# Making Hot and Cold room at the same time with Peltier stack

I am thinking about 2 small boxes with peltier stack middle of them to get a cold room and hot room at the same time.

Is it possible to get -40 degree celsius cold room and 100+ degree celsius hot room?

Don't care about power dissipated. I will create DC power supply for that if it is possible.

• That's how Peltier cell work. – Marko Buršič Jun 16 '17 at 8:07

In my limited experience, 140C is far too much temperature difference for typical Peltier stack. (My experience is limited to building a demonstration board for our own in-house training, using our own (Maxim Integrated) MAX1968/MAX1969 TEC regulator IC. I used a single TEC element with a simple heatsink + fan IC cooler arrangement, and did not address regulating a temperature chamber.) It might be possible with careful component selection and design attention to insulating the hot and cold chambers.

Study the datasheets carefully, for example CUI Inc CP85, the CP85438 is rated 15.4V 8.5A best case deltaT max 75C (measured in a vacuum). But the real story is found in the typical performance chart:

This chart shows a family of curves representing the typical achievable temperature difference, as a function of drive current. At 1.7A, the temperature difference is about delta-T=35C when no heat is being pumped, but drops to delta-T=0C (no heat flow) when 20W is being pumped. At the maximum rated 8.5A drive current, a temperature difference of over delta-T=70C is possible as long as there is little or no heat transfer. At 8.5A this part is capable of pumping a maximum of just over 80W of heat. This is what limits the performance of this component. Also note how close the 6.8A and 8.5A lines are, there is diminishing returns from increasing the drive current.

It is also important to realize that as soon as drive current is removed, heat begins flowing back across the junction, to equalize the hot and cold side. So when the device is powered off, the cold side may feel a sudden temperature increase.

You are asking for a 140 °C difference between the hot and cold sides. Most Peltiers can't do that. Even if so, they will be horribly inefficient at cooling.

A better answer is to use a Peltier between the cold chamber and ambient. Even then, -40 °C is a stretch. You can then use plain resistive heating for the hot box, or possibly a Peltier between it and ambient.

Two separate elements are also the required if you want to regulate the temperature of both boxes.

• Thanks for the input. I think only cold box with peltier and hot box with resistive heater are the way to go. – 유진호 Jun 18 '17 at 23:27

I would agree with Mark, that you are wanting to achieve a bit much of a swing in temperature from ambient.

Assuming ambient is around 23C - then for any kind of efficiency your probably restricted to around 80-85C as seem most commonly in a number of cheap and more expensive cool box / peltier fridge devices.

How big are the chambers?

The main issue will be temperature control as each chamber will directly effect the other, on different days and with different ambient it will be impossible to control the temperature of both accurately with such a setup. So if the application is critical I would say it will not work.

I have tried a similar setup with two columns of water, not as a fixed setup but as an experiment for testing some peltier devices, and controlling the hot side temperature we had significant (in our application) variation on the cold side temperatures day-to-day based on small fluctuation in ambient temps.

-40C is not going to be easy to achieve with such a setup either.