DC fridge freezer as a freezer

[freedomrider]

A small 40-50 watt refrigeration system is not going to remove heat from that space (and the mass placed within it) at the same rate as the 150-200 watt system in a household unit can.

That's my experience as well. It took almost a week to freeze a case of pint sized water bottles in my 50 Quart ARB using 120V power. My cheapo Target brand chest freezer would freeze them overnight. Note that this is not a criticism of the ARB, it's just the nature of a low power device.

 

[cruiseroutfit]

That's my experience as well. It took almost a week to freeze a case of pint sized water bottles in my 50 Quart ARB using 120V power. My cheapo Target brand chest freezer would freeze them overnight. Note that this is not a criticism of the ARB, it's just the nature of a low power device.

What else was in the fridge besides the case of bottles? A full fridge/freezer is a happy fridge/freezer and will work far more efficiently i.e. quicker.



As for freezing items, you bet... any quality 12V fridge/freezer should be able to do so. I have customers that make ice with their Engel's, I can't think of anyone doing it with an ARB unit but they too will reach those temps albeit not as quickly as an Engel imo.

 

[freedomrider]

What else was in the fridge besides the case of bottles? A full fridge/freezer is a happy fridge/freezer and will work far more efficiently i.e. quicker.

Cooling 24 half-liter bottles of water from 25 °C to -20 °C requires 540 kcals of thermal energy to be transferred from inside the fridge to outside the fridge. (24 bottles)*(0.5 L/bottle)*(1 kcal/ L °C)*(45 °C) = 540 kcal
A higher power cooling device should transfer that energy faster and that is indeed what I observed and wrote about.

Regarding the fill level, although a full refrigerator/freezer may indeed be able to maintain temperature more efficiently once the temperature has equilibrated to the set point, when it comes to cooling new contents, it still has to remove the same amount of thermal energy regardless of how full or empty it is. Heat transfer to pre-cooled items may have a minor effect but, in the end, the same amount of energy needs to be transferred from inside to outside.

btw: I'm not in any way saying that a 12V fridge/freezer won't meet the o.p.'s needs, I'm simply providing data from my own observations.

 

[jeep-N-montero]

I don't think you will be happy with the performance of a 12v unit refreezing icepacks for a cooler, they just don't have the capacity to cool icepacks down in any reasonable length of time (they do fine maintaining freezing temps, they just take a long time to get there, especially if non-frozen items are present).

If you have to have a freezer, I would suggest maybe have two units, with the other one operating at fridge temperature.
Another option (since you'll have your generator going) might be one of those standalone icemakers you can get for around $150 or so. Supposedly they'll make a batch of ice in a few minutes to a half hour, which you could then use in your cooler (or put into the freezer overnight and use the next day).

When we go to Moab we have reusable freezer packs that we freeze at night and toss in our lunch bags each day, works just fine. Not sure I would want to try to freeze anything more than a liter in capacity though, have frozen the smaller Gatorade bottles filled with water without issue.

 

[100acrehuphalump]

I just read this review on amazon for the Engel MT45:




5.0 out of 5 stars Fridge/Freezer, May 29, 2012
By Paul V. Lippincott (Newport, NC) - See all my reviews
(REAL NAME)
Verified Purchase(What's this?)
This review is from: Engel MT45F-U1 Dual Voltage AC/DC Portable Fridge/Freezer 43 Qt.
I have used a Koolatron cooler for a number of years in my truck. It just barely keep items cool. My first week in the truck I set the thermostat to three and it froze everything solid. I now run the thermostat at one, and everything is nice and cold. The fridge does not draw that much electric. I have a 12 volt cut off switch and after a weekend the fridge is still running. The old Koolatron would kill my batteries in 24 hours. I am very pleased with my new fridge. It is a bit pricey but hopefully it will be worth it.

They go to five...

I had a Koolatron. Then I bought an Engel 45 which I am very pleased with. I had a really hard time trying to get any of my money back on the pos Warmatron. I ended up giving it away so as not to add the trash at the Expo in May. I found out later the guy I gave it to gave it away too. I love my Engel.

 

[freedomrider]

When we go to Moab we have reusable freezer packs that we freeze at night and toss in our lunch bags each day, works just fine. Not sure I would want to try to freeze anything more than a liter in capacity though, have frozen the smaller Gatorade bottles filled with water without issue.

I do the same thing with small water bottles in the freezer compartment of my 3-way camper fridge. I put new water bottles in as I remove the frozen ones. It works fine and provides ice cold drinking water at the end of a hot day of hiking. I've thought about getting a small 12V fridge/freezer for just such purposes but, as you note, I wouldn't expect it to freeze more than a liter or two per day.

 

[Kartman35]

Let the torture tests begin!!

Ok so I picked up my used Engel MD14F this evening as well as a 12v 5.8A DC power supply, as well as some hardware to wire the thing to my battery.

My first torture test is underway. Even though I never plan to tax the machine in real use this hard, I figure what the hell let's see how much she can take. I've loaded it up with 18 500ml water bottles and placed one temerature probe in the air near the center of the cooler padded with folded up paper towel so as not to rest against a water bottle, and I have another probe suspended in the water in one of the bottles near the center. These probes are connected to my bbq pit controller 'The Stoker' which is sending the info to my laptop via wifi and being graphed. The water started at around 60 degrees and the fridge is in my living room at about 68 degrees. I have it plugged into the adapter and she's humming along.

I'll post the graph in the next few days (as long as the program doesn't crash...it's a little buggy)...either way I'll keep ya posted on how my 'little Engel that could' performs in this and other tests I have planned.

 

[cruiseroutfit]

Cooling 24 half-liter bottles of water from 25 °C to -20 °C requires 540 kcals of thermal energy to be transferred from inside the fridge to outside the fridge. (24 bottles)*(0.5 L/bottle)*(1 kcal/ L °C)*(45 °C) = 540 kcal
A higher power cooling device should transfer that energy faster and that is indeed what I observed and wrote about.

Regarding the fill level, although a full refrigerator/freezer may indeed be able to maintain temperature more efficiently once the temperature has equilibrated to the set point, when it comes to cooling new contents, it still has to remove the same amount of thermal energy regardless of how full or empty it is. Heat transfer to pre-cooled items may have a minor effect but, in the end, the same amount of energy needs to be transferred from inside to outside.

btw: I'm not in any way saying that a 12V fridge/freezer won't meet the o.p.'s needs, I'm simply providing data from my own observations.

Thermodynamics flashback. We can all play with numbers, but your discounting thermal losses and poor heat conduction of stagnant air. Precisely why water at one end of the freezer/fridge will be frozen while water at the other end (furthest from will not. Assuming equal temperature throughout the cabinet including the walls and your simple heat transfer would hold true, in the real world it simply does not. That said you had a fair bit of 'load' within the cabinet. My question was based on similar questions posed in the past whereas the user has a single water bottle in the middle of the fridge and it simply won't freeze despite being inside for days. Load it complete with bottles and things start freezing.

 

[Kartman35]

Results so far

So I turned on the fridge at around 11pm last night. The water went in at about 60F. Sure enough the graphing program crashed after midnight so I started it again and it ran until around 6:45 am before crashing again. Here's the graph from 12:22 to 6:45.
It i now 10AM so after about 11 hours the air temp near the top of the fridge is reading 22.1F and the probe in the water bottle is reading 26F (I guess that the probe tip is resting against the side of the inside of the bottle that it's in) and the water is still liquid.

More results as they come in...

 

[Kartman35]

Quick update

Ok so I just got home from work and it's now 1am so the fridge/water bottles have been running for about 26 hours so far.

This morning when I got up I noticed that the air temp had stabilized at 22-23F and the water temp was 26-27F. The temp dropped from 60ish down to 23 in about 7 hours (since 6:30am), and stayed there all day until I left for work at around 3:30pm. I sort of figured the temp would stay there until the water started freezing and would start dropping at that point.

Interestingly, arriving home 9 hours later, the temps have dropped to 17.6F air and 13.2F water, but no sign of ice yet. I'm scratching my head at how water can be at 13.2F without freezing. Any theories from the thermodynamicists?

Hopefully I'll see some ice by tomorrow morning.

 

[jeep-N-montero]

Ok so I just got home from work and it's now 1am so the fridge/water bottles have been running for about 26 hours so far.

This morning when I got up I noticed that the air temp had stabilized at 22-23F and the water temp was 26-27F. The temp dropped from 60ish down to 23 in about 7 hours (since 6:30am), and stayed there all day until I left for work at around 3:30pm. I sort of figured the temp would stay there until the water started freezing and would start dropping at that point.

Interestingly, arriving home 9 hours later, the temps have dropped to 17.6F air and 13.2F water, but no sign of ice yet. I'm scratching my head at how water can be at 13.2F without freezing. Any theories from the thermodynamicists?

Hopefully I'll see some ice by tomorrow morning.

Some bottled water has added minerals that may lower its freezing point, think of sea water.

 

[CaliMobber]

Want to see a cool trick, pull a bottle out and ********** it againt your hand and Im willing to bet it flash freezes into ice slush. Ive ran into it many times with water bottles, since it cools them soo slow it gets the temp below 32 with out freezing it. kinda like a frog in slow warming water.

https://www.youtube.com/watch?v=ph8xusY3GTM


Also id recommend running the fridge off 120v while the generator is running so you draining the batteries while your trying to charge them.

 

[Kartman35]

Actually there's a better explanation

I'm not a good scientist.

There is a small access door within the main door on top of the fridge that I've been using to check on the water. It seems that the bottles under the door don't freeze as fast as the ones on the other side...In fact the bottle that has the probe in it was already frozen solid as were a few others on the left side last night when I got home. Before bed I swapped the bottles around, and now 15 of 18 bottles are solid ice, air temp is reading 13F and the frozen bottle with the temp probe is reading 12F.

Once everything is solid I'll report the time it took, as well as the lowest temp readings attained, then test 2 will begin which will represent a more 'real world use'. I plan to replace 5 of the frozen bottles with room temp bottles and record how long it would take to freeze the 5 bottles. This will represent the 'ice pack rotation' as I would use camping.

Stay tuned...more to come

 

[craig333]

My edgestar would freeze quite well but when I tried using it on a extended trip to supply ice for the ice chests it didn't cut the mustard. Too slow and too much power consumption.

 

[Kartman35]

Want to see a cool trick, pull a bottle out and ********** it againt your hand and Im willing to bet it flash freezes into ice slush. Ive ran into it many times with water bottles, since it cools them soo slow it gets the temp below 32 with out freezing it. kinda like a frog in slow warming water.

https://www.youtube.com/watch?v=ph8xusY3GTM


Also id recommend running the fridge off 120v while the generator is running so you draining the batteries while your trying to charge them.

Awesome

Sure enough... a little whack and presto....instant ice slush....That was really cool thanks!!

As for running off the generator that's exactly my plan. I already picked up a 12V adapter for the fridge as this model doesn't have AC input.
Trying to see if I can make my battery last 19-20 hours with a 4-5 hour recharge time per day operating as a freezer.