DC Fridge or AC fridge with inverter?

[Hedges]

There isn't any reason a chest freezer can't be converted to a freezer at one end and a refrigerator in the volume that remains.
Upright refrigerators w/freezers and upright freezers seem to use more electricity not only because they may have less insulation, but also to the fact they all have defrost cycles.

That could probably be done, so long as cooling coils only cool one end.

I've converted an upright side-by-side in the other direction, to all freezer. I replaced the refrigerator temperature thermostat with a freezer temperature one, and removed the adjustable baffle between freezer and refrigerator compartments.

Converting a refrigerator/freezer to freezer only

My upright Frigidaire deep-freeze wasn't freezing anything more concentrated than ice cubes any more. Things were mushy and spoiling. Maybe it just needs a refrigerant recharge; I'll look into that later. Went to the store and found they all have 60 or 90 day delivery. Only come out of China...

diysolarforum.com

The way the fridge/freezer works is by chilling the freezer side until refrigerator side reaches desired temperature (e.g. 35 degrees F). The baffle is a crude method to ensure freezer side is much colder. Maybe if operated in a 35 degree environment, the refrigerator side would never get warm enough to activate thermostat, so all the frozen food would thaw?

 

[rcrracer]

That could probably be done, so long as cooling coils only cool one end.

I've converted an upright side-by-side in the other direction, to all freezer. I replaced the refrigerator temperature thermostat with a freezer temperature one, and removed the adjustable baffle between freezer and refrigerator compartments.

Converting a refrigerator/freezer to freezer only

My upright Frigidaire deep-freeze wasn't freezing anything more concentrated than ice cubes any more. Things were mushy and spoiling. Maybe it just needs a refrigerant recharge; I'll look into that later. Went to the store and found they all have 60 or 90 day delivery. Only come out of China...

diysolarforum.com

The way the fridge/freezer works is by chilling the freezer side until refrigerator side reaches desired temperature (e.g. 35 degrees F). The baffle is a crude method to ensure freezer side is much colder. Maybe if operated in a 35 degree environment, the refrigerator side would never get warm enough to activate thermostat, so all the frozen food would thaw?

I'm guessing the coils are in the back and both ends. So build a polyiso tunnel over the back coils that has both openings at one end at the designated freezer end. Use fan to suck cold air out of the tunnel and into the freezer end, when the freezer compartment thermostat calls for the compressor to turn on. Refrigerator compartment to get its cooling from the freezer compartment by using another thermostat, fan, and a flapper door. The problem might then be too much heat extracted by the coil inside the refrigerator compartment causing refrigerated foods to freeze. I think a polyiso tunnel with a horizontal divider in the middle(paperclip/Martinsville looking tunnel) over the rear coils with baffle between the freezer and refrigerator compartments, would work.

 

[12VoltInstalls]

528watt hours is just about what my AC fridge used in the 24 hour test I did yesterday. I'm pretty sure

Certainly not as good as a DC fridge. But......

Let's say your fridge ran in between your 35 and 70watts at 52watts. That's a little more than my AC fridge at about 40watts or so.
My little AC fridge pulled about 4 AC Amps when running.

And lets say it has a 40% cycle rate (60% of the time off and 40% of the time on.
(My fridge cycles about 50% of the time so it could just be an insulation difference here?

40% of 24 hours is 9.6 hours running @ 52watts = 499Watt Hours.

So that DC fridge (albeit larger) is drawing about the same power per day as the mini AC fridge.
unless my math is way off ( always possible)

I was thinking of wrapping my little low budget AC fridge in an insulation wrap and trying aqain just to see.

There is no free lunch. AT SOME POINT ‘efficiency’ runs into us trying to take X-watts of one form of energy and turn it into another form of energy. The means of cooling a fridge is essentially /wasting/ off the high temperature heat we took out of some lower temperature heat.
So your results aren’t that surprising I guess.

I’m just not willing to dump $1250 on a 12VDC fridge. Maybe $400, or $500 but...

I’m also not willing to live out of a refrigerated cooler (those things people are calling a ‘portable fridge.’)

I might be ok with running a small chest freezer with a +32F thermostat. Might be ok with a 4.7cf or 7cf small fridge. Why? At half the money and maybe 15% more energy I can have a fridge AND 200 or 300W more solar. Maybe even another battery or two?

My AEG/magic chef propane is suddenly having trouble staying under 40 after years of dependable service.
I just ordered two more 100W panels. I have a no-freezer “bar fridge.” I’ll buy a 12V water heater element and rig a ‘dump’ circuit for excess solar into a small water heater. And yes, there’s still money left over

 

[robstrom]

Will did a video on this exact subject a year or so ago.
He suggested cheap walmart fridge, add some panels.
Fridge dies in a couple years, so what?
The straight dc small 'coolers' ( dometic, arb etc) are measured in quarts, and typically a 1000 or more.
They better last a lifetime!!

 

[12VoltInstalls]

Will did a video on this exact subject a year or so ago.
He suggested cheap walmart fridge, add some panels.
Fridge dies in a couple years, so what?
The straight dc small 'coolers' ( dometic, arb etc) are measured in quarts, and typically a 1000 or more.
They better last a lifetime!!

I need to look that up. I don’t recall that. Thanks

 

[AstroBob]

I own and use an Iceco fridge similar to this model

 

[Bubba1]

I went with a iceco compressor cooler on my boat. $500ish. So far I like it. 200w of panels and some old lead acid batteries runs the whole boat.

I own and use an Iceco fridge similar to this model

I have the same iceco cooler. Works good.

 

[Batvette]

Why? Which ones are your favorites ?

I had fully intended to buy an Alpicool DC fridge. But their website had bogus contact information (yep, I tried all the phone numbers and all the email addresses, ALL bogus) after a review on Amazon pointed it out.

At this point with my budget, I'd rather buy another battery and another solar panel to increase my power capability than mess with cheap DC fridges. Some have good luck with them, but I'm not much of a gambling man.
I'm sure the pricey DC fridges are good with their Danfoss compressors and better insulation.

Ive had DC fridges from costway (terrible) and whynter (better, but still bricked in 3 years) and think almost all the Chinese brands are a bad investment. 18 months ago I bit the bullet and paid over $1300 for a National Luna Legacy 60l with dual controls. https://www.equipt1.com/collections/national-luna-dual-control/products/60l-legacy-fridge-freezerMade in South Africa. Its very impressive. At the same time I got a Redarc DC-DC charger, made in Australia. So over made in China.

 

[Batvette]

Thanks for the data!!!

While your example fridge is too small, it does very much give one something to think about- especially at some point, the small compressors for small fridges will reach a min limit- so somewhere in the small size area, the compressor narrows down to one version.

So then the question becomes- how to shop for a 'fridge and an inverter that results in a very good result?

A side question- is there a simple accessible output that one can tap into to use as a fan switch? So that I can put a small 12V fan on the heat exchanger to help it work better? My DC fridge has that, and given it's put into a constrained place, that's a good (and cheap) thing to add.

For sure, if this fridge I have dies, I will lean toward a small AC fridge with an appropriate inverter.

BTW, setting up inverter vs. shore power would be as easy as a switch that goes between one and the other. Especially if it's a 3 way switch to allow the fridge to power down between inverter and shore power.

You gotta watch out when attempting that re-engineering stuff. (Which I concede to doing a lot with varying degrees of success)
This one probably has little downside other than wasted energy and time if it doesnt work, but if adding a small fan was worth the energy it uses the degreed professional engineers would have added it.
Another aspect to consider is if you cool the condenser artificially low like that the system may not work properly, for instance the way the expansion valve is calibrated.
Im no HVAC or appliance tech and hey maybe its a good idea. If its cheap and reversible, go for it. It might also be a solution to a problem that doesnt exist.
(Im saying this after mounting a crossflow blower to an xbox 360, which had extraordinary heat related failures and bad lead free solder joints. Im also building a hush enclosure for a predator 2000 inverter generator which will require 1 if not 2 blowers. In both cases taking care to augment not contradict OEM thermodynamics. Like laptop coolers which are a joke)

 

[Hedges]

Guy on the bench next to me was doing thermal experimentation on the first X-box (before it was introduced).

As for the fridge, it was probably optimized for price. And maybe reliability - a fridge without a fan never has fan failures.
My guess is that on a hot day, fan will help it cool. Possibly with less total power consumption, if fan is low enough power. A thermostat attached to the condenser might be good.

Working with a vacuum pump, I found it ran hot but just a little air brought it down to room temperature. It was clear to me that moving air would let it operate in an environment about 20 degrees hotter. The "professional" said its specs only allowed 45 degree environment. But I could see that moving air in a 65 degree environment would give same case temperature as still air in 45 degree environment.

 

[Steve777]

A possibility that I had thought about for some time (although never tried to implement) was to get a fridge with a freezer section, and fill the freezer with water that becomes ice. The idea is to use that ice (which gets frozen during the day when the sun's up) as your overnight cooling for the refrigerated foods. You essentially would have a solar powered refrigerator during the day and an icebox at night.

I have not done the calcs, so it may not be possible to do this with an off the shelf refrig, but I think the concept should work. It may require some air movement in the unit at night depending upon the design and/or a larger freezer section that standard units. But it would seem that a fridge/freezer combo could be used to store solar power for overnight cooling at a much lower cost than batteries.

Of course, this all assume you would have some other power source to recharge the ice on extended cloudy periods, say shore-power or a genny.

Probably not a viable solution for the OP (unless he is into experimenting), but wanted to bring this idea up.

 

[Hedges]

Should work fine. The side-by-side or top freezer has a single thermostat on refrigerator side. When ever fridge gets above 35C or whatever, it cools the freezer. There is a manually adjusted baffle to control how much air spills from freezer to refrigerator.

Frozen water will hold the phase-change temperature of 32 degrees F/0 degrees C.
You can make a concentrated brine solution tuned to the freezer temperature you want. I'm not clear how flat its melting temperature curve is, as (pure water) ice melts and changes concentration of brine.

As I always say here, H20 and NaCl are cheaper than Pb or Li.

With that ice, you can probably go multiple days without power. Just relying on cold food to stay cold I think you can go for a night, except in really hot weather.

 

[Supervstech]

Should work fine. The side-by-side or top freezer has a single thermostat on refrigerator side. When ever fridge gets above 35C or whatever, it cools the freezer. There is a manually adjusted baffle to control how much air spills from freezer to refrigerator.

Frozen water will hold the phase-change temperature of 32 degrees F/0 degrees C.
You can make a concentrated brine solution tuned to the freezer temperature you want. I'm not clear how flat its melting temperature curve is, as (pure water) ice melts and changes concentration of brine.

As I always say here, H20 and NaCl are cheaper than Pb or Li.

With that ice, you can probably go multiple days without power. Just relying on cold food to stay cold I think you can go for a night, except in really hot weather.

Why brine?

 

[Hedges]

Plain water is fine if you just want a refrigerator, nothing kept below freezing.
If you want to keep frozen foods solid, then brine is an option for colder temperatures (e.g. ice cream maker.)

 

[Batvette]

A possibility that I had thought about for some time (although never tried to implement) was to get a fridge with a freezer section, and fill the freezer with water that becomes ice. The idea is to use that ice (which gets frozen during the day when the sun's up) as your overnight cooling for the refrigerated foods. You essentially would have a solar powered refrigerator during the day and an icebox at night.

I have not done the calcs, so it may not be possible to do this with an off the shelf refrig, but I think the concept should work. It may require some air movement in the unit at night depending upon the design and/or a larger freezer section that standard units. But it would seem that a fridge/freezer combo could be used to store solar power for overnight cooling at a much lower cost than batteries.

Of course, this all assume you would have some other power source to recharge the ice on extended cloudy periods, say shore-power or a genny.

Probably not a viable solution for the OP (unless he is into experimenting), but wanted to bring this idea up.

Think youd have a serious problem with frost buildup doing it that way.

 

[Batvette]

Guy on the bench next to me was doing thermal experimentation on the first X-box (before it was introduced).

As for the fridge, it was probably optimized for price. And maybe reliability - a fridge without a fan never has fan failures.
My guess is that on a hot day, fan will help it cool. Possibly with less total power consumption, if fan is low enough power. A thermostat attached to the condenser might be good.

Working with a vacuum pump, I found it ran hot but just a little air brought it down to room temperature. It was clear to me that moving air would let it operate in an environment about 20 degrees hotter. The "professional" said its specs only allowed 45 degree environment. But I could see that moving air in a 65 degree environment would give same case temperature as still air in 45 degree environment.

Sometimes its the bean counters responsible for performance compromises like this. Another factor is fan noise, a lot of people cant stand it. I have some hearing loss and tinnitus from working on jets on carriers in the navy so I actually like a fan in the background.

 

[12VoltInstalls]

Plain water is fine if you just want a refrigerator, nothing kept below freezing.
If you want to keep frozen foods solid, then brine is an option for colder temperatures (e.g. ice cream maker.)

A brine just changes the melting point. The liquid in an ice cream maker transfers heat better (lower temperature heat) so you can freeze the milk, plus the salt-melted ice could be 17*F whereas non-salt melted ice is only going to provide 31-33* water.

to hold a fridge, a 20*F block of frozen plain water is the same energy by volume- in practical terms- as a 20*F block of frozen brine (albeit at 20* a salt brine would likely not even be slushy).

 

[Hedges]

A brine just changes the melting point. The liquid in an ice cream maker transfers heat better (lower temperature heat) so you can freeze the milk, plus the salt-melted ice could be 17*F whereas non-salt melted ice is only going to provide 31-33* water.

to hold a fridge, a 20*F block of frozen plain water is the same energy by volume- in practical terms- as a 20*F block of frozen brine (albeit at 20* a salt brine would likely not even be slushy).

Changes the melting point, yes. That is the point.

At 20 degrees F, plaint water ice wouldn't be slushy. Brine might be depending on concentration.
Ice cream maker suggested concentration has brine around 8 to 12 degrees F

Ice and Salt machines - Dream Scoops

I review three crackers from a budget priced entry level machine to a more expensive top end model.

makeicecream.com

You know the Voltage/Soc curve of lithium? Wide flat area of almost constant voltage as you charge/discharge considerable amount of energy, then voltage shoots up/down beyond the knees?
Ice does the same thing at 32 degrees F.

20 degrees F is past the knee of the curve. Temperature changes linearly with energy extracted (or rather absorbed). As heat from the environment passes through insulation into the freezer/icebox, the block of ice and your frozen foot (ice cream bar, frozen steak) warm up.

At 32 degrees F, heat continues to pass through the insulation, but temperature inside remains constant. What changes is the percentage of water/ice. Ice cream bar and frozen meat are melted/soft. Energy goes into phase change without temperature change.

Once all the ice has melted, temperature resumes its linear increase in proportion to energy absorbed.

File:Water temperature vs heat added.svg - Wikipedia

en.wikipedia.org

Heat flow through the insulation is proportional to temperature difference, so instead of temperature change being linear with time it follows an exponential decay, like an RC discharge curve.

If environment is hotter than 212F (100C), a second flat region occurs there, with phase change from water to steam.
The energy required to turn 100C liquid to 100C vapor is about the same as energy to heat 0C water to 100C water, is about the same as the energy to change 0C ice to 0C water. If pressure is different (e.g. 15 psi pressure cap on radiator), the temperature at which water changes to steam is higher (240 degrees F). If you remove the radiator cap under pressure the water flashes to steam, expelling water and steam which scalds you. As liquid changes to vapor it carries away energy cooling the water which remains, so only a fraction of it turns to steam.

Brine will do something similar. I haven't found a good graph. I think as concentration changes, the freezing point will change. Except, if there is more salt than can be dissolved then brine will always be the same concentration and some salt will remain.

 

[Hendo7]

long thread didn't read all of it but what i did read i didn't see anyone reccomending a off-grid type inverters with dedicated solar panels just for the fridge ,yes they would shut down when theres no sun,but most fridges are insulated well they would keep cool during the night ,maybe to over come that have a small dedicated battery bank if a fridge does kick on at night ?

 

[84bronze]

I think the ac power is the best way to go. The cost of a propane or dc fridge is so expensive upfront and more expensive if you have to replace or repair.

I have a new 15cf freezer that is switchable between fridge and freezer builtin. It uses 2 amps draw when the pump is running or 240w. Lots of sun and solar panels make for a basic system with few moving parts. A small dedicated inverter that can handle the surge of startup. We have a dedicated freezer the same size and it is around 2amps also. Make a huge side by side and off grid.

Winter just have an old broken fridge with an adjustable hole to regulate the temp. Also working on a root cellar.

 

[12VoltInstalls]

^^^ the energy stored in ice was my point, not the temperature behaviors

 

[NwCali]

I didn't even slow down pondering this (and I did consider it). I'd rather a extra panel than a expensive fridge. But I can also use any "waste" heat as it will keep the cabin a little warmer. It'll be a rare day my cabin will see 70 F thru sunlight...if it gets that high ever.

If I lived where it gets hot I might have considered it... But owning a fridge that I'd have to special order doesn't sound like something I'd do.

 

[AstroBob]

12V portable fridges aren't expensive at all: https://www.bougerv.com/collections/car-refrigerator/products/12v-portable-refrigerator-30-quart
If set to cool just below 40f, you can consume as little as 135Wh/24 hours. A single 100 watt panel will give you almost unlimited power when used with even a 24Ah batt.

 

[Batvette]

12V portable fridges aren't expensive at all: https://www.bougerv.com/collections/car-refrigerator/products/12v-portable-refrigerator-30-quart
If set to cool just below 40f, you can consume as little as 135Wh/24 hours. A single 100 watt panel will give you almost unlimited power when used with even a 24Ah batt.

Essentially what you just did was produce a brochure with '80s Yugos and '70s Fiats and declared, "automobiles arent expensive, just pony up a few thousand bucks and youre good to go".
Case in point:

12V Portable Fridge

BougeRV offers you several options for 12V portable fridges, all of them are of good quality and there are many 12v refrigerator to choose from according to your needs.

www.bougerv.com

Second one down is the POS "Costway" slaps their name on and sells on amazon. A dozen other distributors have sprung up and put their silly branding on them since I bought one 2 years ago. In a year or so theyll have disappeared after the bad reviews piled up, to be replaced with other goofy brand names.
They claim to offer warranties, usually a year, but will never make good on them because theyd have to ship them to china for repair. So at best, if bought thru a 3rd party marketplace like ebay or amazon, youll get DOA coverage for about 2 weeks tops after receiving it.
Slightly higher on the quality ladder are actual brands attempting to legitimately build a company- Iceco and Whynter come to mind- theyre around twice the price and should last at least a year maybe 3. Youll still find them dodgey as hell when they break because they have no service network.
If you expect something approaching the durability of your home unit, theres just a handful of players- Engel, ARB, Dometic, National Luna, etc. Start at $1k, around $1400 for something decent sized.

Youll find reviews of buyers of those ~$350 chinese brands like Dingdong and Nevercold that say theyre satisfied, however these asian vendors have mastered manipulating review systems so the horror stories disappear, and if they dont they change the name.
$500 sounded like a bargain when I bought a whynter. Lasted 3 years.
$400 sounded like a bargain when I bought a Costway. Had issues immediately, I nursed it along for 6 months.
If Id have taken the 900 and bought an ARB it would prolly go twice as long as both without the headaches all along.

Like Id have driving a Yugo for 10 years.

 

[AstroBob]

Essentially what you just did was produce a brochure with '80s Yugos and '70s Fiats and declared, "automobiles arent expensive, just pony up a few thousand bucks and youre good to go".
Case in point:

12V Portable Fridge

BougeRV offers you several options for 12V portable fridges, all of them are of good quality and there are many 12v refrigerator to choose from according to your needs.

www.bougerv.com

Second one down is the POS "Costway" slaps their name on and sells on amazon. A dozen other distributors have sprung up and put their silly branding on them since I bought one 2 years ago. In a year or so theyll have disappeared after the bad reviews piled up, to be replaced with other goofy brand names.
They claim to offer warranties, usually a year, but will never make good on them because theyd have to ship them to china for repair. So at best, if bought thru a 3rd party marketplace like ebay or amazon, youll get DOA coverage for about 2 weeks tops after receiving it.
Slightly higher on the quality ladder are actual brands attempting to legitimately build a company- Iceco and Whynter come to mind- theyre around twice the price and should last at least a year maybe 3. Youll still find them dodgey as hell when they break because they have no service network.
If you expect something approaching the durability of your home unit, theres just a handful of players- Engel, ARB, Dometic, National Luna, etc. Start at $1k, around $1400 for something decent sized.

Youll find reviews of buyers of those ~$350 chinese brands like Dingdong and Nevercold that say theyre satisfied, however these asian vendors have mastered manipulating review systems so the horror stories disappear, and if they dont they change the name.
$500 sounded like a bargain when I bought a whynter. Lasted 3 years.
$400 sounded like a bargain when I bought a Costway. Had issues immediately, I nursed it along for 6 months.
If Id have taken the 900 and bought an ARB it would prolly go twice as long as both without the headaches all along.

Like Id have driving a Yugo for 10 years.

Hmmm. Exactly how many 12volt portable fridges do you actually own at the present? I own both an ICECO and a bougeRV. I have had both for over a year now, and have had zero issues. The iceco has a german made compressor, and a 4 year warranty. The bougeRV has a 3 year warranty.
Your car analogy is kinda silly, isn't it? Do you know the history of 1970's "Good Old" american cars?
Your response reminds me of how people once complained about "cheap Japanese junk". Engel, Dometic and ARB are vastly overpriced. I paid $350 new for my ICECO, and $192 for the bougeRV. The ICECO has been running constantly in my garage for the last 4 months as a backup freezer. Zero issues with the ICECO. Zero issues with the bougeRV.

As far as your stories of all these fridges that failed, love to see the evidence. Pictures or it didn't happen.