How to build your own dirt cheap fridge

my family survival How to build your own dirt cheap fridge

This is a guest post and entry in our non-fiction writing contest  by Michael C

I noticed that many people on this blog want to store milk, vegetables, seeds and medication in a refrigerated atmosphere but have yet to buy 2 refrigerators. Remember the “two is one and one is none” motto; you need 2 ways (or more) to cool your food. You could make a Zeer pot, like I did but there is too much humidity and the pots aren’t big enough for 2 gallons of milk.

I can’t buy another (let alone storing a 19 cubic footer) $700 fridge as a spare. The other problem is – I might not have AC to use in the future, regardless of all the solar panels I have. So, I needed a small DC powered fridge that will hold at least 2 gallons of milk and some other stuff.

DSCF0161 300x225 How to build your own dirt cheap fridge

I thought of what MD Creekmore would do – a “Do It Yourself” project. (Mr. Creekmore has a propane fridge but, even though he is a great inspiration, I want to limit my power needs to solar since, that is the only long term solution and also because I have solar) Just like the “MDC made” water filter or electric generator – a person can make a refrigerator. Of course, there will be some technical discussion of the actual properties of said fridge. It will be a bit more involved than the water filter project and, for good reason – you want something a bit more complex.

My most important consideration is that it can be service-able by me, so, the fridge is not going to use Freon. I am going to use a “Peltier junction” cooling unit – already built for the purpose. These units are less efficient heat pumps than an evaporator/condenser cooler but are solid state, small, low power and can be ganged together for more cooling power. Did I mention cheap? At only $35 per unit – you could buy 2 and have one for a spare.

I added fans to the peltier heat sinks (see photo) and they are the only moving parts. They are blowing air “into” the heat sink – an important point here; there is more exposure to cooling air than trying to suck air “out” of the fins. You can have lots of spare fans and they are easily replaced. I wedged some round head screws between the tapered fins to mount the fans on each heat sink. The power cord goes to a car cigar plug (negative ground) with a 10A inline fuse.

For anyone who is not familiar with the peltier device – it is a heat pump that is made like a silicon chip. A DC electric current will get the chip to “pump” heat to one side of the chip leaving the other side cold. Heat sinks (and fans) help to distribute the hot and cold.

The second part is the “containment box” that would consist of the good ol’ beer casket – where they get an icy bath until they meet their drinker. Yes, a cooler, the cooler I selected is 18″ x 10″ x 10″ (1.07 cu. ft. approx.) about 20 quart. A cooler has all the “fridge” properties like waterproof food grade inner walls, foam wall insulation (except the lid), rugged dent resistant outer walls. The other benefits of the cooler are: light weight, portable and you probably have them lying around in a corner from all the camping trips. This cooler will actually fit 3 gallons of milk but the 2 side containers will touch the walls.

Now, a cooler can be expected to work as good as a cooler was designed to work – it melts 2 bags of ice keeping 12 beers cold for a couple of hours. I figured that I would improve the efficiency a little bit. I also figured that this could make for a great article so I wanted to gage any progress I made. I decided to use a 7 dollar temperature monitor with remote sensor, which eliminates the “open fridge door” variable in checking the temperature inside. The sensor was taped to a plastic box (see photo) to keep it off the “floor” of the fridge so that air temperature only would be measured.

Now, what to check, since I am designing a fridge; the “cooling cycle” is the metric to gage. This just records the temperature as the fridge runs – how fast it cools. The other metrics are – lowest temperature and the “warming cycle” which is keeping track of the temperature after the cooler is shut off.

As I add insulation I will keep track of how the numbers stack up. The lowest temperature is the temperature when loses (heat gain) are equal to cooling effort. The cooling effort is (approximately) 60 Watts – that is what the heat pump and both fans consume. (A person could mount 2 cooling units which would double the total cooling power)

The first task involved adding the peltier unit to the cooler. The smaller top heat sink has 2 “fins” that slide out from the grooves on the side. I cut the hole (to the size of the smaller, top heat sink) into the plastic (see photo) with a metal Stanley cutter; the cover is really thick in some areas.

I tested the “bare fridge” (see graph) and found that I could only get a 17F degree drop in temperature. The graph shows a fast rise after the heat pump is turned off and the lowest temp (47F) does not really work for keeping milk cold.

The second test involved adding a cheap space blanket (see photo) to the outside of the cooler. I used cellophane tape to attach an old (12 year) Mylar space blanket to the top and bottom of the cooler. The improvement was noticeable; the test ran longer as the heat pump was shaving 0.3F and 0.2F bits for a while. As long as the temperature kept falling – I would run the cooler.

DSCF0147 300x225 How to build your own dirt cheap fridge

I, next foamed the cover (see photo) and then tested (see graph) a third (and fourth time), the low temp was now down to 40F deg. – good enough for milk. The fourth test was exactly like the third except for shorting the peltier leads together at shutoff, this extended the cool time about 35 minutes at the low end.

Doing this made the peltier junction “fight” the temperature change with its own electric generation thru “temperature difference”. (This efficiency improvement would be – adding a switch to shut off/short leads) Adding expanding foam to the cover was the biggest improvement made, so far, and the cost was small – just 4 bucks.

The poly-urethane foam did not stick to the poly-ethylene cover so clean up was easy. The cover is easy to foam after you have cut the hole in for the heat pump. All the later trials do not vary in the first hour of testing – proving that the foam insulation was a big factor for the fridge.

The next step was to replace the old space blanket with a much better insulation solution. The blanket was interesting but, contains no insulation, just pure heat reflection and with only an 80% rate. I first added aluminum foil (used for grilling) to the top and bottom of the cooler. I wrapped a heavier space blanket around the cooler then doubled the blanket over a fiberglass batt wrapped around the cooler. The space blanket will “seal” the fiberglass in a sandwich and also serve as a double reflective layer. I used duct tape to hold the foil against the sides and for the blanket seal. The foil gives 100% heat reflection but tears too easily, the blanket and insulation “press” the foil against the cooler wall and protect it.

The testing (see graph) shows that the “NASA cooler” can now drop down to 32 F. It also took almost 4 hours to warm up to 60F. A side benefit of the added insulation is that sound levels are down by half, can’t hear the fan inside.

cool cycle 300x206 How to build your own dirt cheap fridge

Things to ponder

This fridge is meant to be run on solar power – just one sixty Watt panel (direct connected) will provide all its power during the day. At night – one can use a battery or plastic “ice blocks” to help keep the cold temperature. A 100 Watt solar panel would provide enough power for the fridge and a battery.

I do not have temperature regulation – peltier cooler does not stop at a pre-set temperature. Right now the cooler cannot go below the freezing mark (32F/ 0 C) no matter how much it runs since it does not have enough power but regulation could be added if saving power became paramount. Remember this fridge was home made and can always be upgraded.

I only measured the air temperature (see chart) inside the fridge; milk (and all other things) will take longer to cool down, maybe 6 hours (per gallon of milk) with this unit. It will also take longer to warm up – a cold gallon of milk will help chill the next gallon of warm milk.

I could reverse the cooling into heating by adding a small “bridge diode” to the fan leads and putting in a reverse-able coupling. The peltier unit comes with a connector – you would need to find the cord to fit the connector. Of course; I already have a solar cooker.

You could go out and buy a cooler with the peltier unit inside although I think that it would cost a little more then my unit. It might be a quite a bit less efficient (no space blanket heat reflection) and the parts replacement will be a question.

Part list

  • Free cooler (18″x10″x10″ size I used, yours can be different)
  • $35 PJT-10 – Large thermoelectric device (allelectronics.com)
  • $6 2X CF-390 – 80mm cooling fan ($3 -allelectronics.com)
  • $4 can expanding foam (hardware store)
  • $1 about 8.5 ft. of thin aluminum cooking foil (free)
  • $13 CW B250 Space (brand) blanket ( EE beprepared.com )
  • $3 about 8.5 ft. (4 X 16”) fiberglass Insulation (hardware store,

———- I had this laying around too)

$62

I know that this fridge does not look “commercial” and I would not blame you if you bought a nice $1400 “Sun Cooler” DC fridge but if your Sun Cooler gives out – you now have the skill to convert a cooler to a fridge. Well, what do you think?

This is an entry in our non-fiction writing contest where you could win:

First Prize) Winner will receive a Nomad – 1 Person Standard Survival Package courtesy of Shepherd Survival Supply, a One Month Food Pack courtesy of Augason Farms, a $150 gift certificate for Remington Ammo courtesy of LuckyGunner.com  and a EcoZoom’s Versa Stove courtesy of EcoZoom stoves. A total prize value of over $875.

Second Prize) Winner will receive two (2) Rothco Sure Paks With Heater courtesy of Camping Survival, a Wise Food Vegetable bucket courtesy of LPC Survival and a Wonder Junior hand grain mill courtesy of Kitchen Kneads. A total prize value of over $509.

Third Prize) Winner will receive 3 – 27 Variety of Non Hybrid, Heirloom Non GMO Survival Seeds, 2 – Fruit Pack of Non Hybrid, Heirloom Non GMO Survival Seeds and 2- First Aid Kit with Sutures in a Waterproof Resealable Bag courtesy of  Be Prepared Now. A total prize value of over $215.

Contest ends on March 30 2012.

Comments

  1. Matt in Oklahoma says:

    That is awesome and something I will attempt soon!

  2. Wow. I have a similar need for a small fridge for medications. This looks like it would do the trick.

  3. templar knight says:

    What do I think? I think this is brilliant, and I really appreciate you coming on here and showing us how it’s done. And thank you, MD, for sponcering this contest. I have a couple of older ice chests that would work. This is great, one of the best entrys I’ve seen.

  4. j.r. guerra in s. tx. says:

    That is SO cool (pun unintended), thats just what the doctor ordered down in in deep south Texas. A diabetic might also want one of these units, should the main refer die at an inconvenient time.

    Thank you for posting this.

  5. Veeery interesting! I wonder about the feasibility of converting the smaller chest freezers into fridges with this technique? I’ll be looking for a broken/junked chest freezer to try this out, maybe with two heat pumps, run off a solar powered battery bank. :)

    • I too thought about using the concept with a chest freezer…only it would not be as portable as the above…very good idea…you guys are really clever…

  6. Michael C, I will admit it, this went right over my head. But I know someone who would understand it so I am printing it out and as soon as I get a chance “DADDY” Lol. I will learn how to make it and he will enjoy showing me. Thanks a bunch.

    • Any questions…just ask.

      • Digital_Angel_316 says:

        Interesting article, good concept.

        I’d like to see more on the battery charger/controller and the backup battery, and a short run down on the battery charge scenario.

        It seems that a fully charged 12V battery run for 12 hours at 5A would require 720WH to fully recharge: (12V x 5A) x 12H. At the end of running the battery overnight for 12 hours the battery would be discharged by that amount.

        Does the battery charger/controller ‘deep cycle’ (bulk) charge at higher currents or do you propose a continuous charge rate of 5A again over the new day’s 12 hours of sunlight to restore the battery to ‘full charge’? This seems like it would take an additional solar panel to be dedicated to battery charge.

        I understand that the proposed design requires less than 70W leaving approximately 2.5A (~30W @ 12V) available for continuous charging, cutting my calculations in half, but still it seems the battery would be undercharged and would need an additional source of charge current.

        Please advise.

        P.S.
        All of this seems to presume solar powered dairy barns and grocery stores or other alternate sources of energy when SHTF.

        On line (grid) power the proposed design would cost less than a quarter ($.25) per day depending on your utilities charge per KWH.

        Another approach to keep that power on and around will be to help take out all those refrigerators/coolers from the bottled beverage coolers at every corner mom and pop store and the walk in coolers at McDonalds as well as to cut the power used by the widget, gadget and whatchamacallit factories still in the U.S.

        Regards, Digital_Angel_316

        • D A,
          Here in Michigan I get more than 12 hours of light (in the summer) so my fridge would keep going with just a 100W panel. I also measured the power taken by the cooler (w/ fans) at just under 60 Watts. You are right – if you only have 12 hours (or less) to charge a battery – you need more than twice as much for running both. A 140W solar panel would work.

          You can set up a smaller charge controller to run a load by connecting it up to “load” terminals. The controller will shut off the load with a LVD (Low Voltage Disconnect) when battery voltage is down. You set where down is.

          P.S.
          Aren’t cows solar powered – don’t they eat green?

          The AC to DC power supply should supply at least 5 amps at 12 volts.

          That would be a load off our grid.

  7. cooolwoods says:

    yup. that post was very good. gotta try that myself. wow going to be tough to beat that one, homemade low voltage fridge….

    stay safe

  8. blindshooter says:

    I have one of the igloo coolers that use this same peltier junction to cool or heat.
    Me and a buddy used it for a week at the national rifle matches at Camp Perry for a week. Stood it up with the cooling element up top and the door opening like a home refrigerator. The only problem we had was condensation pooling and running out when the door was opened. Not a problem in a WW2 prisoner of war hut on the edge of lake Erie but could be a problem if the box was on it’s back like a chest type. I guess a drain could be installed and probably in a grid down situation the thing won’t be opened as much so the condensation might not be as bad.

    Good read, I’m saving the parts list for sure.

    • blindshooter,
      “national rifle matches at Camp Perry” eh? Before my eyes got bad I did some shooting up there, and our club is taking some of our youth rifle team there this year. We’re lucky in that it’s only a few hours north of here. It’s not the grand canyon, but it’s still a national attraction for the right kind of folks.

    • Well, I’m not going to stand my fridge up so I will use a wash cloth to sop up the water at the bottom.

  9. Harold Dean says:

    They have made and sold Peltier Effect beer coolers for years that you place on the seat of your car and plug into the cigarette lighter. They normally hold a six pack but in 94d when I bought the last one, they had increased the size to two six packs. JC Whitney in Chicago used to sell them a lot. The Peltier Effect is a little known phenomenon unles s you happen to be an electrical engineer specializing in solid state circuitry. A large scale usage of this peculiar effect is in Scotland where a plate is at the bottom of the ocean and one on the mountaintop near a small village with the cable being tapped in the middle to provide electricity for the village. Harold

  10. Michael,
    Good article. I’ve worked with Peltier devices, but hadn’t realized that the higher capacity ones had gotten so inexpensive. Thanks also for the part list and the supplier. I’ve purchased things from All in the past but had pretty much forgotten about them.
    I’m thinking that two devices, a couple of deep cell batteries, and 2 or 3 60 watt panels could make a very good setup. With some very simple circuitry you could make a thermostat to keep track of the temperature inside the box and turn on either one or two devices as needed.
    I hadn’t heard of shorting the junction together to keep it cooler, longer (if I’m understanding this correctly), and a quick Google search turned up nothing of value; however, I may not have been using the correct terms. Could you give a brief explanation on the why and how of shorting the junction.
    All in all this is a very inspirational article, and has me making some plans to play with this technology again.

    • OP,

      The chip can “generate” power from a cold & hot source – in reverse of the usual “input voltage/get cold out” way it is used. Shorting the leads together gives “feedback” voltage to the chip. The feedback power causes the chip to run – trying to make the cold side cold, against the cold trying to get out.

      When I was running the tests, I noticed that the top heat sink got real cold and figured that the thin chip inside was letting a lot of cold escape. I also remembered that wind turbines use “shorting” to “brake” the blade spin. Shorting the PM motor generates electromagnetic fields that are opposite the direction of rotation.

      I would find a bigger cooler if I was planning on putting in 2 peltier devices. Other then that sounds like a plan.

      • michael,
        I know that Peltier devices are in essence thermocouples and can be used to generate power, but I hadn’t thought about using that fact to “self generate” and keep the two sides at temperature longer. Good idea and worth playng with. Thanks for the idea and the explanation.

  11. Great Post. Always cool to see ingenuity come forth. I used to live on a sailboat in Florida, and had a fridge that ran off of AC, DC, or propane. A nice option to have 3 power sources to cool things off. They come in differant sizes, and can usually be found at RV supply stores.

  12. Rodney Langley says:

    I’ve been experimenting with this for a while. FYI, you can find the Peltier devices a lot cheaper than that place. Check ebay. I picked up some for about $3 a piece (used) but they work great, and even had some thermo paste on them :)

  13. Repair Mama says:

    Now that is one “cool” project!!

  14. Doug in Arkansas says:

    Excellent post – I’ll be forwarding it to my daughter whose husband is diabetic.

    Back in the early ’90s I had a friend who had a chest with a Peltier junction cooler. He left it plugged in to his lighter socket overnight, and ran his car battery completely down. I believe a person would want to add some sort of cutoff switch to keep the battery from going flat.

  15. SrvivlSally says:

    Hmmm…adding an opening and closing spout in an outside corner (?) for water drain off, maybe inserting a waterproof board at a very slight angle to catch the condensation/water. A little clear silicone for sealing around it a bit-to keep the cold in…? Great idea and well worth a try.

  16. Uncle Charlie says:

    All rocket science to me. You should work for NASA, or did you?

  17. Nice article,
    Reminded me of all the ingenious stuff Joe would come up with in the desert. Give us just a little scrap and we could build a cabin, gym, and bar with a refrigerator. Nothing this elaborate but cool water was better than super heated. Also I got tired of drinking water, I don’t know if it’s happened to anyone else but I recommend having some type of flavoring in your preps at least for the kids.

  18. dragon5126 says:

    before anyone goes and builds this, (all due respect to the author) Go to Wally World and check out the inexpensive compressorless 120 volt dorm refrigerator they sell (dont recall the name, it’s off at college with my daughter). It is a peltier operated cooler. Two years agoit seemed to stop working in her dorm… turned out ambient temps were too high for efficent heat transfer so I just took the back panel off and all went well BUT, I discovered an important trick and been trying to talk the kid ( who is a prepper herself out of it and she wont budge). It is a bigger and better design of this very same cooler presented here, bur runs off a built in 120v to 12v power supply… which could easily be removed or bypassed in several ways to run in a camper, tent, or off emergency power…
    to be sure you found the right one in the store it does not have a freezer and is extremely light. If you wanted to even improve it more buy a can of great stuff spray foam, and disassemble the unit and fill every non essential gap with insulating foam especially the door.

    • dragon5126 says:

      Oh one other point, on units like this the cooler the OUTSIDE temp is the better they work as peltiers work off temerature differential principles. That is the hot side must be able to cool down in order to cool the cold side. so if its 120 degrees it wont get very cold inside, this is true with all peltier devices so a wick type evaporative cooler over proper sized air flow tube on the hot side cooling fan may help you increase efficency but remember the tube gets wet not the air going through it… like a turbo intercooler…