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/diy/ - Do It Yourself

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380796 No.380796 [Reply] [Original]

How's it going guys?
There was a thread on here yesterday with a guy interested in building a super freezer or something along those lines.
I need something similar, but it should be a lot more simple.
Right now I have a little mini fridge in my dorm that get's down to -10c when I crank it all the way up. I have some biological samples coming in soon that I need to keep at -20c.
Any recommendations on how to get that last 10 degrees?
Not sure of the exact make, but I'm guessing its the precursor to this model, so it's similar.
http://www.amazon.com/3-2-cu-ft-Compact-Refrigerator/dp/B000UOL7TY/ref=sr_1_1?s=appliances&ie=UTF8&qid=1358997543&sr=1-1&keywords=ge+mini+fridge

>> No.380802

Change the working fluid and/or modify/bypass the thermostat so that you can get colder than the builtin thermostat allows.

>> No.380803

>>380802
hmm I'm not that knowledgeable about that stuff. I'll have to look into it more I guess.
Thanks

>> No.380805
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380805

Put a fridge inside a fridge. Seriously.

You can get some small 12V coolers intended to go inside cars or on desktops, that may fit inside your fridge. They use Peltier coolers, which only care about temperature *difference*, so the colder the outside, the colder the inside! (Note: you may have to defeat a thermostat).

>> No.380808

>>380805
Something like this?
http://www.amazon.com/TV-Products-Micro-Cool-Fridge/dp/B001ANXRK6/ref=sr_1_3?ie=UTF8&qid=1358999067&sr=8-3&keywords=desktop+fridge

>> No.380812

better insulation helps too

>> No.380813

>>380812
The bottom 90% is a cool temp fridge and the top 10% is a freezer compartment. Maybe if I just insulated the freezer compartment I could trick the thermostat?

>> No.380818

>>380808
Yes, that should work. You will probably have to bypass the thermostat.

Keep in mind that, although Peltier coolers can get very cold, most are only in the 100~200 BTU range so they take a while to reach that temperature. Therefore, set it up and start it running 24 hours before you need to put something in it.

>> No.380846

Fridge inside of a fridge? Not sure if trolling or just stupid. The only thing the would get you some nice low temperatures is dry ice. Buy some.

>> No.380858

>>380846
the fridge inside of a fridge idea isn't as dumb as it sounds. sealed HVAC systems can only pump so much heat... the easier you make it for one to kick heat out of it's condenser the more efficiently it'll run, and the cooler you can get it... one quick and easy way to do this is to run the condenser inside of another fridge using another sealed system... so the first compressor lets the second achieve the temps you want

>> No.380882

>>380796

make that INSANE insulation. seriously, 12" - 16", gas tight, researched high thermal resistance, gasketed, top-opening. it's probably square-law or worse getting that last 10 degrees.