Automating My Air Conditioner | Hacker News Reader

Automating My Air Conditioner

dannyguo.com

38 pointsdguo25 comments

A general note: Arbitrarily cutting and restoring power is a bad idea for a compressor. See the first answer at this link for a detailed explanation:

https://diy.stackexchange.com/questions/145791/how-bad-is-it...

In a nutshell, it takes time for the refrigerant pressure to equalize. An AC with a thermostat will have a timer to prevent an immediate restart after a stop.

Another option is to introduce hysteresis into your control loop as the TFA author has done: Use a distinct power threshold from your off threshold. By setting the power on a couple of degrees higher than the cutoff, it will give the refrigerant pressure time to settle.

To the author: I agree with the other posters. Looks the AC already has a thermostat, just no automatic fan control.

I did something similar to the TFA but instead of switching the power on and off, I signal it with instructions to cool to the minimum and maximum temperature. (This was easy in my case because it has an infrared remote which I can emulate.) I’m assuming that any logic required to be mechanically sympathetic to the compressor is built into the AC’s own controller.

Author here. Thanks for the heads up. From my experience, after it turns off, it tends to stay off for about 30-45 minutes. I hope that's long enough to avoid issues. The comment in the link mentioned delaying 3-5 minutes.

And yep, It was my bad to misunderstand the first knob. I should have read the manual instead of assuming. I added a note to the post.

Certainly more than enough, it only takes a few minutes as mentioned. You could probably lower the temperature gap further.

IME compressors usually have a thermal cutoff . If you do try to start them up too early, you'll know - it won't turn and the cutoff will kick in. Not great for your motor or premises wiring, but it has been designed for.

To the OP, don't regret doing this at all. Thermostats on air conditioners are generally subpar, since they're located on the unit itself. If you want to use the "auto fan" mode to keep noise down, then there ends up being large temperature swings. I think this is because the air stops circulating, while the air near the unit stays cool due to the cold coils.

I've got a plan to automate a dehumidifier Real Soon Now, and I'm planning on using a plug with current monitoring. This way I can sense when the compressor has shut off on its own and then wait several minutes for efficiency's sake.

Mentioning it just because I didn't see it addressed in the article: AC compressors & fans can be a significant current draw. If you want to replicate this project, it's probably worth checking the amperage ratings for whatever smart plug you use. Something intended to switch lights or a room fan may not be up for the task of repeatedly starting a compressor. Even if the AC unit only draws 15 amps (an so is fine to plug into a wall), inrush current could be an issue for an traic or SSR-based smart plug.

Yes, indeed. If it's a cheap one, it's starting current will probably be 4x it's run current. But it's probably a 400 watt unit, and at 1600 watts for starting, barely within spec for the tiny relay in the smart plug. That said, I have blown the relay in one of my smart plugs with switching motors. But I cycle a dehumidifier in a similar way, and that's been running for two years now.

RIB relays[0] are inexpensive and can handle higher loads than smart plugs, if you’re looking for something that can handle higher loads. Above 30A, a contactor or starter would be more appropriate.

[0] 20A relay https://www.functionaldevices.com/support/downloads/datashee...

> If the temperature is above 75°F, the job turns the smart plug on. If the temperature is under 73°F, the job turns the smart plug off.

Would turning on/off a high current A/C like this have any negative consequences? Some A/C units have a cooldown period after you turn them "off" via their button since they need to remove some condensation and perform other normal maintenance. Would that issue apply to cheep window A/Cs?

Yeah you will get condensation with these window units too. It might have a pan that has to be drained.

I believe most window units instruct you to set them at a slight angle so that condensation can drain out the back without manual intervention. At least mine do.

The relay you use to turn it on better be rated for the startup current of the AC unit (which will normally be pretty high).

When turning it off, you should wait at least 1 minute before turning it back on. Repeatedly not waiting a minute will burn out the AC compressors safety circuit.

https://github.com/ct-Open-Source/tuya-convert is useful for re-flashing some widely available smartplugs without opening them up. Then you can use MQTT or HTTP.

Unfortunately some newer plugs are incompatible with the hack (different chipset - https://github.com/ct-Open-Source/tuya-convert/issues/484 ).

Check out Home Assistant. I use Home Assistant to control about 35 TP-Link Kasa devices via local control. Home Assistant supports both local and cloud control of Kasa devices.

I use a mix of ESPHome (using ESP8266 devices) and BLE sensors (feeding back through ESPHome ESP32 based gateways) to gather home air quality data.

I would like to know more about your setup. Can you elaborate?

It sure looks like that thing has a thermostatic control. I’ve got similar window shaker units and they have a distinct click when the thermostat turns on or off and they do an ok job of controlling the temp in the bedrooms.

Definitely, that's what the numbers are for, but it takes a long time to figure out what maps to what temperature

OP here. Wow, that's a good point. I don't know why I assumed that the first knob is just a static control for cooling output. Especially considered that it's labeled "Temperature."

Looking at some customer reviews, I do see some complaints that it doesn't work very well on this model. But still, I should have read the manual. Thanks for correcting me!

Love the spirit of the idea and execution! I would guess the “temperature” knob ties to some sort of trigger relay downstream. You would probably be able to tie in a microcontroller of some sort to control it and maintain the process function like ramp up and cool down. But at the expense of requiring to open up that panel.

In university I had an air conditioner that would turn off when the power went out (regular occurrence, few minutes), so I'd wake up sweltering or otherwise needing to get up/interrupted in order to switch it back on (it had a cabled remote/controller)

The automation was a clothes peg on the power button.

Is anyone aware of an open-source smart plug or smart outlet with a public API? ...That doesn't assume a big-tech integration?

TP-Link Kasa is nice. They can be controlled locally, and the official app (which is needed to initially set up the plug) doesn’t require an account - there’s a “skip” button if you press login.

Thanks, I'll try it out.

Tasmota is a fully open source firmware that can be flashed onto lots of cheap WiFi smart plugs and bulbs, and has a lot of power-user features. "Sonoff" hardware is probably the best supported, and is very cheap.

Right on, I really appreciate it.

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