How to control the temperature in a Peltier based cooler

Can you control the power input of the cooler?

If your digital controller has a switch mode and you can somehow rig the power supply up via an interface relay to this output of the controller, you should be able to have the temperature control the on/off function of the cooler.

You have also to consider the overlap function of the controller which would give you the accuracy of the final temperature. This is called the hysteresis and will define the price of the controller. Smaller hysteresis is more accurate but more expensive.

I don't think you'll be able to do it accurately with an on/off controller, unless it has two outputs with independently settable alarm levels, or unless your ambient is either always above or always below 20°C. The problem is that you have to be able to reverse the polarity of the heatpump. You may get away with reversing the polarity at exactly 20°C, but with only on/off control, you could get some pretty violent 'hunting'.

What tolerance do you need?

To try it out, you could work out the connections to the 'heat/cool' switch, and replace it with a relay, driven by your controller, so that it switches from 'heat' to 'cool' when the temperature goes above 20°C (and obviously, switches back again below 20°C).

WARNING! IF THIS THING IS MAINS-DRIVEN, BE VERY CAREFUL!

Yes you are correct, I forgot you have the third option of fluctuating between too high AND too low ambient.

It should still be possible but perhaps with a simple amount of logic from a small plc or something, maybe a Siemens Logo.

The other option is if the temperature only requires a minimum or maximum but need no control when out of parameter. Too low it will heat, too high it will do nothing and vice versa.

Hmm, getting complicated now thanks to CR4

Dear Users, thanks you for your support.

The accuracy that I need is not much, maybe +-2 (22, 20, 18), I think that I do not need to reverse the polarity, because I think that the temperature will raise from an ambiet temp of 16, then when the desired setpoint is reached the power will be interrupted by the controller.

My controller is not a PID, is a relay based On/off digital controller.

Do not worry about my security, I am an engineer and I know about electrical risk, ever I work with maximum care!

You should, then, be able to use your controller simply to switch the input power on and off. You may need to experiment a bit with the setpoint (and hysteresis, if it's adjustable).

Good luck,

John

forced air circulation with closed condition at clod side

This thread is also in the Mechanical Engineering section also. I have given a solution there. I know the double posting is a pain the... so I will leave it there. I hope it helps

I found the easiest way to control the temperature in my 12V peltier cooler on my Kenworth was to make a small duct to lead air from the air conditioner vent directly to the inlet air side of the cooler. The internal temperature will be consistently 20 degrees below "ambient", and the air coming off the a/c was at 20 degrees. You can store ice cream in it that way.

Please, give me this temperature control circuit report and circuit .so i implement it......