Hi Guys,

I'm starting some planning on a project which (if practical/possible) will be a heater/cooler combination run by a microcontroller.

There is the heating circuit, the cooling circuit and the controller which runs on 12V.

The heating and cooling circuits will be swicthed on/off independently by the controller (not sure how yet, perhaps relays?). Those two circuits will never be closed at the same time. Only one at a time. Other wise both opened.

The point of the device would be to keep a liquid at a constant temperature (with a 0.5 - 1 degree deviation margin).

Everything must be powered by mains, which, here is 220VAC @ 60Hz.

So the first thing I want to figure out is how to power the controller with 12VDC constantly from a 220VAC power source under all three states namely: Circuit 1 switched on, Circuit 2 Switched on or both circuits switched off.

Any suggestion on how I would do accomplish this? I read up on transformers, but they produce a lot of heat. So that got me thinking of these electronic timers you can plug into a wall socket. Surely this don't use transformers to power the display for instance?

Thanks in advance!

 

You are missing some important details such as:

1) range of temperature
2) volume of water, flow rate
3) wattage required

You can do heating or cooling with a single unit. Google Peltier Thermoelectric Cooler (TEC).
Temperature regulation is accomplished using PID (Proportional-Integral-Derivative) algorithms. Google PID controllers.

 

Hi MrChips,

I was thinking of peltiers for both the heating and the cooling (using heatsinks and fans for the cooling part). I don't know how many of each yet, I just want to seperate the different components that I will need.

As for calculations and algorithms, I will still get there, but thanks for the pointer. I will look up PID algorithms.

My first worry however is just how to power a 12VDC controller with a 220VAC power source.

The three circuits will run in parallel I suppose.

 

Sorry... to answer your questions:

1) Probably approximately 20 - 40 degrees celcius.
2) Aimed at pico aquariums, so lets say between 20 and 50 litres.
3) Not sure yet.

 

With the TEC, you use the same unit for heating and cooling. Pass the current in one direction and you get heating. Reverse the current and it cools.

For a 12VDC supply, you simply buy or build a DC power supply. These are readily available off the shelf. You still need to figure out how many watts you will need.

 

Thanks, good point. I could use the same set of peltiers for both heating and cooling.

The reason I was asking the question is because I don't want to use seperate power supplies for the heating/cooling and the 12VDC. So in the end I'll have one plug, plugging into a wall socket.

 

20 to 50 litres is a lot of water.
I presume the tank will be indoors.

What is your typical ambient (room) temperature?
What country/state/location are you?
What is your range of outdoor temperatures?
Do you have air conditioning?

The wattage required for heating and cooling will depend a lot on the answers to the questions above. I am guessing that you will need about 25W.
That is, you have to estimate the typical and worse case heat gain/loss from the tank.

 

Let's assume for now that 25W will be the wattage I'm aiming.

I want to attemp to draw the circuit, even if it is one part at a time.

Where woudl you suggest I start? Shall I look for a circuit diagram for a 12V power supply fed by 220VAC?

 

The 12V power supply is the easy part.
You cannot ignore the important questions.
A 25W TEC is not cheap.
If your requirements call for more heating than cooling then it would be less expensive to use a water heater and a lower wattage TEC for cooling.

You have to determine your heating and cooling requirements before you even worry about electronics.

This is simply proper system design.

Or you can just go out and buy an aquarium temperature controller.

 

You have to determine your heating and cooling requirements before you even worry about electronics.

+100
And I'd forget a TEC for cooling unless you have your heart set on it. They consume about 10X more power than they remove, and you have to dissipate all of that. You'll need heat sinks and fans or maybe liquid cooling to cool the hot side of the TEC. And of course your power supply will have to be beefy to supply all the current you'll need. You might as well apply all that cost and effort directly to the tank you want to cool.

You might be interested in this related project.

 

getting 12VDC from 220AC is NO problem.. There are thousands of off the shelf power supplies for that already.
No point in making your own. You will have enough to do with the micro/TEC,etc.. parts.

Not sure how you can "design a circuit" before you even know whats in it..
You've got thermal/mechanical issues to figure out first though..
Like #1 if you use a single TEC how do you plan to have it cool then remove the cooling section and utilize the hot side. (You don't...you'll need 2 TEC units $$)

Or a single TEC for cooling (Check out the Coolworks ICEprobe) and a typical fish tank heater for heating.

 

Your almost there with a spec.
We have 20 to 50 liters
Ambient temperature (20 to 40C)
Target temperature XX to XXX ??
Time for temperature change (assuming slow)

Assuming peltier for cooling a PC type power supply would probably work.

 

Water evaporating from the tank will probably remove more heat than any TEC. Know your thermodynamics before you start building.

 

getting 12VDC from 220AC is NO problem.. There are thousands of off the shelf power supplies for that already.
No point in making your own. You will have enough to do with the micro/TEC,etc.. parts.

Use an off-the-shelf 12V power supply.
Easier, and a lot safer than designing your own....

This is a circuit I designed, it only does cooling.... as that is all I needed (it is a water cooler). However, you could easily change it to heat as well as cool.
The hall sensor is there to check that a water pump is running (and a buzzer will sound if it is not).


I got a 400W peltier off Ebay. The major problem is the removal of heat when it is in cooling mode. It really produces a lot of heat. Best I managed was a 10 degree drop from ambient. I had a 5 litre water loop, being heated with around 400W of graphics cards