I have an air conditioner switch rated at 32A/240V AC - how do I turn this on using Arduino and Relay.

I'm based in India and I am unable to find a relay switch rated higher than this.

I don't want to try anything that results in a fire hazard. My aim is to switch on the AC with my mobile phone. I'm using Arduino Uno with a 2.4GHz transceiver for communication.


4 Answers 4


Just go with a solid state relay: you can search on ebay for SSR-40DA (240V, 40A, from China around 4$) or, better, SSR-100DA (240V, 100A, from China around 6$). For 32A you should definitely mount it on an heatsink (they sell quite a lot of them on ebay).

The main advantage of that kind of SSR is that you can command them directly from the arduino. No transistors, no limiting resistors, just connect the ground and the pin and you are done.

With a relay my arduino halted often (probably because of the 5V-12V boost, but it was necessary to drive the 12V relay). In the end I switched to an SSR and... Works like a charm. And since it is quite cheap I suggest you to use it.


I don't want to try anything that results in a fire hazard.

That's a good idea.

Besides those toy relays there are real ones: 440 V AC * 63 A (Around there, you can find smaller ones too)

BTW: Don't rely on what's printed on the relay itself, with cheap Arduino relay modules. 230V and some current need proper handling by the PCB board as well (size and distance of the copper tracks on the scondary side)

If you want a solution that could be certified (or certifiable) as "safe" there probably won't be an Arduino involved or being built by anyone asking questions like you do ;( (sorry)


The simple answer is: you need to find a relay rated high enough for the voltage and current. There's no way you can make a small relay handle a large current, and relays cannot be joined together to share the load.

If a relay is not available in your country (and I seriously doubt that - you're probably just looking in the wrong places - instead of looking for things on Amazon or eBay try looking at proper industrial electronics suppliers) then you would have to come up with something more creative.

How about designing and building a small electro-mechanical system that physically changes the position of the existing switch for you? Solenoids to press the right bits of the switch, or motors to turn the right bit round, etc.


What about staying with small relay and just add a contactor? The relay will deal with the low current 230v to drive the contactor and the contactor would deal with the high current.


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