Stacking of Peltier units - Part 2

In this video, I will try to show some trick and tips regarding the Peltier cooling and the cooling of the Peltier too. I attempted to reach very low temperatures on the top of the second stage, but the experiment sort of failed, and I could not go more than below -40°C. I expected more based on the calculations. It seems like that the hot side goes much higher than I expect it to go.