Heat/Cool/Maintain water temperature

Hi folks,

I am building a system that can heat/cool/maintain a certain water temperature. I have a 110vac automatic temperature controller, two 12vdc cooler/warmer units, and two ac to dc 12v converters one for each warmer/cooler unit.

When the warmer/cooler units are performing a heat operation the polarity of the wires going to the heat sync within the units are reversed. Since the switching operation is going to be controlled automatically by the temperature controller I want to install a relay between the warmer/cooler and the heat sync that activates when the temp controller switches to the warm function.

My problem is that I do not know which type of relay to use. The relay would need to be activated with 110vac and switch 12vdc on the load side. It would also have to reverse the polarity of the load wires. Any ideas oh which relay I could use for this operation?

I attached a quick schematic of the section of the project that I described. Any help would be greatly appreciated.

Thanks!

You can use a common 12V automotive relay and power it with a "wall wart" (to step down from 110V to 12V). That approach is however heavy and a pain to look at.

Instead, I'm pretty sure the temperature controller works with a DC voltage much less than 110V, maybe 12V. You take a look inside to confirm that.
If that's the case you could power all your project with a single 12VDC power supply.

Polarity can be reversed using an H bridge.

Just by curiosity, the heat/cooling units you are talking about are Peltier Cells?

https://www.newark.com/te-connectiv...ay-4pdt-120vac-3a-plug/dp/16M9042?Ntt=16M9042

See attached. verify your current requirement does not exceed 3A