High Current Appliances Switching (Airconditioner) Help

Hi everyone. I need some expert advice :slight_smile: I have some experiences in microcontrollers and robotics so the software and hardware parts aren't really problems provided devices used don't require high current. I'm currently working on a new project that switches appliances. I've done everything nicely but one. Since I don't have any experience in switching high current appliances such as an airconditioner, I'm kind of paranoid to try the real thing even if I have the theoritical calculations. I'm currently using an 8 channel relay with a maximum of 10A for the relays. Is this safe enough to switch a...let's say a 1.5 hp airconditioner? Or do I need another kind of relay? In this kind of scenario, what would be the best thing to do? If the relays I currently have aren't enough, is there another option that I can make use of this module? Like connecting these to another kind of higher current relay? Thank you everyone. Any advice would greatly be appreciated :slight_smile:

You need to know the voltage you're switching, and the current that the load will be drawing, and whether the load is inductive or not, and whether the relay is rated to switch that voltage and that current for an inductive/non-inductive load as applicable. Designing circuits to switch mains voltages safely is not trivial and I'd suggest you stay away from that unless you've been trained in the subject. It's all too easy to design something that seems to work but puts you or others around you at risk.

There are commercially available devices that deal with the problem for you and just have a safely protected TTL signal in and switched mains out - power switch tail is a well known one.

fulong_wu:
Hi everyone. I need some expert advice :slight_smile: I have some experiences in microcontrollers and robotics so the software and hardware parts aren't really problems provided devices used don't require high current. I'm currently working on a new project that switches appliances. I've done everything nicely but one. Since I don't have any experience in switching high current appliances such as an airconditioner, I'm kind of paranoid to try the real thing even if I have the theoritical calculations. I'm currently using an 8 channel relay with a maximum of 10A for the relays. Is this safe enough to switch a...let's say a 1.5 hp airconditioner? Or do I need another kind of relay? In this kind of scenario, what would be the best thing to do? If the relays I currently have aren't enough, is there another option that I can make use of this module? Like connecting these to another kind of higher current relay? Thank you everyone. Any advice would greatly be appreciated :slight_smile:

Why not use AC building switch? setup Arduino as remote control.

Hi :slight_smile: Thank you very much for all your replies. I've already reviewed the Powertail Switch and I think it's the best answer to my problem now :slight_smile: I do have another question. If the setup were to have the airconditioner plugged right into the powertail switch directly, would this be safe enough? Or do I need to have something like a circuit breaker to have the arduino to control it? Thank you.

By the way, will this relay be safe and good enough to replace the Powertail switch? Thank you.

http://www.ebay.com/itm/Solid-State-Relay-SSR-40DA-40A-24-380V-AC-Control-Module-Fast-Switching/370812003082?_trksid=p2045573.m2042&_trkparms=aid%3D111000%26algo%3DREC.CURRENT%26ao%3D1%26asc%3D27%26meid%3D8221446036006433950%26pid%3D100033%26prg%3D1011%26rk%3D2%26sd%3D281114885330%26

What kind of A/C unit is this? I mean - why can't you just switch it using whatever it currently provides? I mean, I have a small room unit on my shop, and it has a small digital control board that is probably toggling 5 or 12 volt relays to turn on the compressor and/or fan. My house units, on the other hand, use a standard electronic thermostat that use either reed relays or transistors to toggle the larger relays in the roof unit that (IIRC) are powered by 24 VAC (generated from the 240 VAC mains voltage on-board by a step-down transformer); in this case, these relays then power larger contactors (basically big bulky relays) that control the motors and compressor and such.

In other words - try to hack the interface you already have. That said - I suspect maybe a powertail might be the better option; if you weren't able to come to the conclusion that the system itself is already likely "open" enough to hack it, you might end up doing yourself harm trying, from a lack of knowledge of what to do. Not saying this to be mean, just stating what I am thinking to keep you from harm until you learn more.

No no, you're not being mean. I always learn from people :slight_smile: So thank you for the advice. The only thing I'm paranoid about is that...since I'm switching a high current appliance, the Powertail with a max 15A tolerance might not be enough. Initial current goes up as high as 3x the normal flow, so I was just being cautious, and I had to ask about the 40A relay :slight_smile: Any additional thoughts about it before I go for the final decision? Thank you everyone :slight_smile: