12V DC Compressor Refrigerator

[tominphx]

Hi All, this is version 2.0 a continuation of my previous thread "OUT WITH THE NEW", a quest for a more efficient refrigerator. At the suggestion of another forum member I'm starting a new thread, so here goes....................

My current refrigerator draws 4.4 amps/hr, fortunately where we camp in the summer and the way we load and use the refrigerator we are able to maintain a +/- 50% duty cycle, which is about 53AH/day. We also camp unplugged from mid June to mid October. The first 2-2 1/2 months are on the Washington and Oregon Coast. We have encountered 3 to 7 days of rain (no sun to speak of) and last year was a bit chillier than previous years, so heat was involved also.
Given the above I would like to find a more efficient (12V) refrigerator in the 4 to 5 CF range. Ideally power consumption would be in the 1.5 to 2.5 Amps/hr. range.

If anyone has real world knowledge or data of a brand and size that might meet my needs please let me know.

Cheers, Tom

[AlbertF]

Originally Posted by tominphx

My current refrigerator draws 4.4 amps/hr, fortunately where we camp in the summer and the way we load and use the refrigerator we are able to maintain a +/- 50% duty cycle, which is about 53AH/day. We also camp unplugged from mid June to mid October. The first 2-2 1/2 months are on the Washington and Oregon Coast. We have encountered 3 to 7 days of rain (no sun to speak of) and last year was a bit chillier than previous years, so heat was involved also.
Given the above I would like to find a more efficient (12V) refrigerator in the 4 to 5 CF range. Ideally power consumption would be in the 1.5 to 2.5 Amps/hr. range.

It would be great to find a refrigerator that efficient; I'm not aware of any. However, even if such a unit exists, it might be more cost effective to add batteries and/or solar panels and/or a generator to fill the gap when the sun doesn't shine.

How many days are you typically without a hookup? With our trailer, I use four days as a practical limit because of gray water capacity. I would relate battery and solar needs to that.

[field & stream]

Originally Posted by AlbertF

……….How many days are you typically without a hookup? With our trailer, I use four days as a practical limit because of gray water capacity. I would relate battery and solar needs to that.

I guess this depends on your trailer and camping style, because four days is not at all a limit in our experience. We almost always stay in campgrounds without hookups, but most of them have dump stations. Plus with our careful use of water we routinely go 7-10 days without having to dump. In contrast, these power hungry fridges can wipe out storage in 2 days.

[sfranklin]

Originally Posted by field & stream

I guess this depends on your trailer and camping style, because four days is not at all a limit in our experience. We almost always stay in campgrounds without hookups, but most of them have dump stations. Plus with our careful use of water we routinely go 7-10 days without having to dump. In contrast, these power hungry fridges can wipe out storage in 2 days.

Not sure if you are saying you have an LP fridge or a 12v compressor type fridge. My LP fridges I could boondock for nearly 10 days at a time, no solar, no generator. Not too sure I'll get more than a few days with this 9cf unit in my 2024, even with 300w of solar and 200a of lith batteries, and for the first time in several decades, I'm packing my LP powered generator because I simply don't know yet how the 12v fridge will behave in the wild. I've read in many places around 4 days with full solar input, to 1-2 days with or without solar.

I think Albert is on the right track and his comments only amplify the larger the fridge gets. It all boils down to running the numbers and plugging in the right tool for the job that comes closest to checking all the need/want boxes as for a fridge that effic, I too am not sure it exists.

[uncle_bob]

Hi

Your fridge pulls some amount of current when it's running. Let's say that's 10A. If it ran all the time, you would use up 240AH a day.

Your fridge has a duty cycle. This varies with the outside temp and the temp the fridge is set to. It could be 10% in late fall and 70% camping out in the "never below 80 degrees all night long" sort of heat. At 10% your "10A" fridge would use 24AH. At 70% your "10A" fridge would use 168 AH.

The gotcah here is that your use case vs somebody else's use case likely are not the same. They may well get 48AH a day on their fridge using at their campsite. You could easily get twice that with the exact same fridge.

Our propane fridge pulls right at 1.2A off of the battery all the time, no matter what. Temperature does not matter. We're going to run through a bit over 24 AH a day with the propane unit. It has a control board in it and a few other items that pull DC current.

If you don't mind the small size, there are Dometic coolers that will run down in the 24 AH a day range when set to 40F internal and at 70F "outside". They are "cooler sized" and not what I'd call a fridge.

What temp *should* a fridge get to? The food safety folks say that whole inside of the fridge should be at or below 40F all the time. With our propane unit .... not going to happen in the hot summer. Below 48F over the entire insides? .... maybe / maybe not.

What temp should the freezer get to? Same folks seem to think 0F. Again, the propane beast is never getting there in the summer. If we're lucky the ice cream won't melt . On the freezer side the temps relate a lot to "how long will you try to keep it" and "how much will it degrade". ( degrade does not mean become a hazard, just that it's not as nice as it once was).

How important are those "food safety expert" numbers? You will find a lot of threads here debating that pretty much forever and ever. Some of them are based on "my fridge is at 47 degrees and I'm not dead right now" sort of logic. No, you can't argue that it *always* will harm you. How lucky do you feel?

Is the propane a big upgrade over the fridge in our first trailer? You bet it is. Heading off every other day for another giant block of ice was quite a chore with that one.

Fun !!!

Bob

[tominphx]

Hi all, I guess I wasn't clear, I have only plugged in (electric) once in ten years with SOB of trailer. We mainly stay in Nat.Park, Forest Service, St.Park and BLM dispersed camps (boondocking) campgrounds and no KOA or RV Parks. We are usually good for two weeks without needing to dump, I usually carry an additional 10-15 gals. water. Battery capacity is 400AH supported by 500W of solar.

The point I was trying to make is, coastal PNW weather can be and is very unpredictable. Last year's weather was unusual in that we had more than one occasion of rain and heavy cloud cover lasting 5 to 7 days. Then add in unusual
marine layers hanging in until well past noon. Evenings and mornings were unusually cool and windy requiring the use of heat to take the chill off. Given all this, made harvesting solar difficult at best!

This year won't be a problem as we are committed to two months of camp hosting with the added perk of electrical power. Future years not so much!

Cheers, Tom

[tominphx]

AlbertF, Thus far I have two possible candidates, one advertises 2.2 amp draw at 12VDC (that's a 50% improvement) the other is indicating 1.75 amp draw but can not determine if at 12 or 24VDC. I do know from first hand that there are a few portable chest type refrig/frzr that operate in the .5 to 1 amp range.

field and stream, think we are like minded on this subject!

sfranklin, Current unit is 12VDC., after our first summer in the Basecamp I added an additional 200W of solar to the roof because my 300W portables were being stretched a little thin.

uncle_bob, Thanks for the re-hash, did have that stored in my pea brain but sometimes it's difficult for me to get it out there!

To all, Cheers, Tom

[jrowan]

I installed a Novakool RFU6400D in 2021. This is a single compressor unit with bottom freezer drawer with 6.8 cubic feet. I installed the fridge after I had installed 300 Ah of lithium, but before I installed any solar (I have 400 watts now). I also have a victron 712 shunt monitor.

After I installed the fridge I did some experiments over the span of a couple of weeks with the trailer in my driveway to determine average consumption. This was summer in coastal central California, so not too hot, probably 70F and usually sunny. I kept some food/drinks in the fridge and opened the fridge/freezer a few times each day. Probably a little less than typical usage, but not too far out.

As delivered, the fridge had a resistor installed in the compressor circuit that makes it run at full speed. With that configuration and the temperature knob at 7 (full cold), it was consuming 70Ah per day. I was not happy with that.

After that, I removed the resistor, which makes the compressor run at its lowest speed. The consumption then went to 50Ah per day.

After that, I lowered the temperature knob to 4 (middle) and the consumption went to about 25-30Ah per day. I ran with this configuration for 1.5 weeks. Some days it was 25Ah. One day I put a 6 pack of warm beer in the fridge and it consumed 30Ah that day.

This is where I've left the settings ever since (no resistor, knob at 4). We find the stuff in the fridge stays plenty cold. Some parts of the fridge space are actually too cold for vegetables, and for the most part everything is as cold as our home fridge. The freezer drawer is cold enough to keep stuff frozen in the back of the drawer, but stuff in the front of the drawer slowly thaws after a few days. We've boondocked in places where the day time temperature is up to 95F, and the fridge keeps up fine.

It's harder to decipher real world consumption now that I have solar and we have lots of other loads while we're camping. The consumption definitely goes up during hot days (on 95F days, the duty cycle is pretty much 100%). But we always choose places that cool off at night, so the duty cycle drops off then. In any case, it doesn't really matter since those hot sunny days that make the fridge work hard also provide lots of solar power. Since you're specifically asking about Oregon/Washington on rainy days, I'm sure that you can achieve 30Ah per day with this fridge.

Jason

[tominphx]

Jason, thank you for your response, very helpful in doing my due diligence. Do you happen to know the model number you purchased?

Cheers, Tom

[jrowan]

See screenshot attached. This was from Sure Marine in Seattle. Probably much more expensive now....

[richard5933]

Nearly all the compressor fridges use a similar cooling strategy and nearly identical compressors. I don't think you'll find the efficiency there.

But, the ability to super-insulate would make any fridge more efficient.

Not sure how much room you have around the fridge in the current cabinetry or how much access you have, but it seems to me that super insulating the box of the fridge would be the way to go. Also, finding a way to efficiently remove the heat of the compressor from the cabinet holding the fridge would help keep the fridge cool more efficiently.

[uncle_bob]

Hi

The "knob settings" on any fridge are highly variable in terms of what they mean. You very much need to grab a thermometer of some sort to know what's going on. IR thermometers are nice, they do have an issue with emissitivity and also with reflections. Flying blind temperature wise is not a great idea.

Any single compressor / single cooling system setup is going to have a problem with uniformity. The freezer and fridge sections will never be quite right. That's just the nature of the beast.

Is a 50F spot down at the furthest point away from the cooling setup "ok" in a single system? The food safety folks would very much say not. A jug of milk sitting there for a few days also would likely say not as well. A bunch of veg that could have been left out on the counter would be ok there ....

Lots of variables.

Bob

[tominphx]

richard 5933, additional insulation has always been the plan along with forced ventilation.

uncle_bob, yes good point, food safety is always a concern, we travel with a digital thermometer in the fridge, foods capable of accepting a partial freese, to the back and up near the freezer, veggies and similar to the front and down low. We always maintain a minimum temp of 40 degrees and adjust accordingly for ambient conditions.

Cheers, Tom

[AlbertF]

Originally Posted by tominphx

Hi all, I guess I wasn't clear, I have only plugged in (electric) once in ten years with SOB of trailer. We mainly stay in Nat.Park, Forest Service, St.Park and BLM dispersed camps (boondocking) campgrounds and no KOA or RV Parks. We are usually good for two weeks without needing to dump, I usually carry an additional 10-15 gals. water. Battery capacity is 400AH supported by 500W of solar.

The point I was trying to make is, coastal PNW weather can be and is very unpredictable. Last year's weather was unusual in that we had more than one occasion of rain and heavy cloud cover lasting 5 to 7 days. Then add in unusual
marine layers hanging in until well past noon. Evenings and mornings were unusually cool and windy requiring the use of heat to take the chill off. Given all this, made harvesting solar difficult at best!

This year won't be a problem as we are committed to two months of camp hosting with the added perk of electrical power. Future years not so much!

Cheers, Tom

That's an impressive amount of battery and solar capacity.

With your use case and your experience to date, I think you are the one to teach the rest of us about long-term boondocking with with a 12V compressor refrigerator. Please keep us informed about what you end up doing in the future.

[tominphx]

AlbertF, Thanks, I think we are still tent camping only with solar, batteries and a fridge.
Always thinking about conserving and it becomes second nature, at least while camping, not sure that applies at home.

Cheers, Tom

[Wazbro]

Originally Posted by tominphx

richard 5933, additional insulation has always been the plan along with forced ventilation.

uncle_bob, yes good point, food safety is always a concern, we travel with a digital thermometer in the fridge, foods capable of accepting a partial freese, to the back and up near the freezer, veggies and similar to the front and down low. We always maintain a minimum temp of 40 degrees and adjust accordingly for ambient conditions.

Cheers, Tom

Don't forget the amp draw of the forced ventilation. If you get a fridge with 1.5 amp less draw, .75 amp less with 50% duty-cycle you would be loosing ground if your forced ventilation has an average draw of 1 amp.

[richard5933]

Originally Posted by Wazbro

Don't forget the amp draw of the forced ventilation. If you get a fridge with 1.5 amp less draw, .75 amp less with 50% duty-cycle you would be loosing ground if your forced ventilation has an average draw of 1 amp.

Yes and no...

First, there are some fans with about .25 - .5 amp draw. They don't move a lot of air, but you don't need a lot of air to move to do the job if the cabinet and airflow are designed properly.

Second, if the fans are assisting in the correct way they will produce a savings overall by reducing the duty-cycle.

And, if the fans are on a thermo-control so they run only when needed it can help even more.

The Vitrifrigo DC compressor fridge on my previous unit came from the factory with only a single fan on the compressor coils to shed heat. Combined with having no forced ventilation to pull heat from the rear of the cabinet meant a pretty high duty cycle.

After talking with a technician at the company I added a second fan on the compressor (one pulled out and one pushed in from the other side). This greatly helped the coils shed heat. Each fan pulled only .25 amps. Then I aded an exhaust fan at the top of the cabinet to help pull the heat from the around the fridge which helped even more.

These super-efficient fans cost more than the ones on Aliexpress or eBay, but that's because they can do a better job and sip electrons slowly.

[Jum]

Originally Posted by jrowan

I installed a Novakool RFU6400D in 2021. This is a single compressor unit with bottom freezer drawer with 6.8 cubic feet. I installed the fridge after I had installed 300 Ah of lithium, but before I installed any solar (I have 400 watts now). I also have a victron 712 shunt monitor.

As delivered, the fridge had a resistor installed in the compressor circuit that makes it run at full speed.

Jason

I thought any of their models that ended with a D were dual compressor?

I bought a Novakool R5810 last year and love it, except the latch. I remember seeing the resistor but haven't gotten around to doing any testing since I installed my lithium/solar/etc system over the winter. Then again, I have 800W and 560Ah so it's not a big concern really but if I can optimize it, I will eventually.

That's interesting that you ended up with the thermostat ~4 with no resistor/slowest speed. I end up around 3-1/2 with it from the factory. I know it's not repeatable from unit to unit, but still.

[Vantair]

A little off topic but to do with efficient low power refrigeration options from the OP, years ago we purchased a Blizzard Box brand 12/24vdc/120v cooler and did some testing. This showed less than 1Ah average draw @ 12vdc for a sizable auxiliary cooler in addition to our stock AS propane fridge freezer.

We can now go 3.5weeks (many trips) self contained without shopping for cold food. Also being kind to the AS battery bank.

So impressed we did a end user video as this info was not in the spec sheet
or on-line and thought others would like to know.(No relation to the model or manufacturer)

https://www.youtube.com/watch?v=HeTYph0l5dE

skip to 15:30 to get to the draw info.

[jrowan]

Originally Posted by Jum

I thought any of their models that ended with a D were dual compressor?

You'd think so, but no. According to the brochure I got at the time, the dual compressor is RFU6406D. RFU6400D is single compressor. The D doesn't stand for DC either, because they append DC or ACDC on the end of the part number.

Originally Posted by Jum

I bought a Novakool R5810 last year and love it, except the latch. I remember seeing the resistor but haven't gotten around to doing any testing since I installed my lithium/solar/etc system over the winter. Then again, I have 800W and 560Ah so it's not a big concern really but if I can optimize it, I will eventually.

Yeah the latch is awful, but at least it hasn't broken after 4 years. The other issue is the knob moves on its own during travel, always to 7. I rigged up a piece of rubber to hold the knob in place.

Originally Posted by Jum

That's interesting that you ended up with the thermostat ~4 with no resistor/slowest speed. I end up around 3-1/2 with it from the factory. I know it's not repeatable from unit to unit, but still.

The compressor speed has nothing to do with the setpoint temperature of the knob (unless you need the higher speed to achieve the desired temperature). A higher compressor speed just mean it gets to the setpoint faster. If you can achieve the desired setpoint temperature at the lowest compressor speed, that will be the most efficient, even if it means the compressor duty cycle is actually higher. I actually wired my resistor into a little push button switch so I can easily "activate" the resistor if needed on super hot days, but I've never needed to do that in real life.