identified one will connect to one or the other of the two remaining terminals. A two way switch SPST is simply on/off. I have over 100 relays in my home automation system, and it has not had a single failure in about 20 years. I used top of the line relays, not the hobby relays sold as Arduino add on's.– GilCommented May 20, 2021 at 5:13
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Can you send me links to the ones you used @Gil– rohithrathod banothCommented May 20, 2021 at 5:29
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And are the ones you used 3 way relays? @Gil– rohithrathod banothCommented May 20, 2021 at 5:30
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Why are you trying to emulate a 3-way switch? Just automate 1 of the switches and control it from 2 different places. There are COTS products that do exactly this. Further, likely you need two solid state switches to emulate a 3 way switch. So solid state switches are not "off the table", they are just expensive alternatives to reasonably priced relays. Respond if you want me to draft a solution based on these comments. Otherwise do pick an answer to your question. Pick a "best" or "correct" answer. Don't leave future stackexchange users in similar situations wondering what you finally did.– st2000Commented May 20, 2021 at 13:16
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I'm not trying to emulate 2 3-way switches I'm trying to replace one of my 3-way switches with a relay so that I can control with node MCU and also the 2nd 3-way switch– rohithrathod banothCommented May 20, 2021 at 14:25
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2 Answers
Like Gil said, it sounds like what you are calling a two-way switch is actually a three-way switch. These are typically wired like this (but not always, make sure to double check!):
To replace one of the two switches with a relay, you can simply connect a SPDT relay with the load/hot wire (depending on which side you're adding the relay from) to the common contact, and then the two traveler wires to the normally open and normally closed contacts. This effectively takes your existing wiring and directly swaps in a relay -- after all, the relay is literally a switch, just electrically activated instead of manually.
I can't speak to the reliability or lack thereof of a specific model of relay, but a normal power relay is more than adequate for home automation in almost all cases; you don't need anything too fancy. Yes, there will be a mechanical point of failure, but they are typically rated for 100,000+ actuations minimum on a decent relay (like this one from SparkFun, for example) which will take quite some time to reach. Avoid the super cheap relays both for safety and reliability, and you should be fine.
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Is this a good relay in your opinion @Reid Sox-Harris electronicscomp.com/1-channel-5v-relay-module?search=Relay Commented May 20, 2021 at 7:06
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2Personally in this situation I would choose a latching relay so you don't have to keep it energised for extended periods.– MajenkoCommented May 20, 2021 at 10:28
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@rohithrathodbanoth If you trust the datasheet, that isn't bad (claimed min. 100k actuations, 10A@240V). I might look for a higher-amperage relay depending on your expected load. And like Majenko said, a latching relay would better for this application.– ReidCommented May 22, 2021 at 2:58
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@Majenko I have a question about latching relays will the relay retain its state even after the power is removed like the 5v wire is removed or disconnected Commented May 23, 2021 at 3:35
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@rohithrathodbanoth Yes, the relay will retain its state. Whether the Arduino will, though, is another matter.– MajenkoCommented May 23, 2021 at 9:25
I have not had good luck with these relays, the modules themselves are OK I just solder in a new relay. Try looking for: "solid state 3 way switch" I found this on my first try. DPST 1NO 1NC 8Amp Power Relay Module. It was labeled "OONO". Consider what happens when the power fails in just the controls, light circuit or both. What will you have then, and then when the power comes back on. I use larger relays and have not have any failures, they are rated at 20A 277V with 24VDC coile.
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i did not find any solid state relays or switches with 3 way switching can give a link if you can Commented May 22, 2021 at 8:20
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Not directly, it has one NO and 1 NC which when combined one side of each you have a SPDT.– GilCommented May 23, 2021 at 1:42