Hi, im starting a marine aquarium and cant afford a chiller for it, i have thought of wiring a simple thermister to the aircon remote's power button, i want to have the thermostat's probe in the aquarium water and have it connected to the On/Off button on the remote, i want the aircon to come on when the temp in the tank gets too high and when the correct temp is reached the aircon shuts off. i'm not a complete noob, i have some experience with building simple circuits and whatnot, but have never tried designing something on my own, i wouldnt know where to start. If someone can point me in a good direction, or thay know of a similar circuit that can do what im trying to do, please share

Thanks.

 

My first thoughts are to consider physics of the tank/room/aircon before the electronics.

I assume the tank is in a room and the aircon cools the room.
When the tank gets too hot, the aircon has to cool the room.

What makes the tank hot?
If it is a heater, then you need to improve the control on the heater first.
If it is the light, try improving the airflow around the light in the top of the tank.

The tank, full of water has a large thermal mass, it will take a long time to cool compared with the air in the room. If you are running the aircon based on the temperature of the tank, I think you will have some large temperature swings befor the thing settles down, if ever.

May be you need to consider keeping the room cool (let the aircon measure and be controlled by the room temperature.) by running the aircon at about the best temperature for the fish. That way the tank should be at about the same temperature as the room.

Just my AUD0.02 worth.

JimB

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its actually the outside temp causing heat in the tank. I live In the North Wast of Australia, i have thought of keeping the aircon on constantly at 26 degres or so but what im trying to do is bring my power bill down, as it is a small room with an aircon rated for a room twice the size the aircon would only have to be on in short bursts to cool the room, mabe i could just have the thermostat reading the air temp instead of the tank temp so there are less fluctuations in temp.

i have thought of using alternate cooling method such as an evaporative cooling tower but because it is so humid here evaporative cooling simply wont work.

 

Doesn't your aircon already have a thermostat?.

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it will only read the temp inside the aircon. the aircon is always drawing in air near the cool air output so it doesnt work effeciantly as if the thermostat was placed in the middle of the room. also when the thermostat does "kick in" it only turns the compressors in the aircon off, though the compressors use the most power, the large fans are still going. when the thermostat does cut the commpressors its not for long, im not sure why because i could turn the aircon on for 15 minuits and then turn it off and the temp would remain the same for about 15 mins if all windows and doors are shut.
this wont be my cooling system forever, im just going to use it for this summer and then i will buy a chiller when i can afford it.

Thanx Isaac

 

So the outside temp is heating the room and then the room is heating the tank. So you need to keep the room cool.


OK so the aircon has plenty of oomph and can keep the room cool.
Have you tried insulating the room? We have the opposite problem here, we use insulation to keep the heat in, sounds like you need to use it to keep the heat out.


Sounds like a good idea to me.

JimB

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the room is insualted, it is a brick house but the heat gets in through the windows, and i dont want to block out the window with insulation. its not the sun thats heating the room its actually the window acting as a heat transfer from the outside to the inside. outside the average temperatur in the summer season is about 38 degres celcius and on a hot day it can reach 45 degres celcius. insulation would be a good idea in a cooler climate but since it is so hot outside the aircon is a must. BTW i just set the aircon on 16 degres celcius and shut the door about 15 minuits ago and now its like a fridge in here.

Thanks for your help. now we have established i need this could someone help me with the design?

 

bump

Isaac1223

 

do you realize how expensive it's going to be to run an air conditioner to stabilize water temperature? How about a Peltier module instead that runs off a 12vdc power supply. You can wire it to a thermal switch of a predetermined temperature value.

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They're very inefficient. to get 5W of cooling power, you'd probably have to feed 10W of power in and then get rid of 15W of heat. If you don't remove the full 15W, then the cold side actually heats up. useful in very limited situations (they were used in cooling computer chips when overclocking for a while)

i did my homework

 

maybe so but you're cooling an entire room at a current draw of near 15amps (if it's a window mount unit) and a whole lot more if it's a central air system. A 12vdc supply at a few amps is far less costly on your monthly electric bill, even if the device is inefficient.

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what im trying to do is lower my electical bill but still have an efficient cooling system. i have spoken to people who have tried this and they said it is not worth thinking about. it simplu wont work. since its a small room i think this could work well. untill i buy a proper chiller in 6 months time.

 

OK how about a room dehumidifier then? You can place the frosty condenser coil unit next to the aquarium glass, and evaporate the water inside it simultaneously!!!!

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Your aircon already has a thermostat, leave it ON all the time and let the thermostat keep the room at a suitable temperature, that prevents the tank getting too hot. It's going to more efficient than trying to cool the room (and tank) down when it's already too hot - due to the thermal lag of the water, which would take ages to cool down to room temperature with your aircon.

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