Can I control AC Power with Relays ?Started by 4 years ago●12 replies●latest reply 4 years ago●91 views
We have an Air Conditioner at the Factory that doesn't have a timer. We need to control it just to turn on at a certain time, and turn off at the rest of the day. As you can see it is only 1 ON and 1 OFF cycle for the whole day.
My worries is that this AC is made for a factory, so it has high current. The ratings are probably 5.7A during operation and about 11 A at startup.
I was wondering if I could develop a simple circuit with a microcontroller and a relay to make this function, but I'm not sure if it is safe to use relays for that or not. These are the relays available in the market for me:
SSR - 5V - 40A https://ram-e-shop.com/product/re47/
Mechanical Relay 5V - 30 A https://ram-e-shop.com/product/relay-module-5vdc-3...
Also I was thinking of a simple Atmega16L for the microcontroller, would that be sufficient?
I would love to hear any recommendations or suggestions regarding this project.
I'll concur but add that a homebuilt controller gives insurance carriers an obvious scapegoat if something goes wrong. That it's a commercial / industrial property, I'd have certified HVAC folks do it.
I would agree with CustomSarge. Work with the supplier of the HVAC system if possible. They're the first port of call for a technical solution to your requirement.
You could go the route you are suggesting, but you also have to consider warranties, etc when talking about commercial equipment.
So I was thinking of an alternative solution, the AC already has a remote control that controls it's on and off with the built in controllers of the AC. Is it possible to make a simple circuit that produces the same result of using the ON/OFF buttons on the remote control?
Yes. There are several ways to do that Depending on how the remote is setup. For example:
1) If the remote is IR, you can figure out what the protocol is by either research and reverse engineering and then use a microcontroller and an IR LED to duplicate the on and off commands.
2) You could solder wires on the button contacts of the remote and then use a microcontroller to, or even a 555 with the desired period, to close the contact as your timer.
Aha. I think these could be much easier to start experimenting with.
Thank you so much for the help.
I've built several IR "substitutes" by finding carrier freq (o'scope), and buying an IR receiver (Sharp / Vishay etc). Program a micro to record the pattern, maybe save to flash.
Then a 555 sets carrier and drives an IR LED while the recording micro issues the pattern.
I use one version countless times a day - its relays mute the external TV sound system (internal turned off), by a harmless TV remote button (menu return).
The ways to control high power always start with "what kind of load?". Voltage (AC/DC), steady state current, inductive, resistive, inrush demand all limit your choices.
Aha. Firstly, thank you so much for helping.
So I don't currently have an Oscilliscope, can I check the frequency using Arduino or any Microcontroller directly?.
Also which of these IR recievers should I use?:
The timer is easy, depending on the range, a 555 feeding a high number of stage divider. The CD4020 & CD4040 are a couple I use. The high power switching is not as easy. Solid state and contact relays, MOSFETs and IGBTs are all candidates. Again, it's the characteristics of the load that narrow your choices.
Not having an o'scope makes this tougher. I'd contact local schools / colleges. One with an electronics department usually is happy to help, but use them to learn, don't have them do Your work. You could also ask them if anyone would be willing to help you build this, at least the IR I/O.
A micro could be written to count the carrier at the transmitter LED, but the pattern will give inconsistent results.
"Most" IR control is 38kHz. Since the Vishay TSOP series is ~$.45 each, you could start there. Write the code and make the 555 carrier adjustable. Again, not having an o'scope Really makes this a lot tougher.
If you're at the start of learning electronic design/build, an o'scope and freq generator are important tools. PC/Laptop o'scope interfaces are <$100 and are a fine place to start. A whole bunch of simple generators are at "http://www.discovercircuits.com/F/function.htm". Pawn shops and estate sales are options too. But I'm USA, I have no idea what options you have.
Getting started these days is unbelievably easier than when I did - 51 years ago.
Have you tried the Hantek O'scope ? Probably that's the most affordable option for me right now, but I have no experience with those so I'm not sure if that will do.
No, seen but never used a USB / laptop 'scope. But the 6022BE at <$60 on Amazon, if it works as reviewed it's a good starter unit.
A colleague recently needed to get one and we spec'd a Rygol. An amazing 4 channel 100MHz color LCD for <$350. I paid $1500 for my 2 channel 60MHz Tektronix, but that was Several years ago.
Test equipment, being a tool, has the adage "the better you get, the happier you'll be".