DIY Fridge, Freezer?
August 28, 2018 11:17 AM   Subscribe

We'd like to build a small-ish fridge and small freezer, probably using peltier elements.

The fridge and freezer will be separate units, located in different parts of the kitchen.

- Roughly 2' deep, 3' wide, and 3' tall
- hinged door on the front
- partial hinged top for "deli prep fridge" use (keeping small containers of salad/sandwich ingredients readily accessible)
- probably something like 2" thick foam insulation?

- Roughly 2x2x2'
- Plan to direct waste heat into a food dehydrator built above the freezer
- probably something like 2" thick foam insulation, maybe more?

We know peltier elements are less efficient than compressors, but like the idea of using peltier elements for simplicity, compactness, relative silence, and lack of toxic refrigerants.

1) Can/should we do this with peltier elements? Seems like the fridge should work fine - people all over YouTube are making "mini coolers" with them - but I've read that the temperature differential between the hot and cold faces can't be more than 20 or 30 degrees. This is for a studio-sized house in the Pacific Northwest with foot-thick walls. Temperatures are relatively stable. We don't use AC. Does that make a peltier freezer impossible?
2) What can we line it with to make the interior easy to clean?
3) Will we need to worry about defrosting or water draining out?
posted by sibilatorix to Technology (5 answers total) 7 users marked this as a favorite
You will not be happy with a peltier system. Too much draw for too little cooling.

What you need is a small danfoss compressor - this can run at 12/120v and works like an actual fridge/freezer. There are a bunch of companies that make these for use in vehicles (best camping upgrade ever!!!).

I'm on mobile at the moment. If I get a chance and remember when I get home, there were a couple of companies that sold the cooling units as a kit - for use in like sailboats and RVs where custom cabintry was desired. I'm blanking on them right this second.

It is a totally doable project. The compressor systems come more or less complete - you just need to build the enclosure to fit. They are far more efficient than peltiers - my fridge draws 5 amps at 12v (60watts) at startup and then 3.75v (~40 watts) running. Kept full and out of the sun, it would run for days off my truck battery even in the southwest desert.
posted by Pogo_Fuzzybutt at 12:03 PM on August 28, 2018 [5 favorites]

Found it! Dometic sells compressor/evaporator kits that allow you build your own custom fridge/freezer.

They are 12/24 volt, so you'll want a transformer from 120v. Or you can do a battery minder --> 12v battery --> fridge compressor and get some uptime in the event of a power outage as well.

You can make the interior out of whatever you like - a metal fab place can make you a stainless steel or aluminum box for the interior. It doesn't have to be thick metal, 1/8" would be way overkill, and probably cost ~100 bucks or so. Paint it with an nice enamel or have it powdercoated and it will be easy to clean.

Defrosting and draining is still a concern - anywhere you have moisture and a temperature differential, you'll get condensation. Also spills. A wire basket or baskets will make removing things, cleaning, and putting them back easy.

Again, this isn't a super complicated project. Good luck and have fun!
posted by Pogo_Fuzzybutt at 12:54 PM on August 28, 2018 [1 favorite]

The peltier effect does limit the temperature difference you can create across a bimetallic junction depending on the metals. The maximum you can create is 70°C which seems like enough. This will be 1/4 as efficient as a regular fridge though which mean it will need a relatively larger heat sink/radiator than a regular fridge (possibly benefited from active cooling; I.e., a fan) and will heat up your apartment 4x as much.

I’m as big a fan of the thermoelectric effect as the next guy (or maybe even bigger) but I agree that this isn’t a very practical idea for a fridge. Since being homemade already makes it something of a stunt fridge anyway maybe that doesn’t matter!
posted by aubilenon at 1:39 PM on August 28, 2018

I dunno, running a dehydrator off the excess heat changes the overall efficiency, even though I do believe the general comments above on efficiency.

But to look at the full impact/energy budget, you need to compare your (cool idea) fridge/dehydrator to running a compressor fridge and heater/fan/dehydrator both of similar volumes.
posted by SaltySalticid at 5:48 PM on August 28, 2018

There do exist premade peltier "wine coolers" and such. Consensus seems to be that they don't work all that well, but they do work in situations where compressor-based coolers may not be the best choice. (Insufficient starting current is a common issue)

The reason I mention them is that you could take some lessons from what others are doing. I believe the EEVBlog YT channel has a teardown of one such unit. I believe he ended up turning it into an oven, actually.

If you have a good way to transport the heat away from the hot side, they can be reasonably efficient. Most of the efficiency figures you see (and most of the commercial products you see) just use a heatsink and a dinky fan, which is obviously quite far from the best that can be done with reasonable effort, being pretty much the bare minimum.
posted by wierdo at 9:11 PM on August 28, 2018

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