Thanks, Labrat101.
I have not had much success stacking Peltiers in the past. They quickly reach a point where they just pump the energy they generate themselves.
The chest freezer is only a few years old so I assume it will be a modern green variety (and thus incapable of reaching high temperature differentials.)
I will try to find a larger and smaller cool boxes but it is not dissimilar to stacking Peltiers. Outside freezer should be capable of removing heat at the rate that internal boxes generate.
Leo
At the moment I am using a chest freezer that reaches -42C inside within an hour of turning on empty at room temperature.
I put a small 12V car coolbox with its "electronics" removed and Peltier/fan connected to external PSU and this setup goes to -50C..-55C inside the coolbox.
Hi Leo. I'm also interested in reaching -60 C or thereabout. My research so far has only yielded expensive environmental chambers; The Chinese and therefore hopefully relatively inexpensive www.lib-industry.com quoted their smallest chamber T-50 last year at USD 7300 for -70 C and USD 13800 for -86 C. And shipping weight is 180 kg so that incurs a real cost too. And then the hassle of moving and housing the 1 m3 unit (inner space is 320*350*450 mm). Interestingly, humidity control only added a marginal cost.
Without being an expert, I doubt -60 C is possible with peltiers regardless how small the temperature delta is. In fact I'd be thankful if you want to share details/pictures of your current setup for -50 - -55 C? It's a good result as is.
I believe virology labs routinely use -70 freezers - might be worth looking at surplus/ebay.
The problem with stacking peltiers is that each layer needs to pump the waste heat of the next, and the low efficiency means you get diminishing returns. A while ago I took apart a 3-layer stack from some sat-comms gear, and that used something like an 8x10" first layer to cool a postage-stamp sized third layer.
I believe virology labs routinely use -70 freezers - might be worth looking at surplus/ebay.In the US they like the -70 freeze, but this is -70 F which is -54° and thus about the dry ice temperature.
They come up occasionally on eBay - but are mad money new. There's one on eBay (https://www.ebay.co.uk/itm/164955721747) at the moment for £5K - which if it works is a fair price.
Thanks for the details, Leo
I think your setup can be refined by replacing the car cooler with an optimized custom build. One idea is to connect the peltier hot side to a metal plate pressed against the wall of the freezer. Then the heat transport would be more efficient, not going through the air. And you would get rid of the heat-generating fan.
If my own experiments don't give enough cold, this is the way I'll go myself.They come up occasionally on eBay - but are mad money new. There's one on eBay (https://www.ebay.co.uk/itm/164955721747) at the moment for £5K - which if it works is a fair price.
Sort of proves my point; that one weighs 550 kg and runs on 3 phase AC. It's a commitment.
I found a middle road in lab freezer Porkka Lab Line PRO 11. It looks like a regular top-loading freezer, 130 liter capacity, goes to -60 C. Cost new (in Sweden) is USD 2800 plus VAT. I don't expect it to have the temperature stability or fine control of a climate chamber, so an inner chamber is still desirable.
Thanks for the details, Leo
I think your setup can be refined by replacing the car cooler with an optimized custom build. One idea is to connect the peltier hot side to a metal plate pressed against the wall of the freezer. Then the heat transport would be more efficient, not going through the air. And you would get rid of the heat-generating fan.
If my own experiments don't give enough cold, this is the way I'll go myself.
So the compressor will need fan cooling will help . These small compressors when new can run under extreme conditions . But not Guaranteed
..
If your compressor has 2 small pipes at the very bottom of the compressor these are
Oil cooling pipes and will give better performance @ lower suction cooling return.
So the compressor will need fan cooling will help . These small compressors when new can run under extreme conditions . But not Guaranteed
..
If your compressor has 2 small pipes at the very bottom of the compressor these are
Oil cooling pipes and will give better performance @ lower suction cooling return.Interesting, I am going to take it apart when I have more time and have a look.
There are a few -86C freezers on eBay for £2k+ but they are huge for my purposes.
Leo