Coldest possible home storage

[mikeselectricstuff]

The problem with stacking peltiers is that each stage needs to take not only the heat from the "load" , but also the waste heat from the peltier below. Ages ago I took apart a Sat-comms front-end that used 3 layers of peltiers to cool the front-end. From memory, the first was about 20x20mm, the second about 60x60, and the last about 200x300mm.

[BradC]

Not sure what would work well for a second stage that goes down to -80C, but R410a should work well for the first, targeting a mid stage temperature of about -30C.

Ethylene works quite well. CO2 will work also if you add enough argon to stop it turning to dry ice in the evaporator but that turns out to be a pretty tricky problem.
R23 is what you really want, but it's not very amateur friendly unless you happen to have either a license or a "mate".

Plenty of info on building simple cascades in the overclockers forum. There are some neat auto-cascades also, but they are bordering on witchcraft and unless you've built yourself some decent refrigeration systems in the past probably well past your average skill level.